A control method of a photovoltaic power supply system, a photovoltaic power supply system and equipment

Abstract

The application discloses a control method of a photovoltaic power supply system, the photovoltaic power supply system and equipment, and relates to the technical field of photovoltaic power supply systems. The control method comprises the following steps: collecting the open-circuit voltage of each photovoltaic string in at least two photovoltaic strings; comparing the open-circuit voltage with a voltage threshold value; for any photovoltaic string, if the open-circuit voltage of the photovoltaic string is less than or equal to the voltage threshold value, the photovoltaic string is confirmed as a non-connected photovoltaic string, and the voltage of the non-connected photovoltaic string is clamped, so as to solve the technical problem that the photovoltaic side is repeatedly restarted when only part of photovoltaic strings is connected in the prior art.

Description

Technical Field

[0001] This invention relates to the field of photovoltaic power supply technology, and in particular to a control method, photovoltaic power supply system and equipment for a photovoltaic power supply system. Background Technology

[0002] Photovoltaic-storage-DC-flexible is a new type of power distribution method that includes four elements: photovoltaic power generation, high-efficiency energy storage, DC power transmission, and flexible power consumption. Therefore, it is simply called photovoltaic-storage-DC-flexible.

[0003] In a photovoltaic power supply system integrating photovoltaic power generation and energy storage, a DC contactor is added to the photovoltaic side to isolate the photovoltaic system from the power receiving system (such as an air conditioning system). The photovoltaic side can include multiple photovoltaic power supply terminals, and the number of connected photovoltaic power supply terminals can be adjusted according to actual power supply needs. In addition, to simplify wiring and reduce costs, the negative terminals of multiple photovoltaic inputs can be shared.

[0004] When the open-circuit voltage of the photovoltaic input meets the activation condition, insulation resistance testing can be performed. During this process, both the positive and negative DC contactors of the photovoltaic input are open. Once the insulation resistance test passes, the positive and negative contactors are closed, and the system enters the working state. In practical engineering applications, there may be situations where only some strings of multiple photovoltaic systems are connected. Taking two photovoltaic systems as an example, when only one photovoltaic system is connected to the power receiving system, the insulation resistance test passes, and the power receiving equipment operates normally. However, an induced voltage will appear at the terminals of the other photovoltaic system. When the voltage of the other system reaches the activation condition, all contactors will be opened, and the insulation resistance test will be performed again. This results in repeated restarts of the photovoltaic system, affecting normal photovoltaic power generation and customer use.

[0005] There is currently no effective solution to the technical problem of repeated restarts in photovoltaic power supply systems when only a portion of the photovoltaic strings are connected to the photovoltaic side. Summary of the Invention

[0006] The purpose of this invention is to overcome the above-mentioned technical deficiencies and provide a control method, photovoltaic power supply system and equipment for a photovoltaic power supply system, so as to solve the technical problem of repeated restarts when only a portion of the photovoltaic strings are connected on the photovoltaic side in related technologies.

[0007] To achieve the above-mentioned technical objectives, the present invention adopts the following technical solution:

[0008] According to one aspect of the present invention, a control method for a photovoltaic power supply system is provided, comprising:

[0009] In at least two photovoltaic strings, the open-circuit voltage of each photovoltaic string is collected;

[0010] Compare the open-circuit voltage with the voltage threshold.

[0011] For any photovoltaic string, if the open-circuit voltage of the photovoltaic string is less than or equal to the voltage threshold, the photovoltaic string is identified as an unconnected photovoltaic string, and the voltage of the unconnected photovoltaic string is clamped.

[0012] Optionally, the method further includes:

[0013] Photovoltaic strings with open-circuit voltage greater than the voltage threshold are identified as photovoltaic strings that need to be connected. Insulation impedance detection is performed on the photovoltaic strings that need to be connected. After the insulation impedance detection is passed, the switching element of the photovoltaic string that needs to be connected is controlled to close.

