CN102067436A - System and method for integrating local maximum power point tracking into an energy generating system having centralized maximum power point tracking - Google Patents

Abstract

A system for integrating local maximum power point tracking (MPPT) into an energy generating system (10) having centralized MPPT is provided. The system (10) includes a system control loop (16,32,22) and a plurality of local control loops (12,14). The system control loop (16,32,22) comprises a system operating frequency, and each local control loop (12,14) comprises a corresponding local operating frequency. Each of the local operating frequencies is spaced apart from the system operating frequency by at least a predefined distance. For a particular embodiment, a settling time corresponding to the local operating frequency of each local control loop (12,14) is at least five times faster than a time constant corresponding to the system operating frequency.

Description

System and method for integrating local maximum power point tracking into an energy generating system with centralized maximum power point tracking

Technical Field

The disclosure generally relates to energy generating systems. More specifically, the disclosure relates to systems and methods for integrating local maximum power point tracking into an energy generating system with centralized maximum power point tracking.

Background

Solar and wind power provide renewable and non-polluting sources of energy relative to conventional non-renewable, polluting sources of energy such as coal or oil. Solar and wind power have therefore become increasingly important sources of energy that can be converted into electrical energy. For solar energy, photovoltaic panels arranged in arrays typically provide a means to convert solar energy into electrical energy. Similar arrays may be used to harvest wind or other natural energy sources.

In operating photovoltaic arrays, Maximum Power Point Tracking (MPPT) is typically used to automatically determine at what voltage or current the array should be operated to produce maximum power output at a particular temperature and solar radiation. While it is relatively simple to implement MPPT for the overall array when the array is under ideal conditions (i.e., the same radiation, temperature, and electrical characteristics for each panel in the array), MPPT for the overall array is more complex when there is a mismatch or partial shadowing. In this case, MPPT techniques cannot provide accurate results because of the relatively optimal condition of multimodal power versus voltage characteristics of mismatched arrays. Thus, only some of the array panels operate ideally. Since for an array comprising rows of panels, the most inefficient panel determines the overall panel current and efficiency, this results in a dramatic reduction in the power generated.

Thus, some photovoltaic systems provide a DC-DC converter for each panel in the array. Each DC-DC converter performs MPPT to search for the maximum power point of its corresponding panel. However, the presently proposed systems using distributed MPPT processing generally do not contemplate using centralized MPPT control with distributed MPPT control at the DC-AC conversion level. Instead, either distributed MPPT or centralized MPPT is used. As such, the design of MPPT controllers embedded in DC-AC stages and MPPT controllers in DC-DC converters in each panel remains a problem for systems using both MPPT control types.

DC-DC converters are only suitable for operation without centralized MPPT control if they lack the explicit features to allow different types of MPPT control along with operation. In particular, the interaction between distributed MPPT control and centralized MPPT control may cause system oscillation and cause the panel to operate away from its maximum power point. Also, if there is no synchronization between the two different MPPT controllers, the DC-DC converter may start operating before the DC-AC stage starts operating. In such a case, the DC-AC stage cannot distribute or convert the power provided by the DC-DC converter, allowing the line voltage to be increased an unlimited amount, and possibly causing damage to certain components of the system. Further, if there is no communication between the MPPT controllers, an isolation phenomenon may occur, which may cause the DC-AC stage to stop extracting power and the DC-DC converter to continuously generate power. This causes the input voltage of the DC-AC stage to grow uncontrollably.

Drawings

For a more complete understanding of the disclosure and features thereof, reference is now made to the following descriptions taken in conjunction with the accompanying drawings, in which:

FIG. 1A illustrates an energy generating system that integrates local Maximum Power Point Tracking (MPPT) into centralized MPPT, according to one embodiment of the present disclosure;

FIG. 1B illustrates an energy generating system that may be centrally controlled, according to one embodiment of the disclosure;

FIG. 2 illustrates a partial converter of FIG. 1A or FIG. 1B according to one embodiment of the disclosure;

FIG. 3 shows a detail of the local converter of FIG. 2 according to an embodiment of the disclosure;

fig. 4A illustrates a method for implementing MPPT in the local converter of fig. 2 according to one embodiment of the present disclosure;

fig. 4B illustrates a method for implementing MPPT in the local converter of fig. 2 according to an embodiment of the disclosure;

FIG. 5 illustrates an energy generating system including a central array controller that enables selection between centralized MPPT and distributed MPPT for the energy generating system, according to one embodiment of the disclosure;

FIG. 6 is the array of FIG. 5 with portions masked, according to one embodiment of the disclosure;

fig. 7A-C are graphs showing voltage versus power characteristics for three photovoltaic panels corresponding to fig. 6;

FIG. 8 illustrates a method of selecting between centralized MPPT and distributed MPPT for the energy generation system of FIG. 5, in accordance with one embodiment of the present disclosure;

FIG. 9 is a system showing a local controller activating and deactivating a local converter in an energy generating system, according to one embodiment of the disclosure;

FIG. 10 is a graph showing an example of device voltage changes over time, according to one embodiment of the disclosure;

FIG. 11 illustrates the initiator of FIG. 9 in accordance with one embodiment of the disclosure; and

FIG. 12 illustrates a method for enabling or disabling the local converter of FIG. 9, according to one embodiment of the present disclosure.

Detailed Description

DETAILED DESCRIPTION FIGS. 1 through 12, discussed below, and the various embodiments used to describe the principles of the present invention in this patent document are by way of illustration only and should not be construed in any way to limit the scope of the invention. Those skilled in the art will understand that the principles of the present invention may be applied to any type of suitably arranged device or system.

Fig. 1A illustrates an energy generating system 10 that integrates local Maximum Power Point Tracking (MPPT) into a centralized MPPT, in accordance with one embodiment of the present disclosure. The energy generating system 10 includes a plurality of Energy Generating Devices (EGDs) 12, each coupled to a corresponding local converter 14, the EGDs 12 and the corresponding local converters 14 being combined to form an energy generating array 16. The photovoltaic system 10 also includes a DC-AC converter 22 coupled to the local converter 14 and operable to receive current and voltage from the local converter 14.

For a particular embodiment, as described in the disclosure, the energy generation system 10 may comprise a photovoltaic system and the energy generation device 12 may comprise a Photovoltaic (PV) panel. However, it should be appreciated that the energy generation system 10 may include any other energy generation system of a suitable kind, such as a wind turbine system, a fuel cell system, and the like. For such embodiments, the energy generating device 12 may include a wind turbine, a fuel cell, or the like. Also, the energy generating system 10 may be a grounded system or a floating system.

The PV panels 12 in the array 16 are disposed on strings 24. for the illustrated embodiment, the array 16 includes two strings 24, with each string 24 including three panels 12. However, it should be appreciated that array 16 may include any suitable number of strings 24, and each string 24 may include any suitable number of panels 12. And for the embodiment depicted, the panels 12 in each string 24 are arranged in a series connection. Thus, the output voltage of each local converter 14 remains close to its input voltage, and supplies the input port of the high voltage-to-DC-AC converter 22, which for some embodiments may operate at an input voltage between 150V and 500V. Thus, transformer-based converters (such as those used in parallel configuration strings) are not required, resulting in the ability to implement high efficiency and low cost local converters 14.

Each PV panel 12 is capable of converting solar energy to electrical energy. Each local converter 14 is coupled to a corresponding panel 12 and is capable of reshaping the voltage-to-current input relationship caused by the panel 12 so that the power generated by the panel 12 of the array 16 can be utilized by a load (not shown in fig. 1A). The DC-AC converter 22 is coupled to the array 16 and is capable of converting a load Direct Current (DC) generated by the local converter 14 into an Alternating Current (AC), the load being coupled to the DC-AC converter 22. DC-AC converter 22 includes a central MPPT control block 32 that provides centralized MPPT by calibrating the MPP of array 16.

The MPPT automatically determines the voltage or current at which the array 16 or panel 12 should operate to produce maximum power output for a particular temperature and solar radiation. While implementing centralized MPPT is relatively simple for the overall array when the array is under ideal conditions (i.e., the same radiation, temperature, and electrical characteristics for each panel in the array), MPPT is more complex for the overall array when there is a mismatch or partial shadowing. In this case, MPPT techniques do not provide accurate results because of the relatively optimal condition of the multimodal power versus voltage characteristics of the mismatched array 16. Thus, only some of the panels 12 of the array 16 operate ideally, resulting in a dramatic drop in power production. Therefore, to address this issue, each local converter 14 can provide a local MPPT for its corresponding panel 12. In this manner, each panel 12 can operate at its own Maximum Power Point (MPP), whether under ideal or mismatched or masked conditions. For embodiments in which energy generation device 12 comprises a wind turbine, MPPT may be used to adjust the blade pitch of the wind turbine. It should also be appreciated that MPPT may be used to optimize systems 10 including other types of energy generation devices 12.

The energy generating system 10 is provided with a system control loop for the overall system 10 that is controlled by the central MPPT control block 32, and a local control loop for each panel 12 that is controlled by the corresponding local inverter 14. The operating frequencies of the loops are separated by at least a predetermined distance to avoid system oscillation and to avoid panel 12 operating away from its MPP. For one embodiment, the system control loop is a closed loop system including an array 16, a central MPPT control block 32, and a DC-AC converter 22. In addition, each local control loop is a closed loop system including a panel 12 and corresponding local converter 14.

For some embodiments, each local converter 14 is designed such that the settling time of the local control loop of the converter 14 is faster than the time constant of the system control loop. In a particular embodiment, the settling time of each local control loop is at least five times faster than the time constant of the system control loop. Thus, in steady state, the array 16 of panels 12 may be used as a power source for the DC-AC converter 22, with the energy being the sum of the maximum available energy for each panel 12. Meanwhile, the central MPPT control block 32 may implement a normal optimization algorithm, and finally, the central MPPT control block 32 may set the string voltage to a value that maximizes the performance of the local converter 14.

In this way, system oscillations caused by dynamic reactions between the system control loop and the local control loop can be avoided. Further, the panel 12 is generally operable at its MPP. Also, synchronization between the system and the local loop is possible to avoid damage that may result from an unlimited increase in string voltage. Finally, isolating the DC-AC converter 22, which would cause the DC-AC converter 22 to stop absorbing energy and cause uncontrolled input voltage growth, can be avoided.

FIG. 1B illustrates an energy generating system 100 capable of centralized control, according to one embodiment of the disclosure. The energy generating system 100 includes a plurality of Energy Generating Devices (EGDs) 102, each coupled to a corresponding local converter 104, the energy generating devices 102 and the local converters 104 together forming an energy generating array 106. For a particular embodiment, as described in the disclosure, the energy generation system 100 may comprise a photovoltaic system and the energy generation device 102 comprises a Photovoltaic (PV) panel. However, it should be appreciated that the energy generation system 100 may include any other suitable kind of energy generation system, such as a wind turbine system, a fuel cell system, and the like. For such embodiments, the energy generating device 102 may include a wind turbine, a fuel cell, or the like. Also, the energy generating system 100 may be a grounded system or a floating system.

