CN114499259B - Single-phase five-level photovoltaic grid-connected inverter and control method thereof - Google Patents
Single-phase five-level photovoltaic grid-connected inverter and control method thereof Download PDFInfo
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M7/00—Conversion of ac power input into dc power output; Conversion of dc power input into ac power output
- H02M7/42—Conversion of dc power input into ac power output without possibility of reversal
- H02M7/44—Conversion of dc power input into ac power output without possibility of reversal by static converters
- H02M7/48—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode
- H02M7/53—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal
- H02M7/537—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters
- H02M7/5387—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration
- H02M7/53871—Conversion of dc power input into ac power output without possibility of reversal by static converters using discharge tubes with control electrode or semiconductor devices with control electrode using devices of a triode or transistor type requiring continuous application of a control signal using semiconductor devices only, e.g. single switched pulse inverters in a bridge configuration with automatic control of output voltage or current
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J3/00—Circuit arrangements for ac mains or ac distribution networks
- H02J3/38—Arrangements for parallely feeding a single network by two or more generators, converters or transformers
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/08—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters
- H02M1/088—Circuits specially adapted for the generation of control voltages for semiconductor devices incorporated in static converters for the simultaneous control of series or parallel connected semiconductor devices
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02M—APPARATUS FOR CONVERSION BETWEEN AC AND AC, BETWEEN AC AND DC, OR BETWEEN DC AND DC, AND FOR USE WITH MAINS OR SIMILAR POWER SUPPLY SYSTEMS; CONVERSION OF DC OR AC INPUT POWER INTO SURGE OUTPUT POWER; CONTROL OR REGULATION THEREOF
- H02M1/00—Details of apparatus for conversion
- H02M1/12—Arrangements for reducing harmonics from ac input or output
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- H—ELECTRICITY
- H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER
- H02J—CIRCUIT ARRANGEMENTS OR SYSTEMS FOR SUPPLYING OR DISTRIBUTING ELECTRIC POWER; SYSTEMS FOR STORING ELECTRIC ENERGY
- H02J2300/00—Systems for supplying or distributing electric power characterised by decentralized, dispersed, or local generation
- H02J2300/20—The dispersed energy generation being of renewable origin
- H02J2300/22—The renewable source being solar energy
- H02J2300/24—The renewable source being solar energy of photovoltaic origin
- H02J2300/26—The renewable source being solar energy of photovoltaic origin involving maximum power point tracking control for photovoltaic sources
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- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
- Y02E10/00—Energy generation through renewable energy sources
- Y02E10/50—Photovoltaic [PV] energy
- Y02E10/56—Power conversion systems, e.g. maximum power point trackers
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Abstract
The invention provides a single-phase five-level photovoltaic grid-connected inverter with active power decoupling and boosting functions and a control method thereof. The five-level inverter consists of a photovoltaic cell, a bus capacitor, a first half-bridge reversing circuit, a second half-bridge boosting circuit, a third half-bridge T-shaped three-level circuit and a filter circuit. The upper end and the lower end of the first half-bridge reversing circuit are connected with the anode and the cathode of the bus capacitor, and the middle point of the bridge arm is connected with the negative end of the power grid. The positive electrode of the photovoltaic cell is connected to the midpoint of the second half-bridge circuit through a direct current filter inductor to form the second half-bridge boost circuit together. The input end of the third half-bridge T-shaped three-level circuit is connected with the photovoltaic cell, the upper end and the lower end of the third half-bridge T-shaped three-level circuit are connected with the anode and the cathode of the bus capacitor, the middle point of the third half-bridge T-shaped three-level circuit is connected with one end of the filter circuit, and the other end of the filter circuit is connected to the anode of the power grid. The power decoupling of the single-phase five-level inversion system can be automatically realized by controlling the voltage of the photovoltaic cell to be a constant value and the grid-connected current to be a sine value in real time through a closed loop. The proposed inverter topology and control strategy have the functions of boosting and decoupling active power while realizing multi-level output, and can effectively improve the tracking efficiency and reliability of the maximum power point of the photovoltaic inverter system.
