Photovoltaic power generation system and method for determining system insulation impedance

Abstract

The present application provides a photovoltaic power generation system and a method for determining the insulation impedance of the system. At least one conversion circuit and at least one control circuit are provided in the photovoltaic power generation system, and each conversion circuit is connected to the positive end of at least one photovoltaic string via the positive bus of a DC circuit, and each conversion circuit is connected to the negative end of at least one photovoltaic string via the negative bus of the DC circuit; so that the control circuit can determine the ground voltage of the negative bus used to determine the first ground impedance of the photovoltaic power generation system during at least two adjustments of the conversion circuit to which it is connected. In this way, the PID effect of at least one photovoltaic string can be suppressed, and the ground impedance of the photovoltaic power generation system can be detected, which can effectively improve the detection accuracy of the ground impedance of the photovoltaic power generation system. There is no need to provide a separate insulation impedance detection device, which can achieve the purpose of cost saving.

Description

Technical Field

[0001] The present application relates to the field of photovoltaic technology, and in particular to a photovoltaic power generation system and a method for determining the insulation impedance of the system. Background Art

[0002] Solar photovoltaic (PV) power generation technology is a low-carbon, environmentally friendly, and green energy technology that is gaining increasing popularity. Typically, solar PV power generation is achieved through a PV power generation system, which primarily consists of PV modules and inverters.

[0003] Photovoltaic modules are commonly subject to potential-induced degradation (PID), which causes the output power of the photovoltaic panels to decay, leading to a loss of power generation for the entire photovoltaic power generation system. Furthermore, the PID effect of photovoltaic modules causes the potential difference between the glass layer and the metal encapsulation material of the photovoltaic module to generate leakage current, causing negative charge to accumulate on the surface of the cell, thereby reducing the surface passivation effect of the cell. Furthermore, to ensure the power supply continuity and safety of photovoltaic power generation systems, insulation impedance testing is often required.

[0004] However, in the prior art, when an anti-PID device and an insulation monitor device (IMD) are simultaneously configured in an AC circuit of a photovoltaic power generation system, the operation of the anti-PID device may cause misdetection by the IMD device. Summary of the Invention

[0005] Embodiments of the present application provide a photovoltaic power generation system and a method for determining the insulation impedance of the system, so as to suppress the PID effect of a photovoltaic string set in the photovoltaic power generation system and perform insulation impedance detection on the photovoltaic power generation system.

[0006] In a first aspect, an embodiment of the present application provides a photovoltaic power generation system.

[0007] As an example, the photovoltaic power generation system may include at least one conversion circuit and at least one control circuit, each control circuit being connected to each conversion circuit in a one-to-one correspondence; wherein each conversion circuit is connected to the positive terminal of at least one photovoltaic string through a positive bus of a DC circuit, and each conversion circuit is connected to the negative terminal of at least one photovoltaic string through a negative bus of a DC circuit; thereby, each conversion circuit can be used to adjust the ground voltage of the negative terminal or positive terminal of at least one photovoltaic string at least twice; each control circuit can be used to determine the ground voltage of the negative bus during the process in which the conversion circuit to which it is connected adjusts the ground voltage of the negative terminal or positive terminal of at least one photovoltaic string at least twice; wherein the ground voltage of the negative bus is used to determine the first ground impedance of the photovoltaic power generation system.

[0008] It should be understood that determining the voltage of the negative bus to ground during at least two voltage adjustments may mean determining a value of the voltage of the negative bus to ground each time an adjustment is made.

[0009] In an embodiment of the present application, at least one conversion circuit and at least one control circuit are provided in a photovoltaic power generation system, and each conversion circuit is connected to the positive terminal of at least one photovoltaic string via a positive bus of a DC circuit, and each conversion circuit is connected to the negative terminal of at least one photovoltaic string via a negative bus of the DC circuit; so that the control circuit can determine the ground voltage of the negative bus used to determine the first ground impedance of the photovoltaic power generation system during at least two adjustments of the conversion circuit to which it is connected. In this way, the PID effect of at least one photovoltaic string can be suppressed, and the ground impedance of the photovoltaic power generation system can be detected, which can effectively improve the detection accuracy of the ground impedance of the photovoltaic power generation system. There is no need to provide a separate insulation impedance detection device, thereby achieving the purpose of cost savings.

[0010] In one possible design, the photovoltaic power generation system further includes a data collector, which is respectively in communication with each control circuit. The voltage to ground of the negative bus of the DC circuit connected to each conversion circuit is used to determine the first impedance to ground of the photovoltaic power generation system in a variety of implementations, including but not limited to the following two:

[0011] In method 1, each control circuit can send the negative bus voltage to the ground determined by it to the data collector; then the data collector can determine the first ground impedance of the photovoltaic power generation system based on the negative bus voltage to the ground determined by at least one control circuit.

[0012] In Method 1, each control circuit can directly transmit the ground voltage of the negative bus corresponding to the connected conversion circuit to the data collector. The data collector can then directly calculate the first ground impedance of the photovoltaic power generation system based on the ground voltage of the negative bus. This effectively improves the efficiency of determining the first ground impedance of the photovoltaic power generation system.

[0013] Method 2: Each control circuit can calculate the second ground impedance of the conversion circuit connected to it based on the ground voltage of the negative bus determined by it, and send the second ground impedance to the data collector; then the data collector can determine the first ground impedance of the photovoltaic power generation system based on the second ground impedance of at least one conversion circuit.

[0014] In method 2, each control circuit sends the second impedance to ground of the conversion circuit connected to it to the data collector, so that the data collector can calculate the first impedance to ground of the photovoltaic power generation system based on the second impedance to ground of all the conversion circuits, thereby making the determined first impedance to ground of the photovoltaic power generation system more accurate and effectively reducing the calculation amount of the data collector.