The photovoltaic system 100 includes a central stack controller 110 and also includes a DC-AC converter 112, or other suitable load for use in the case where the system 100 is operating as a parallel type system. It should be appreciated, however, that the system 100 may operate as a standalone system by coupling the array 106 to a battery charger or other suitable energy storage device instead of the DC-AC converter 112.

The PV panels 102 in the array 106 are arranged in strings 114. For the embodiment, array 106 includes two strings 114, each string 114 including three panels 102. However, it should be appreciated that the array 106 may include any suitable number of strings 114, and each string 114 may include any suitable number of panels 102. Also for the illustrated embodiment, the panels 102 in each string 114 are connected in series. Thus, when supplying high voltage to the input port of the DC-AC converter 112, the output voltage of each local converter 104 is still close to its input voltage. And for some embodiments the DC-AC converter 112 operates with an input voltage between 150V and 500V. Thus, transformer-based converters for strings in a parallel configuration are not required, which results in the ability to implement high performance and low cost local converters 104.

Each PV panel 102 is capable of converting solar energy to electrical energy. Each local converter 104 is coupled to a corresponding panel 102 and is capable of reshaping the input relationship of the input voltage to the current supplied by the panel 102 so that the power generated by the panel 102 of the array 106 can be utilized by a load (not shown in fig. 1B). The DC-AC converter 112 is coupled to the array 106 and is capable of converting a load Direct Current (DC) generated by the local converter 104 into an Alternating Current (AC), which may be coupled to the DC-AC converter 112.

Maximum Power Point Tracking (MPPT) automatically determines the voltage or current at which panel 102 should operate to produce maximum power output for a particular temperature and solar radiation. While it is fairly straightforward to implement centralized MPPT for the entire array 106 when the array 106 is in ideal conditions (i.e., the same radiation, temperature, and electrical characteristics for each panel 102 in the array 106). However, MPPT for the entire array 106 is more complicated when there is a mismatch or partial occlusion, for example. In this case, MPPT techniques do not provide accurate results because of the relatively optimal condition of the multimodal power versus voltage characteristics of the mismatched array 106. Thus, only some panels 102 in the array 106 operate ideally, resulting in a sharp drop in energy. Thus, to address this issue, each local converter 104 may provide a local MPPT for its corresponding panel 102. In this manner, each panel 102 can operate at its own maximum energy point (MPP), whether in an ideal, mismatched or occluded condition. For embodiments in which the energy generating device 102 comprises a wind turbine, MPPT may be used to adjust the blade pitch of the wind turbine. It should also be appreciated that MPPT may be used to optimize systems 100 including other types of energy generating devices 102.

The central array controller 110 is coupled to the array 106 and is capable of communicating with the array 106 via a wired connection (e.g., serial or parallel bus) or a wireless connection. The central group controller 110 may include a diagnostic module 120 and/or a control module 125. The diagnostic module 120 can monitor the photovoltaic system 100 and the control module 125 can control the photovoltaic system 100.

The diagnostic module 120 can receive local converter data for the local converters 104 and device data for the panels 102 to which the local converters 104 correspond from each local converter 104 in the array 106. As used herein, "device data" refers to output voltage, output current, temperature, radiation, output power, etc. of the panel 102. Similarly, "local converter data" refers to local converter output voltage, local converter output current, local converter output power, and the like.

The diagnostic module 120 is also capable of generating reports on the system 100 and providing the reports to an operator. For example, the diagnostic module 120 can display some or all of the device data and local transducer data for viewing by an operator. In addition, the diagnostic module 120 can provide some or all of the device data and local transducer data to the control module 125. The diagnostic module 120 can also analyze the data in any suitable manner and provide the analysis results to an operator and/or the control module 125. For example, the diagnostic module 120 can determine the statistics of the various panels 102 based on any suitable time period, such as hourly, daily, weekly, or monthly.

The diagnostic module 120 can also provide error monitoring for the array 106. Based on the data received from the local transducer 104, the diagnostic module 120 may identify one or more panels 102 that have a flaw, such as a failed panel 102, a shadowed panel 102, a dirty panel 102, and so on. The diagnostic module 120 may also notify the operator when a panel 102 with a flaw should be replaced, repaired, or cleaned.

The control module 125 can actually control the array 106 by sending control signals to one or more local converters 104. For example, the control module 125 may send a bypass control signal to the particular local converter 104 that has failed the corresponding panel 102. The bypass control signal causes the local converter 104 to bypass the panel 102, effectively removing the panel 102 from the array 106 without affecting the operation of other panels 102 in the same string 114 (as with the bypassed panel 102).

In addition, the control module 125 can send control signals to one or more local converters 104, which direct the local converters to adjust their output voltages or currents. For some embodiments, the MPPT function of local converter 104 may be shifted to central array controller 110. For these embodiments, the control module 125 may also calibrate the MPP of each panel 102 and transmit a switch ratio command to each local switch 104 based on the calibration to cause each panel 102 to operate at its own MPP, as determined by the control module 125.

The control module 125 may also receive commands from an operator and initiate the commands. For example, an operator may direct control module 125 to either parallel or independent system 100, and control module 125 may respond to the operator by setting system 100 to be either parallel or independent of system 100.

Thus, by utilizing the central array controller 110, the photovoltaic system 100 provides better utilization on a panel basis. Also, the system 100 increases flexibility by mixing different sources. The central array controller 110 also provides better protection and data collection for the entire system 100.

FIG. 2 illustrates a local transducer 204 according to one embodiment of the disclosure. The local converters 204 may represent one of the local converters 104 of fig. 1A or one of the local converters 104 of fig. 1B, however, it should be appreciated that the local converters 204 may be provided in the energy generation system in any suitable manner without departing from the scope of the disclosure. Furthermore, although shown coupled to an energy generating device 202 referred to as a PV panel, it should be understood that the local converter 204 may be coupled to a single cell of a PV panel or a subset of panels of a photovoltaic array, or to another energy generating device 202, such as a wind turbine, fuel cell, etc.

The local converter 204 includes a power stage 206 and a local controller 208, which further includes an MPPT module 210 and an optional communication interface 212. The power stage 206 may include a DC-DC converter that can receive panel voltages and currents as inputs from the PV panel 202 and reshape the input voltage-to-current relationship to generate output voltages and currents.

The communication interface 212 of the local controller 208 can provide a communication channel between the local switch 204 and a central array controller (e.g., the central array controller 110 of fig. 1B). However, for embodiments where the local converters 204 do not communicate with the central group controller, the communication interface 212 may be omitted.

MPPT module 210 can receive panel voltage and current as inputs from panel 202 and can receive output voltage and current from power stage 206 if the algorithm used requires it. Based on these inputs, MPPT module 210 can provide signals to control power stage 206. In this manner, the MPPT module 210 of the local controller 208 can provide MPPT for the PV panel 202.

By providing MPPT, MPPT module 210 maintains the corresponding panel 202 at a substantially fixed operating point (i.e., a fixed voltage V corresponding to the maximum power point of panel 202)_panAnd current I_pan). Thus, for a given fixed solar radiation, in steady state, if the local converter 204 corresponds to the relative or absolute maximum power point of the panel 202, the input power of the local converter 204 is fixed (i.e., P_pan＝V_pan·I_pan). In addition, the local converter 204 has a relatively high performance, and thus, the output power is nearly equal to the input power (i.e., P)_out≒P_pan)。

Fig. 3 shows details of the local converter 204 according to an embodiment of the disclosure. For this embodiment, power stage 206 is implemented as a single-inductor, four-switch synchronous buck-boost switching regulator, and MPPT module 210 includes a power stage regulator 302, an MPPT control block 304, and two analog-to-digital converters (ADCs) 306 and 308.

ADC 306 is capable of scaling and quantizing analog panel voltage V_panAnd simulating the panel current I_panTo generate a digital panel voltage and a digital panel current, respectively. It should be appreciated that although panel voltage and panel current are described, for any suitable energy generating device 202 (e.g., wind turbine, fuel cell, etc.), V_panMay be referred to as the output device voltage and I_panMay be referred to as the output device current. The ADC 306 coupled to the MPPT control block 304 and the communication interface 212 can also provide digital panel voltages and currents to the MPPT control block 304 and the communication interface 212. Similarly, the ADC 308 is capable of scaling and quantizing the analog output voltage and the analog output current to generate a digital output voltage and a digital output current, respectively. The ADC 308, which is also coupled to the MPPT control block 304 and the communication interface 212, can provide digital output voltage and current signals to the MPPT control block 304 and the communication interface 212. The communication interface 212 can be providedFor the digital panel voltage and current signals generated by ADC 306 and the digital output voltage and current signals generated by ADC 308 to the central array controller.

The MPPT control block 304 coupled to the power stage regulator 302 can receive the digital panel voltage and current from the ADC 306 and the digital output voltage and current from the ADC 308. Based on at least some of the digital signals. The MPPT control block 304 can generate a switch ratio command for the power stage regulator 302. The switch ratio command contains the switch ratio for the power stage regulator 302 to use when operating the power stage 206. For embodiments where the MPPT control block 304 is capable of generating the conversion command based on the digital panel voltage and current (rather than based on the digital output voltage and current), the ADC 308 only provides the digital output voltage and current to the communication interface 212 and not to the MPPT control block 304.

For some embodiments, power stage regulator 302 includes a buck-boost mode control logic and a digital pulse width regulator. The power stage regulator 302 can operate the power stage 206 in different modes by generating a Pulse Width Modulation (PWM) signal based on the conversion ratio provided by the MPPT control block 304. the MPPT control block 304 can calibrate the conversion ratio of the PWM signal for the power stage 206.

The power stage regulator 302 is coupled to the power stage 206 and is capable of operating the power stage 206 according to the conversion ratio generated by the MPPT control block 304 by operating the power stage 206 using a duty cycle and a mode that are determined according to the conversion ratio. For embodiments in which power stage 206 is implemented as a buck-boost converter, possible modes of power stage 206 include a downgrade mode, an upgrade mode, a buck-boost mode, a bypass mode, and a stop mode.