Description
Technical Field
The invention relates to the technical field of power electronics and the field of photovoltaic new energy power generation, in particular to a single-phase photovoltaic five-level grid-connected inverter with active power decoupling and boosting functions and a control strategy thereof.
Background
With the increasing exhaustion of traditional fossil energy sources and the increasing severity of environmental pollution problems, clean energy sources such as photovoltaic power generation and the like have become hot spots of current world research. The photovoltaic inverter is used as an important component of a photovoltaic power generation system, and plays a vital role in safe and reliable operation of the system and efficient energy utilization.
With the development of power electronics technology and the development of the strategy of the photovoltaic industry of 'silicon in copper out', photovoltaic inverters are developed towards high efficiency, high power density and medium and high voltage. Compared with the traditional three-level inverter, the multi-level inverter has the advantages of small voltage stress, low grid-connected current harmonic wave, small filter inductance and the like, and is widely applied to medium-high voltage occasions. However, the conventional multilevel inverter requires a large number of components and has single functions, so that the utilization rate of the components is low.
In addition, in a single-phase inverter system, the inherent frequency doubling power pulsation of the system can influence the power quality of grid-connected current, and the tracking efficiency of the maximum power point of the system is reduced. To buffer the doubling power ripple, there are generally two types of methods: 1) A larger electrolytic capacitor or an LC series resonant circuit is incorporated at the DC side; 2) An active decoupling circuit is additionally added. The method is simple and direct, but the cumbersome electrolytic capacitor or LC resonance circuit reduces the power density and reliability of the system; and the second method needs an extra hardware circuit, which increases the cost of the system.
Disclosure of Invention
The invention provides a single-phase five-level photovoltaic grid-connected inverter and a control strategy thereof, and aims to reduce the cost of a photovoltaic power generation system while achieving the functions of multi-level output, boosting, power decoupling and the like of the single-phase photovoltaic power generation system.
In order to achieve the above purpose, the embodiment of the invention provides a single-phase five-level photovoltaic grid-connected inverter with active power decoupling and boosting functions and a control strategy thereof, and the specific technical scheme is as follows:
in a first aspect, an embodiment of the present invention provides a single-phase five-level photovoltaic grid-connected inverter topology, including a photovoltaic cell, a bus capacitor, a first half-bridge reversing circuit, a second half-bridge boosting circuit, a third half-bridge T-type three-level circuit, and a filter circuit; wherein,
The first half-bridge reversing circuit consists of an upper bridge arm switch tube S 1 and a lower bridge arm switch tube S 2; the second half-bridge boosting circuit consists of an upper bridge arm switch tube S 3,S4, a lower bridge arm switch tube S 3,S4 and a direct-current filter inductor; the third half-bridge T-shaped three-level circuit consists of an upper bridge arm switch tube S 6、S7, a lower bridge arm switch tube S 5 and a midpoint switch tube S 5; the filter circuit is composed of an L-type filter or an LC or LCL-type filter.
The collector of the switching tube S 1 of the first half-bridge reversing circuit is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 1 is connected with the electrode of the switching tube S 2, the connecting point is the midpoint of the first half-bridge reversing circuit, and the midpoint is connected with the negative electrode of the power grid; the emitter of the switch tube S 2 is connected with the cathode of the bus capacitor;
The collector of the switching tube S 3 of the second half-bridge boosting circuit is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 3 is connected with the electrode of the switching tube S 4, the connection point is the midpoint of the second half-bridge boosting circuit, and the midpoint is connected with one end of the direct current filter inductor L 1; the other end of the direct current filter inductor L 1 is connected with the positive electrode of the photovoltaic cell; the emitter of the switch tube S 4 is connected with the cathode of the bus capacitor;
The collector of the third half-bridge T-shaped three-level circuit switching tube S 6 is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 6 is connected with the electrode of the switching tube S 7, the connection point is a midpoint of the T-shaped three-level circuit, the midpoint is connected with one end of the switching tube S 5, and the other end is connected with one end of the alternating current filter; the other end of the switching tube S 5 is connected with the positive electrode of the photovoltaic cell, and the emitter of the switching tube S 7 is connected with the negative electrode of the bus capacitor; the other end of the alternating current filter circuit is connected with the positive electrode of the power grid.
