Photovoltaic power generation system

Abstract

Provided is a photovoltaic power generation system (1) comprising: a plurality of solar cell blocks (10) that are connected in series; a plurality of bypass diodes (20) that respectively connect both ends of the plurality of solar cell blocks (10); a voltage detector (31) that detects the voltage of a series connection circuit (30) of the solar cell blocks (10); a current detector (32) that detects the current of the series connection circuit (30) of the solar cell blocks (10); a voltage regulator (41) that regulates the operating voltage of the series connection circuit (30) of the plurality of solar cell blocks (10) to a set voltage; and a control device (50) that controls the set voltage on the basis of the detection values of the voltage detector (31) and the current detector (32). The control device (50) has: a characteristic measurement unit (52) that measures the power-voltage characteristic and the current-voltage characteristic by changing the set voltage; and a voltage setting unit (53) that sets the set voltage to a peak-time voltage at which no peak-time voltage at which the current in the current-voltage characteristic exceeds a predetermined current threshold exists on the high voltage side, among peak-time voltages at which the power in the power-voltage characteristic reaches a peak.

Description

Photovoltaic power generation system 【0001】 The present invention relates to a photovoltaic power generation system. 【0002】 A photovoltaic power generation system in which a plurality of solar cell blocks each formed by connecting a plurality of solar cells in series are further connected in series is used. In such a photovoltaic power generation system, only some of the solar cells may be shaded, resulting in a voltage drop that may limit the overall power or cause heat generation and lead to a failure. By connecting a bypass diode in parallel with each solar cell block, the output of the solar cell block whose output has decreased until a voltage drop is caused by the current supplied from other solar cell blocks can be bypassed, thereby suppressing a decrease in the output of the entire photovoltaic power generation system (see, for example, Patent Document 1). 【0003】 Japanese Patent Application Laid-Open No. 2017-147931 【0004】 When only some of the solar cells in a solar cell block are shaded and the bypass diode of that solar cell block operates, the shaded solar cells act as a resistor that consumes the power output by the other solar cells in the same solar cell block, and hot spots may occur. Therefore, an object of the present invention is to provide a photovoltaic power generation system capable of preventing hot spots. 【0005】(1) A photovoltaic power generation system according to one aspect of the present invention comprises a plurality of solar cell blocks, each having a plurality of solar cells connected in series; a plurality of bypass diodes connecting both ends of the plurality of solar cell blocks and bypassing the corresponding solar cell block when a reverse voltage may be generated in the corresponding solar cell block; a voltage detector for detecting the voltage of the series connection circuit of the solar cell blocks; a current detector for detecting the current of the series connection circuit of the solar cell blocks; a voltage regulator for adjusting the operating voltage of the series connection circuit of the plurality of solar cell blocks to a set voltage; and a control device for controlling the set voltage based on the detected values ​​of the voltage detector and the current detector, wherein the control device comprises a characteristic measurement unit for measuring power voltage characteristics and current voltage characteristics by changing the set voltage; and a voltage setting unit for setting the set voltage to a peak voltage where, among the peak voltages where the power in the power voltage characteristics is at its peak, there is no peak voltage on the high voltage side where the current in the current voltage characteristics exceeds a predetermined current threshold. 【0006】 (2) In the photovoltaic power generation system of (1), the voltage setting unit may set the set voltage to the voltage at which the power in the power voltage characteristic is maximized among the peak voltages at which there is no peak voltage on the high voltage side at which the current in the current voltage characteristic exceeds a predetermined current threshold. 【0007】 (3) In the photovoltaic power generation systems of (1) to (2), the voltage setting unit may perform a voltage setting procedure that includes the steps of: setting the voltage at which the power in the power voltage characteristics is maximum as the reference voltage; comparing the current in the current voltage characteristics at the peak voltage adjacent to the high voltage side of the reference voltage in the current voltage characteristics with the current threshold; setting the reference voltage in the power voltage characteristics as the set voltage if the current in the current voltage characteristics at the peak voltage is less than or equal to the current threshold; and changing the reference voltage to the peak voltage adjacent to the high voltage side of the reference voltage in the power voltage characteristics if the current in the current voltage characteristics at the peak voltage exceeds the current threshold. 【0008】(4) In the photovoltaic power generation systems of (1) to (3), the solar cell may have a perovskite photoelectric conversion layer. 【0009】 (5) In the photovoltaic power generation systems of (1) to (3), the solar cell may be a crystalline silicon solar cell that is stacked on a perovskite solar cell having a perovskite photoelectric conversion layer and outputs power independently of the perovskite solar cell. 