For this embodiment, power stage regulator 302 can operate power stage 206 in the up-down mode when the conversion ratio CR falls within the up-down range; when the conversion ratio CR is less than the ramp range, the power stage regulator 302 can operate the power stage 206 in the degraded mode; when the conversion ratio CR is greater than the lifting range, the power level is adjustedThe machine 302 can operate the power stage 206 in the upgrade mode. The lifting range comprises a value substantially equal to 1. For example, for a particular embodiment, the lift range includes 0.95 to 1.05. When the power stage 206 is in degraded mode, if CR is less than the maximum degraded conversion ratio CR_buck，maxThe power stage regulator 302 can operate the entire power stage 206 in a degraded configuration. Similarly, if CR is greater than the minimum upgrade conversion ratio CR_boost，minThe power stage regulator 302 can operate the entire power stage 206 in an upgraded configuration.

Finally, when the conversion ratio is larger than CR_buck，maxAnd is less than CR_boost，minThe power stage regulator 302 can alternately operate the power stage 206 in the downgraded configuration and the upgraded configuration. In this case, the power stage regulator 302 may implement time-division multiplexing to alternate between downgrade and upgrade configurations. Therefore, when the conversion ratio is closer to CR_buck，maxWhen in the degraded configuration, the power stage regulator 302 operates the power stage 206 more frequently than in the upgraded configuration. Similarly, when the conversion ratio is closer to CR_boost，minWhen the power stage regulator 302 operates the power stage 206 more frequently in the upgraded configuration than in the downgraded configuration. When the conversion ratio is close to CR_buck，maxAnd CR_boost，minAt an intermediate point in between, the power stage regulator 302 operates the power stage 206 in the derated configuration at a frequency comparable to the frequency at which the power stage 206 is operated in the upgraded configuration. For example, when power stage 206 is in the buck-boost mode, power stage regulator 302 may, on average, alternate operating power stage 206 in the downgraded configuration and the upgraded configuration.

For the embodiment, the power stage 206 includes four switches 310a-d, and an inductance L and a capacitance C. For some embodiments, switch 310 may comprise an N-channel power MOSFET. For a particular embodiment, the transistors may comprise gallium nitride devices on silicon. However, it should be appreciated that the switch 310 may be implemented in other suitable ways without departing from the scope of the disclosure. In addition, the power stage 206 may include one or more drivers (not shown in fig. 3) to drive the switch 310 (e.g., a gate of a transistor). For example, for a particular embodiment, a first driver may be coupled between power stage regulator 302 and transistors 310a and 310b to drive the gates of transistors 310a and 310b, and a second driver may be coupled between power stage regulator 302 and transistors 310c and 310d to drive the gates of transistors 310c and 310 d. For this embodiment, the PWM signals generated by the power stage regulator 302 are supplied to drivers that respectively drive the gates of their respective transistors 310 according to the PWM signals.

For the illustrated embodiment, in operating the power stage 206, the power stage regulator 302 can generate digital pulses to control the switch 310 of the power stage 206. For the embodiments described below, the switches comprise transistors. For degraded formation, power stage regulator 302 turns off transistor 310c and turns on transistor 310 d. The pulses then alternately turn on and off transistors 310a and 310b, causing power stage 206 to operate as a step-down regulator. For this embodiment, the duty cycle of the transistor 310a is equal to the duty cycle D, which is included in the slew rate command generated by the MPPT control block 304. For upgrade mode, power stage regulator 302 turns transistor 310a on and transistor 310b off. The pulses alternately turn on and off transistor 310c and transistor 310d to cause power stage 206 to operate as an upgraded regulator. For this embodiment, the duty cycle of transistor 310c is equal to 1-D.

For the buck-boost mode, the power stage regulator 302 performs time-division multiplexing between the downgrade and upgrade configurations, as described above. Power stage regulator 302 generates control signals for the degraded switch pair of transistors 310a and 310b, and the upgraded switch pair of transistors 310c and 310 d. The duty cycle of the transistor 310a is fixed at the corresponding CR_buck，maxThe duty cycle of the transistor 310c is fixed at the corresponding CR_boost，minThe duty cycle of (a). The ratio between downgrade and upgrade make-up operations over a specified period of time is linearly proportional to D.

When the output voltage approaches the panel voltage, the power stage 206 operates in the up-down mode. In this case, the inductor current ripple and voltage switching stresses are much less for the embodiment than for SEPIC and conventional buck-boost converters. Also, the power stage 206 may achieve higher performance than conventional buck-boost converters.

For some embodiments, as will be described in detail below in conjunction with fig. 4A, MPPT control block 304 may operate in one of four modes: sleep mode, track mode, hold mode, and bypass mode. The MPPT control block 304 may operate in the sleep mode when the panel voltage is less than a predetermined primary threshold voltage. In sleep mode, MPPT control block 304 turns off transistors 310 a-d. For example, for some embodiments, the MPPT control block 304 can generate a slew rate command that causes the power stage regulator 302 to turn off the transistors 310a-d when the MPPT control block is in the sleep mode. Thus, the power stage 206 is in the stop mode and the panel 202 is bypassed, which effectively prevents removal of the panel 202 in the photovoltaic system in which the panel 202 is used.

The MPPT control block 304 operates in the tracking mode when the panel voltage rises above the primary threshold voltage. In this mode, MPPT control block 304 performs maximum power point tracking on panel 202 to determine the optimal conversion ratio of power level regulator 302. And in this mode, the power stage regulator 302 places the power stage 206 in the downgrade mode, the upgrade mode, or the buck-boost mode, depending on the currently generated slew rate command.

Additionally, for some embodiments, the MPPT control block 304 may also include a stop register, which may be modified by an operator of the system or any suitable control process (e.g., a control process provided in the central array controller) to force the MPPT control block 304 to maintain the power stage 206 in the stop mode. For this embodiment, the MPPT control block 304 does not begin operating in the tracking mode unless (i) the panel voltage exceeds the primary threshold voltage, and (ii) the stop register indicates that the MPPT control block 304 will move the power stage 206 out of the stop mode.

When the MPPT control block 304 finds the optimal conversion ratio, the MPPT control block 304 may operate in the hold mode for a predetermined period of time. In this mode, the MPPT control block 304 may continue to provide the same conversion ratio determined to be the optimal conversion ratio in the tracking mode to the power stage regulator 302. And in this mode, such as in tracking mode, the power stage 206 is in a degraded mode, an upgraded mode, or a buck-boost mode depending on the optimal slew rate provided by the slew rate command. After a predetermined period of time, the MPPT control block 304 may revert to the tracking mode to ensure that the optimum conversion ratio does not change, or if the conditions of the panel 102 change, a new optimum conversion ratio may be found.

As described in more detail below in conjunction with fig. 5-8, the central array controller may set the MPPT control block 304 and the power stage 206 to the bypass mode when the panels (e.g., panel 202) in the photovoltaic array are uniformly illuminated and there is no mismatch between the panels 202. In the bypass mode, for some embodiments, transistors 310a and 310d are turned on and transistors 310b and 310c are turned off to make the panel voltage equal to the output voltage. For other embodiments, the power stage 206 may include an optional switch 312, and the power stage 206 may couple the input port to the output port to equalize the output voltage to the panel voltage. In this manner, the local converter 204 may be substantially removed from the system when local MPPT is not required, thereby maximizing performance and increasing lifetime by reducing losses associated with the local converter 204.

Thus, as described above, the MPPT control block 304 can operate in the sleep mode and place the power stage 206 in the stop mode bypassing the panel 202. The MPPT control block 304 can also operate in a tracking mode or a hold mode. In either mode, the MPPT control block 304 is capable of placing the power stage 206 in one of a degraded mode, an upgraded mode, and a ramped mode. Finally, the MPPT control block 304 can operate in a bypass mode, in which the local converter 204 is bypassed, allowing the panel 202 to be directly coupled to the other panels 202 in the array, and place the power stage 206 in the bypass mode.

By operating the local converter 204 in this manner, the string current of the panel string comprising the panel 202 is independent of the individual panel currents. Instead, the string current is set by the string voltage and the total string power. In addition, the unmasked panel 202 may continue to operate at the highest power point regardless of the condition that portions of other panels in the string are masked.

For an alternative embodiment, when the MPPT control block 304 finds the optimal conversion ratio, the MPPT control block 304 may not operate in the hold mode but in the bypass mode when the optimal conversion ratio corresponds to the up-down mode of the power stage 206. In the buck-boost mode, the output voltage approaches the panel voltage. Thus, the panel 202 can operate near its maximum power point by bypassing the local converter 204, thus increasing performance. As in the previous embodiment, the MPPT control block 304 periodically reverts from the bypass mode to the tracking mode to verify whether the optimum conversion ratio falls within the up-down mode range.

For some embodiments, the MPPT control block 304 can gradually adjust the conversion ratio for the power stage regulator 302 rather than the normal step change to avoid stress on the transistors, inductors, and capacitors of the power stage 206. For some embodiments, the MPPT control block 304 may implement different MPPT techniques to adjust the panel voltage or conductivity, rather than the conversion ratio. In addition, MPPT control block 304 may adjust the reference voltage, rather than the conversion ratio, for dynamic input voltage regulation.

In addition, MPPT control block 304 enables a relatively fast and smooth transition between the stop mode of power stage 206 and other modes. MPPT control block 304 may include a non-volatile memory capable of storing a previous maximum power point state, such as a conversion ratio. For this embodiment, when the MPPT control block 304 transitions to the sleep mode, the MPPT state is stored in the non-volatile memory. When the MPPT control block 304 subsequently reverts to the tracking mode, the stored maximum power point state may be used as the initial maximum power point state. In this manner, the transition time between stop and other modes may be significantly reduced for the power stage 206.

For some embodiments, the MPPT control block 304 may also provide over-power and/or over-voltage protection for the local converter 204. Because of the signal V_panAnd I_panMPPT control block 304 is fed forward through ADC 306, and MPPT control block 304 attempts to extract the maximum power. If the power stage 206 outputs an open circuit, the output voltage of the local converter 204 reaches a maximum value. Therefore, for over-power protection, the output current of the local converter 204 can be used as a signal to turn on and off the MPPT control block 304. For this embodiment, if the output current drops too low, the MPPT control block 304 may set the conversion ratio such that the panel voltage is nearly equal to the output voltage.

For over-voltage protection, the MPPT control block 304 may have a maximum conversion ratio for the conversion ratio command that the MPPT control block 304 does not exceed. Therefore, if the conversion ratio continues to be higher than the maximum conversion ratio, the MPPT control block 304 limits the conversion ratio to the maximum value. This ensures that the output voltage does not increase beyond the corresponding maximum value. The value of the maximum conversion ratio may be fixed or adaptive. For example, adaptive slew-rate limiting may be achieved by sensing the panel voltage and calculating an estimate of the output voltage corresponding to the next programmed value of the slew rate based on the slew rate of the power stage 206.

