JP2005276942A - Solar cell power generator and system, and control method therefor - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve such a problem that, if the number of serial connections of solar cells forming a solar cell string, the voltage drop of the solar cell string is large when a partial shade is generated, and electric power generated in the solar cell string is greatly reduced, and as a result, a bypass diode for preventing the solar cell from being applied by a reverse voltage can prevent only the breakage of the solar cell, and it cannot substantially contribute to power generation so much as a current bypass for the partial shade, and to eliminate a bypass diode for the solar cell and enable the serial connection use of the solar cells with a low peak inverse voltage. <P>SOLUTION: A comparison circuit 9 inputs a minimum cell voltage Vc that a minimum cell voltage selection circuit 7 selects and outputs, inputs a specified voltage Vs that is set by a specified voltage setter 8, and outputs a stop signal 14 to a switching control circuit 10 when Vs is smaller than Vc. The switching control circuit 10 stops a gate driving signal when the comparison circuit 9 outputs the stop signal 14, and keeps the stop of the gate driving signal until the comparison circuit 9 stops outputting the stop signal 14. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a photovoltaic power generation apparatus and system, and a control method thereof.

  In general, a solar cell module is configured by connecting a large number of solar cells in series, and the solar cell modules are connected in series to form a string, thereby obtaining DC generated power to be supplied to an inverter or a DC / DC converter. ing. Then, the AC power output from the inverter is linked to the commercial power system, or the DC power output from the DC / DC converter is supplied to the load to effectively use the generated power of the solar cell module.

  In a solar cell module in which a large number of solar cells are connected in series, the solar cells in some areas will not generate electricity due to the insolation of some areas (hereinafter referred to as “partial shade”). When the power generation amount (or the power generation amount decreases), a reverse voltage is applied to the solar battery cell. Solar cells have a limit in the reverse voltage that can be withstood due to their structure. Therefore, as in the solar cell module 101 shown in FIG. 1, a bypass diode 103A-103D is provided in parallel with each solar cell 102A-102D to prevent a large reverse voltage from being applied to the solar cell 102A-102D. .

  However, the technique of providing a bypass diode in parallel with the solar battery cell has the following problems.

  (1) If the reverse withstand voltage of the solar cell is lower than the forward voltage drop of the bypass diode, the connection of the bypass diode cannot be a countermeasure for the reverse voltage, and such solar cells should be connected in series. I can't.

  (2) The bypass diode needs a current capacity sufficient to allow the maximum output current Isc of the solar battery cell to flow, and is never cheap. Furthermore, in the bypass diode, there is a power loss multiplied by its forward drop voltage and Isc, but this loss power becomes a heat loss of the bypass diode, so the heat dissipation of the bypass diode must also be taken into consideration. This increases the cost of the module.

Japanese Patent Laid-Open No. 3-24768

  The present invention solves the above-mentioned problems individually or collectively, and an object thereof is to eliminate the need for a bypass diode of a solar battery cell.

  Another object is to enable the use of series connection of solar cells having a low reverse withstand voltage.

  The present invention has the following configuration as one means for achieving the above object.

  The solar power generation device of the present invention is provided in each of the solar battery modules in which a plurality of solar battery blocks each including one or more solar battery cells are connected in series, and detects a voltage across the solar battery block. A plurality of voltage detection means, a power conversion means for converting power output from the solar cell module, and a power conversion based on a result of comparing a voltage between both ends detected by the plurality of voltage detection means with a predetermined voltage. Control means for controlling the means.

  The solar power generation system of the present invention includes a plurality of the above-described solar power generation devices, and further includes an inverter that converts electric power output from the plurality of solar power generation devices into commercial AC power.

  The control method according to the present invention includes a plurality of solar battery modules each including one or more solar battery cells connected in series, and a plurality of solar battery blocks that detect a voltage across the solar battery block. And a voltage conversion means for converting the power output from the solar cell module, and a both-end voltage and a predetermined voltage detected by the plurality of voltage detection means. The power conversion means is controlled based on the result of comparing the above.

