Solar power generation system

Abstract

This solar power generation system comprising a plurality of solar cell blocks, each of which includes one or more solar cells and independently outputs power, and an output circuit that outputs power from the plurality of solar cell blocks to the outside, wherein the output circuit comprises: a single main busbar that connects the solar cell blocks in series; a plurality of bypass units that are respectively provided for the solar cell blocks to bypass the solar cell blocks; a plurality of switching units that are respectively provided for the solar cell blocks to switch the state of each solar cell block between a connected state in which the solar cell block is electrically inserted in the main busbar and an internal loop state in which the solar cell block is disconnected from the main busbar and short-circuited via a load resistor; a plurality of block output detection units that each detect the voltage or current of a load resistor; and a switching control unit that controls the bypass units and the switching units on the basis of the values detected by the block output detection units.

Description

Photovoltaic power generation system

[0001] The present invention relates to a photovoltaic power generation system.

[0002] A photovoltaic power generation system including a plurality of solar cell panels is used. In such a photovoltaic power generation system, only some of the solar cell panels may be shaded, which may limit the overall power or cause overheating and lead to failure. Therefore, it has been proposed to monitor the outputs of a plurality of solar cell panels (or groups including a plurality of solar cell panels) respectively, and switch the connection form of the solar cell panels or disconnect the solar cell panels with low output so as to optimize the overall output (see, for example, Patent Document 1).

[0003] Japanese Patent Application Laid-Open No. 2014-107878

[0004] When disconnecting a solar cell panel, the output of the disconnected solar cell panel cannot be measured. Therefore, it is desired to provide means for appropriately determining whether the disconnected solar cell block should be reconnected to the system. Accordingly, an object of the present invention is to provide a photovoltaic power generation system capable of appropriately determining the reconnection of a disconnected solar cell block.

[0005] (1) A photovoltaic power generation system according to an aspect of the present invention includes a plurality of solar cell blocks each including one or more solar cells and independently outputting power, and an output circuit that outputs power from the plurality of solar cell blocks to the outside. The output circuit includes a single main trunk that connects the solar cell blocks in series, a plurality of bypass portions provided for each of the solar cell blocks to bypass the solar cell blocks, a connection state provided for each of the solar cell blocks to electrically insert the solar cell block into the main trunk, and an internal loop state that keeps the voltage across both ends of the solar cell block at a positive voltage by disconnecting the solar cell block from the main trunk and short-circuiting it through a load resistor. A plurality of switching portions for switching, a plurality of block output detectors for detecting the voltage or current of the load resistor respectively, and a switching control portion for controlling the bypass portion and the switching portion based on the detection values of the block output detectors.

[0006] (2) In the solar power generation system of (1), the switching control unit may switch the switching unit to the connected state if the ratio of the current value of the load resistor to the current value of the main circuit increases by a certain standard or more compared to the value immediately after switching to the internal loop state.

[0007] (3) In the photovoltaic power generation systems of (1) to (2), the output circuit may further include a main voltage detector for detecting the voltage of the main circuit, a main current detector for detecting the current of the main circuit, a voltage adjustment unit for adjusting the voltage of the main circuit, and an MPPT control unit for controlling the voltage adjustment unit to maximize the power of the main circuit based on the detected value of the main voltage detector and the detected value of the main current detector.

[0008] (4) In the photovoltaic power generation system of (3), the block output detector is configured to detect the voltage of the solar cell block, and the switching control unit may change the set voltage of the voltage adjustment unit so that the current of the main circuit is greater than the current of the maximum power point, bypass the solar cell block whose rate of change of the detected value of the block output detector is greater than or equal to a predetermined standard than others using the corresponding bypass unit, and switch the corresponding switching unit to the internal loop state.

[0009] (5) In the solar power generation systems of (1) to (3), the switching control unit may temporarily put the bypass unit into a bypass state when the switching unit is in the connected state, and if the power of the main circuit increases due to the switching to the bypass state, the switching unit may switch to the internal loop state.

[0010] (6) In the photovoltaic power generation systems of (1) to (5), the one or more solar cells may include tandem solar cells in which a perovskite solar cell and a crystalline silicon solar cell are stacked.

[0011] According to the present invention, a solar power generation system can be provided that suppresses hot spots by maintaining a positive voltage across the disconnected solar cell block, and can also appropriately determine when to reconnect the disconnected solar cell block.

[0012] This is a circuit diagram showing the configuration of a solar power generation system according to the first embodiment of the present invention. This is a circuit diagram showing the configuration of a solar power generation system according to the second embodiment of the present invention.