In addition, for the illustrated embodiment, the power stage 206 includes an optional unidirectional switch 314. When the power stage 206 is in the stop mode, an optional switch 314 is included to allow the panel 202 to be bypassed, thereby removing the panel 202 from the array and allowing other panels 202 to continue operating. For particular embodiments, unidirectional switch 314 may comprise a diode. However, it should be appreciated that the unidirectional switch 314 may comprise any other suitable type of unidirectional switch without departing from the scope of the disclosure.

Fig. 4A illustrates a method 400 for implementing MPPT in the local converter 204 according to an embodiment of the disclosure. The embodiment of the method 400 is merely illustrative. Other embodiments of the method 400 may be implemented without departing from the scope of the disclosure.

The method 400 begins with the MPPT control block operating in sleep mode (step 401). For example, the MPPT control block may generate a slew rate command to cause the power stage regulator 302 to turn off either the transistors 310a-d or the power stage 206, thereby placing the power stage 206 in a stop mode and bypassing the panel 202.

While in sleep mode, MPPT control block 304 monitors panel voltage V_panAnd comparing the panel voltage with the primary threshold voltage V_th(step 402). For example, the ADC 306 may convert the panel voltage from an analog signal to a digital signal and provide the digital signal to the MPPT control block 304, which stores a primary threshold voltage for comparison with the digital panel voltage.

The MPPT control block 304 continues to operate in the sleep mode as long as the panel voltage remains below the primary threshold voltage (step 402). In addition, as described above, when the stop buffer indicates that the power stage 206 remains in the stop mode, the MPPT control block 304 remains in the sleep mode. However, once the panel voltage exceeds the primary threshold voltage (step 402), the MPPT control block 304 generates a slew rate command for operating the power stage 206, the slew rate command including the initial slew rate (step 403). For example, for one embodiment, MPPT control block 304 begins by converting ratio 1. Alternatively, the MPPT control block 304 can store the optimum conversion ratio determined in the previous tracking mode. For this embodiment, the MPPT control block 304 may initialize the conversion ratio to be the same as the previously determined optimal conversion ratio. Also, the conversion ratio command generated by the MPPT control block 304 is supplied to the power stage regulator 302, which operates the power stage 206 using the initial conversion ratio.

At this time, the MPPT control block 304 monitors the panel current I_panAnd output electricityStream I_outAnd comparing the panel current and the output current with a threshold current I_th(step 404). For example, ADC 306 may convert the panel current from an analog signal to a digital signal and supply the digital panel current to MPPT control block 304, ADC 308 may convert the output current from an analog signal to a digital signal and supply the digital output current to MPPT control block 304, which stores a threshold current for comparison with the digital panel current and the digital output current. As long as the current I_panAnd I_outAt least one of which remains below the threshold current (step 404), MPPT control block 304 continuously monitors the current level. However, once the currents exceed the threshold current (step 404), the MPPT control block 304 begins operating in tracking mode, which includes initializing the tracking variable T to 1 and initializing a counter (step 406).

Although not shown in the method 400 of fig. 4A, it should be appreciated that while in the tracking mode, the MPPT control block 304 may continue to monitor the panel voltage and compare the panel voltage to a secondary threshold voltage that is less than the primary threshold voltage. If the panel voltage decreases below the secondary threshold voltage, the MPPT control block 304 resumes the sleep mode. By using a secondary threshold voltage that is less than the primary threshold voltage, MPPT control block 304 is immune to noise, thus preventing MPPT control block 304 from constantly switching between sleep and tracking modes.

After setting the values of the tracking variables and initializing the counters, MPPT control block 304 calculates initial power for panel 202 (step 408). For example, ADC 306 may provide digital panel current and panel voltage signals (I)_panAnd V_pan) To the MPPT control block 304, the MPPT control block 304 then multiplies the signals to determine the device (or panel) power (I)_pan·V_pan) Is started.

After calculating the initial power, the MPPT control block 304 modifies the conversion ratio in the first direction and generates a conversion ratio command including the modified conversion ratio (step 410). For example, for some embodiments, MPPT control block 304 may increase the conversion ratio. For other embodiments, the MPPT control block 304 may reduce the conversion ratio. After a period of time has elapsed to stabilize the system, MPPT control block 304 calculates the current power for panel 202 (step 412). For example, the ADC 306 may provide digital panel current and panel voltage signals to the MPPT control block 304, and the MPPT control block 304 then multiplies these signals together to determine the current value of the panel power.

The MPPT control block 304 then compares the now calculated power with the previously calculated power, which is the initial power (step 414). If the current power is greater than the previous power (step 414), the MPPT control block 304 modifies the conversion ratio in the same direction as the previous modification and generates an updated conversion ratio command (step 416). For some embodiments, the conversion ratio is modified higher or lower with an equal increase. For other embodiments, the conversion ratio can be modified higher or lower in linear or non-linear increments to optimize the system response. For example, for some systems, if the conversion ratio is far from the optimum, it is preferable to use larger increments and then smaller increments as the optimum is approached.

The MPPT control block 304 also determines whether the tracking variable T is equal to 1, indicating that the conversion ratio has changed in the same direction as the previous calculation because the conversion ratio has changed before the previous calculation (step 418). Thus, when T equals 1, the panel power increases in the same direction as the previous change in the conversion ratio. In this case, after the system is allowed to stabilize for a period of time, the MPPT control block 304 again calculates the current power of the panel 202 (step 412) and compares the current power with the previous power (step 414). However, if the MPPT control block 304 determines that T is not equal to 1, indicating that the conversion ratio has changed in the opposite direction to the previous calculation because the conversion ratio has changed before the previous calculation (step 418), the MPPT control block 304 sets T to 1 and increments the counter (step 420).

The MPPT control block 304 then determines whether the counter exceeds a counter threshold C_th(step 422). If the current counter value does not exceed the counter threshold (422), after allowing the system a period of time to stabilize, the MPPT control block 304 again calculates the current power of the panel 202 (412) and compares the current power with the previous power (414) to determine if the panel power is increasing or decreasing.

If the MPPT control block 304 determines that the current power is not greater than the previous power (step 414), the MPPT control block 304 modifies the conversion ratio in the opposite direction to the previous modification and generates an updated conversion ratio command (step 424). The MPPT control block 304 also determines whether the tracking variable T is equal to 2, which indicates that the conversion ratio has been modified in the opposite direction to the previous calculation because the conversion ratio has changed before the previous calculation (step 426). In this case, after the system is allowed to stabilize for a period of time, the MPPT control block 304 again calculates the current power of the panel 202 (step 412) and compares the current power with the previous power (step 414).

However, if the MPPT control block 304 determines that T is not equal to 2, indicating that the conversion ratio has been modified in the same direction as the previous calculation because the conversion ratio has changed before the previous calculation (step 426), the MPPT control block sets T to 2 and increments the counter (step 428). MPPT control block 304 then determines whether the counter exceeds a counter threshold value C_th(step 422), as described above.

If the counter does not exceed the counter threshold (step 422), indicating that the conversion ratio has alternately changed several times in the first direction and the second direction, the times being greater than the counter threshold, the MPPT control block 304 finds the optimum conversion ratio corresponding to the maximum power point of the panel 202, and the MPPT control block 304 begins operating in the hold mode (step 430).

While in the hold mode, the MPPT control block 304 may set a timer and reinitialize the counter (step 432). When the timer expires (step 434), the MPPT control block 304 may revert to the tracking mode (step 436) and calculate the current power (step 412) to compare the current power with the power that the MPPT control block 304 last calculated in the tracking mode (step 414). In this way, the MPPT control block 304 can ensure that the optimal conversion ratio is not changed, or that a different optimal conversion ratio can be found when the conditions of the panel 202 change.

Although fig. 4A shows an example of a method 400 for tracking the maximum power point of the energy generating device 202, various modifications may be made to the method 400. For example, although the method 400 is described with reference to photovoltaic panels, the method 400 may be used with other energy generating devices 202, such as wind turbines, fuel cells, and the like. Further, although the method 400 is described with reference to the MPPT control block 304 of fig. 3, it should be appreciated that the method 400 may be used with any suitably configured MPPT control block without departing from the scope of the disclosure. Additionally, for some embodiments, if the MPPT control block 304 determines that the optimal conversion ratio is equivalent to the up-down mode of the power stage 206 in step 430, the MPPT control block 304 may operate in the sleep mode rather than the hold mode. For such embodiments, the time after the sleep mode for the timer expiration may be the same or different than the time for the timer in the hold mode. Also, although shown as a series of steps, the steps in method 400 may overlap, occur in parallel, occur multiple times, or occur in a different order.

Fig. 4B illustrates a method 450 for implementing MPPT in the local converter 204 according to another embodiment of the disclosure. For a particular embodiment, the method 450 of FIG. 4B may correspond to a portion of the method 400 of FIG. 4A. For example, the steps described in method 450 generally correspond to steps 403, 408, 410, 412, 414, 416, and 424 of method 400. However, the method 450 includes additional details beyond the steps. For another particular embodiment, the method 450 may be implemented independently of the method 400 and is not limited to the implementation of the method 400 described above. Moreover, as with method 400, method 450 described below is merely illustrative. Other embodiments of the method 450 may be implemented without departing from the scope of the disclosure.

The method 450 includes steps 452, 454, and 456 of the boot-up setAs a start. Initially, MPPT control block 304 sets converter conversion ratio M to minimum conversion ratio M_min(step 452). Then, MPPT control block 304 sets previous converter conversion ratio M_oldIs M, M_oldFor the conversion ratio of the previous MPPT iteration and for the current MPPT iteration setting the conversion ratio M as M_old+ Δ M, where Δ M is the delta in the increase in the conversion ratio between iterations (step 454). If the value of M set in this step is less than the initial conversion ratio M_startFor implementing MPPT (step 456), then M_oldAnd M are updated as described above, such that both are increased by Δ M (step 454). Once M reaches or exceeds M_startIs received (step 456), the boot group is complete and the method proceeds to step 458.

MPPT control block 304 sets M to a value M_startThe value of "sign" is set to 1, and the value of sign indicates the MPPT perturbation direction in each iteration of the MPPT process (step 458). At this time, MPPT control block 304 senses the input voltage and current (V) supplied by ADC 306_inAnd I_in) And senses the output voltage and current (V) supplied by the ADC 308_outAnd I_out) (step 460). The MPPT control block 304 also calculates an average input voltage and current (V)_{in av}And I_{in av}) And average output voltage and current (V)_{out av}And I_{out av}) Then, with V_{in av}×I_{in av}The input power is calculated (step 460).

For some embodiments, the average input voltage and current and the average output voltage and current are calculated at the second half of the MPPT perturbation interval. For a particular embodiment with a 50MHz frequency, the input voltage and current may be sampled at 12.5kHz, and the average input voltage and current and the average output voltage and current are calculated at 750 Hz.