【0010】 According to the present invention, it is possible to provide a photovoltaic power generation system that can prevent excessive heat generation caused by a large current flowing through a shaded solar cell. 【0011】 This is a circuit diagram showing the configuration of a photovoltaic power generation system according to one embodiment of the present invention. This is a flowchart showing the voltage setting procedure in the photovoltaic power generation system of Figure 1. These are the simulation results of the power voltage characteristics and current voltage characteristics of the photovoltaic power generation system of Figure 1. These are simulation results of the power voltage characteristics and current voltage characteristics of the photovoltaic power generation system of Figure 1, with a different shading rate than Figure 3. These are simulation results of the power voltage characteristics and current voltage characteristics of the photovoltaic power generation system of Figure 1, with a different shading rate than Figures 3 and 4. 【0012】 Embodiments of the present invention will be described below with reference to the drawings. Figure 1 is a circuit diagram showing the configuration of a photovoltaic power generation system 1 according to one embodiment of the present invention. 【0013】 The solar power generation system 1 comprises a plurality of solar cell blocks 10, a plurality of bypass diodes 20 connecting both ends of the plurality of solar cell blocks 10, a series connection circuit 30 connecting the plurality of solar cell blocks 10 in series, an output circuit 40 that outputs power from the series connection circuit 30 to the outside, and a control device 50 that controls the output circuit 40. 【0014】The solar cell block 10 has multiple solar cells 11 connected in series by a series connection circuit 30, each independently outputting power. In the illustrated example, the solar cell block 10 has 14 solar cells 11 connected in series. The solar cell block 10 may also have solar cells 11 partially connected in parallel, such as by connecting parallel connections of solar cells 11 in series. Each solar cell 11 may be a single solar cell, a submodule (distributed in multiple locations within a solar panel) in which multiple solar cells are connected, or a module (individual solar panel) in which multiple solar cells are sealed. If the solar cell 11 is a submodule or module, it may include a bypass diode. Therefore, the photovoltaic power generation system 1 may consist of a single solar cell panel, or it may be a photovoltaic power generation device or photovoltaic power generation plant including multiple solar cell panels. In the case of crystalline silicon solar cells, although a decrease in output according to the intrinsic temperature coefficient is observed at high temperatures, the change is mainly reversible, and the heat resistance of the solar cell itself is considered to be high. However, if the heat generation state continues, it may cause thermal degradation or thermal damage to the surrounding module members, and the heat generation suppression according to the present invention is effective. On the other hand, perovskite solar cells have low heat resistance and have been reported to undergo irreversible thermal degradation at high temperatures. Therefore, when the solar cell 11 has a perovskite photoelectric conversion layer (for example, when the solar cell 11 is a single-type solar cell having a perovskite photoelectric conversion layer, or a two-terminal tandem solar cell having a perovskite photoelectric conversion layer and a crystalline silicon photoelectric conversion layer), or when the solar cell 11 is stacked with a perovskite solar cell having a perovskite photoelectric conversion layer and is a crystalline silicon solar cell that outputs power independently of the perovskite solar cell (for example, when the solar cell 11 is the bottom cell of a four-terminal tandem solar cell and is stacked on a top cell consisting of a perovskite solar cell (not shown)), the effect of the present invention in suppressing heat generation becomes particularly pronounced, as will be explained in detail below. When the solar cell 11 is a two-terminal tandem solar cell, its configuration is not limited to two junctions, but may consist of three or more junctions stacked together.Furthermore, in the case of a four-terminal tandem solar cell, the present invention is effective for both the top cell group and the bottom cell group. 【0015】 The bypass diodes 20 are connected in series with the solar cell blocks 10 via a series connection circuit 30 and in parallel with each other. The bypass diodes 20 are connected in a direction that allows current to pass from the negative output terminal to the positive output terminal of the solar cell block 10, and prevent voltage drop by bypassing the corresponding solar cell block when a reverse voltage may be generated in the corresponding solar cell block 10 due to current flowing in from another solar cell block 10. In other words, when the voltage drop caused by the shaded solar cell 11 acting as a resistor becomes greater than the voltage generated by the solar cell 11 converting incident light into photoelectricity in the corresponding solar cell block, the bypass diodes 20 suppress the inflow of current from other solar cell blocks 10 to the corresponding solar cell block, thereby mitigating the output reduction due to voltage drop in the shaded solar cell 11. 【0016】 The series connection circuit 30 connects multiple solar cells 11 in series. The series connection circuit 30 is equipped with a voltage detector 31 for detecting the voltage of the series connection circuit 30 and a current detector 32 for detecting the current of the series connection circuit 30. 