[0013] Embodiments of the present invention will be described below with reference to the drawings. In the descriptions of embodiments described later, the same reference numerals may be used for components similar to those described earlier, and redundant descriptions may be omitted.

[0014] [First Embodiment] Figure 1 is a circuit diagram showing the configuration of a solar power generation system 1 according to the first embodiment of the present invention. The solar power generation system 1 comprises a plurality of solar cell blocks 10 and an output circuit 20 that outputs power from the plurality of solar cell blocks 10 to the outside.

[0015] Each solar cell block 10 includes one or more solar cells 11 and outputs power independently. The connection configuration of the solar cells 11 within the solar cell block 10 is not particularly limited, but it is preferable that they be configured to output approximately equal currents when the light incidence conditions are the same. In the illustrated example, each solar cell block 10 has 14 solar cells 11 connected in series. Each solar cell 11 may be a single solar cell, a submodule (distributed in multiple locations within a solar cell panel) in which multiple solar cells are connected, or a module (individual solar cell panel) in which multiple solar cells are sealed. 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. Furthermore, the effects of the present invention are particularly pronounced when the solar cell 11 is a tandem-type solar cell (including those in which the perovskite solar cell and the crystalline silicon solar cell are recognized as separate solar cells in terms of the circuit) in which a relatively heat-sensitive perovskite solar cell and a crystalline silicon solar cell whose photoelectric conversion efficiency changes relatively large depending on the light incidence conditions are stacked.

[0016] The output circuit 20 includes one main circuit 21, multiple bypass sections 22, multiple switching sections 23, multiple block output detectors 24, a main circuit voltage detector 25, a main circuit current detector 26, a voltage adjustment section 27, an MPPT control section 28, and a switching control section 29.

[0017] The main circuit 21 connects the solar cell blocks 10 in series and outputs power to the outside from the solar cell blocks 10. In other words, the solar cell blocks 10 can be inserted into the main circuit 21 in series with each other.

[0018] A bypass section 22 is provided for each solar cell block 10 and bypasses the corresponding solar cell block 10. In other words, the bypass section 22 is a circuit that has a short-circuit switch 221 that short-circuits the corresponding solar cell block 10.

[0019] The switching unit 23 is provided for each solar cell block 10 and switches between a connected state in which the corresponding solar cell block 10 is electrically inserted into the main circuit 21 and an internal loop state in which the corresponding solar cell block 10 is disconnected from the main circuit 21 and short-circuited via the load resistor 231. For this reason, the switching unit 23 may be a circuit having a selection switch 232 that connects a common contact connected to one output terminal of the solar cell block 10 to either a first selection contact connected to the main circuit 21 or a second contact connected to the other end of the load resistor 231, one end of which is connected to the other output terminal of the solar cell block 10. Preferably, the value of the load resistor 231 is selected so that the voltage across the solar cell block 10 in the internal loop state is maintained at an appropriate positive voltage. As a specific example, the value of the load resistor 231 may be the value obtained by dividing the value of the optimal operating voltage of the solar cell block 10, calculated from the rated output parameters of each solar cell 11, by the value of the optimal operating current.

[0020] The block output detector 24 detects the voltage or current of the load resistor 231 in the internal loop state. In this embodiment, the block output detector 24 is configured to constantly detect the voltage of the solar cell block 10. The voltage and current of the load resistor 231 can be converted from each other using the resistance value of the load resistor 231. In this embodiment, a block output detector 24 is provided for each solar cell block 10, but a single block output detector may be configured to selectively detect either the voltage or current of the load resistor 231.

[0021] The main voltage detector 25 detects the voltage of the main circuit 21. The main current detector 26 detects the current of the main circuit 21. The voltage adjustment unit 27 adjusts the voltage of the main circuit 21. The voltage adjustment unit 27 may be configured, for example, by a DC-DC converter.

[0022] The MPPT control unit 28 performs well-known maximum power point tracking control. Specifically, the MPPT control unit 28 controls the set voltage of the voltage adjustment unit 27 to maximize the power of the main circuit 21 based on the detected values ​​of the main circuit voltage detector 25 and the main circuit current detector 26.