[0015] In one possible design, the photovoltaic power generation system also includes at least one sampling circuit, each sampling circuit is connected to the positive bus and / or the negative bus; each sampling circuit is connected to each conversion circuit in a one-to-one correspondence; each conversion circuit may also include at least one boost circuit, each boost circuit is connected to the output end of a photovoltaic string.

[0016] In which, each of the boost circuits can be used to increase the DC voltage generated by at least one photovoltaic string before transmitting it to the power grid in the photovoltaic power generation system when it is determined that the output power of at least one photovoltaic string is lower than a preset value; then, each sampling circuit can sample the value of the increased DC voltage and the current value of the voltage to ground of the negative terminal or positive terminal of at least one photovoltaic string based on the first voltage range; and then each conversion circuit can receive the value of the increased DC voltage and the current value of the voltage to ground from the sampling circuit connected thereto, and adjust the voltage to ground of the negative terminal or positive terminal of at least one photovoltaic string at least twice based on the value of the increased DC voltage and the current value of the voltage to ground.

[0017] In this design, the voltage conversion circuit can adjust the ground voltage of the positive terminal or negative terminal of each photovoltaic string according to the boosted DC voltage, making the voltage adjustment more precise.

[0018] It should be understood that there are multiple ways for each control circuit to determine the voltage relative to ground of the negative bus connected to the conversion circuit connected thereto, including but not limited to the following ways:

[0019] In mode 1, each sampling circuit is connected to each control circuit in a one-to-one correspondence. When each sampling circuit is connected to the negative bus, each control circuit can control the sampling circuit connected thereto to sample the voltage of the negative bus relative to ground based on a second voltage range; wherein the second voltage range is smaller than the first voltage range.

[0020] In mode 1, each control circuit can control the sampling circuit connected thereto to directly sample the voltage of the negative bus to ground, thereby effectively improving the efficiency of obtaining the negative bus voltage.

[0021] In mode 2, each sampling circuit is connected to each control circuit in a one-to-one correspondence; when each sampling circuit is connected to the positive bus and the negative bus, respectively, each control circuit, when used to determine the voltage of the negative bus to ground, is specifically used to: control the connected sampling circuit to sample a first voltage of the positive bus to ground and a second voltage between the positive bus and the negative bus based on a second voltage range; wherein the second voltage range is smaller than the first voltage range; and determine the difference between the first voltage and the second voltage as the voltage of the negative bus to ground.

[0022] In method 2, each control circuit can determine the voltage of the negative bus to ground based on the positive bus voltage to ground and the voltage between the positive bus and the negative bus collected by the sampling circuit connected to it, thereby effectively improving the accuracy of the acquired negative bus voltage to ground.

[0023] It should be understood that in Method 1 and Method 2, each sampling circuit uses a smaller voltage sampling range to collect the voltage of the negative bus to ground, which effectively improves the accuracy of voltage sampling, making the collected voltage value more accurate, and thus making the impedance to ground of the photovoltaic power generation system determined based on the collected voltage value more accurate.

[0024] In one possible design, each conversion circuit specifically includes a current-limiting resistor connected in series between the positive bus or the negative bus and the ground line; the voltage of the negative bus to ground includes a first voltage value determined by the control circuit at time t0 and a second voltage value determined at time t1; wherein the interval between time t0 and time t1 is a preset time. Specifically, in the above-mentioned method 1, the data collector determines the first impedance to ground of the photovoltaic power generation system based on the voltage to ground of at least one negative bus, which conforms to the following formula:

[0025]

[0026] Wherein, Rx is the first impedance to ground, i is an integer greater than or equal to 1; N is the number of conversion circuits; is the first current value flowing through the current-limiting resistor in the i-th conversion circuit at time t0; is the second current value flowing through the current-limiting resistor in the i-th conversion circuit at time t1; is the first voltage value determined for the i-th control circuit, A second voltage value is determined for the i-th control circuit.

[0027] In this design, the data collector can determine the first impedance to ground of the photovoltaic power generation system based on the first voltage value, second voltage value, first current value, and second current value corresponding to each conversion circuit; in this way, the error impact of the conversion circuit voltage adjustment on the system insulation impedance detection can be effectively reduced, and the accuracy of the determined first impedance to ground of the photovoltaic power generation system can be effectively improved.

[0028] It should be understood that before determining the first ground impedance of the photovoltaic power generation system, the data collector needs to obtain the first current value and the second current value corresponding to each conversion circuit. There are multiple ways for the data collector to obtain the first current value and the second current value corresponding to each conversion circuit, including but not limited to the following ways:

[0029] Method 1: The conversion circuit also includes an adjustable power supply, one end of the adjustable power supply is connected to the negative bus or the positive bus, and the other end is grounded through a current-limiting resistor; the adjustable power supply is used to adjust the ground voltage of the negative terminal or the positive terminal of at least one photovoltaic string at least twice; each sampling circuit can collect a third voltage value of the adjustable power supply in the conversion circuit connected to it at time t0, and collect a fourth voltage value of the adjustable power supply in the conversion circuit connected to it at time t1, and send the third voltage value and the fourth voltage value to the control circuit connected to it; furthermore, the data collector can receive the third voltage value and the fourth voltage value of the adjustable power supply in the conversion circuit connected to it from each control circuit, and determine the first current value flowing through the current-limiting resistor at time t0 based on the first voltage value, the third voltage value and the pre-stored resistance value of the current-limiting resistor; and determine the second current value flowing through the current-limiting resistor at time t1 based on the second voltage value, the fourth voltage value and the resistance value of the current-limiting resistor.

[0030] In mode 1, the data collector can obtain the first current value and the second current value corresponding to each conversion circuit by calculation. No current sensor is required in the conversion circuit, which can save costs.