[0014] Optionally, if at least two photovoltaic strings are connected to a common negative terminal, the switching element controlling the photovoltaic strings to be connected will close, specifically including:

[0015] The positive terminal switching element and the common negative terminal switching element of the photovoltaic string to be connected are both closed.

[0016] Optionally, the photovoltaic string further includes a power transistor, one end of which is connected to the positive terminal of the photovoltaic string through an inductor and a switching element, and the other end of which is connected to the negative terminal of the photovoltaic string.

[0017] The clamping of the voltage of the unconnected photovoltaic strings specifically includes:

[0018] The switching element of the unconnected photovoltaic string is closed, and the power transistor on the unconnected photovoltaic string is turned on.

[0019] Optionally, if the open-circuit voltage of all photovoltaic strings in the at least two photovoltaic strings is less than or equal to the voltage threshold, then the switching elements of all photovoltaic strings are controlled to remain in the open state.

[0020] According to another aspect of the present invention, a photovoltaic power supply system is provided, comprising:

[0021] At least two photovoltaic strings;

[0022] The sampling unit, connected to the photovoltaic string, is used to collect the open-circuit voltage of each photovoltaic string;

[0023] The control unit is used to compare the open-circuit voltage with the voltage threshold. For any photovoltaic string, if the open-circuit voltage of the photovoltaic string is less than or equal to the voltage threshold, the photovoltaic string is identified as an unconnected photovoltaic string, and the voltage of the unconnected photovoltaic string is clamped.

[0024] Optional:

[0025] Each photovoltaic string includes: a positive line for the photovoltaic string and a common negative line;

[0026] The positive terminal circuit of the photovoltaic module string includes: a first switching element, an inductor, and a positively connected diode connected in series between the positive terminal output of the photovoltaic string and the positive terminal input of the powered load;

[0027] The common negative line includes a second switching element connected between the negative output terminal of the photovoltaic string and the negative input terminal of the powered load.

[0028] Both the first and second switching elements are connected to the control unit.

[0029] Optional:

[0030] Each photovoltaic string is equipped with a clamping circuit;

[0031] The control unit is specifically used to clamp the voltage of the unconnected photovoltaic string through the clamping circuit.

[0032] Optionally, the clamping circuit includes:

[0033] The transistor has its base connected to the control unit, its collector connected between the inductor and the diode, and its emitter connected between the second switching element and the negative input terminal of the powered load.

[0034] Optionally, if the powered load is a compressor, the positive input terminal of the compressor's drive circuit is connected to the positive line of each photovoltaic string, and the negative input terminal of the compressor's drive circuit is connected to the common negative line.

[0035] Optional:

[0036] If the powered load is a non-compressor, the non-compressor is connected to the DC bus via a bidirectional DC / AC controller, the positive terminal of the DC bus is connected to the positive terminal line of the photovoltaic string, and the negative terminal of the DC bus is connected to the common negative terminal line.

[0037] A DC bus capacitor is connected between the positive and negative terminals of the DC bus.

[0038] According to another aspect of the present invention, an apparatus is also provided, comprising:

[0039] Powered load;

[0040] The photovoltaic power supply system described above is connected to the powered load.

[0041] Optionally, the device is an air conditioner, and the powered load is the compressor of the air conditioner.

[0042] The photovoltaic power supply system, control method, and equipment provided by this invention, in a photovoltaic power supply system containing at least two photovoltaic strings, detect the open-circuit voltage of the photovoltaic strings. When the open-circuit voltage is less than or equal to a preset voltage threshold, the photovoltaic string is identified as an unconnected string, and its voltage is clamped to prevent it from being affected by connected photovoltaic strings and from reaching the activation voltage. This avoids the problem of repeated photovoltaic restarts that occur when only some photovoltaic strings are connected, achieving adaptive control of photovoltaic connection. Furthermore, it does not require changes to the hardware structure of the photovoltaic power supply system; the aforementioned technical problems can be solved simply through open-circuit voltage sampling and control logic. Attached Figure Description