Then, before enabling the MPPT process, MPPT control block 304 determines whether the temperature and current are acceptable (step 462). For one particular embodiment, the MPPT control block 304 includes an overheat pin capable of receiving an overheat signal when the temperature exceeds a predetermined threshold. For this embodiment, MPPT control block 304 determines that the temperature is unacceptable when the over-temperature signal indicates that the threshold has been exceeded.

For a particular embodiment, the MPPT control block 304 may compare the output current I_outWith average input current I_{in av}And an upper limit I of the minimum current threshold_{min hi}Determining whether the current is acceptable to ensure that the output current and the average input current are sufficient before starting the MPPT process, and by comparing the average output current I_{out av}With maximum output current I_{out max}To ensure that the average output current is not too high. For this embodiment, the MPPT control block 304 determines that the current is acceptable when the output current and the average input current are both greater than the upper limit of the minimum current threshold and when the average output current is less than the maximum output current. Alternatively, the MPPT control block 304 determines that the current is unacceptable when the output current, either the average input current, is less than the upper limit of the minimum current threshold or the average output current is greater than the maximum output current.

For a specific embodiment, the MPPT control block 304 may also include an overcurrent pin capable of receiving an overcurrent signal when the average output current exceeds the maximum output current. For example, the maximum output current value can be assigned to the over-current pin via the resistive voltage divider. Then, when the maximum output current is exceeded, the over-current pin receives the over-current signal.

When the MPPT control block 304 determines that the temperature and/or current is not acceptable (step 462), reset the value of M to M_startAnd resets the "sign" value to 1 (step 458). Setting the value of M to be M when the temperature is too high_startThis typically results in operating the panel 202 away from the MPPT, thereby reducing the power delivered by the converter 204. In addition, M may be_startThe operating point is selected to minimize the loss of the local converter 204. For example, for a particular embodiment, M may be selected_startIs 1. Therefore, when the temperature is highReturning to M when it is unacceptably high_startTypically resulting in a temperature drop due to the reduced power. In addition, when the average output current is too high due to the output short circuit, the value M is set to be M_startThis causes the panel voltage to be forced to zero.

When the MPPT control block 304 determines that both the temperature and the current are acceptable (step 462), MPPT processing is enabled. For the particular embodiment described above, the MPPT control block 304 determines that the temperature and current are acceptable when the temperature and average output current are both low and the output current and average input current are both high. This results in the ability to start and stop synchronization between the local converter 204 and the DC-AC converter 22 or 112. For this embodiment, each local switch 204 is at a fixed switching rate at power-on and operates in this state for a period of time sufficient to bring the system 10 or 100 to a steady state. If the DC-AC converter 22 or 112 does not begin its operation at this time, the local converter 204 will quickly charge its capacitance to a fixed voltage. For example, the fixed voltage can be generated by the open panel voltage and the initial conversion ratio M_startAnd (4) giving. Once this state is reached, the input and output currents of the local converter 204 are virtually zero.

For this embodiment, synchronization may be provided by sensing the output (or input) current of the local converter 204 and allowing MPPT only when the sensed current exceeds a certain threshold. When DC-AC converter 22 or 112 begins normal operation, the output (or input) current of local converters 204 exceeds a minimum threshold value, and all local converters 204 begin their MPPT operation at the same time that DC-AC converter 22 or 112 begins its MPPT operation. Likewise, the same technique may cause the local converter 204 to synchronously stop when the DC-AC converter 22 or 112 is interrupted for any reason (e.g., isolated).

For the method 450 of FIG. 4B, the MPPT process is performed with the previous input power P_{in old}Set to the current input power P_inAs a start (step 464). Thus, at the very beginning, the previous input power is set to the input calculated at step 460The value of the power. MPPT control Block 304 sets the value of M to M_old+ sign value × Δ M, and then M_oldIs set to M (step 466). Thus, the conversion ratio is adjusted by Δ M in the direction specified by the sign value by adjusting M_oldThe value changes to the same value and the final conversion ratio can be used in subsequent iterations.

Next, MPPT control block 304 determines whether the conversion ratio M falls within a predetermined range and whether the average output voltage is too high. For the embodiment described, when the conversion ratio is less than the maximum conversion ratio M_maxAnd is greater than the minimum conversion ratio M_minThe conversion ratio is within a predetermined range. And for the embodiment described, when the average output voltage exceeds the maximum output voltage V_{out max}The average output voltage is considered too high.

Thus, if M is greater than M_maxOr is V_{out av}Greater than V_{out max}(step 468), the MPPT control block 304 sets the sign value to-1 (step 470), which reduces, if continued, the conversion ratio in subsequent iterations of the MPPT process, as described in more detail below. Similarly, if M is less than M_min(step 472), the MPPT control block 304 sets the sign value to 1 (step 474), which causes (if continued) an increase in the conversion ratio in subsequent iterations of the MPPT process, as described in more detail below.

Therefore, when the average output voltage is greater than the maximum output voltage (step 470), instead of simply turning off the switches in the converter stage, the local converter 204 is allowed to continue to operate, and the MPPT control block 304 can reduce the conversion ratio to prevent the local converter 204 from exceeding the maximum output voltage. This has the advantage of allowing energy harvesting even under very large mismatch conditions that would normally cause the average output voltage to exceed the rated voltage of some components.

At this time, MPPT control block 304 senses the input voltage and current (V) supplied by ADC 306_inAnd I_in) And senses the output voltage and current (V) supplied by the ADC 308_outAnd I_out) (step 476). The MPPT control block 304 also calculates an average input voltage and current (V)_{in av}And I_{in av}) And average output voltage and current (V)_{out av}And I_{out av}) Then, with V_{in av}×I_{in av}The input power is calculated (step 476).

The MPPT control block 304 then determines the current input power P_inWhether or not it is greater than the previous input power P_{in old}It is calculated in the previous iteration (step 478). If the current input power is not greater than the previous input power (step 478), the MPPT control block 304 sets the sign value to (-sign)_old) Changing the value of a "symbol", wherein the symbol_oldIs multiplied by the current symbol value prior to-1 (step 480). Thus, in subsequent iterations of the MPPT process, the conversion ratio is modified in a different direction than in the current iteration if the MPPT process continues, as described in more detail below.

If the current input power is greater than the previous input power (step 478), the MPPT control block 304 holds the value of "sign" (step 482). Thus, in subsequent iterations of the MPPT process, the conversion ratio is modified in the same direction as in the current iteration if the MPPT process continues, as described in more detail below.

The MPPT control block 304 determines whether the temperature and current are acceptable to continue the MPPT process (step 484). For the particular embodiment described above, where the MPPT control block 304 includes an over-temperature pin, the MPPT control block 304 may determine that the temperature is unacceptable when the over-temperature signal indicates that a threshold value has been exceeded.

For a particular embodiment, the MPPT control block 304 may compare the output current I_outAnd an average input current I_{in av}And a minimum current threshold lower limit I_min，lowDetermining whether the current is acceptable to ensure that the output current and the average input current are sufficiently high before continuing the MPPT process, and comparing the average output current I_out，avAnd the maximum output current I_out，maxTo ensure that the average output current is not too large. For this embodiment, the MPPT control block 304 determines that the output current and/or the average input current is acceptable when the current is greater than the minimum current threshold lower limit and when the average output current is less than the maximum output current. Alternatively, the MPPT control block 304 determines that the output current and the average input current are both less than the lower limit of the minimum current threshold or that the average output current is greater than the maximum output current. By enabling the MPPT process using the upper limit of the minimum current threshold value (step 462) and stopping the MPPT process using the lower limit of the minimum current threshold value (step 484), the MPPT control block 304 may prevent multiple starts and stops of the MPPT process that may occur if the output and average input currents approach a single current threshold value for enabling and stopping the MPPT process.

When MPPT control block 304 determines that the temperature and/or current is unacceptable (step 484), the MPPT process is stopped. At this time, the value of M is reset to M_startThe "sign" value is reset to 1 (step 458), and the method continues as previously described. When the MPPT control block 304 determines that both the temperature and the current are acceptable (step 484), the value P of the previous input power_{in old}Set to the value P of the current input power_in(step 464), the MPPT control block 304 starts MPPT processing and then repeats as described above.

Although fig. 4B illustrates a method 450 for implementing MPPT for energy generating device 202, various modifications may be made to method 450. For example, although the method 450 is described with reference to photovoltaic panels, the method 450 may be used with other energy generating devices 202, such as wind turbines, fuel cells, and the like. Further, although the method 450 is described with reference to the MPPT control block 304 of fig. 3, it should be appreciated that the method 450 may be used in any suitably configured MPPT control block without departing from the scope of the disclosure. Also, although shown as a series of steps, the steps in method 450 may overlap, occur in parallel, occur multiple times, or occur in a different order. For a particular embodiment, it should be appreciated that in MPPT processing, the acceptability determination in step 484 with respect to temperature and current may be performed continuously by MPPT control block 304, rather than only once in each iteration.

FIG. 5 illustrates an energy generating system 500, according to one embodiment of the disclosure, the energy generating system 500 including a plurality of energy generating devices 502 and a central array controller 510, the central array controller 510 being capable of selecting between centralized and distributed MPPT for the energy generating system 500. For the illustrated embodiment, the energy generating system is referred to as a photovoltaic system 500, and photovoltaic system 500 includes an array of photovoltaic panels 502, each photovoltaic panel 502 coupled to a local converter 504.

Each local converter 504 includes a power stage 506 and a local controller 508. Furthermore, for some embodiments, each local converter 504 may be bypassed via an optional internal switch (e.g., switch 312). When bypassed, the output voltage of the local converter 504 is substantially equal to its input voltage. In this manner, losses related to the operation of the local converter 504 may be minimized or even eliminated (when the local converter 504 is not needed).

In addition to the central array controller 510, embodiments of the system 500 also include a conversion stage 512, a grid 514, and a data bus 516. The central group controller 510 includes a diagnostic module 520, a control module 525, and an optional switching stage (CS) optimizer 530. In addition, the illustrated embodiment provides an integral controller 540 for the conversion stage 512. However, it should be appreciated that the integral controller 540 may be located in the central array controller 510 rather than in the conversion stage 512. Also, the CS optimizer 530 may be located in the conversion stage 512 rather than in the central group controller 510.

For some embodiments, the panel 502 and the local converters 504 represent the panel 102 and the local converters 104 of fig. 1B, and/or represent the panel 202 and the local converters 204 of fig. 2 or 3, the central array controller 510 may represent the central array controller 110 of fig. 1B, and/or the conversion stage 512 may represent the DC-AC converter 112 of fig. 1B. In addition, the diagnostic module 520 and the control module 525 may represent the diagnostic module 120 and the control module 125 of FIG. 1B, respectively. However, it should be appreciated that the components of system 500 may be implemented in any suitable manner. The conversion stage 512 may include a DC-AC converter, a battery charger, or other energy storage device, or any other suitable means. Pane 514 may include any suitable load capable of operating in accordance with the energy generated by photovoltaic system 500.