  According to the present invention, the bypass diode of the solar battery cell can be made unnecessary. Therefore, it is possible to eliminate the cost increase factor of the solar cell module related to the heat dissipation measures of the bypass diode. In addition, the bypass diode is difficult to integrate because of a large heat loss. On the other hand, the voltage detection unit, the control unit for controlling the power conversion unit, etc. can be integrated, and the cost reduction is expected due to the mass production effect. . Therefore, for example, the voltage detection unit, the minimum cell voltage selection circuit, the specified voltage setting unit, the comparison circuit, and the switching control circuit, which will be described later, are weak power circuits that hardly generate heat loss. It is desirable to reduce costs by doing so. In addition, for example, a control circuit that prevents the reverse voltage from being applied to the cell is integrated with the switching control circuit of the power conversion device to form an IC chip, thereby reducing the cost.

  Moreover, the series connection use of the photovoltaic cell with a low reverse withstand voltage can be enabled.

  DESCRIPTION OF EMBODIMENTS Hereinafter, a photovoltaic power generation apparatus and system according to embodiments of the present invention will be described in detail with reference to the drawings.

[Overview]
The inventors noticed that the effect of the bypass diode is small when a series of solar cells (hereinafter referred to as “solar cell string”) is configured with a small number of solar cell modules. The reason is that since the number of solar cells in the solar cell string in series is small, the voltage drop of the solar cell string when a partial shade occurs is large, and the generated power of the solar cell string is greatly reduced. In other words, the bypass diode has only the meaning of preventing the destruction of the solar battery cell, and it can be said that it does not contribute much to power generation even as a current bypass when a partial shade occurs.

  Further, when a photovoltaic power generation system is configured by connecting many solar cell strings in parallel, even if the output of one solar cell string is stopped or reduced, the influence on the entire system is small.

  If all the output of the solar cell string is stopped or reduced, the current flowing through the solar cell module becomes zero or lower, so that the reverse voltage applied to each solar cell is eliminated or greatly reduced, and the bypass diode is reduced. Even if it deletes, a photovoltaic cell is not destroyed. Furthermore, if a solar cell module having an AC module or a DC / DC converter having a power converter for each solar cell module as a solar power generation device constituting the solar power generation system, means for controlling the output to the solar cell module Is built in, and the output of the solar cell module can be easily controlled.

  Furthermore, since a large number of small-capacity power converters are provided in one system, mass production of power converters can be expected. Therefore, the control circuit of the present invention and the switching control circuit of the power conversion device are integrated into an IC chip, so that it can be configured at low cost. As a result, it is possible to construct an inexpensive solar power generation system that does not have a bypass diode that is difficult to be integrated into an IC chip because a large current flows and generates a large amount of heat.

[Constitution]
FIG. 2 is an overview diagram of the photovoltaic power generation system, and FIG. 3 is a block diagram showing an example of the configuration of the photovoltaic power generation system.

  As shown in FIGS. 2 and 3, the photovoltaic power generation system of Example 1 converts the DC power generated by a plurality of DC / DC converter-equipped solar cell modules 1 into AC power by an inverter 2, and commercial power system Connect to 3. 2 and 3 show an example of a grid interconnection system in which three solar cell modules 1 are connected in parallel. The number of parallel solar cell modules 1 depends on the installation area of the solar cell module 1 and the generated power. Can be set arbitrarily.

● Solar cell module 1
The solar cell module 1 composed of the solar cell module 1a and the DC / DC converter 1b is installed outdoors such as a roof where sunlight is irradiated without being blocked, and the number of solar cells connected in series is limited and compared. The output voltage is configured to be low.

  In the vicinity of the solar cell module 1a, there is provided a DC / DC converter 1b that boosts the output power of the low-voltage / high-current solar cell module 1a and converts it into high-voltage / small-current DC power. This is intended to reduce transmission loss of a relatively long transmission path to the inverter 2 in the room.