[0043] Figure 1 A flowchart illustrating a control method for a photovoltaic power supply system provided in an embodiment of the present invention;

[0044] Figure 2 This is a schematic diagram of a photovoltaic power supply system provided in an embodiment of the present invention;

[0045] Figure 3 A flowchart illustrating a control method for a photovoltaic power supply system provided in an embodiment of the present invention;

[0046] Figure 4 A schematic diagram of a photovoltaic power supply system provided in another embodiment of the present invention;

[0047] Figure 5 This is a schematic diagram of the device structure provided in one embodiment of the present invention. Detailed Implementation

[0048] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort should fall within the scope of protection of the present application.

[0049] In related technologies, for photovoltaic power supply systems containing multiple photovoltaic strings, there is currently no effective solution to the technical problem of repeated restarts when only some photovoltaic strings are connected on the photovoltaic side.

[0050] To address the aforementioned problems, this invention proposes a control method, a photovoltaic power supply system, and equipment for a photovoltaic power supply system, thereby resolving the technical issue of repeated restarts that occur when only a portion of the photovoltaic strings are connected to the photovoltaic side in related technologies. A detailed description follows.

[0051] Example 1

[0052] According to an embodiment of the present invention, a control method for a photovoltaic power supply system is provided. To facilitate the description of the controlled components involved in the control method, a photovoltaic power supply system controlled by this method is first described as an example.

[0053] As an example, a photovoltaic (PV) power supply system includes at least two PV strings. Each PV string is connected to the load of the device to be powered via a switching element, such as a DC contactor. The number of PV strings connected to the load is adjusted by controlling the opening and closing of the switching element. For example, in an air conditioner, the load could be the air conditioner's compressor. In practical applications, depending on power demand or limitations imposed by the arrangement of the PV panels, it may be necessary to connect only a portion of the PV strings. Figure 2 For example, it includes two photovoltaic strings, both of which are connected to the compressor drive (i.e., the compressor drive circuit) of the air conditioner. The compressor drive circuit is connected to the motor M. In actual use, it is possible that both photovoltaic strings are connected to the compressor drive circuit, or it is possible that only one photovoltaic string is connected to the compressor drive circuit.

[0054] As mentioned earlier, when only some photovoltaic strings are connected, induced voltage will appear at the photovoltaic terminals of the other unconnected photovoltaic strings. When the voltage reaches the activation condition, the switching elements of all photovoltaic strings will be disconnected, and the insulation resistance test will be performed again, resulting in the problem of repeated photovoltaic restarts, which affects the normal power generation of photovoltaics and customer use.

[0055] Therefore, the present invention provides a control method for a photovoltaic power supply system, combined with Figure 1 ,include:

[0056] S101, in at least two photovoltaic strings, collect the open-circuit voltage of each photovoltaic string.

[0057] For example, a sampling unit can be configured for the photovoltaic power supply system and connected to the front end of the photovoltaic string switching element to collect the open-circuit voltage.

[0058] S103, compare the open-circuit voltage with the voltage threshold.

[0059] After obtaining the open-circuit voltage of each photovoltaic string in step S101, the open-circuit voltage of each photovoltaic string is compared with a preset voltage threshold, and a corresponding control strategy is executed on the photovoltaic string according to the comparison result (as described below). This voltage threshold can be set as the turn-on voltage for the photovoltaic string connection, and the turn-on voltage can be set according to the actual situation of the connection system.

[0060] S105, for any photovoltaic string, if the open-circuit voltage of the photovoltaic string is less than or equal to the voltage threshold, the photovoltaic string is identified as an unconnected photovoltaic string, and the voltage of the unconnected photovoltaic string is clamped.

[0061] In step S105, photovoltaic strings with open-circuit voltages less than or equal to the voltage threshold are identified as unconnected photovoltaic strings. To prevent the induced voltage generated by other connected photovoltaic strings from reaching the activation voltage for photovoltaic string connection, in step S105, the unconnected photovoltaic string is clamped, so that the voltage at the terminal of the photovoltaic string is clamped and cannot reach the activation voltage, thus preventing it from starting. Consequently, the switching elements of the entire photovoltaic power supply system will not be disconnected to re-perform insulation impedance detection, thereby solving the technical problem of repeated restarts of the photovoltaic power supply system when only some photovoltaic strings are connected.