Each local controller 508 can provide the data of the corresponding panel 502 and the local converter data to the central array controller 510 via the data bus 516 or via a wireless connection. Based on this data, the diagnostic module 520 can determine whether the panel 502 is operating in a quasi-ideal condition, i.e., the panel 502 is not mismatched and is illuminated substantially uniformly. In this case, the diagnostic module 520 can cause the control module 525 to place the system 500 in a centralized mppt (cmppt) mode. To accomplish this, the control module 525 can send a stop signal to each local controller 508 via the data bus 516 to stop the local converter 504 by operating the local converter 504 in the bypass mode. The control module 525 can also send an enable signal to the overall controller 540.

In the bypass mode, the local controller 508 no longer implements MPPT and the output voltage of the power stage 506 is substantially equal to the panel voltage of the panel 502. Thus, losses associated with operating the local converter 504 may be minimized and the performance of the system 500 may be maximized. When local converter 504 is operating in the bypass mode, global controller 540 can implement the CMPPT for the array of panels 502.

The diagnostic module 520 can also determine whether certain panels 502 are occluded or not matched (i.e., certain panels 502 have different characteristics than other panels 502 in the array). In this case, the diagnostic module 520 can cause the control module 525 to place the system 500 in a distributed mppt (dmppt) mode. To accomplish this, control module 525 can send an enable signal to each local controller 508 via data bus 516 to enable local converter 504 by allowing normal operation of local converter 504. The control module 525 can also send a stop signal to the overall controller 540.

When some panels 502 are occluded, the diagnostic module 520 can also determine that some occluded panels 502 are partially occluded. In this case, in addition to causing the control module 525 to place the system 500 in the DMPPT mode, the diagnostic module 410 can also perform a full diagnostic scan of the system 500 to ensure that the local controller 508 of the partially obscured panel 502 can find the true maximum power point, rather than the local maximum. For embodiments in which the energy generating device 502 comprises a wind turbine, the diagnostic module 520 can determine whether certain wind turbines are "shaded" due to changing wind patterns, hills, or other wind blocking structures, or other wind affecting conditions.

The photovoltaic system 500 is illustrated in fig. 6 and 7A-C with partial shading. Fig. 6 shows the photovoltaic array 600 in a partially shaded condition. Fig. 7A-C are graphs 700, 705, and 710 showing voltage versus power characteristics for the three photovoltaic panels corresponding to fig. 6.

The array has three strings 610 of photovoltaic panels. The three panels in string 610C are labeled panel A, panel B, and panel C. It should be understood that these panels may represent panel 502 of fig. 5 or in any other suitably arranged photovoltaic system. Some panels are completely covered or partially covered by the masked region 620.

In the illustrated embodiment, panel A is fully illuminated, panel B is partially obscured by obscured area 620, and panel C is fully obscured by obscured area 620. The voltage versus power characteristic in graph 700 in fig. 7A corresponds to panel a, the voltage versus power characteristic in graph 705 in fig. 7B corresponds to panel B, and the voltage versus power characteristic in graph 710 in fig. 7C corresponds to panel C.

Thus, as shown in the graph 705, the partially masked panel B has a local maximum 720 that is different from the actual maximum power point 725. The diagnostic module 520 of the central array controller 510 can determine that panel B is partially obscured and perform a full diagnostic scan to ensure that the local controller 508 for which panel B is operating at its actual maximum power point 725, rather than the local maximum point 720. Instead of operating at the actual maximum power point (e.g., point 725), a panel 502 operating at the local maximum power point (e.g., point 720) is referred to as an "under-implemented" panel 502.

For a particular embodiment, the diagnostic module 520 may identify the partially obscured panel 502 as follows. First, the diagnostic module 520 assumes that panels 1,.. and N are sub-combinations of panels 502 in the array under consideration that have the same characteristics, and assumes that P has the same characteristics_pan，iIs a combination of [1]The output power of the ith panel 502. Therefore, the temperature of the molten metal is controlled,

P_pan，max≥P_pan，i≥P_pan，min，

wherein P is_pan，maxTo optimally implement the output power, P, of the panel 502_pan，minThe output power of the panel 502 is implemented for worst case.

The diagnostic module 520 also defines a variable by

The probability that the ith panel 502 is fully or partially blocked can be expressed by the following equation:

wherein k is a constant less than or equal to 1. The following steps are carried out:

ρ_min≤ρ_i≤ρ_max

wherein, <math><mrow><msub><mi>&rho;</mi><mi>min</mi></msub><mo>=</mo><mfrac><mrow><mi>k</mi><mrow><mo>(</mo><msub><mi>P</mi><mrow><mi>pan max</mi></mrow></msub><mo>-</mo><msub><mi>P</mi><mrow><mi>pan max</mi></mrow></msub><mo>)</mo></mrow></mrow><msub><mi>P</mi><mrow><mi>pan max</mi></mrow></msub></mfrac><mo>=</mo><mn>0</mn></mrow></math> and is <math><mrow><msub><mi>&rho;</mi><mi>max</mi></msub><mo>=</mo><mfrac><mrow><mi>k</mi><mrow><mo>(</mo><msub><mi>P</mi><mrow><mi>pan max</mi></mrow></msub><mo>-</mo><msub><mi>P</mi><mrow><mi>pan min</mi></mrow></msub><mo>)</mo></mrow></mrow><msub><mi>P</mi><mrow><mi>pan max</mi></mrow></msub></mfrac><mo>.</mo></mrow></math>

The diagnostic module 520 also defines (p)_DMPPT) Is a probability function (p)_max) Makes DMPPT necessary. Therefore, if (ρ)_max) Greater than (rho)_DMPPT) Then DMPPT is enabled. In addition, (ρ)_diag) Defined as a probability function (p)_max) Such that a diagnostic function is necessary to determine whether any of the panels 502 that are partially obscured are operating at their MPP. Therefore, if (ρ)_max) Greater than (rho)_diag) The diagnostic module 520 identifies the panel 502 as being partially obscured and performs a scan on the identified panel 502.

For relatively small panel 502 mismatches, the diagnostic module 520 may still enable the DMPPT, but for larger mismatches, the diagnostic module 520 may also implement a full diagnostic scan. As such, (ρ)_DMPPT) Is generally less than (p)_diag) The value of (c).

Thus, for some embodiments, when (ρ)_max)＜(ρ_DMPPT) When so, the diagnostic module 520 can determine that the system 500 should operate in CMPPT mode when (ρ)_DMPPT)＜(ρ_max)＜(ρ_diag) The system 500 should operate atIn DMPPT mode, and when (ρ)_max)＞(ρ_diag) The system 500 should operate in DMPPT mode with a full diagnostic scan.

For such embodiments, the full diagnostic scan may include (ρ)_j＞ρ_diag) A full scan of the voltage versus power characteristics of each panel j. The diagnostic module 520 may individually scan the characteristics of each panel 502 according to the timing given by the central array controller 510. In this manner, the conversion stage 512 may continue to operate normally.

The CS optimizer 530 optimizes the operating point of the conversion stage 512 when the system 500 operates in DMPPT mode. For one embodiment, the operating point of the conversion stage 512 may be set to a constant. However, for embodiments using the CS optimizer 530, the operating point of the conversion stage 512 may be optimized by the CS optimizer 530.

For one particular embodiment, the CS optimizer 530 can determine the optimal operating point of the conversion stage 512 as follows. For the ith power stage 506, its duty cycle is defined as D_iAnd its conversion ratio is defined as M (D)_i). The power stage 506 is designed to have a nominal conversion ratio M₀. Therefore, as close to M as possible₀While operating the power stage 506 can provide higher efficiency, reduce stress, and reduce the likelihood of output voltage saturation. For a power stage 506 comprising a step-up-down converter, M₀May be 1.

Thus, the principle of optimization can be defined as follows:

<math><mrow><mfrac><mrow><munderover><mi>&Sigma;</mi><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mi>N</mi></munderover><mi>M</mi><mrow><mo>(</mo><msub><mi>D</mi><mi>i</mi></msub><mo>)</mo></mrow></mrow><mi>N</mi></mfrac><mo>=</mo><msub><mi>M</mi><mn>0</mn></msub></mrow></math>

then the process of the first step is carried out,

<math><mrow><munderover><mi>&Sigma;</mi><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mi>N</mi></munderover><mi>M</mi><mrow><mo>(</mo><msub><mi>D</mi><mi>i</mi></msub><mo>)</mo></mrow><mo>=</mo><munderover><mi>&Sigma;</mi><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mi>N</mi></munderover><mfrac><msub><mi>I</mi><mrow><mi>pan</mi><mo>,</mo><mi>i</mi></mrow></msub><msub><mi>I</mi><mrow><mi>out</mi><mo>,</mo><mi>i</mi></mrow></msub></mfrac><msub><mi>&eta;</mi><mi>i</mi></msub><mo>&ap;</mo><mfrac><mn>1</mn><msub><mi>I</mi><mi>LOAD</mi></msub></mfrac><munderover><mi>&Sigma;</mi><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mi>N</mi></munderover><msub><mi>I</mi><mrow><mi>pan</mi><mo>,</mo><mi>i</mi></mrow></msub></mrow></math>

wherein, I_pan，iIs the input current, I, of the ith power stage 506_out，iIs the output current, η, of the ith power stage 506_iIs the efficiency, I, of the ith power stage 506_LOADIs the input current of the switching stage 512. The principle of optimization can therefore be rewritten as follows:

<math><mrow><msub><mi>I</mi><mi>LOAD</mi></msub><mo>=</mo><mfrac><mrow><munderover><mi>&Sigma;</mi><mrow><mi>i</mi><mo>=</mo><mn>1</mn></mrow><mi>N</mi></munderover><msub><mi>I</mi><mi>pan i</mi></msub></mrow><mrow><mi>N</mi><msub><mi>M</mi><mn>0</mn></msub></mrow></mfrac></mrow></math>

the CS optimizer 530 can be optimized by using standard current mode control techniques at the input port of the conversion stage 512, such that the input current of the conversion stage 512 is set to I_LOAD。

Fig. 8 illustrates a method 800 of selecting either a centralized MPPT or a distributed MPPT for an energy generating system 500, according to an embodiment of the disclosure. The embodiment of the method 800 is merely illustrative. Other embodiments of the method 800 may be implemented without departing from the scope of the disclosure.