[0023] The switching control unit 29 controls the bypass unit 22 and the switching unit 23 based on the detected value of the block output detector 24. Specifically, the switching control unit 29 may be configured to open the bypass unit 22 and switch the switching unit 23 to the connected state when the detected value of the block output detector 24 exceeds a predetermined connection threshold. In other words, the switching control unit 29 monitors the current to the load resistor 231 of the solar cell block 10 that is disconnected from the main circuit 21, and when the value of the current in the disconnected solar cell block 10 increases sufficiently, for example, when the ratio of the current flowing in the internal loop to the value of the current flowing in the main circuit 21 increases by a certain standard (e.g., 5%) or more compared to the ratio immediately after switching to the internal loop state, the switching control unit 29 reconnects the solar cell block 10 to the main circuit 21. The determination of switching to the connected state by the switching control unit 29 may be performed at predetermined intervals. In this embodiment, a single switching control unit 29 controls all the bypass units 22 and the switching unit 23, but a switching control unit may be provided for each solar cell block 10. Furthermore, the switching control unit 29 may be configured integrally with the MPPT control unit 28.

[0024] Furthermore, the switching control unit 29, for example via the MPPT control unit 28, changes the set voltage of the voltage adjustment unit 27 so that the current of the main circuit 21 is greater than the current at the maximum power point, bypasses the solar cell block 10 whose rate of change of the detected value (voltage) of the block output detector 24 is greater than a predetermined standard than others using the corresponding bypass unit 22, and switches the corresponding switching unit 23 to the internal loop state. The offset of the current from the maximum power point is preferably a slight increase of, for example, 0.5% to 5%, and may be the offset for the maximum power point in the hill climbing control that can be performed as maximum power point tracking control by the MPPT control unit 28. In other words, the decision to switch to the internal loop state in the switching control unit 29 may be performed in conjunction with the maximum power point tracking control by the MPPT control unit 28. The "predetermined standard" for switching to the internal loop state can be set, for example, as a ratio (for example, 2 times) to the average value of the rate of change of the voltage of all other solar cell blocks 10.

[0025] Furthermore, the switching control unit 29 may be configured to temporarily bypass one bypass unit 22 when the switching unit 23 is connected, and if the power of the main circuit breaker 21 increases due to the switch to the bypass state, it will maintain the bypass state of the bypass unit 22 and switch the corresponding switching unit 23 to an internal loop state. In other words, one solar cell block 10 is temporarily bypassed to check the detected values ​​of the main circuit breaker voltage detector 25 and the main circuit breaker current detector 26. If the output increases, it can be determined that the bypassed solar cell block 10 caused a decrease in output current due to the effects of shading or dirt, which in turn reduced the output current of other blocks, resulting in a decrease in output. In this case, the bypassed solar cell block 10 is disconnected from the main circuit breaker 21 and operation continues. If the power of the main circuit breaker 21 does not increase when the bypass unit 22 is bypassed, it can be determined that the bypassed solar cell block 10 did not have a negative impact. In this case, the bypass unit 22 is opened and the corresponding solar cell block 10 is electrically reinserted into the main circuit breaker 21.

[0026] The photovoltaic power generation system 1, having the above configuration, can prevent an overall decrease in output by disconnecting the solar cell block 10 whose output has decreased due to the effects of shading or other factors. Furthermore, the photovoltaic power generation system 1 can create an internal loop state with the disconnected solar cell block 10 using the load resistor 231, and since the output at a more realistic operating point than the open-circuit voltage can be confirmed, the timing for reconnecting the disconnected solar cell block 10 can be appropriately determined. Unlike the photovoltaic power generation system 1, it is also conceivable to experimentally connect the solar cell block 10 to the main circuit 21 to determine whether it is appropriate to connect the solar cell block 10 to the main circuit 21. However, if the solar cell 11 includes a tandem solar cell in which perovskite solar cells and crystalline silicon solar cells are stacked, there is a risk that the crystalline silicon solar cells that are shaded will create hot spots when experimentally connected to the main circuit, damaging the stacked perovskite solar cells. In contrast, the photovoltaic power generation system 1 can determine whether it is appropriate to connect the solar cell block 10 to the main circuit 21 without experimentally connecting the solar cell block 10 to the main circuit 21, thus preventing damage to the perovskite solar cells due to hot spots, and the effect is significant. If the solar cell block 10 is experimentally connected to the main circuit 21 while the effects of shading and other factors have not been resolved, there is a high possibility that the overall output will decrease. Therefore, the photovoltaic power generation system 1 can prevent this output decrease. In addition, unlike systems that use bypass diodes, the photovoltaic power generation system 1 does not have a double-peaked P-V curve, so the output can be easily maximized even with maximum power point tracking control using only simple hill-climbing control.

[0027] [Second Embodiment] Figure 2 is a circuit diagram showing the configuration of a photovoltaic power generation system 1A according to the second embodiment of the present invention. The photovoltaic power generation system 1A comprises a plurality of solar cell blocks 10 and an output circuit 20A that outputs power from the plurality of solar cell blocks 10 to the outside.