[0062] Furthermore, the control methods for photovoltaic power supply systems also include:

[0063] Step S107: Identify photovoltaic strings with open-circuit voltage greater than the voltage threshold as photovoltaic strings that need to be connected, and perform insulation impedance detection on the photovoltaic strings that need to be connected. After the insulation impedance detection is passed, control the switching element of the photovoltaic strings that need to be connected to close.

[0064] In step S107, photovoltaic strings with open-circuit voltages greater than the voltage threshold are identified as photovoltaic strings requiring connection. A normal connection control strategy is implemented for these strings, which involves first performing an insulation impedance test. If the test passes, the switching element is closed normally, connecting the string to the load. Simultaneously, as described in step S105, the voltage of unconnected photovoltaic strings is clamped, preventing accidental activation due to the connection of these strings. This avoids the problem of repeated restarts of the photovoltaic power supply system when only some photovoltaic strings are connected.

[0065] by Figure 2 Taking a photovoltaic power supply system with two photovoltaic strings as an example, if the open-circuit voltage of the first photovoltaic string is detected to be greater than the voltage threshold, while the open-circuit voltage of the second photovoltaic string is less than or equal to the voltage threshold, then the first photovoltaic string is identified as the one that needs to be connected, while the second photovoltaic string is identified as the one that is not connected. Furthermore, for the first photovoltaic string, an insulation impedance test is performed. After the insulation impedance test passes, the switching element of the first photovoltaic string is closed, connecting it to the powered load, and the power supply equipment is allowed to operate normally. For the second photovoltaic string, its voltage is clamped to prevent it from reaching the opening voltage required for photovoltaic string connection, thus avoiding the problem of repeated restarts of the photovoltaic power supply system that occurs when only one photovoltaic string is connected.

[0066] Conversely, if the open-circuit voltage of both photovoltaic strings is greater than the voltage threshold, it is confirmed that both photovoltaic strings need to be connected to the power supply. In this case, the insulation impedance of the first photovoltaic string is tested first, and if it passes, the insulation impedance of the second photovoltaic string is tested. If both insulation impedance tests pass, the switching elements, such as DC contactors, at the positive and negative terminals of the first and second photovoltaic strings are closed, and the system enters normal operation.

[0067] Furthermore, the control method for photovoltaic modules also includes: step S109, if the open-circuit voltage of all photovoltaic strings in the at least two photovoltaic strings is less than or equal to the voltage threshold, then the switching elements of all photovoltaic strings are controlled to remain in the off state.

[0068] At this point, since none of the photovoltaic strings meet the required activation voltage, it is only necessary to keep the switching elements of all photovoltaic strings in the off state. That is, no active control strategy needs to be executed, thus saving the power consumption of the control system.

[0069] Figure 3 Another embodiment of the control method for a photovoltaic power supply system is illustrated. At the start of the method, the open-circuit voltage of the photovoltaic system is sampled. Then, it is determined whether the photovoltaic voltage value is greater than a reference value (i.e., the voltage threshold described above). If the determination result is yes (Y), the photovoltaic voltage value is greater than the reference value, and the photovoltaic wiring is normally connected, initiating insulation impedance detection. If the determination result is no (N), the photovoltaic voltage value is less than or equal to the reference value, confirming that the photovoltaic string is not connected. The control unit sends a control signal to the photovoltaic string, turning on its positive contactor and power transistor to achieve voltage clamping, finally completing the control process.

[0070] by Figure 2 Taking a photovoltaic power supply system with two photovoltaic strings as an example, if the open-circuit voltage of the first photovoltaic string and the open-circuit voltage of the second photovoltaic string are both detected to be less than a preset voltage threshold, then the first DC contactor K1, the second DC contactor K2, and the third DC contactor K3 will all be kept in the open state, thus achieving the result that neither photovoltaic string is connected to a powered load.