[0031] Method 2: The conversion circuit further includes an adjustable power supply and a current sensor; one end of the adjustable power supply is connected to the negative bus or the positive bus, and the other end is grounded through a current-limiting resistor; wherein the current sensor can be arranged between the adjustable power supply and the negative bus or the positive bus, or the current sensor can also be arranged in the adjustable power supply, and the embodiment of the present application does not make specific limitations. wherein the adjustable power supply can be used to adjust the voltage to the ground of the negative terminal or the positive terminal of at least one photovoltaic string at least twice; the current sensor can sample a first current value at time t0 and a second current value at time t1, and send the first current value and the second current value to a control circuit connected to the conversion circuit; and then the data collector can receive the corresponding first current value and second current value in each conversion circuit from the control circuit.

[0032] In method 2, the first current value and the second current value corresponding to each conversion circuit are collected by the current sensor in each conversion circuit, which effectively reduces the calculation amount of the data collector and effectively improves the efficiency of the data collector in obtaining the first current value and the second current value corresponding to each conversion circuit.

[0033] In one possible design, the conversion circuit specifically includes a current-limiting resistor connected in series between a positive bus or a negative bus and a ground line; the voltage of the negative bus to ground includes a first voltage value determined by the control circuit at time t0 and a second voltage value determined at time t1; wherein time t0 and time t1 are separated by a preset time length; specifically, each control circuit calculates a second impedance to ground of the conversion circuit connected thereto based on the negative bus voltage to ground determined thereby, such that the second impedance complies with the following formula:

[0034]

[0035] Among them, R i is the second impedance to ground of the i-th conversion circuit, is the first current value flowing through the current-limiting resistor in the i-th conversion circuit at time t0; is the second current value flowing through the current-limiting resistor in the i-th conversion circuit at time t1; is the first voltage value determined for the i-th control circuit, A second voltage value is determined for the i-th control circuit.

[0036] Specifically, the data collector determines, based on the second impedance to ground of at least one conversion circuit, that the first impedance to ground complies with the following formula:

[0037]

[0038] Wherein, i is an integer greater than or equal to 1; R x is the first impedance to ground, N is the number of conversion circuits, R iis the second impedance to ground of the i-th conversion circuit.

[0039] In this design, the data collector can determine the first impedance to ground of the photovoltaic power generation system based on the second impedance to ground of all conversion circuits in the photovoltaic power generation system; in this way, the efficiency of the determined first impedance to ground of the photovoltaic power generation system can be effectively improved.

[0040] It should be understood that before each control circuit determines the second impedance to ground of the conversion circuit to which it is connected, it needs to obtain the first current value and the second current value corresponding to the conversion circuit. There are multiple ways to implement each control circuit obtaining the first current value and the second current value corresponding to the conversion circuit to which it is connected, including but not limited to the following ways:

[0041] Method 1: The conversion circuit further includes an adjustable power supply, one end of which is connected to a negative bus or a positive bus, and the other end of which is connected to a ground line via a current-limiting resistor; the adjustable power supply is used to adjust the voltage of the negative terminal or the positive terminal of at least one photovoltaic string to ground at least twice; each sampling circuit can collect a third voltage value of the adjustable power supply in the conversion circuit connected thereto at time t0, and collect a fourth voltage value of the adjustable power supply in the conversion circuit connected thereto at time t1, and send the third and fourth voltage values ​​to the control circuit connected thereto. The control circuit can then receive the third and fourth voltage values ​​of the adjustable power supply in the conversion circuit connected thereto; and determine a first current value flowing through the current-limiting resistor at time t0 based on the first and third voltage values ​​and the pre-stored resistance value of the current-limiting resistor; and determine a second current value flowing through the current-limiting resistor at time t1 based on the second and fourth voltage values ​​and the resistance value of the current-limiting resistor.

[0042] In mode 2, the conversion circuit further includes an adjustable power supply and a current sensor; one end of the adjustable power supply is connected to the negative bus or the positive bus, and the other end is grounded via a current-limiting resistor; the current sensor is disposed between the adjustable power supply and the negative bus or the positive bus, or the current sensor is disposed in the adjustable power supply; the adjustable power supply can be used to adjust the voltage relative to ground at the negative terminal or the positive terminal of at least one photovoltaic string at least twice; the current sensor can be used to sample a first current value at time t0 and a second current value at time t1, and transmit the first current value and the second current value to a control circuit connected to the conversion circuit.

[0043] In one possible design, each conversion circuit also includes an inverter circuit, and each inverter circuit is arranged between at least one photovoltaic string and the power grid in the photovoltaic power generation system. There is a DC circuit between each inverter circuit and at least one photovoltaic string, and there is an AC circuit between each inverter circuit and the power grid; when the inverter circuit is not operating, the first impedance to ground is the impedance to ground of at least one DC circuit; when the inverter circuit is operating, the first impedance to ground is the parallel impedance value of the impedance to ground of at least one DC circuit and the impedance to ground of at least one AC circuit; and then the data collector can determine the impedance to ground of at least one AC circuit based on the impedance to ground of at least one DC circuit and the parallel impedance value.

[0044] In this design, the data logger can determine the ground impedance of all DC circuits in the photovoltaic power generation system, as well as the parallel impedance of all DC circuits and all AC circuits based on the operating status of the inverter circuit. This allows for better insulation impedance testing of the DC and AC circuits in the photovoltaic power generation system, further enhancing the system's safety.

[0045] In one possible design, the data collector may also issue an array insulation impedance detection command to each control circuit, thereby causing each control circuit to determine the ground voltage of the negative bus of the DC current source, where the converter circuit connected to it is located, based on the detection command. Optionally, the detection command may include a preset period, and each control circuit may periodically determine the ground voltage of the negative bus according to the preset period.