  The DC / DC converter 1b changes the output operating point of the solar cell module 1a as the input source while changing the on / off ratio (duty ratio) of the switching operation to make the output voltage (for example, about 320V) constant. Can do. Therefore, the DC / DC converter 1b performs maximum power operating point tracking (MPPT) control of the solar cell module 1a by monitoring the input power or output power and changing the operating point of the solar cell module 1a.

Note that the solar cell module 1 can obtain an output power of about 60 W at the rated time (irradiation of 1 kW / m ² ).

● Inverter 2
The inverter 2 converts the DC power output from the solar cell module 1 into commercial AC power by high-frequency switching using a bridge circuit. The inverter 2 connects the input DC power to the commercial power system 3 by performing publicly known output current control and output voltage control.

  The inverter 2 is assumed to convert DC power (maximum 60 W, approximately 320 V) input from the three solar cell modules 1 into single-phase three-wire commercial AC power (200 V, approximately 180 W).

[Configuration of solar cell module]
FIG. 4 is a diagram showing a detailed configuration example of the solar cell module 1. As shown in FIG.

  The solar cell module 1a has a plurality of solar cells 4 connected in series. Further, the solar cell module 1 includes a cell voltage detection unit 6, a cell voltage minimum value selection circuit 7, a specified voltage setting unit 8, a comparison circuit 9, a switching control circuit 10, a DC / DC converter main circuit 11 and the like which will be described later.

● Solar cell 4
Types of solar cells 4 include those using an amorphous silicon system for the photoelectric conversion part, polycrystalline silicon, and those using crystalline silicon. What is the solar cell 4 used in this example? Any kind is acceptable. Generally, a solar cell using amorphous silicon is a thin film and tends to have a low reverse withstand voltage compared to crystalline silicon. In the present embodiment, a solar battery cell 4 having the following characteristics in which amorphous silicon is laminated in three layers is used.
Rated solar radiation: 1kW / m ² Ambient temperature 25 ℃
Short-circuit current Isc: 12.0A
Open circuit voltage Voc: 2.0V
Maximum operating point current Ipm: 10.0A
Maximum operating point voltage Vpm: 1.5V
Maximum output Pmax: 15W
Reverse withstand voltage: -2.0V

● Solar cell module 1a
If the number of series-connected solar cells 4 constituting the solar cell module 1a is too small, the step-up ratio of the DC / DC converter 1b increases and the conversion efficiency of the DC / DC converter 1b decreases. On the other hand, when connecting the solar cells 4 in series, it is necessary to provide a non-power generation region that does not generate power between the solar cells 4 having different potentials. Therefore, if the number of series is increased, the active area (power generation region) of the solar cell module 1a is increased. The conversion efficiency of the solar cell module 1a is reduced. In view of such circumstances, in this embodiment, the solar battery module 1a is configured by connecting four solar battery cells 4 in series. The rated output characteristics of the solar cell module 1a are as follows.
Rated solar radiation: 1kW / m ² Ambient temperature 25 ℃
Short-circuit current Isc: 12.0A
Open circuit voltage Voc: 8.0V
Maximum operating point current Ipm: 10.0A
Maximum operating point voltage Vpm: 6.0V
Maximum output Pmax: 60W

  In the present embodiment, a solar cell string (solar cell module series body) is constituted only by the solar cell module 1a.

● Cell voltage detector 6
The cell voltage detection circuit 6 provided in each of the four solar cells 4A-4D may have any configuration as long as the potential difference between the positive electrode and the negative electrode of each solar cell can be detected. In this embodiment, an operational amplifier is used to form a differential amplifier with a single amplification factor, and the cell voltage detection circuit 6 is formed.

  In order to enable the cell voltage detector 6 composed of an operational amplifier to output a negative voltage, a small DC / DC converter (not shown) is provided at the input terminal of the DC / DC converter 1b, and the operational amplifier has a negative power supply. Etc. are necessary.

● Minimum cell voltage selection circuit 7
The minimum cell voltage selection circuit 7 inputs all the outputs of the cell voltage detection circuit 6 and selects and outputs those minimum values. The minimum value of the cell voltage indicates the cell voltage of the solar battery cell 4 in which the amount of power generation is the lowest due to a shadow or the like, and the cell voltage can be negative (reverse voltage state) depending on the degree of shading.