The single-phase five-level inverter topology can output five levels in a power frequency period, and specifically comprises the following steps: when the switching tube S 2,S7 is turned on or the switching tube S 1,S6 is turned on and other switching tubes are turned off, the output voltage V ab of the converter is 0; when the switching tubes S 2 and S 5 are turned on and the other switching tubes are turned off, the output voltage V ab of the converter is V pv; when the switching tubes S 2 and S 6 are turned on and the other switching tubes are turned off, the output voltage V ab of the converter is V dc; when the switching tubes S 1 and S 5 are turned on and the other switching tubes are turned off, the output voltage V ab of the converter is V pv-Vdc; when the switching tubes S 1 and S 7 are on and the other switching tubes are off, the converter output voltage V ab is-V dc.
In a second aspect, an embodiment of the present invention provides a control strategy for a single-phase five-level photovoltaic grid-connected inverter, which is applied to the single-phase five-level photovoltaic grid-connected inverter in the first aspect, and the control method includes:
The inversion function is completed by the first half-bridge reversing circuit and the third half-bridge T-shaped three-level circuit; the boosting function, the active power decoupling function and the photovoltaic maximum power point tracking function are completed by the second half-bridge boosting circuit.
Wherein, the control implementation steps of the inversion part are as follows:
Step 11: setting the voltage reference of the bus capacitor as U dcref, making a difference between the reference voltage of the bus capacitor and the feedback voltage processed by the frequency doubling trap, inputting the value obtained after the difference into a voltage outer ring controller, and outputting the voltage outer ring controller as the amplitude value of the current inner ring reference;
Step 12: multiplying the current reference amplitude value by the cosine value of the locking angle of the phase-locked loop to obtain a current loop reference, and sending the current loop reference and the grid-connected feedback current into a current loop controller after making a difference;
Step 13: the current loop controller outputs a modulated wave, compares the modulated wave with a phase-shifted carrier or a laminated carrier, and generates a PWM wave to drive the switching tube S 1,S2,S5,S6,S7.
The control implementation steps of the boosting and power decoupling part are as follows:
step 21: obtaining a photovoltaic cell reference voltage U pvref through a maximum power point tracking algorithm, and sending the difference between the reference voltage and the feedback voltage into a voltage loop controller, wherein the voltage loop controller outputs the reference voltage as a current loop reference;
Step 22: the current reference and the feedback current are fed into a current loop controller after being differenced, and the current loop controller outputs modulated waves;
Step 23: the modulated wave is compared with the carrier wave to generate a PWM wave to drive the switching transistors S 3 and S 4.
Further, in step 21, the voltage loop controller needs to use a multi-resonant controller or a repetitive controller with 3 times, 5 times, 7 times, etc. odd harmonic suppression capability to realize power decoupling of the photovoltaic input side and the inverter output side.
The invention provides a single-phase five-level photovoltaic grid-connected inverter and a control strategy thereof, and compared with the prior art, the single-phase five-level photovoltaic grid-connected inverter has the following advantages:
1. The number of switching devices is small, and the cost is low. The proposed inverter topology can realize the boosting and five-level output functions only by seven switches, so that the system cost is reduced while the multifunction of the photovoltaic inverter is realized;
2. High reliability and high power density. According to the control strategy, the natural decoupling of the power of the system can be realized without an additional hardware circuit, and a small thin film capacitor can be used for replacing a heavy electrolytic capacitor, so that the reliability and the power density of the system are improved.
Therefore, the scheme provided by the invention is very suitable for a single-phase photovoltaic power generation system.
Drawings
Fig. 1 is a topology structure diagram of a single-phase five-level photovoltaic grid-connected inverter according to an embodiment of the present invention;
Fig. 2-3 are schematic diagrams of modulation diagrams and operating principles of the single-phase five-level photovoltaic inverter shown in fig. 1;
FIG. 4 is a schematic diagram of a single-phase five-level inverter control strategy shown in FIG. 1;
FIG. 5 is a diagram of dynamic and steady state simulation waveforms according to an embodiment of the present invention.