[0046] In this design, each control circuit can periodically determine the ground voltage of the negative bus of the DC current of the conversion circuit connected to it according to the detection command issued by the data collector, thereby effectively realizing the periodic detection of the ground impedance of the photovoltaic power generation system and effectively ensuring the safe operation of the photovoltaic power generation system.

[0047] In a second aspect, an embodiment of the present application provides a method for determining system insulation impedance, which is applied to a data collector in a photovoltaic power generation system, wherein the photovoltaic power generation system further includes at least one control circuit and at least one conversion circuit, each control circuit being connected to each conversion circuit in a one-to-one correspondence; and the data collector is respectively connected to each control circuit in communication;

[0048] The method includes: a data collector receives the voltage to ground of the negative bus determined by each control circuit, and determines a first impedance to ground of the photovoltaic power generation system according to the voltage to ground of at least one negative bus; or

[0049] The data collector receives the second ground impedance of the conversion circuit connected to each control circuit determined by each control circuit, and determines the first ground impedance of the photovoltaic power generation system according to the second ground impedance of at least one conversion circuit.

[0050] It should be understood that the negative bus is the negative bus of the DC circuit where the conversion circuit connected to each control circuit is located, and the second impedance to ground is calculated by the control circuit based on the negative bus voltage to ground determined by it.

[0051] In one possible design, the conversion circuit includes a current-limiting resistor connected in series between the positive bus and the ground line; the voltage of the negative bus to ground includes a first voltage value determined by the conversion circuit at time t0 and a second voltage value determined at time t1; wherein, the interval between time t0 and time t1 is a preset time length; the data collector determines the first impedance to ground of the photovoltaic power generation system based on the voltage to ground of at least one negative bus, specifically including: the data collector determines the first impedance to ground of the photovoltaic power generation system based on the first current value, second current value, first voltage value, and second voltage value corresponding to each conversion circuit.

[0052] There are many ways to obtain the first current value and the second current value, including but not limited to the following:

[0053] Method 1: The data collector receives the third voltage value of the adjustable power supply in each conversion circuit at time t0 and the fourth voltage value at time t1; determines the first current value flowing through the current limiting resistor at time t0 based on the first voltage value, the third voltage value and the resistance value of the current limiting resistor stored in advance; and determines the second current value flowing through the current limiting resistor at time t1 based on the second voltage value, the fourth voltage value and the resistance value of the current limiting resistor.

[0054] Mode 2: The data collector receives a first current value flowing through the current limiting resistor collected by the current sensor in each conversion circuit at time t0 and a second current value flowing through the current limiting resistor collected at time t1.

[0055] In one possible design, there is at least one AC circuit between at least one inverter circuit included in at least one conversion circuit and the power grid; the at least one inverter circuit corresponds one-to-one to the at least one AC circuit; when the at least one inverter circuit is not operating, the first impedance to ground is the impedance to ground of the at least one DC circuit; when the at least one inverter circuit is operating, the first impedance to ground is the parallel impedance value of the impedance to ground of the at least one DC circuit and the impedance to ground of the at least one AC circuit; the data collector determines the impedance to ground of the at least one AC circuit based on the impedance to ground of the at least one DC circuit and the parallel impedance value.

[0056] In a third aspect, an embodiment of the present application provides a chip, which is coupled to a memory and is used to read and execute program instructions stored in the memory to implement the method described in the second aspect of the embodiment of the present application or any possible design of the second aspect, the method described in the third aspect or any possible design of the third aspect.

[0057] The technical effects that can be achieved in any of the second to third aspects mentioned above can be specifically described with reference to the technical effects brought about by any possible design in the first aspect mentioned above, and will not be repeated here.

[0058] These and other aspects of the present application will become more readily apparent from the description of the following embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] The following is a brief introduction to the drawings required for describing the embodiments.

[0060] Figure 1 A schematic diagram of the architecture of a photovoltaic power generation system applicable to an embodiment of the present application;

[0061] Figure 2 A schematic diagram of a scenario in which a PID device is applicable;

[0062] Figure 3 A schematic diagram of a scenario in which an IMD device is applicable;

[0063] Figure 4 It is a structural schematic diagram of an insulation impedance detection device;

[0064] Figure 5 A schematic structural diagram of a possible photovoltaic power generation system provided in an embodiment of the present application;

[0065] Figure 6A A schematic diagram of a possible conversion circuit provided in an embodiment of the present application;

[0066] Figure 6B A schematic diagram of the structure of another possible conversion circuit provided in an embodiment of the present application;

[0067] Figure 7 A schematic structural diagram of another possible photovoltaic power generation system provided in an embodiment of the present application;

[0068] Figure 8 A schematic diagram of a possible sampling circuit provided in an embodiment of the present application;

[0069] Figure 9 A schematic structural diagram of another possible photovoltaic power generation system provided in an embodiment of the present application;

[0070] Figure 10A flow chart of a method for determining system insulation impedance provided in an embodiment of the present application;

[0071] Figure 11 A flowchart of another method for determining system insulation impedance provided in an embodiment of the present application. DETAILED DESCRIPTION

[0072] The present application will be described in further detail below with reference to the accompanying drawings. The specific operating methods in the method embodiments can also be applied to device embodiments or system embodiments. It should be noted that in the description of the present application, "at least one" refers to "one or more". Among them, "multiple" refers to two or more. In view of this, "multiple" can also be understood as "at least two" in the embodiments of the present application. In addition, it should be understood that in the description of the present application, words such as "first" and "second" are only used for the purpose of distinguishing the description, and cannot be understood as indicating or implying relative importance, nor can they be understood as indicating or implying order.