● Regulatory voltage setting section 8
The specified voltage setting unit 8 is for setting a specified voltage in consideration of the reverse withstand voltage of the solar battery cell 4. The reverse withstand voltage of the solar battery cell 4 of the present embodiment has a margin of −2.0V, for example, −1.2V is set as the specified voltage. The specified voltage setting unit 8 may be configured to arbitrarily adjust the specified voltage using a variable resistor or the like, or the specified voltage may be fixed by dividing the fixed resistor.

● Comparison circuit 9
The comparison circuit 9 includes a cell voltage (minimum cell voltage) of the solar battery cell 4 in which the amount of power generation has fallen the most due to a shadow, etc. -1.2V) is input. When the minimum cell voltage falls below the specified voltage, the comparison circuit 9 outputs a stop signal 14 indicating that the DC / DC converter is stopped to the switching control circuit 10.

  Without using the minimum cell voltage selection circuit 7, all outputs of the cell voltage detection circuit 6 and the specified voltage of the specified voltage setting unit 8 are input to the comparison circuit 9, and one of the cell voltages falls below the specified voltage. In such a case, the stop signal 14 may be output.

  Since these cell voltage detection unit 6, minimum cell voltage selection circuit 7, specified voltage setting unit 8, comparison circuit 9, and switching control circuit 10 are weak power circuits that generate little heat loss, they are integrated into an IC chip. It is desirable to reduce the cost by adopting such a configuration.

[Operation of solar cell module]
The solar cell module 1 operates as follows.

● Normal operation with no partial shade Fig. 5 shows the IV curve of solar cell 4 in the state where all cells are not lit at the rated solar radiation (1kW / m ² ), and Fig. 6 shows the solar cell module It is a figure which shows IV curve of 1a.

  The switching control circuit 10 of the DC / DC converter 1b that inputs the output power of the solar cell module 1a having the characteristics shown in FIG. 6 adjusts the duty ratio of the switching element 13 while monitoring the detection value of the input power detection unit 12. Thus, the operating point of the solar cell module 1a is controlled so that the solar cell module 1a operates at the maximum output operating point (point A shown in FIG. 6). Since the output of the solar cell module 1a at this time is a point B (6.0V, 10A) shown in FIG. 6, a current of 10A flows through all the solar cells 4, and the operating point of the solar cell 4 is as shown in FIG. It becomes point C shown in (1.5V, 10A).

● Operation during Partial Shade Next, the operation when one of the four solar cells 4 becomes a cocoon will be described. However, the solar radiation conditions shall be rated solar radiation (1kW / m ² ). FIG. 7 is a diagram showing an IV curve of a solar cell 4 that is a ridge, and FIG. 8 is a diagram showing an IV curve of the solar cell module 1a when one of the four solar cells 4 is a cocoon.

  Similar to the normal operation, the switching control circuit 10 of the DC / DC converter 1b adjusts the duty ratio of the switching element 13 so as to operate at the maximum output operating point (point D shown in FIG. 8, 30.6 W). The operating point of the solar cell module 1a is controlled. At this time, the output of the solar cell module 1a is the point E (5.25V, 5.83A) shown in FIG. 8, and a current of 5.83A flows through all the solar cells 4, so that the solar cell 4 is in a cocoon. The operating point is the point F (0.15V, 5.83A) shown in FIG. 7, and the operating point of the solar cell 4 that is not a saddle is the point G (1.71V, 5.83A) shown in FIG.

  Thus, in the partial shade state in which some of the solar cells 4 constituting the solar cell module 1a are wrinkled, the operating voltage of the wrinkled solar cells 4 is low.

  When the shadow is further increased, the operating voltage of the solar cell 4 that has become a trap becomes even lower, and eventually reaches the specified voltage (−1.2 V) set in the specified voltage setting unit 8. FIG. 9 and FIG. 10 are diagrams showing the IV curve (FIG. 9) of the solar cell 4 that has become a saddle and the IV curve (FIG. 10) of the solar cell module 1a at that time.