The method 800 begins with the diagnostic module 520 setting a timer (step 802). The diagnostic module 520 may trigger the initialization of the method 800 in a round-robin fashion using a timer. The diagnostic module 520 then analyzes the energy generating devices, such as the panels 502, in the energy generating system 500 (step 804). For example, for some embodiments, the diagnostic module 520 may calculate the panel power P for each panel 502_panWhile panel 502 is analyzed and then according to P_panDetermines a number of other values as described above with respect to fig. 5. For example, the diagnostic module 520 may determine the calculated value P_panMaximum and minimum values of (P, respectively)_pan，maxAnd P_pan，min) The maxima and minima are then used to calculate the probability (ρ) that the panel 502 of each panel 502 is fully or partially occluded. The diagnostic module 520 may also determine a maximum value (ρ) of the calculated rate_max)。

After analyzing panel 502 (step 804), diagnostic module 520 may determine whether photovoltaic system 500 is operating in a quasi-ideal condition (step 806). For example, for some embodiments, the diagnostic module 520 may calculate a maximum value (ρ) of the probability that the panel 502 is occluded_max) And a predetermined DMPP threshold (ρ)_DMPPT) For comparison. If ρ_maxLess than rho_DMPPTThe maximum output power and the minimum output power of the panels 502 are close enough, so the mismatch between the panels 502 can be considered as minimal and the system 500 can be considered to operate in a quasi-ideal state. Likewise, if ρ -_maxNot less than rho_DMPPTThe maximum output power and the minimum output power of the panels 502 are sufficiently different such that the probability of mismatch between the panels 502 cannot be considered as minimal and the system 500 is considered to be not operating under quasi-ideal conditions.

If the diagnostic module 520 determines that the system 500 is not operating in a quasi-ideal condition (step 806), the control module 525 enables the local controller 508 (step 808) and disables the global controller 540 (step 810), thereby placing the system 500 in DMPPT mode. Thus, in this case, the local controller 508 implements MPPT for each panel 502.

Because the DMPPT mode is used for relatively small mismatches between panels 502, the diagnostic module 520 may determine that the system 500 is not operating in a quasi-ideal condition even when the probability of occluded panels 502 is low (but not extremely low). Therefore, upon entering the DMPPT mode, the diagnostic module 520 determines whether the probability of the occluded panel 502 is high (step 812). For example, the diagnostic module 520 may determine the probability (ρ) that the panel 502 is obscured_max) And a predetermined diagnostic threshold (p)_diag) For comparison. If ρ_maxGreater than rho_diagThe maximum output power and the minimum output power of the panels 502 are sufficiently different, so that the probability of mismatch between the panels 502 is considered relatively high, and therefore, the probability of at least one panel 502 being shielded is high.

If the probability that a panel 502 is occluded is high (step 812), the diagnostic module 520 performs a full property scan for any panel 502 that is likely to be occluded (step 814). For example, the diagnostic module 520 may compare the probability of the panel being occluded (ρ) to a diagnostic threshold (ρ) by comparing, for each panel 502_diag). If p of a particular panel 502 is greater than p_diagIf the output power of a particular panel 502 is sufficiently different from the maximum output power of a panel 502 in the system 500, the probability that the particular panel 502 is at least partially shielded is relatively high.

In performing a full characteristic scan, the diagnostic module 520 may perform a voltage versus power characteristic scan individually for each panel 502 that is likely to be shadowed, according to the timing provided by the central array controller 510. In this manner, the conversion stage 512 may continue to operate normally during the scan.

If during any full performance scan, the diagnostic module 520 determines that any panel 502 is under-implemented (i.e., operating at a local Maximum Power Point (MPP), such as local MPP 720, rather than an actual MPP, such as MPP 725), the control module 525 may provide a correction for the under-implemented panel 502 (step 816).

At this point, or if the probability that the panel 502 is occluded is not high (step 812), the diagnostic module 520 determines whether the timer expires (step 818), indicating that the method 800 must be initialized again. Upon expiration of the timer (step 818), the diagnostic module 520 resets the timer (step 820) and begins analyzing the panel 502 again (step 804).

If the diagnostic module 520 determines that the system 500 is operating in a quasi-ideal condition (step 806), the control module 525 disables the local controller 508 (step 822) and enables the global controller 540 (step 824), thereby placing the system 500 in the CMPPT mode. Thus, in this case, the overall controller 540 implements MPPT for the entire system 500.

And at this point the diagnostic module 520 determines whether the timer has expired (step 818), indicating that the method 800 must be initialized again. Upon expiration of the timer (step 818), the diagnostic module 520 resets the timer (step 820) and begins analyzing the panel 502 again (step 804).

Although fig. 8 shows an example of a method 800 of selecting between centralized and distributed MPPT, various changes may be made to the method 800. For example, although the method 800 is described in connection with a photovoltaic system, the method 800 may be used with other energy generating systems 500, such as wind turbine systems, fuel cell systems, and the like. Still further, although the method 800 is described in conjunction with the system 500 of FIG. 5, it should be appreciated that the method 800 may be used with any suitably configured energy generating system without departing from the scope of the disclosure. Moreover, although a series of steps is shown, the steps in method 800 may overlap, occur in parallel, occur multiple times, or occur in a different order.

Fig. 9 illustrates a system 900 for a local controller 908 for starting and stopping a local converter 904 in an energy generating system, according to one embodiment of the disclosure. The system 900 includes an energy generating device 902 (referred to as a photovoltaic panel 902), and a local converter 904. The local converter 904 includes a power stage 906, a local controller 908, and an initiator 910.

The local converter 904 may represent one of the local converters 104 in fig. 1B, 204 in fig. 2 or 3, and/or one of the local converters 504 in fig. 5, however, it should be appreciated that the local converter 904 may be implemented in any suitably arranged energy generating system without departing from the scope of the disclosure. Thus, it should be appreciated that the system 900 may be coupled in series and/or in parallel to other similar systems 900 to form an energy generating array.

For the illustrated embodiment, actuator 910 is coupled between panel 902 and local controller 908. For some embodiments, the starter 910 can start and stop the local controller 908 based on the output voltage of the panel 902. When the output voltage of panel 902 is too low, initiator 910 can provide substantially zero supply voltage to local controller 908, thereby turning off local controller 908. When the output voltage of the panel 902 is high, the initiator 910 can provide a non-zero supply voltage to the local controller 908 to make the local controller 908 operational.

It should be appreciated that the initiator 910 may activate and deactivate the local controller 908 in any suitable manner other than providing a supply voltage to the local controller 908. For example, for an alternative embodiment, the initiator 910 may set one or more pins of the local controller 908 to activate and deactivate the local controller 908. For another alternative embodiment, the initiator 910 may write a first predetermined value into a first register of the local controller 908 to activate the local controller 908 and a second predetermined value (which may be the same or different from the first predetermined value depending on the particular implementation) into the first register or a second register of the local controller 908 to deactivate the local controller 908.

Thus, the system 900 enables the spontaneous operation of the local converter 904 without the use of batteries or external power sources. When the solar radiation is high enough, the panel voltage V is output_panTo make the starter910 begin generating a non-zero supply voltage V_CCThe level of (c). At this point, the local controller 908 and/or the central array controller (not shown in fig. 9) may begin to perform start-up procedures, such as initialization of registers, preliminary voltage comparisons between panels 902, analog-to-digital converter calibration, frequency synchronization or interpolation, synchronous start-up of the power stage 906 and/or the central array controller, etc. Similarly, prior to stopping system 900, a stopping procedure may be implemented, such as in the case of a stand-alone application, synchronization with a backup unit, synchronization with power stage 906 stopping, and the like. The initiator 910 can remain activated during the stopping procedures.

Further, for some embodiments, the initiator 910 can provide over-power protection for the local converter 904. As described above in connection with fig. 3, the MPPT control block 304, which is part of the local controller 208, may provide over-power protection. However, as an alternative embodiment to a system that includes initiator 910, initiator 910 could instead provide such protection. Thus, for this alternative embodiment, if the output current drops too low, the starter 910 may shut down the MPPT function of the local controller 908, causing the panel voltage V to go low_panIs almost equal to the output voltage V_out。

FIG. 10 is a graph 920 showing the change in device voltage over time for system 900, according to an embodiment of the disclosure. For photovoltaic panel 902, the voltage at starter 910 starts the level (V) at the solar radiation level_t-on) In the case of a nearby oscillation, the same voltage start level is used as the voltage stop level (V)_t-off) Undesirable multiple starts and stops of the system 900 may occur. Therefore, as shown in fig. 920, a lower voltage stop level is used to avoid this phenomenon. By using a lower voltage stop level, the system 900 can maintain consistent activation until the solar radiation level drops sufficiently such that the panel voltage drops below the voltage activation level. Thus, frequent starts and stops may be avoided, providing noise immunity to the system 900.

For some embodiments, after the panel voltage exceeds the voltage enable level at which the local controller 908 is enabled, if the panel voltage drops below the voltage enable level, the local controller 908 starts the stop procedure to be able to stop more quickly than if the panel voltage continues to drop below the voltage stop level. Further, for some embodiments, the local controller 908 may, in some cases, shut down the initiator 910 and itself before the voltage stop level is reached.

FIG. 11 shows an initiator 910 according to an embodiment of the disclosure. For this embodiment, the starter 910 includes a power source 930, a plurality of resistors R1, R2, R3, and a diode D. Resistors R1 and R2 are coupled IN series between the Input Node (IN) of the power supply 930 and ground. The diode and resistor R3 are coupled in series between the output node (OUT) of the power supply 930 and the node 940, and the resistors R1 and R2 are coupled at the node 940. In addition, the stop node (SD) of the power supply 930 is also coupled to the node 940.

The power supply 930 can receive the panel voltage V at the input node_panAnd generates a supply voltage V at the output node for the local controller 908_CC. If the voltage level of the stop node determined by the control circuit of the power supply 930 exceeds the predetermined voltage V₀The stop node of the power supply 930 enables operation of the power supply 930 and if the voltage level of the stop node drops below a prescribed voltage V₀The stop node stops the operation of the power supply 930.