[0073] Figure 1 This is a schematic diagram of the architecture of a photovoltaic power generation system applicable to the embodiments of the present application. Figure 1 As shown, the photovoltaic power generation system includes a photovoltaic unit 1, an inverter 2, and a power grid 4; a DC circuit is connected between the photovoltaic unit 1 and the inverter 2, and an AC circuit is connected between the inverter 2 and the power grid 4.

[0074] The photovoltaic unit 1 can absorb irradiated energy and convert it into a DC voltage. In the embodiments of the present application, the photovoltaic unit 1 can specifically be a photovoltaic string, or a photovoltaic string assembly consisting of at least one photovoltaic string. It should be understood that a photovoltaic string can also be referred to as a photovoltaic panel.

[0075] The inverter 2 is used to convert the DC voltage generated by the photovoltaic unit 1 into an AC voltage, so that the electric energy generated by the photovoltaic unit 1 can be converted into AC power and input into the grid 4.

[0076] Optionally, the photovoltaic power generation system may further include a transformer 3 . The transformer 3 is used to convert the AC voltage output by the inverter 2 to match the voltage standard required by the power grid 4 .

[0077] However, due to the electrical structure of inverter 2, a bias voltage may exist between the positive or negative terminals of the photovoltaic panels in photovoltaic unit 1 relative to the ground. This can cause the photovoltaic panels to experience potential induced degradation (PID), causing the output power of photovoltaic unit 1 to decay, thereby reducing the output power of the entire photovoltaic power generation system and the revenue of the photovoltaic power generation system. Furthermore, due to the PID effect in photovoltaic unit 1, the potential difference between the glass layer and the metal encapsulating material of the photovoltaic panels in photovoltaic unit 1 can generate leakage current, causing negative charge to accumulate on the surface of the cell, thereby reducing the surface passivation effect of the cell.

[0078] In order to suppress the PID effect of the photovoltaic unit 1, in one implementation, an anti-PID device can be set in the AC circuit of the photovoltaic power generation system. The anti-PID device injects a DC voltage component into the AC circuit of the photovoltaic power generation system and adjusts the positive-to-ground voltage (PV+) or negative-to-ground voltage (PV-) of the photovoltaic panel in the photovoltaic unit 1 according to the DC voltage component to suppress the PID effect of the photovoltaic panel. Figure 2 As shown, an anti-PID device is provided in the AC circuit of the photovoltaic power generation system. The anti-PID device injects voltage into the virtual midpoint of the AC circuit, thereby adjusting the voltage of the photovoltaic unit to the ground, thereby avoiding the PID effect of the photovoltaic unit.

[0079] In addition, in order to ensure the power supply continuity and safety of the photovoltaic power generation system, it is often necessary to perform insulation impedance testing on the photovoltaic power generation system. In one possible implementation, an insulation monitoring device (IMD) is set in the AC circuit of the photovoltaic power generation system. Figure 3 As shown, the IMD is set in the AC circuit of the photovoltaic power generation system. By injecting a voltage of a certain frequency and amplitude into the two phases of the AC circuit and detecting the current flowing through the internal resistor of the IMD, the ground impedance detection of the photovoltaic power generation system is realized.

[0080] See Figure 4 , Figure 4 The schematic diagram of the structure of an insulation impedance detection device is shown. In this device, an anti-PID device and an IMD device are configured in the AC circuit of a photovoltaic power generation system. However, after the anti-PID device injects a compensation voltage into the photovoltaic strings in the photovoltaic power generation system, the compensation voltage will be detected by the IMD device through the common ground leakage circuit, which will cause the IMD to misdetect the ground impedance of the photovoltaic power generation system and trigger a ground insulation impedance fault alarm. Therefore, in Figure 4In the insulation impedance detection device shown, the anti-PID device and the IMD device are operated simultaneously, resulting in a problem of low insulation impedance detection accuracy.

[0081] In view of this, the present application provides a photovoltaic power generation system and a method for determining the insulation impedance of the system, so as to improve the insulation impedance detection accuracy of the photovoltaic power generation system and effectively reduce the system cost.

[0082] Figure 5 A schematic structural diagram of a possible photovoltaic power generation system provided in an embodiment of the present application is shown. The photovoltaic power generation system may include at least one conversion circuit and at least one control circuit.

[0083] Among them, each control circuit is connected to each conversion circuit in a one-to-one correspondence. For example, control circuit 1 is connected to conversion circuit 1, control circuit 2 is connected to conversion circuit 2, ..., and so on. Control circuit N is connected to conversion circuit N.

[0084] It should be understood that in practical applications, each control circuit and the conversion circuit connected thereto may be provided in an inverter or in a DC maximum power point tracking (MPPT) combiner box, and this is not specifically limited in the present embodiment. Alternatively, the conversion circuit may be understood as the circuit corresponding to the inverter or DC MPPT combiner box.

[0085] The specific hardware implementation of each conversion circuit can be achieved through specific circuit components such as resistors, capacitors, switches, etc.

[0086] The specific hardware implementation of each control circuit can be achieved through a field-programmable gate array (FPGA), an application specific integrated circuit (ASIC), a system on chip (SoC), a central processor unit (CPU), a network processor (NP), a digital signal processor (DSP), a microcontroller unit (MCU), a programmable logic device (PLD) or other integrated chips.

[0087] Each conversion circuit is connected to at least one photovoltaic string (e.g. Figure 5The positive terminal (PV+) of the M (shown) is connected to the negative terminal (PV-) of at least one photovoltaic string through the negative bus (BUS-) of the DC circuit, so that each conversion circuit can adjust the ground voltage of the negative terminal or positive terminal of at least one photovoltaic string at least twice. It should be understood that when the number of conversion circuits in the photovoltaic power generation system (i.e., N) is greater than or equal to 2, each conversion circuit is connected in parallel. The specific values ​​of M and N can be the same or different, and are not specifically limited in the embodiments of the present application.