[ Reference numerals description ]
1-A first half-bridge commutation circuit; 2-a second half-bridge boost circuit; 3-a third half-bridge T-type three-level circuit; a 4-filter circuit;
Detailed Description
In order to make the technical problems, technical solutions and advantages to be solved more apparent, the following detailed description will be given with reference to the accompanying drawings and specific embodiments.
As shown in fig. 1, a single-phase five-level photovoltaic grid-connected inverter with active power decoupling and boosting functions comprises a photovoltaic cell PV, a bus capacitor C dc, a first half-bridge reversing circuit, a second half-bridge boosting circuit, a third half-bridge T-type three-level circuit and a filter circuit; wherein,
The first half-bridge reversing circuit consists of an upper bridge arm switch tube S 1 and a lower bridge arm switch tube S 2; the second half-bridge boosting circuit consists of an upper bridge arm switch tube S 3,S4, a lower bridge arm switch tube S 3,S4 and a direct-current filter inductor; the third half-bridge T-shaped three-level circuit consists of an upper bridge arm switch tube S 6、S7, a lower bridge arm switch tube S 5 and a midpoint switch tube S 5; the filter circuit is composed of an L-type filter or an LC or LCL-type filter.
The collector of the switching tube S 1 of the first half-bridge reversing circuit is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 1 is connected with the electrode of the switching tube S 2, the connecting point is the midpoint of the first half-bridge reversing circuit, and the midpoint is connected with the negative electrode of the power grid; the emitter of the switch tube S 2 is connected with the cathode of the bus capacitor;
The collector of the switching tube S 3 of the second half-bridge boosting circuit is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 3 is connected with the electrode of the switching tube S 4, the connection point is the midpoint of the second half-bridge boosting circuit, and the midpoint is connected with one end of the direct current filter inductor L 1; the other end of the direct current filter inductor L 1 is connected with the positive electrode of the photovoltaic cell; the emitter of the switch tube S 4 is connected with the cathode of the bus capacitor;
The collector of the third half-bridge T-shaped three-level circuit switching tube S 6 is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 6 is connected with the electrode of the switching tube S 7, the connection point is a midpoint of the T-shaped three-level circuit, the midpoint is connected with one end of the switching tube S 5, and the other end is connected with one end of the alternating current filter; the other end of the switching tube S 5 is connected with the positive electrode of the photovoltaic cell, and the emitter of the switching tube S 7 is connected with the negative electrode of the bus capacitor; the other end of the alternating current filter circuit is connected with the positive electrode of the power grid.
It should be noted that, the switching tube S 5 is formed by reversely connecting two conventional unidirectional switching tubes in series; the other switching tubes are all composed of switching tubes with anti-parallel diodes.
Fig. 2 and 3 are a modulation waveform diagram and an operation schematic diagram based on the single-phase five-level inverter shown in fig. 1, respectively.
As shown in fig. 3 (a) and 3 (b), when the switching tube S 2,S7 is turned on or the switching tube S 1,S6 is turned on and the other switching tubes are turned off, the output voltage of the converter is at 0 level;
As shown in fig. 3 (c), when the switching transistors S 2 and S 5 are turned on and the other switching transistors are turned off, the output voltage of the converter is V pv;
As shown in fig. 3 (d), when the switching transistors S 2 and S 6 are turned on and the other switching transistors are turned off, the output voltage of the converter is V dc;
As shown in fig. 3 (e), when the switching transistors S 1 and S 5 are turned on and the other switching transistors are turned off, the output voltage of the converter is V pv-Vdc;
As shown in fig. 3 (f), when the switching transistors S 1 and S 7 are on and the other switching transistors are off, the converter output voltage is-V dc.
Based on the single-phase five-level inverter shown in fig. 1, the embodiment of the invention provides a control strategy for the circuit, and a control structure schematic diagram of the control strategy is shown in fig. 4. Wherein, the control of the system comprises an inversion part, a boosting part and a power decoupling part.