When the power supply 930 is turned off, the diode does not conduct and the voltage at the termination node is represented by:

$V_{\mathrm{SD},t-\mathrm{on}}=V_{\mathrm{pan}}\frac{R_2}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HPA00001278906100051.png,HPA00001278906100061.png"\; state="\{\{state\}\}">R</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HPA00001278906100051.png,HPA00001278906100131.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}$

when the voltage V is_SDt-onOver value V₀At this time, the diode starts to conduct, and the voltage at the stop node becomes:

$V_{\mathrm{SD},t-\mathrm{off}}={\mathrm{<figure-callout\; id="2"\; label="V\; pan\; R"\; filenames="HPA00001278906100051.png,HPA00001278906100131.png"\; state="\{\{state\}\}">V</figure-callout>}}_{\mathrm{pan}}\frac{R_{}}{}\frac{{}_2//R_3}{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HPA00001278906100051.png,HPA00001278906100061.png"\; state="\{\{state\}\}">R</figure-callout>}}_1+{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HPA00001278906100051.png,HPA00001278906100131.png"\; state="\{\{state\}\}">R</figure-callout>}}_2//R_3}+(V_{\mathrm{cc}}-V_d)\frac{{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HPA00001278906100051.png,HPA00001278906100061.png"\; state="\{\{state\}\}">R</figure-callout>}}_1//R_2}{R_3+{\mathrm{<figure-callout\; id="1"\; label="R"\; filenames="HPA00001278906100051.png,HPA00001278906100061.png"\; state="\{\{state\}\}">R</figure-callout>}}_1//{\mathrm{<figure-callout\; id="2"\; label="R"\; filenames="HPA00001278906100051.png,HPA00001278906100131.png"\; state="\{\{state\}\}">R</figure-callout>}}_2}$

wherein, V_dIs a diode drop, and. When the voltage V is_SD，t-offDown to below V₀At this time, the power supply 930 is turned off. The turn-on and turn-off voltage thresholds can be determined according to the resistance values of the resistors R1, R2, and R3.

FIG. 12 shows a method 1200 for starting and stopping a local converter 904, according to an embodiment of the disclosure. The embodiment of the method 1200 is merely illustrative. Other embodiments of the method 1200 may be implemented without departing from the scope of the disclosure.

The method 1200 begins with the energy generating device or panel 902 operating in an open circuit condition (step 1202). In this condition, the starter 910 does not start the local converter 908 because the panel voltage output by the panel 902 is too low. Starter 910 monitors the panel voltage (V)_pan) Until the panel voltage exceedsVoltage start level (V)_t-on) Until then (step 1204).

Once the initiator 910 determines that the panel voltage has exceeded the voltage enable level (step 1204), the initiator 910 begins to enable the local converter 904 by turning on the local controller 908 (step 1206). For example, the initiator 910 may be activated by generating a non-zero supply voltage V for the local controller 908_CCAnd the local converter 904 is started. For other embodiments, the initiator 910 may initiate the local translator 904 by setting one or more pins of the local controller 908, or by writing a first predetermined value into a first register of the local controller 908. The local controller 908 and/or the central array controller then performs a start-up procedure on the local converter 904 (step 1208). For example, the start-up procedure may include initialization of registers, preliminary voltage comparisons between panels 902, analog-to-digital converter calibration, frequency synchronization or interpolation, synchronous start-up of a series of panels including power stage 906, and the like.

The local controller 908 operates the power stage 906 at a predetermined conversion ratio (step 1210) until other power stages 906 in the string are operated (step 1212). Once each panel 902 in the string has an operating power stage 906 (step 1212), the local controller 908 sources the panel current (I)_pan) And the starting current level (I)_min) Are compared (step 1214). If the panel current is greater than the activation current level (step 1214), the local controller begins operating normally (step 1216). Thus, the local controller 908 begins implementing MPPT for the power stage 906.

In this manner, the activation of all local controllers 908 in the energy generating system may be synchronized automatically. Additionally, if only a subset of panels 902 in the photovoltaic system generate a voltage high enough to activate the starter 910, a unidirectional switch (e.g., switch 314) may be included in each power stage 906 to allow operation of the remaining panels 902.

The local controller 908 continuously compares the panel current to the enable current level (step 1218). If the panel current is less than the start-up current level (1218), the local controller 908 sets a stop timer (1220). The local controller 908 then operates the power stage 906 again at the predetermined conversion ratio (step 1222). The local controller 908 and/or the central array controller then performs a stop procedure for the local converter 904 (step 1224). For example, the stopping procedure may include synchronization with the backup unit, synchronization with the power stage 906 stopping, etc. in the case of a stand-alone application.

The local controller 908 then determines whether the stop timer has expired (step 1226). This allows the panel current to rise to a time exceeding the activation current level. Thus, the local controller 908 prepares for a stop, but waits to ensure that a stop should actually be performed.

Thus, as long as the stop timer has not expired (step 1226), the local controller 908 will still compare the panel current to the start-up current level (step 1228). If the panel current continues to remain at less than the start-up current level (step 1228), the local controller 908 continues to wait for the expiration of the stop timer (step 1226). If the panel current becomes greater than the start-up current level (step 1228) before the timer expires (step 1226), the local controller 908 can again operate normally by performing MPPT on the power stage 906 (step 1216).

However, if the stop timer expires (step 1226) when the panel current is less than the start-up current level (step 1228), then the local controller 908 turns off the power stage 906 and the local controller 908 and again operates the panel 902 in an open circuit condition (step 1230). For some embodiments, starter 910 may be implemented by generating a zero supply voltage V_CCThe local controller 908 completes the stopping of the local converter 904. For other embodiments, the initiator 910 may complete the stopping of the local converter 904 by setting one or more pins of the local controller 908, or by writing a second predetermined value into a first register or a second register of the local controller 908. At this point, the initiator 910 again monitors the panel voltage until the panel voltage exceeds the voltage initiation level (step 1204), reinitializing the initiation of the initiationAnd (6) processing.

Although fig. 12 shows an example of a method 1200 for starting and stopping the local converter 904, various changes may be made to the method 1200. For example, although the method 1200 is described in terms of photovoltaic panels, the method 1200 may be used with other energy generating devices 902, such as wind turbines, fuel cells, and the like. Further, although the method 1200 is described with reference to the local controller 908 and the initiator 910 of fig. 9, it should be appreciated that the local controller 908 and the initiator 910 may be used with any suitably configured energy generating system without departing from the scope of the disclosure. Also, although shown as a series of steps, the steps in method 1200 may overlap, occur in parallel, occur multiple times, or occur in a different order.

Although the description above refers to particular embodiments, it should be understood that certain components, systems, and methods described may be used in a horizontal electrophoresis tank (sub-cell), a single cell, a panel (i.e., a battery array), a panel array, and/or a system of panel arrays. For example, although the local converters are each connected to a panel, similar systems may be implemented with a local converter connected to each cell in a panel, or a local converter connected to each row of panels. Furthermore, some of the components, systems, and methods described above may be used in other energy generating devices besides photovoltaic devices, such as wind turbines, fuel cells, and the like.

The definitions of certain words and phrases used herein are set forth by those of ordinary skill in the art. The term "couple" and its derivatives refer to any direct or indirect communication between two or more elements, whether or not those elements are in physical contact with one another. The terms "transmit", "receive", and "communicate", and derivatives thereof, encompass both direct and indirect communication. The terms "including" and "comprising" and derivatives thereof mean including but not limited to. The term "or" is inclusive, meaning and/or. The term "each" means each of at least one subcombination of the referenced items. The terms "associated with" and derivatives thereof are intended to include, be inclusive, be interconnected with, include, be inclusive, be connected to or connected to, be coupled to or coupled to, communicate with, cooperate with, be interposed in, be juxtaposed in, be proximate to, be joined to or joined with, have certain properties, etc.

While the disclosure has been described with reference to specific embodiments and associated methods, alterations and combinations of such embodiments and methods will be readily apparent to those skilled in the art. Accordingly, the above description of example embodiments does not define or constrain this disclosure. Other changes, substitutions, and alterations are also possible without departing from the spirit and scope of this disclosure, as defined by the following claims.

Claims (20)

1. A system for integrating local Maximum Power Point Tracking (MPPT) into an energy generating system having centralized MPPT, comprising:

a system control loop including a system operating frequency; and

a plurality of local control loops, each local control loop including a corresponding local operating frequency, wherein each of the local operating frequencies is separated from the system operating frequency by at least a predetermined distance.

2. The system of claim 1, wherein the system control loop comprises a closed loop system and each of the local control loops comprises a closed loop system.

3. The system of claim 1, wherein the system control loop comprises an array of energy generating devices and a DC-AC converter comprising a central MPPT control block capable of providing MPPT to the array.

4. The system of claim 1, wherein each of the local control loops includes an energy generating device and a local converter, the local converter being capable of providing MPPT to the energy generating device.

5. The system of claim 1, wherein the system operating frequency comprises a corresponding time constant of the system control loop.

6. The system of claim 5, wherein each of the local operating frequencies includes a corresponding settling time of the local control loop corresponding to the local operating frequency.

7. The system of claim 6, wherein the settling time of each local control loop is faster than the time constant of the system control loop.

8. The system of claim 6, wherein the settling time of each of the local control loops is at least five times faster than the time constant of the system control loop.

9. A system for integrating local Maximum Power Point Tracking (MPPT) into an energy generating system having centralized MPPT, comprising:

a system control loop comprising an array of energy generating devices and a DC-AC converter comprising a central MPPT control block capable of providing MPPT to the array, wherein the system control loop is capable of operating based on a system operating frequency; and

a plurality of local control loops, each of the local control loops including one of the energy generating devices and a local converter capable of providing MPPT to the energy generating device, wherein each of the local control loops is operable based on a corresponding local operating frequency, and wherein each of the local operating frequencies is separated from the system operating frequency by at least a predetermined distance.

10. The system of claim 9, wherein the system control loop comprises a closed loop system and each of the local control loops comprises a closed loop system.

11. The system of claim 9, wherein the system operating frequency comprises a corresponding time constant of the system control loop.

12. The system of claim 11, wherein each of the local operating frequencies includes a corresponding settling time of the local control loop corresponding to the local operating frequency.

13. The system of claim 12, wherein the settling time of each local control loop is faster than the time constant of the system control loop.

14. The system of claim 12, wherein the settling time of each of the local control loops is at least five times faster than the time constant of the system control loop.

15. A method for integrating local Maximum Power Point Tracking (MPPT) into an energy generating system having centralized MPPT, comprising:

providing a system control loop including a system operating frequency, and

a plurality of local control loops are provided, each local control loop including a corresponding local operating frequency, wherein each of the local operating frequencies is separated from the system operating frequency by at least a predetermined distance.

16. The method of claim 15, wherein the system operating frequency comprises a corresponding time constant of the system control loop.

17. The method of claim 16, wherein each of the local operating frequencies includes a corresponding settling time of the local control loop corresponding to the local operating frequency.

18. The method of claim 17 wherein the settling time of each local control loop is faster than the time constant of the system control loop.

19. The method of claim 17 wherein the settling time of each of the local control loops is at least five times faster than the time constant of the system control loop.

20. The method of claim 15, wherein the system control loop includes an array of energy generating devices and a DC-AC converter including a central MPPT control block that provides MPPT for the array, and wherein each of the local control loops includes one of the energy generating devices and a local converter that provides MPPT for the energy generating device.

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