【0017】 The output circuit 40 outputs the power of the multiple solar cell blocks 10 output from the series connection circuit 30 to the outside after voltage adjustment. The output circuit 40 may also be configured to convert the DC power output from the series connection circuit 30 to AC power. The output circuit 40 includes a voltage regulator 41 that adjusts the operating voltage of the series connection circuit 30 to a set voltage set by the control device 50. The voltage regulator 41 may be configured as a well-known DC-DC converter, or it may also have a DC-AC converter. 【0018】The control device 50 controls the set voltage of the voltage regulator 41 based on the detected values ​​of the voltage detector and the current detector. The control device 50 may be composed of one or more computer devices that include, for example, memory, a processor, an input / output interface, etc., and execute an appropriate control program. The control device 50 has an MPPT control unit 51, a characteristic measurement unit 52, and a voltage setting unit 53. Note that these components of the control device 50 are classifications of the functions of the control device 50 and do not necessarily have to be clearly distinguishable in terms of physical configuration and program configuration. 【0019】 The MPPT control unit 51 performs well-known maximum power point tracking control. That is, the MPPT control unit 51 controls the set voltage of the voltage regulator 41 to maximize the output power of the photovoltaic power generation system 1 based on the detected values ​​of the voltage detector 31 and the current detector 32. Specifically, the MPPT control unit 51 may be configured to perform well-known hill-climbing control, which involves temporarily increasing or decreasing the set voltage by a small amount and moving the set voltage in the direction of increased output. 【0020】 The characteristic measurement unit 52 temporarily interrupts the maximum power point tracking control by the MPPT control unit 51 and changes the set voltage of the voltage regulator 41 to measure the power voltage characteristics (P-V curve) and current voltage characteristics (I-V curve). The power voltage characteristics and current voltage characteristics may be measured at regular time intervals, or when the output of the solar power generation system 1 changes to a predetermined standard or higher during the maximum power point tracking control by the MPPT control unit 51. 【0021】The voltage setting unit 53 sets the voltage regulator 41 to a peak voltage where, among the peak voltages where the power in the power-voltage characteristic is at its peak, there is no peak voltage on the high-voltage side where the current in the current-voltage characteristic exceeds a predetermined current threshold. In other words, the voltage setting unit 53 sets to a peak voltage where, among the peak voltages in the power-voltage characteristic, the current in the current-voltage characteristic at a peak voltage adjacent to the high-voltage side is below the current threshold, or the peak voltage on the highest voltage side in the power-voltage characteristic. Preferably, the voltage setting unit 53 sets the voltage to the voltage where the power in the power-voltage characteristic is at its maximum among the peak voltages where, among the peak voltages where, among the peak voltages where, among the peak voltages where, among the current in the current-voltage characteristic does not exceed a predetermined current threshold, there is no peak voltage on the high-voltage side where the current exceeds a predetermined current threshold, the peak voltage where the power in the power-voltage characteristic is at its maximum is often the peak voltage on the lowest voltage side. Therefore, the voltage setting unit 53 may set the voltage to the lowest voltage peak voltage among the peak voltages adjacent to the high voltage side where the current in the current-voltage characteristic is below the current threshold. 【0022】 Specifically, the voltage setting unit 53 may be configured to perform a voltage setting procedure that includes the steps of: setting the voltage at which the power is maximum in the power voltage characteristics as the reference voltage; comparing the current in the current voltage characteristics at the peak voltage adjacent to the high voltage side of the reference voltage in the current voltage characteristics with the current threshold; setting the reference voltage in the power voltage characteristics as the set voltage if the current in the current voltage characteristics at the peak voltage is less than or equal to the current threshold; and changing the reference voltage to the peak voltage adjacent to the high voltage side of the reference voltage in the power voltage characteristics if the current in the current voltage characteristics at the peak voltage exceeds the current threshold. 【0023】Figure 2 shows in detail an example of a voltage setting procedure that can be performed by the voltage setting unit 53. This voltage setting procedure is as follows: Step S1: Extract power peaks and number them sequentially from the low voltage side to n, and set the number of the peak with the maximum power to m; Step S2: Confirm whether the peak with the maximum power is the peak on the highest voltage side (whether m=n or not); Step S3: If in Step S2 the peak with the maximum power was the peak on the highest voltage side, set the number k0 of the peak corresponding to the set voltage to n; Step S4: If in Step S2 the peak with the maximum power was not the peak on the highest voltage side, set the loop parameter k, which is the number indicating the peak position of the reference voltage, to m; (k+1) The process includes: comparing the current I(k+1) at the nth peak with a current threshold Ith (step S5); increasing the loop parameter k by 1 if the current I(k+1) in step S5 is not less than or equal to the current threshold Ith (step S6); checking whether the loop parameter k has reached the number of power peaks n (step S7); and setting the peak number k0 corresponding to the set voltage to the value of the current loop parameter k if the current I(k+1) in step S5 is less than or equal to the current threshold Ith and the loop parameter k has reached the number of power peaks n in step S7 (step S8). If the loop parameter k has not reached the number of power peaks n in step S7, the process returns to step S5. 