The control implementation steps of the inversion part are as follows:
Step 11: setting the voltage reference of the bus capacitor as U dcref, making a difference between the reference voltage of the bus capacitor and the feedback voltage processed by the frequency doubling trap G noth(s), inputting the value obtained after the difference into a voltage outer ring controller G iv(s), and outputting the voltage outer ring controller as the amplitude I m of the current inner ring reference; wherein the transfer function of the frequency doubling trap is:
Where ζ is the bandwidth coefficient and ω n＝4πf0,f0 is the fundamental frequency.
Step 12: multiplying the current reference amplitude value by the sine value of the locking angle of the phase-locked loop to obtain a current loop reference I gref, and sending the current loop reference I gref to a current loop controller G ii(s) after the current loop reference is differenced with the grid-connected feedback current;
Step 13: the current loop controller outputs a modulated wave v m1, compares the modulated wave with a phase-shifted carrier or a laminated carrier v cr, and generates a PWM wave to drive the switching tube S 1,S2,S5,S6,S7.
The control implementation steps of the boost and power decoupling part are as follows:
Step 21: the photovoltaic cell reference voltage U pvref is obtained through a maximum power point tracking algorithm, the reference voltage and the feedback voltage are fed into a voltage loop controller G bv(s) after being subjected to difference, and the voltage loop controller outputs a current loop reference I lref;
Step 22: the current reference and the feedback current are fed into a current loop controller G bi(s) after being differenced, and the current loop controller outputs a modulation wave v m2;
Step 23: the PWM wave is generated by comparing the modulated wave with the carrier v tr to drive the switching transistors S 3 and S 4.
It should be emphasized that in step 21, the voltage loop controller G bv(s) needs to use a multi-resonant controller or a repetitive controller with 3 times, 5 times, 7 times, etc. odd harmonic suppression capability to avoid the pulsating power from penetrating to the photovoltaic cell side, so as to realize the natural power decoupling of the photovoltaic input side and the inverter output side.
In order to verify the superior performance of the proposed topology and control strategy, a single-phase five-level photovoltaic grid-connected inverter simulation platform shown in fig. 1 is constructed, and the system parameters are shown in the following table 1. Fig. 5 (a) is a simulation waveform diagram in a steady state, and fig. 5 (b) is a dynamic simulation waveform diagram of the system at the time of abrupt illumination. From the above figures, it can be seen that the system provided by the invention has the advantages of boosting and five-level output, and simultaneously realizes good power decoupling, so that the system is very suitable for single-phase photovoltaic power generation systems.
Table 1 system parameters
While the foregoing is directed to the preferred embodiments of the present invention, it will be appreciated by those skilled in the art that various modifications and adaptations can be made without departing from the principles of the present invention, and such modifications and adaptations are intended to be comprehended within the scope of the present invention.
Claims (7)
1. The single-phase five-level photovoltaic grid-connected inverter with the active power decoupling and boosting functions is characterized by comprising a photovoltaic cell, a bus capacitor, a first half-bridge reversing circuit, a second half-bridge boosting circuit, a third half-bridge T-shaped three-level circuit and a filter circuit;
The first half-bridge reversing circuit consists of an upper bridge arm switch tube S 1 and a lower bridge arm switch tube S 2; the second half-bridge boost circuit consists of an upper bridge arm switch tube S 3,S4, a lower bridge arm switch tube S 3,S4 and a direct current filter inductor, the third half-bridge T-shaped three-level circuit consists of an upper bridge arm switch tube S 6、S7, a lower bridge arm switch tube S 6、S7 and a midpoint switch tube S 5, and the filter circuit consists of an L-shaped filter or an LC or LCL-shaped filter;
The collector of the switching tube S 1 of the first half-bridge reversing circuit is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 1 is connected with the electrode of the switching tube S 2, the connecting point is the midpoint of the first half-bridge reversing circuit, the midpoint is connected with the negative electrode of the power grid, and the emitter of the switching tube S 2 is connected with the negative electrode of the bus capacitor;
The collector of the switching tube S 3 of the second half-bridge boosting circuit is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 3 is connected with the electrode of the switching tube S 4, the connecting point is the midpoint of the second half-bridge boosting circuit, the midpoint is connected with one end of the direct current filter inductor L 1, the other end of the direct current filter inductor L 1 is connected with the positive electrode of the photovoltaic cell, and the emitter of the switching tube S 4 is connected with the negative electrode of the bus capacitor;
The collector of the third half-bridge T-shaped three-level circuit switching tube S 6 is connected with the positive electrode of the bus capacitor, the emitter of the switching tube S 6 is connected with the electrode of the switching tube S 7, the connecting point is a midpoint of the T-shaped three-level circuit, the midpoint is connected with one end of the switching tube S 5 and one end of the alternating current filter, the other end of the switching tube S 5 is connected with the positive electrode of the photovoltaic cell, the emitter of the switching tube S 7 is connected with the negative electrode of the bus capacitor, and the other end of the alternating current filter circuit is connected with the positive electrode of the power grid.