  The solar cell module 1a operates at an operating point (point H, 4.15V, 4.6A shown in FIG. 10) at which maximum power is obtained by MPPT control. Operates at (-1.2V, 4.6A). In this partial shade state, that is, when any operating voltage of the solar battery cell 4 falls below the specified voltage, the present embodiment stops the power conversion operation of the DC / DC converter 1b.

[control]
FIG. 11 is a flowchart showing an operation example of the comparison circuit 9, and FIG. 12 is a flowchart showing an operation example of the switching control circuit 10.

  The comparison circuit 9 inputs the minimum cell voltage Vc selected and output by the minimum cell voltage selection circuit 7 (S1), inputs the specified voltage Vs set in the specified voltage setting unit 8 (S2), and inputs the minimum cell voltage Vc. Is compared with the specified voltage Vs (S3), if Vc ≦ Vs, the process returns to step S1, and if Vs <Vc, a stop signal 14 is output to the switching control circuit 10 (S4), and then the standby state is entered (S4). S5). The restart after the stop may be configured to release the stop signal 14 and release the stop of the DC / DC converter 1b after a predetermined time using a timer circuit (not shown). Of course, when stopping / restarting is repeated several times, it means that the surface of the solar cell module 1 is soiled, the light shield is attached, the presence of objects that continuously form shadows, etc., so the inverter 2 is warned. It is desirable to be configured to send a signal and alert the user.

  On the other hand, the switching control circuit 10 outputs the gate drive signal of the switching element 13 (S11), inputs the stop signal 14 (S12), and whether or not the stop signal 14 is active (the comparison circuit 9 outputs the stop signal 14). (S13), when the stop signal 14 becomes active, the gate drive signal is stopped (S14), and the stop signal 14 is canceled by the determination in step S15 (the comparison circuit 9 is stopped). Stop the gate drive signal until output 14 is stopped). When the stop signal 14 is canceled, the process returns to step S11, and a gate drive signal is output.

  Thus, the cell voltage of each solar cell 4 is detected by the cell voltage detection circuit 6, and when any cell voltage of the solar cell 4 exceeds the specified voltage (below the specified voltage), the DC / DC converter 1b To stop. When the operation of the DC / DC converter 1b is stopped, the current of the solar cell module 1a is almost zero, each solar cell 4 is in an open state, and the voltage becomes the open voltage Voc. No reverse voltage is applied to the battery cell 4 (point J shown in FIG. 9).

  Thus, according to the present embodiment, the countermeasure against the reverse voltage of the solar battery cell 4 can be realized at low cost without using a bypass diode. Further, by setting the specified voltage to about 0 volts, it is possible to use solar cells having a reverse withstand voltage lower than the forward drop voltage of the bypass diode in series connection.

  In the above description, an example in which the configuration in which the solar cell module 1a and the DC / DC converter 1b are integrated has been described. However, it is also possible to have a configuration in which they are separated. In that case, the cell voltage detection unit 6 and the minimum cell voltage selection unit 7 are provided in the solar cell module 1a, the specified voltage setting unit 8 and the comparison circuit 9 are provided in the DC / DC converter 1b, and the minimum cell voltage is set via the signal line. May be transmitted from the solar cell module 1a to the DC / DC converter 1b. At this time, if noise superimposed on the signal line becomes a problem, a method of amplifying and transmitting the signal, digitizing and transmitting the signal, the cell voltage detection unit 6 in the solar cell module 1a, the minimum cell voltage A configuration in which the selection unit 7, the specified voltage setting unit 8, and the comparison circuit 9 are provided to transmit the stop signal 14 to the DC / DC converter 10 may be employed.