【0024】The current threshold Ith can be determined, for example, using an allowable multiple Xa that expresses the allowable power consumption of a shaded solar cell 11 as a multiple of the output of a single solar cell 11 under standard irradiation conditions, the standard operating current Ipm under standard irradiation conditions of a single solar cell, and the number of solar cells 11 in series s within the solar cell block 10, as Ith = Ipm * Xa / (s - 1) ... (1). In the photovoltaic power generation system 1, the operating current at the peak of the P-V curve decreases as the peak on the high-voltage side increases. If the number of solar cells 11 in series s and the allowable multiple Xa are the same for all solar cell blocks 10, in the voltage setting procedure in Figure 2, in step S5, the suitability of operating at the k-th peak can be determined by comparing the current I(k+1) at the (k+1)-th peak adjacent to the high-voltage side with the current threshold Ith. In other words, if the current I(k+1) at the (k+1)th peak adjacent to the high-voltage side exceeds the current threshold Ith, it can be determined that it is preferable to operate with one or more bypassed solar cell blocks 10 incorporated. Furthermore, the allowable multiplier Xa can be set to 0, in which case the set voltage will always be the voltage corresponding to the highest voltage peak of the power voltage characteristic. 【0025】To explain in more detail, when operating at the k-th peak, the bypass diode 20 operates, but when operating at the (k+1)-th peak, the current in the solar cell block 10 that does not have the bypass diode 20 operating is limited by the shaded solar cell 11 in the range from the k-th peak voltage (more precisely, a voltage slightly higher than the k-th peak voltage) to the (k+1)-th peak voltage. The change in current in this voltage range is extremely small, and the current at the k-th peak in the solar cell block 10 that is bypassed when operating at the k-th peak is approximately equal to the current I(k+1) at the (k+1)-th peak of the entire photovoltaic power generation system 1. Therefore, if the current I(k+1) at the (k+1)-th peak exceeds the current threshold Ith, it is considered that the heat generated by the solar cell 11 that is shaded by the solar cell block 10 that is bypassed when operating at the k-th peak will be excessive. Accordingly, it can be determined that operation at the (k+1)-th peak without bypassing the solar cell block 10 that is bypassed when operating at the k-th peak is preferable. 【0026】Figures 3 to 5 show the simulation results of the power-voltage characteristics and current-voltage characteristics of the photovoltaic power generation system 1 under different shading conditions. The simulated photovoltaic power generation system 1 comprises three solar cell blocks 10, each having 14 solar cells 11 connected in series, as described above. In the simulation, it was assumed that a portion of one solar cell 11 in each of the two solar cell blocks 10 was shaded. The shading rates of the solar cells 11 were 15% and 50% in Figure 3, 15% and 85% in Figure 4, and 68% and 75% in Figure 5. Also, with the number of series cells s = 14, the standard operating current Ipm = 7.51 A, and the allowable multiplier Xa = 4, the current threshold Ith = 2.31 A was set according to the above formula (1). In Figure 3, the peak power / peak current were 60.3 W / 7.48 A, 120.5 W / 6.72 A, and 116.3 W / 3.96 A, respectively, from the low voltage side. As a result, there are no peaks where the peak current is below the current threshold Ith, so the peak voltage on the highest voltage side becomes the set voltage. In Figure 4, the peak power / peak current were 60.3W / 7.48A, 120.5W / 6.72A, and 36.0W / 1.18A, starting from the low voltage side. As a result, the third peak current from the low voltage side is below the current threshold Ith, so the second peak voltage becomes the set voltage. In Figure 5, the peak power / peak current were 60.3W / 7.48A, 49.6W / 2.52A, and 59.7W / 1.98A, starting from the low voltage side. As a result, the third peak current from the low voltage side is below the current threshold Ith, so the second peak voltage may be set as the set voltage according to the voltage setting procedure in Figure 2, but since the third peak power is greater than the second peak power, it is preferable to set the third peak voltage as the set voltage. 【0027】 As described above, in the photovoltaic power generation system 1, the set voltage is a peak voltage in which there is no peak voltage in the current-voltage characteristic that exceeds a predetermined current threshold on the high-voltage side. This prevents a large current from flowing through the shaded solar cell 11 and causing excessive heat generation. 【0028】Although embodiments of the present invention have been described above, the present invention is not limited to the embodiments described above, and various modifications and variations are possible. For example, a different current threshold may be set for each solar cell block, and all peaks on the high-voltage side of the peak used to determine suitability may be compared with the corresponding current threshold. 【0029】 1. Solar power generation system 10. Solar cell block 11. Solar cell 20. Bypass diode 30. Series connection circuit 31. Voltage detector 32. Current detector 40. Output circuit 41. Voltage regulator 50. Control device 51. MPPT control unit 52. Characteristic measurement unit 53. Voltage setting unit