[0088] For example, the conversion circuit 1 can be connected to the positive ends of the photovoltaic strings 11, 12, ..., and 1M through the positive bus of the DC circuit 1, and connected to the negative ends of the photovoltaic strings 11, 12, ..., and 1M through the negative bus of the DC circuit 1.

[0089] For another example, the conversion circuit 2 can be connected to the positive ends of the photovoltaic strings 21, 22, ..., and 2M through the positive bus of the DC circuit 2, and can be connected to the negative ends of the photovoltaic strings 21, 22, ..., and 2M through the negative bus of the DC circuit 2.

[0090] By analogy, the conversion circuit N can be connected to the positive ends of the photovoltaic strings N1, N2, ..., and MN through the positive bus of the DC circuit N, and can be connected to the negative ends of the photovoltaic strings N1, N2, ..., and MN through the negative bus of the DC circuit N.

[0091] Each control circuit may determine the ground voltage of the negative bus of the DC circuit in which the conversion circuit is located during at least two adjustments by the conversion circuit to which it is connected to the ground voltage of the negative terminal or the positive terminal of at least one photovoltaic string. It should be understood that the ground voltage of the negative bus can be used to determine the first ground impedance of the photovoltaic power generation system.

[0092] For example, the control circuit 1 is connected to the conversion circuit 1 , and during the process in which the conversion circuit 1 performs at least two voltage adjustments on the photovoltaic strings 11 , 12 , etc., the control circuit 1 can determine the voltage of the negative bus of the DC circuit 1 to the ground.

[0093] It should be understood that after each conversion circuit performs a voltage adjustment, the control circuit connected thereto can determine the voltage relative to ground of the negative bus of the DC circuit in which the conversion circuit is located. Therefore, the voltage relative to ground of the negative bus determined by each conversion circuit during at least two voltage adjustments can include at least two voltage values.

[0094] For example, taking the number of voltage adjustments as two, the control circuit may determine the first voltage value at time t0 after the conversion circuit connected thereto performs the first voltage adjustment, and determine the second voltage value at time t1 after the conversion circuit performs the second voltage adjustment. For another example, taking the number of voltage adjustments as three, the control circuit may determine the first voltage value at time t0 after the conversion circuit connected thereto performs the first voltage adjustment, determine the second voltage value at time t1 after the conversion circuit performs the second voltage adjustment, and determine the third voltage value at time t2 after the conversion circuit performs the third voltage adjustment. It should be understood that the embodiments of the present application do not specifically limit the number of voltage adjustments.

[0095] In an embodiment of the present application, at least one conversion circuit and at least one control circuit are provided in a photovoltaic power generation system, and each conversion circuit is connected to the positive terminal of at least one photovoltaic string via a positive bus of a DC circuit, and each conversion circuit is connected to the negative terminal of at least one photovoltaic string via a negative bus of the DC circuit; so that the control circuit can determine the ground voltage of the negative bus used to determine the first ground impedance of the photovoltaic power generation system during at least two adjustments of the conversion circuit to which it is connected. In this way, the PID effect of at least one photovoltaic string can be suppressed, and the ground impedance of the photovoltaic power generation system can be detected, which can effectively improve the detection accuracy of the ground impedance of the photovoltaic power generation system. There is no need to provide a separate insulation impedance detection device, thereby achieving the purpose of cost savings.

[0096] In one possible implementation, Figure 5 The photovoltaic power generation system shown may also include a power grid, and the output end of each conversion circuit in the photovoltaic power generation system may be connected to the power grid. Specifically, each conversion circuit may be connected to the power grid via an AC cable, where the AC cable may be a single-phase cable or a three-phase cable, which is not specifically limited in this embodiment of the application.

[0097] In the embodiments of the present application, the above-mentioned conversion circuit can be implemented in multiple ways.

[0098] For example, Figure 6A As shown, the conversion circuit may include an adjustable power supply 1 , a current limiting resistor 2 , and a relay switch 3 .

[0099] It should be understood that the specific product implementation of the adjustable power supply 1 can be an ICDC power chip, and of course it can also be other chips, which is not limited in the embodiment of the present application.

[0100] In one possible embodiment, one end of the adjustable power supply 1 is connected to the negative bus of the DC circuit via a relay switch 3, and the other end of the adjustable power supply 1 is grounded via a current-limiting resistor 2. This allows the adjustable power supply 1 to be indirectly connected to the negative terminal of at least one photovoltaic string via the negative bus. In this manner, the adjustable power supply 1 can adjust the voltage relative to ground of the negative terminal of at least one photovoltaic string at least twice. Specifically, the adjustable power supply 1 can adjust the voltage relative to ground of the negative terminal of each photovoltaic string by injecting a target voltage value into the negative terminal of each photovoltaic string to raise the voltage relative to ground above the positive terminal.

[0101] In another possible embodiment, one end of the adjustable power supply 1 is connected to the positive bus of the DC circuit via a relay switch 3, and the other end of the adjustable power supply 1 is grounded via a current-limiting resistor 2, thereby indirectly connecting the adjustable power supply 1 to the positive terminal of at least one photovoltaic string via the negative bus. In this manner, the adjustable power supply 1 can be used to adjust the voltage relative to ground of the positive terminal of at least one photovoltaic string at least twice. Specifically, the voltage adjustment of the positive terminal of each photovoltaic string relative to ground by the adjustable power supply 1 can be performed by injecting a target voltage value into the positive terminal of each photovoltaic string to adjust the voltage relative to ground to below the negative terminal.