[0071] As an example, the photovoltaic power supply system provided in this embodiment of the invention includes multiple photovoltaic strings, each of which includes a positive terminal line and a negative terminal line. In this embodiment, to save space and cost in circuit layout, the negative terminal line of the photovoltaic string is a common negative terminal line. The positive terminal line of the photovoltaic string, starting from its positive output terminal (i.e., the voltage input terminal), sequentially includes a first switching element connected in series, an inductor, and a positively connected diode. The common negative terminal line includes a second switching element connected between the negative output terminal of the photovoltaic string and the negative input terminal of the powered load. Both the first and second switching elements are connected to a control unit.

[0072] The first and second switching elements can be DC contactors, with a positive DC contactor installed at the positive output terminal of the photovoltaic string and a negative DC contactor installed at the negative output terminal. For example... Figure 2 In this configuration, a first DC contactor K1 is installed in the first photovoltaic string, and a third DC contactor K3 is installed in the second photovoltaic string. A second DC contactor K2 is installed in the common negative line.

[0073] Furthermore, the photovoltaic string also includes a clamping circuit, allowing the control unit to clamp any unconnected photovoltaic strings by controlling the clamping circuit. Specifically, the clamping circuit may include a power transistor, with one end connected to the node between the inductor and the diode, and the other end connected to the negative terminal of the photovoltaic string. For example, the power transistor can be a bipolar transistor, with its base connected to the control unit, its collector connected to the node between the inductor and the diode, and its emitter connected between the second switching element and the negative input terminal of the powered load. Further, another diode is connected in parallel with the transistor, its cathode connected to the emitter of the transistor, and its anode connected to the collector of the transistor. Initially, the power transistor is in the off state. When clamping the photovoltaic string is required, the first switching element controlling the positive line of the photovoltaic string is closed, and the power transistor is turned on.

[0074] by Figure 2 Taking the two photovoltaic strings as an example, the positive output terminal PV1+ of the first photovoltaic string is connected to the positive input terminal of the compressor drive circuit via a series connection of a first DC contactor K1, a first inductor L1, and a positively connected first diode D1. The first power transistor Q1 is a bipolar transistor, with its collector connected between the first inductor L1 and the first diode D1, and its emitter connected between the second DC contactor K2 and the negative input terminal of the compressor drive circuit. Similarly, the positive input terminal PV2+ of the second photovoltaic string is connected to the positive input terminal of the compressor drive circuit via a third DC contactor K3, a second inductor L2, and a positively connected second diode D2. The second power transistor Q2 is a bipolar transistor, with its collector connected between the second inductor L2 and the second diode D2, and its emitter connected between the second DC contactor K2 and the negative input terminal of the compressor drive circuit, i.e., connected to the common negative output terminal PV- of both photovoltaic strings. As mentioned earlier, a shared DC contactor, namely the second DC contactor K2, is also installed on the common negative line. This not only simplifies the wiring structure, but also reduces the power consumption of the control system by requiring only one set of shared switching elements to be controlled during the control of the negative terminal switching elements.

[0075] Furthermore, if the load is not a compressor, the photovoltaic power supply system also includes a DC bus capacitor C1 and a bidirectional DC / AC controller. The non-compressor is connected to the DC bus through the bidirectional DC / AC controller. One side of the bidirectional DC / AC controller is connected to the AC grid, and the other side is connected to the positive and negative terminals of the DC bus capacitor C1 through the positive terminal Vbus+ and the negative terminal Vbus- of the DC bus. That is, the DC bus capacitor C1 is connected across the positive and negative terminals of the DC bus.