[0028] The output circuit 20A includes one main circuit 21, multiple bypass sections 22, multiple switching sections 23, multiple block output detectors 24, block bypass diodes 30, a main circuit voltage detector 25, a main circuit current detector 26, a voltage adjustment section 27, an MPPT control section 28, and a switching control section 29A.

[0029] The block bypass diodes 30 are connected in parallel with the solar cell block 10 and the block output detector 24, respectively, and are connected to or disconnected from the main circuit 21 by the corresponding switching unit 23 together with the solar cell block 10 and the block output detector 24. When the solar cell block 10 is inserted into the main circuit 21 and a back electromotive force is generated in the solar cell block 10, the block bypass diodes 30 cause the current from the main circuit 21 to flow around the solar cell block 10, thereby suppressing voltage drop and heat generation in the solar cell block 10.

[0030] The switching control unit 29A may be configured to switch the switching unit 23 to an internal loop state when the corresponding block output detector 24 detects a negative voltage with reference to the output direction of the solar cell block while the switching unit 23 is in a connected state. The switching control unit 29A of this embodiment may also be configured to determine whether or not to return to a connected state based on the detection of the block output detector 24 in the internal loop state, similar to the switching control unit 29 of the first embodiment.

[0031] Even in a solar power generation system 1A that is short-circuited via a bypass diode, it is possible to appropriately determine whether or not to return to the connected state, thereby preventing a decrease in the overall output of the solar power generation system 1A and the unnecessary occurrence of hot spots due to shaded solar cells 11.

[0032] 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, in the photovoltaic power generation system according to the present invention, the switching control unit may determine whether or not to switch the switching unit to the internal loop state by other means. Also, in the photovoltaic power generation system according to the present invention, the MPPT control unit is not essential. In order to simplify the communication of control signals, the photovoltaic power generation system according to the present invention may have a switching control unit for each solar cell block.

[0033] 1. 1A Solar power generation system 11 Solar cell 10 Solar cell block 20. 20A Output circuit 21 Main circuit 22 Bypass section 221 Short-circuit switch 23 Switching section 231 Load resistor 232 Selection switch 24 Block output detector 25 Main circuit voltage detector 26 Main circuit current detector 27 Voltage regulation section 28 MPPT control section 29. 29A Switching control section 30 Block bypass diode

Claims

1. A photovoltaic power generation system comprising: a plurality of solar cell blocks, each containing one or more solar cells and independently outputting power; an output circuit for outputting power from the plurality of solar cell blocks to the outside; the output circuit comprising: a single main circuit connecting the solar cell blocks in series; a plurality of bypass sections provided for each solar cell block and bypassing the solar cell block; a plurality of switching sections provided for each solar cell block for switching between a connection state in which the solar cell block is electrically inserted into the main circuit and an internal loop state in which the solar cell block is disconnected from the main circuit and short-circuited via a load resistor; a plurality of block output detectors for detecting the voltage of each solar cell block; and a switching control section for controlling the bypass sections and the switching sections based on the detected values ​​of the block output detectors.

2. The photovoltaic power generation system according to claim 1, wherein the switching control unit switches the switching unit to the connected state when the ratio of the current value of the load resistor to the current value of the main circuit increases by a certain standard or more compared to the value immediately after switching to the internal loop state.

3. The photovoltaic power generation system according to claim 1 or 2, further comprising: an output circuit; a main voltage detector for detecting the voltage of the main circuit; a main current detector for detecting the current of the main circuit; a voltage adjustment unit for adjusting the voltage of the main circuit; and an MPPT control unit for controlling the voltage adjustment unit to maximize the power of the main circuit based on the detected value of the main voltage detector and the detected value of the main current detector.

4. The photovoltaic power generation system according to claim 3, wherein the block output detector is configured to detect the voltage of the solar cell block, the switching control unit changes the set voltage of the voltage adjustment unit so that the current of the main circuit is greater than the current at the maximum power point, bypasses the solar cell block whose rate of change of the detected value of the block output detector is greater than or equal to a predetermined standard than others using the corresponding bypass unit, and switches the corresponding switching unit to the internal loop state.

5. The photovoltaic power generation system according to claim 1 or 2, wherein the switching control unit temporarily puts the bypass unit into a bypass state when the switching unit is in the connected state, and switches the switching unit back into the internal loop state when the power of the main circuit increases due to the switch to the bypass state.

6. The photovoltaic power generation system according to claim 1 or 2, wherein the one or more solar cells include a tandem solar cell in which a perovskite solar cell and a crystalline silicon solar cell are stacked.

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