[0102] Optional, see Figure 6B The conversion circuit may further include a current sensor 4 (e.g., a Hall sensor), one end of which is connected to the negative bus of the DC circuit and the other end is connected to the relay switch 3, and may be used to collect the current flowing through the current-limiting resistor 2. It should be understood that when the conversion circuit is connected to the positive bus, one end of the current sensor 4 may be connected to the positive bus and the other end to the relay switch 3, and may also be used to collect the current flowing through the current-limiting resistor 2. In other embodiments, the current sensor 4 may also be disposed within the adjustable power supply 1.

[0103] See Figure 7 The photovoltaic power generation system provided in the embodiment of the present application may further include at least one sampling circuit (eg, sampling circuit 1, sampling circuit 2).

[0104] Each sampling circuit is connected to each conversion circuit in a one-to-one correspondence. It should be understood that each sampling circuit and its connected conversion circuit can be integrated into a single inverter or a DC MPPT combiner box, enabling separate sampling of the inverter or DC MPPT combiner box. This effectively improves the granularity of voltage sampling in photovoltaic power generation systems.

[0105] Specifically, such as Figure 7As shown, each sampling circuit can be connected to the positive bus and / or negative bus of the DC circuit to achieve connection with the conversion circuit. For example, sampling circuit 1 is connected to the positive bus and / or negative bus of DC circuit 1, and is then connected to conversion circuit 1. It should be understood that each sampling circuit can also be directly connected to the conversion circuit, and this embodiment of the application is not specifically limited thereto.

[0106] The sampling circuit in the embodiment of the present application can be implemented in various ways in practical applications.

[0107] For example, Figure 8 As shown, each sampling circuit may include a first sampling subcircuit and a second sampling subcircuit. The first sampling subcircuit may be disposed between the positive bus and the negative bus to sample the voltage between the positive bus and the negative bus; the second sampling subcircuit may be disposed between the positive bus and the ground to sample the voltage of the positive bus relative to ground. It should be understood that the second sampling subcircuit may also be disposed between the negative bus and the ground to sample the voltage of the negative bus relative to ground, and this embodiment of the present application does not specifically limit this.

[0108] like Figure 7 As shown, in one possible implementation, each control circuit in the photovoltaic power generation system is connected to each sampling circuit in a one-to-one correspondence. For example, control circuit 1 is connected to sampling circuit 1, control circuit 2 is connected to sampling circuit 2, and so on, with control circuit N being connected to sampling circuit N.

[0109] It should be noted that there are many ways to implement the specific value of the target voltage value used by the above-mentioned adjustable power supply 1 for voltage adjustment. Taking the adjustable power supply 1 in the conversion circuit 1 as an example to adjust the voltage to the ground of the negative terminal of the photovoltaic string 11, the following methods are included but not limited to:

[0110] In Method 1, sampling circuit 1 is connected to control circuit 1. Sampling circuit 1 samples the current DC voltage between the positive and negative bus lines of DC circuit 1 and the current voltage to ground at the negative terminal of PV string 11. The sampling circuit 1 then transmits these DC voltage and ground voltage values ​​to control circuit 1 in the form of electrical signals. Control circuit 1 can then determine the difference between the DC voltage and the ground voltage as the target voltage for voltage regulation by adjustable power supply 1. This improves voltage regulation efficiency for adjustable power supply 1.

[0111] Method 2: The sampling circuit 1 is connected to the control circuit 1. When the conversion circuit 1 determines that the output power of at least one photovoltaic string is lower than a preset value, the conversion circuit 1 increases the DC voltage generated by the photovoltaic string 11. The sampling circuit 1 then samples the value of the increased DC voltage and the current value of the voltage to ground at the negative terminal of the photovoltaic string 11, and transmits the value of the increased DC voltage and the current value of the voltage to ground at the negative terminal of the photovoltaic string 11 to the control circuit 1 in the form of an electrical signal. The control circuit 1 can then determine the difference between the value of the increased DC voltage and the current value of the voltage to ground as the target voltage value for voltage adjustment by the adjustable power supply 1. In this way, the adjustable power supply 1 can perform voltage adjustment based on the boosted DC voltage in the DC circuit of the photovoltaic power generation system, making the adjustment of the voltage to ground at the negative terminal of each photovoltaic string more precise, more effectively suppressing the PID effect of the photovoltaic string group, and thereby effectively improving the gain of the photovoltaic power generation system.

[0112] Specifically, the sampling circuit 1 may sample the DC voltage and the voltage of the negative terminal of the photovoltaic string 11 to the ground based on a first voltage range (eg, 0-1500 V).

[0113] It should be understood that in the embodiment of the present application, the process in which each conversion circuit performs at least two voltage adjustments on the ground voltage of the positive terminal or negative terminal of at least one photovoltaic string connected thereto is similar to the above-mentioned method 1 and method 2 and will not be repeated here.

[0114] In a possible implementation, each sampling circuit may sample the third voltage value at time t0 and the fourth voltage value at time t1 of the adjustable power supply 1 in the conversion circuit 1 connected thereto, and send them to the control circuit connected to the conversion circuit.

[0115] In one possible embodiment, each conversion circuit may further include at least one boost circuit. When each boost circuit determines that the output power of at least one photovoltaic string to which it is connected is lower than a preset value, the DC voltage generated by the at least one photovoltaic string is increased and then transmitted to the power grid in the photovoltaic power generation system.

[0116] In another possible embodiment, each conversion circuit may also include at least one boost circuit and an inverter circuit. When each boost circuit determines that the output power of at least one photovoltaic string connected to it is lower than a preset value, the DC voltage generated by the at least one photovoltaic string is increased and then transmitted to the inverter circuit. The inverter circuit can convert the DC voltage into an AC voltage and transmit it to the power grid in the photovoltaic power generation system.