Claims

1. A solar power generation system comprising: a plurality of solar cell blocks, each having a plurality of solar cells connected in series; a plurality of bypass diodes connecting both ends of the plurality of solar cell blocks, each bypassing the corresponding solar cell block when a reverse voltage may be generated in the corresponding solar cell block; a voltage detector for detecting the voltage of the series connection circuit of the solar cell blocks; a current detector for detecting the current of the series connection circuit of the solar cell blocks; a voltage regulator for adjusting the operating voltage of the series connection circuit of the plurality of solar cell blocks to a set voltage; and a control device for controlling the set voltage based on the detected values ​​of the voltage detector and the current detector, wherein the control device comprises: a characteristic measurement unit for measuring power voltage characteristics and current voltage characteristics by changing the set voltage; and a voltage setting unit for setting the set voltage to a peak voltage where, among the peak voltages where the power in the power voltage characteristics is at its peak, there is no peak voltage on the high voltage side where the current in the current voltage characteristics exceeds a predetermined current threshold.

2. The photovoltaic power generation system according to claim 1, wherein the voltage setting unit sets the set voltage to the voltage at which the power in the power voltage characteristic is maximized among the peak voltages where there is no peak voltage on the high voltage side in which the current in the current voltage characteristic exceeds a predetermined current threshold.

3. The photovoltaic power generation system according to claim 1 or 2, wherein the voltage setting unit performs a voltage setting procedure comprising: setting the voltage at which the power in the power voltage characteristics is maximum as the reference voltage; comparing the current in the current voltage characteristics at the peak voltage adjacent to the high voltage side of the reference voltage in the current voltage characteristics with the current threshold; setting the reference voltage in the power voltage characteristics as the set voltage if the current in the current voltage characteristics at the peak voltage is less than or equal to the current threshold; and changing the reference voltage to the peak voltage adjacent to the high voltage side of the reference voltage in the power voltage characteristics if the current in the current voltage characteristics at the peak voltage exceeds the current threshold.

4. The photovoltaic power generation system according to claim 1 or 2, wherein the solar cell has a perovskite photoelectric conversion layer.

5. The photovoltaic power generation system according to claim 1 or 2, wherein the solar cell is a crystalline silicon solar cell stacked on a perovskite solar cell having a perovskite photoelectric conversion layer, and outputs power independently of the perovskite solar cell.

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