[0076] It should be understood that, Figure 1 The illustrated embodiment presents the topology of a residential photovoltaic (storage) DC air conditioning system. Based on this, by simply sampling the open-circuit voltage using a sampling unit and inputting the open-circuit voltage signal to the control unit, the aforementioned control strategy can be executed to resolve the issue of repeated restarts of the photovoltaic power supply system when only a portion of the photovoltaic strings are connected. Of course, in other embodiments, the control strategy provided in this embodiment can also be applied to other photovoltaic power supply systems based on similar principles, and the corresponding circuit structure will be adaptively modified. For example, the specific clamping circuit may differ from... Figure 2 The results are different.

[0077] In summary, this embodiment avoids the problem of repeated photovoltaic restarts that occur when only a portion of the photovoltaic strings are connected, achieving adaptive control of photovoltaic access. Furthermore, it does not require changes to the hardware structure of the photovoltaic power supply system; the aforementioned technical problems can be solved simply through open-circuit voltage sampling and control logic.

[0078] Example 2

[0079] According to an embodiment of the present invention, a photovoltaic power supply system is provided, combined with Figure 4 The photovoltaic power supply system includes:

[0080] At least two photovoltaic modules with a string length of 25;

[0081] The sampling unit 23 is connected to the photovoltaic string 25 and is used to collect the open-circuit voltage of each of the at least two photovoltaic strings.

[0082] The control unit 21 is used to compare the open-circuit voltage with the voltage threshold. For any photovoltaic string, if the open-circuit voltage of the photovoltaic string is less than or equal to the voltage threshold, the photovoltaic string is identified as an unconnected photovoltaic string, and the voltage of the unconnected photovoltaic string is clamped.

[0083] The control unit 21 may specifically include a memory and a processor. The memory stores a computer program that can be executed by the processor to implement the control method described in Embodiment 1 above.

[0084] Optionally, specific examples in this embodiment, such as the structure of the photovoltaic string and the control method executed by the control unit, can refer to the examples described in the above embodiments, and will not be repeated here.

[0085] This embodiment avoids the problem of repeated photovoltaic restarts that occur when only a portion of the photovoltaic strings are connected, achieving adaptive control of photovoltaic access. Furthermore, it does not require changes to the hardware structure of the photovoltaic power supply system; the aforementioned technical problems can be solved simply through open-circuit voltage sampling and control logic.

[0086] Example 3

[0087] According to embodiments of the present invention, a device is also provided, which combines Figure 5 It includes:

[0088] Powered load 32;

[0089] A photovoltaic power supply system 31 is connected to the powered load 32.

[0090] Optionally, the device is an air conditioner, and the powered load is the compressor of the air conditioner.

[0091] The structure of the powered load 32 and the photovoltaic power supply system 31, as well as the control method of the photovoltaic power supply system 31, can be referred to the description in Embodiment 1 above, and will not be repeated here.

[0092] This embodiment avoids the problem of repeated photovoltaic restarts that occur when only a portion of the photovoltaic strings are connected, achieving adaptive control of photovoltaic access. Furthermore, it does not require changes to the hardware structure of the photovoltaic power supply system; the aforementioned technical problems can be solved simply through open-circuit voltage sampling and control logic.

[0093] The sequence numbers of the embodiments in this application are for descriptive purposes only and do not represent the superiority or inferiority of the embodiments.

[0094] In the above embodiments of this application, the descriptions of each embodiment have different focuses. For parts not described in detail in a certain embodiment, please refer to the relevant descriptions of other embodiments.

[0095] In the embodiments provided in this application, the described device embodiments are merely illustrative. For example, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the displayed or discussed mutual couplings, direct couplings, or communication connections may be through some interfaces, indirect couplings, or communication connections between units or modules, and may be electrical or other forms.

[0096] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0097] The above description is only a preferred embodiment of this application. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of this application, and these improvements and modifications should also be considered within the scope of protection of this application.