  If the number of solar cells in the solar cell string is small, the voltage drop of the solar cell string when the partial shade occurs is large, and the generated power of the solar cell string is greatly reduced. It can be said that even if the output of the solar cell module 1 is stopped during the period of occurrence of the occurrence, there is no significant effect on the total power generation amount. Accordingly, it only has the meaning of preventing the destruction of the solar battery cell, and it is possible to reduce bypass diodes that are difficult to be integrated into an IC chip due to a large heat loss, thereby reducing the cost of the solar battery module.

  Hereinafter, the photovoltaic power generation apparatus and system according to the second embodiment of the present invention will be described, but the same reference numerals are given to substantially the same configurations as those in the first embodiment, and the detailed description thereof will be omitted.

  In Example 1, when a reverse voltage exceeding a specified voltage was applied to the solar battery cell 4, the current flowing through the solar battery cell 4 was interrupted to prevent the reverse voltage from being applied. That is, the operation of the DC / DC converter 1b is stopped by the stop signal 14 of the comparison circuit 9.

  In Example 2, the ratio of time to turn on the switching element 13 is reduced by the signal of the comparison circuit (referred to as “decreasing the duty ratio”), the output current of the solar cell module 1a is limited, and the solar cell module 1a Is operated in a state deviating from the optimum operating point (maximum power operating point), thereby setting the operating point at which no reverse voltage is applied to the solar cell 4 that has become a saddle. In this way, even when a partial shade occurs, the operation of the solar cell module 1 is not completely stopped, and when the partial shade is eliminated, an operation for returning to the optimum operating point in a short time becomes possible.

  FIG. 13 is a block diagram illustrating a configuration example of the solar cell module 1 according to the second embodiment. The comparison circuit 19 and the switching control circuit 20 are different from the configuration of the solar cell module 1 according to the first embodiment.

  The comparison circuit 19 compares the minimum cell voltage Vc with a specified voltage Vs (for example, -1.2V), and switches a suppression signal 21 indicating that the output current of the DC / DC converter 1b is suppressed when Vs <Vc. Output to the control circuit 20.

  As in the first embodiment, all the outputs of the cell voltage detection circuit 6 and the specified voltage of the specified voltage setting unit 8 are input to the comparison circuit 9 without using the minimum cell voltage selection circuit 7, and the cell voltage A configuration may be adopted in which the suppression signal 21 is output when any of the voltages falls below the specified voltage.

  Next, the operation of the solar cell module 1 in Example 2 will be described. The operation at normal time (when no partial shade is generated), the minimum cell voltage is a specified voltage (for example, -1.2 The operation in the case of V) or higher is the same as that in the first embodiment. The difference from Example 1 is that the influence of partial shade is large, and when the minimum cell voltage becomes lower than the specified voltage, the output voltage of DC / DC converter 1b is limited to increase the operating voltage, and the minimum cell voltage The operation is continued so that the voltage does not fall below the specified voltage.

  FIG. 14 is a flowchart showing an operation example of the comparison circuit 19, and FIG. 15 is a flowchart showing an operation example of the switching control circuit 20.

  The comparison circuit 19 inputs the minimum cell voltage Vc (S21), inputs the specified voltage Vs (S22), compares the minimum cell voltage Vc and the specified voltage Vs (S23), and if Vs <Vc, switching control is performed. The suppression signal 21 is output to the circuit 10 (S24). If Vc ≦ Vs, the suppression signal 21 is canceled (equivalent to nothing if the suppression signal 21 is not output) (S25), and then the process goes to step S21. Return.

  On the other hand, the switching control circuit 20 receives the suppression signal 21 (S31), determines whether the suppression signal 21 is active (whether the comparison circuit 19 outputs the suppression signal 21) (S32), and suppresses the suppression signal. If 21 is active, the current command value D for MPPT control is subtracted, for example, by “1” (D = D−1) (S33), and the process returns to step S31. Therefore, as long as the suppression signal 21 is active, the current command value D is subtracted by, for example, “1”, and the input current (solar cell) of the DC / DC converter 1b until Vc ≦ Vs and the suppression signal 21 is released. The output current of module 1a) decreases.