2. The single-phase five-level photovoltaic grid-connected inverter according to claim 1, wherein the bidirectional switching tube S 5 in the circuit is composed of two conventional unidirectional switching tubes connected in series in opposite directions, and the switching tubes S 1,S2,S3,S4,S6,S7 are composed of switching tubes with antiparallel diodes.
3. The single-phase five-level photovoltaic grid-connected inverter according to claim 1, wherein five levels can be output in one power frequency period, respectively:
The switching tube S 2,S7 or the switching tube S 1,S6 is turned on, other switching tubes are turned off, and the output voltage V ab of the converter is 0;
Switching on the switching tubes S 2 and S 5, switching off the other switching tubes, and outputting voltage V ab of the converter to be V pv;
Switching on the switching tubes S 2 and S 6, switching off the other switching tubes, and outputting voltage V ab of the converter to be V dc;
switching on the switching tubes S 1 and S 5, switching off the other switching tubes, and outputting voltage V ab of the converter to be V pv-Vdc;
Switching on the switching tubes S 1 and S 7, switching off the other switching tubes, and enabling the output voltage V ab of the converter to be-V dc;
wherein V pv is photovoltaic voltage, and V dc is direct current bus voltage.
4. The control method of the single-phase five-level photovoltaic grid-connected inverter according to any one of claims 1 to 3 comprises the following steps:
The inversion function is completed by the first half-bridge reversing circuit and the third half-bridge T-shaped three-level circuit; the boosting function, the active power decoupling function and the photovoltaic maximum power point tracking function are completed by the second half-bridge boosting circuit.
5. The control method of the single-phase five-level photovoltaic grid-connected inverter according to claim 4, wherein the control implementation step of the inversion section is as follows:
Step 11: setting the voltage reference of the bus capacitor as U dcref, making a difference between the reference voltage of the bus capacitor and the feedback voltage processed by the frequency doubling trap, inputting the value obtained after the difference into a voltage outer ring controller, and outputting the voltage outer ring controller as the amplitude value of the current inner ring reference;
Step 12: multiplying the current reference amplitude value by the cosine value of the locking angle of the phase-locked loop to obtain a current loop reference, and sending the current loop reference and the grid-connected feedback current into a current loop controller after making a difference;
Step 13: the current loop controller outputs a modulated wave, compares the modulated wave with a phase-shifted carrier or a laminated carrier, and generates a PWM wave to drive the switching tube S 1,S2,S5,S6,S7.
6. The control method of the single-phase five-level photovoltaic grid-connected inverter according to claim 4, wherein the control implementation steps of the step-up and power decoupling portion are as follows:
step 21: obtaining a photovoltaic cell reference voltage U pvref through a maximum power point tracking algorithm, and sending the difference between the reference voltage and the feedback voltage into a voltage loop controller, wherein the voltage loop controller outputs the reference voltage as a current loop reference;
Step 22: the current reference and the feedback current are fed into a current loop controller after being differenced, and the current loop controller outputs modulated waves;
Step 23: the modulated wave is compared with the carrier wave to generate a PWM wave to drive the switching transistors S 3 and S 4.
7. The method according to claim 6, wherein the voltage loop controller in step 21 is a multi-resonant controller or a repetitive controller with 3 times, 5 times, 7 times, etc. odd harmonic suppression capability to achieve power decoupling between the photovoltaic input side and the inverter output side.
Priority Applications (1)
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