Claims

1. A control method for a photovoltaic power supply system, characterized in that, include: In at least two photovoltaic strings, the open-circuit voltage of each photovoltaic string is collected; Compare the open-circuit voltage with the voltage threshold. For any photovoltaic string, if the open-circuit voltage of the photovoltaic string is less than or equal to the voltage threshold, the photovoltaic string is identified as an unconnected photovoltaic string, and the voltage of the unconnected photovoltaic string is clamped. The photovoltaic string also includes a power transistor, one end of which is connected to the positive terminal of the photovoltaic string through an inductor and a switching element, and the other end of which is connected to the negative terminal of the photovoltaic string. The clamping of the voltage of the unconnected photovoltaic strings specifically includes: The switching element of the unconnected photovoltaic string is closed, and the power transistor on the unconnected photovoltaic string is turned on.

2. The control method for a photovoltaic power supply system according to claim 1, characterized in that, The method further includes: Photovoltaic strings with open-circuit voltage greater than the voltage threshold are identified as photovoltaic strings that need to be connected. Insulation impedance detection is performed on the photovoltaic strings that need to be connected. After the insulation impedance detection is passed, the switching element of the photovoltaic string that needs to be connected is controlled to close.

3. The control method for the photovoltaic power supply system according to claim 2, characterized in that, If at least two photovoltaic strings are connected to a common negative terminal, the switching element controlling the connection of the photovoltaic strings to be connected will close, specifically including: The positive terminal switching element and the common negative terminal switching element of the photovoltaic string to be connected are both closed.

4. The control method for the photovoltaic power supply system according to claim 1, characterized in that, If the open-circuit voltage of all photovoltaic strings in the at least two photovoltaic strings is less than or equal to the voltage threshold, then the switching elements of all photovoltaic strings are controlled to remain in the open state.

5. A photovoltaic power supply system, characterized in that, The system comprising the method according to any one of claims 1 to 4, wherein the system includes: At least two photovoltaic strings; The sampling unit, connected to the photovoltaic string, is used to collect the open-circuit voltage of each photovoltaic string; The control unit is used to compare the open-circuit voltage with the voltage threshold. For any photovoltaic string, if the open-circuit voltage of the photovoltaic string is less than or equal to the voltage threshold, the photovoltaic string is identified as an unconnected photovoltaic string, and the voltage of the unconnected photovoltaic string is clamped.

6. The photovoltaic power supply system according to claim 5, characterized in that, Each photovoltaic string includes: a positive line for the photovoltaic string and a common negative line; The positive terminal circuit of the photovoltaic module string includes: a first switching element, an inductor, and a positively connected diode connected in series between the positive terminal output of the photovoltaic string and the positive terminal input of the powered load; The common negative line includes a second switching element connected between the negative output terminal of the photovoltaic string and the negative input terminal of the powered load. Both the first and second switching elements are connected to the control unit.

7. The photovoltaic power supply system according to claim 6, characterized in that, Each photovoltaic string is equipped with a clamping circuit; The control unit is specifically used to clamp the voltage of the unconnected photovoltaic string through the clamping circuit.

8. The photovoltaic power supply system according to claim 7, characterized in that, The clamping circuit includes: The transistor has its base connected to the control unit, its collector connected between the inductor and the diode, and its emitter connected between the second switching element and the negative input terminal of the powered load.

9. The photovoltaic power supply system according to any one of claims 6-8, characterized in that, If the powered load is a compressor, the positive input terminal of the compressor's drive circuit is connected to the positive line of each photovoltaic string, and the negative input terminal of the compressor's drive circuit is connected to the common negative line.

10. The photovoltaic power supply system according to claim 9, characterized in that, If the powered load is a non-compressor, the non-compressor is connected to the DC bus via a bidirectional DC / AC controller, the positive terminal of the DC bus is connected to the positive terminal line of the photovoltaic string, and the negative terminal of the DC bus is connected to the common negative terminal line. A DC bus capacitor is connected between the positive and negative terminals of the DC bus.

11. A device, characterized in that, include: Powered load; The photovoltaic power supply system according to any one of claims 5-10, wherein the photovoltaic power supply system is connected to the powered load.

12. The device according to claim 11, characterized in that, The device is an air conditioner, and the electrical load is the compressor of the air conditioner.

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