  If the suppression signal 21 is not active, the switching control circuit 20 performs known and publicly used MPPT control. The outline of the MPPT control shown in FIG. 15 is that the current command value is D = D-1 (initial value-1) (S34), and the output power of the solar cell module 1a at that time is recorded as the output power 1 (S35), The current command value is D = D + 2 (that is, initial value +1) (S36), the output power of the solar cell module 1a at that time is recorded as output power 2 (S37), and the recorded output power values are compared. (S38) If output power value 1 ≤ output power value 2 (initial value +1), return to step S31, and if output power value 1> output power value 2, set the current command value to D = D-2 (ie, initial Value-1) (S39), and then the process returns to step S31. The maximum power operating point is tracked by repeatedly adjusting the current command value.

  Next, operating points of the solar battery cell 4 and the solar battery module 1a when the suppression signal 21 is output from the comparison circuit 19 will be described.

  FIG. 16 is a diagram showing an IV curve of a solar cell 4 that is a ridge, and FIG. 17 is a diagram showing an IV curve of the solar cell module 1a when one of the four solar cells 4 is a cocoon.

  In FIG. 17, the operating point at which the maximum power of the solar cell module 1a is obtained is K point. In that case, the operating point of the solar cell 4 that has become a saddle is a point L as shown in FIG. 16, which is significantly lower than a specified voltage (for example, −1.2 V). However, in such a case, as shown in FIG. 15, the current command value is reduced until the minimum cell voltage exceeds the specified voltage, the duty ratio of the switching element 13 is reduced, and the operation of the solar cell 4 that has become a trap The point shifts from the L point in the direction of small current and large voltage, and the solar cell 4 operates at the M point. In FIG. 16, the reverse voltage is applied beyond the specified voltage. Actually, however, the control is performed so that the operating point does not exceed the M point, so the specified voltage (for example, -1.2 V) is used. The voltage will not drop below.

  As a result of such control, the operating point of the solar cell module 1a is the N point and the maximum power cannot be obtained, but the reverse voltage exceeding the specified voltage is not applied to the solar cell 4 that has become a saddle, The operation of the power generation device can be continued. Of course, if the solar radiation of the solar cell 4 that has become a saddle is restored, the operating point of the solar cell module 1a is shifted to the optimal operating point by MPPT control, as shown in FIG.

  Thus, also in Example 2, the reverse voltage countermeasure of the solar battery cell 4 can be configured at low cost without using a bypass diode. In addition, by setting the specified voltage to about 0V, it is possible to use solar cells whose reverse withstand voltage is lower than the forward drop voltage of the bypass diode in series connection.

  Hereinafter, the photovoltaic power generation apparatus and system according to the third embodiment of the present invention will be described, but the same reference numerals are given to substantially the same configurations as the first and second embodiments, and the detailed description thereof will be omitted.

  When there is a margin in the reverse withstand voltage of the solar battery cell 4, a means for detecting the minimum cell voltage can be arranged across the plurality of solar battery cells 4. For example, when the reverse withstand voltage of the solar battery cell 4 is equal to or higher than the maximum voltage of the solar battery cell 4 (low temperature, open voltage at high solar radiation), one cell voltage detection unit 6 is connected to the two solar battery cells 4 connected in series. If provided, the same effect as in the first and second embodiments can be obtained. In this case, when the output voltage of the two solar cells 4 connected in series becomes negative, the power conversion operation of the DC / DC converter 1b is stopped in the same manner as in Example 1, or Example 2 so that it does not become negative. It is sufficient to suppress the current command value in the same manner as.

  FIG. 18 is a block diagram illustrating a configuration example of the solar cell module 1 according to the third embodiment. In FIG. 18, the solar cell module 1a composed of the solar cells 4A, 4B, 4C, 4D is divided into two blocks, and the solar cell block 22 is divided into the solar cells 4A and 4B, and the solar cells 4C and 4D. The solar cell block 23 is configured by the above. Further, the two cell voltage detectors 6 are arranged so as to detect the potential difference between both ends of the solar battery blocks 22 and 23. Here, the solar cell block refers to one or more serial bodies of the solar cells 4 that are the measurement target of the cell voltage detector 6. In that sense, in each of Examples 1 and 2, each of the solar battery cells 4 is a solar battery block.

  With such a configuration, when the output voltage of the solar cell block becomes negative, the power conversion operation of the DC / DC converter 1b is stopped as in the first embodiment, or the current command value is suppressed as in the second embodiment. Just do it.

  Thus, if the cell voltage detector 6 is provided across the plurality of solar cells 4, the required number of the cell voltage detectors 6 can be reduced, and the cost of the solar cell module 1 can be reduced.

The figure which shows the structure of a solar cell module, Overview of solar power generation system, Block diagram showing a configuration example of a solar power generation system, The figure which shows the detailed structural example of the solar cell module 1, A diagram showing the IV curve of a solar cell when all the cells are not lit at the rated solar radiation (1kW / m ² ), Figure showing the IV curve of the solar cell module 1a, The figure which shows the IV curve of the photovoltaic cell which became the cocoon, The figure which shows IV curve of the solar cell module 1a when one of the four solar cells becomes a cocoon, The figure which shows IV curve of the photovoltaic cell 4 which became a cage, Figure showing the IV curve of the solar cell module 1a, A flowchart showing an operation example of the comparison circuit, A flowchart showing an operation example of the switching control circuit; Block diagram showing a configuration example of the solar cell module of Example 2, A flowchart showing an operation example of the comparison circuit, A flowchart showing an operation example of the switching control circuit; The figure which shows the IV curve of the photovoltaic cell which became the cocoon, The figure which shows IV curve of the solar cell module 1a when one of the four solar cells becomes a cocoon, 6 is a block diagram showing a configuration example of a solar cell module 1 of Example 3. FIG.

Claims (9)

A solar battery module in which a plurality of solar battery blocks including one or more solar battery cells are connected in series;
A plurality of voltage detection means provided in each of the solar cell blocks, for detecting a voltage across the solar cell block;
Power conversion means for converting the power output from the solar cell module;
A photovoltaic power generation apparatus comprising: a control unit that controls the power conversion unit based on a result of comparing a predetermined voltage with both-end voltages detected by the plurality of voltage detection units.   2. The solar power generation device according to claim 1, wherein the solar battery block is one solar battery cell.   3. The control unit according to claim 1 or 2, wherein when the both-end voltage detected by any of the voltage detection units exceeds the predetermined voltage, the control unit stops the power conversion operation of the power conversion unit. The described solar power generator.   3. The control unit according to claim 1 or 2, wherein the control unit controls a power conversion operation of the power conversion unit so that a voltage between both ends detected by the plurality of voltage detection units does not exceed the predetermined voltage. The described solar power generator.   The control means performs maximum power following operation of the power conversion means if the both-end voltages detected by the plurality of voltage detection means do not exceed the predetermined voltage, and the both-end voltages detected by the plurality of voltage detection means are the predetermined voltage. 3. The photovoltaic power generation apparatus according to claim 1, wherein the power conversion means is operated to follow the maximum power so that the voltage across both ends thereof is in a range not exceeding the predetermined voltage.   6. The solar power generation device according to claim 1, wherein the predetermined voltage is set based on a reverse withstand voltage of the solar cell block.   7. The solar power generation device according to claim 1, further comprising an inverter that converts electric power output from the power conversion means into commercial AC power. Having a plurality of solar power generation devices according to any one of claims 1 to 6,
Furthermore, it has an inverter which converts the electric power output from these solar power generation devices into commercial alternating current power, The solar power generation system characterized by the above-mentioned. A plurality of solar battery modules each having one or more solar battery cells connected in series, a plurality of voltage detecting means provided in each of the solar battery blocks, and detecting a voltage across the solar battery block; and A method for controlling a photovoltaic power generation apparatus having power conversion means for converting power output from a solar cell module,
A control method, comprising: controlling the power conversion unit based on a result of comparing a predetermined voltage with both-end voltages detected by the plurality of voltage detection units.

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