[0117] It should be noted that, since each control circuit in the photovoltaic power generation system provided by the embodiment of the present application is connected one-to-one with each sampling circuit (see Figure 7), so that each control circuit can determine the ground voltage of the negative bus connected to the sampling circuit through the sampling circuit connected thereto.

[0118] Exemplarily, the control circuit 1 is connected to the sampling circuit 1, and the control circuit 1 can determine the voltage of the negative bus of the DC circuit 1 relative to the ground through the sampling circuit 1. Specifically, the control circuit 1 determines the voltage of the negative bus relative to the ground in a variety of ways, including but not limited to the following ways:

[0119] In Method 1, sampling circuit 1 is connected to the negative bus. Each control circuit 1 can control sampling circuit 1 to directly sample the negative bus voltage relative to ground based on a second voltage range (e.g., 0-70V). This second voltage range is smaller than the first voltage range. This allows control circuit 1 to more efficiently obtain the negative bus voltage relative to ground.

[0120] Method 2: When the first sampling sub-circuit in sampling circuit 1 is connected to the positive bus of DC circuit 1, and the second sampling sub-circuit in sampling circuit 1 is connected between the positive bus and the negative bus of DC circuit 1, control circuit 1 controls the first sub-sampling circuit to sample a first voltage of the positive bus relative to ground based on a second voltage range. Control circuit 1 controls the second sub-sampling circuit to sample a second voltage between the positive bus and the negative bus based on a second voltage range. The second voltage range is smaller than the first voltage range. Control circuit 1 determines the difference between the first and second voltages as the voltage of the negative bus relative to ground. This effectively improves the accuracy of the acquired voltage of the negative bus relative to ground.

[0121] It should be understood that in both Mode 1 and Mode 2, the sampling circuit 1 uses a smaller sampling range to collect voltage, which effectively improves the sampling accuracy, making the collected voltage value more accurate, and thus making the ground impedance of the photovoltaic power generation system determined based on the collected voltage value more accurate.

[0122] See Figure 9 The photovoltaic power generation system provided in the embodiment of the present application may further include a data collector.

[0123] The data collector is connected to each control circuit in a variety of communication modes. Specifically, the data collector can be connected to control circuits 1, 2, ..., and N via programmable logic controller (PLC), RS485, or network communication, allowing each control circuit 1 to transmit its determined data (e.g., the voltage relative to ground of the negative bus of DC circuit 1) to the data collector.

[0124] It should be noted that there are multiple implementations for the ground voltage of the negative bus of the DC circuit determined by each control circuit to be used to determine the first ground impedance of the photovoltaic power generation system.

[0125] In Embodiment 1, each control circuit can send its determined negative bus voltage to ground to a data collector. The data collector can then determine the first impedance to ground of the photovoltaic power generation system based on the at least one negative bus voltage to ground determined by at least one control circuit. This effectively improves the efficiency of determining the first impedance to ground of the photovoltaic power generation system.

[0126] In Embodiment 2, each control circuit can calculate the second impedance to ground of its connected conversion circuit based on the negative bus voltage to ground determined by it, and send this second impedance to a data collector. The data collector can then determine the first impedance to ground of the photovoltaic power generation system based on the second impedance to ground of at least one conversion circuit. This makes the determined first impedance to ground of the photovoltaic power generation system more accurate and effectively reduces the computational effort of the data collector.

[0127] In embodiment 3, each control circuit can calculate the second impedance to ground of the conversion circuit to which it is connected based on the voltage to ground of the negative bus it determines. The first control circuit in the photovoltaic power generation system (e.g., control circuit 2) can receive the second impedance to ground of the conversion circuit to which it is connected from other control circuits in the photovoltaic power generation system (e.g., control circuit 1, control circuit N, etc.) other than the first control circuit. The first control circuit can then use the second impedance to ground of all the conversion circuits to determine the first impedance to ground of the photovoltaic power generation system. In this way, there is no need to set up a data collector in the photovoltaic power generation system, effectively saving a lot of resources. It should be understood that the first conversion circuit can be selected by the operation and maintenance personnel themselves, or it can be pre-set by engineering and technical personnel.

[0128] Taking control circuit 1 as an example, the following describes the process of each control circuit determining the second impedance to ground of the conversion circuit connected thereto in Implementation Modes 2 and 3.

[0129] As an example, the voltage to ground of the negative bus of the DC circuit 1 where the conversion circuit 1 is located may include a first voltage value determined by the control circuit 1 at time t0 and a second voltage value determined at time t1; wherein, the time interval between time t0 and time t1 is a preset time length.

[0130] In one possible implementation, the control circuit 1 may also receive a third voltage value at time t0 and a fourth voltage value at time t1 of the adjustable power supply 1 in the conversion circuit 1, and determine a first current value flowing through the current-limiting resistor in the conversion circuit 1 at time t0 based on the first voltage value, the third voltage value, and the pre-stored resistance value of the current-limiting resistor; and determine a second current value flowing through the current-limiting resistor at time t1 based on the second voltage value, the fourth voltage value, and the resistance value of the current-limiting resistor. Furthermore, the control circuit 1 may determine the second impedance to ground of the conversion circuit 1 based on the first voltage value, the second voltage value, the first current value, and the second current value corresponding to the conversion circuit 1. In this way, the detection accuracy of the insulation impedance in the photovoltaic power generation system is effectively improved.

[0131] In one possible implementation, the control circuit 1 determines the first current value flowing through the current-limiting resistor in the conversion circuit 1 at time t0 based on the first voltage value, the third voltage value, and a pre-stored resistance value of the current-limiting resistor. Specifically, if the first voltage value is U1, the third voltage value is U3, and the current-limiting resistor is R0, then the first current value is I1 = (U1 - U3) / R0. The control circuit 1 determines the second current value in a similar manner to the process of determining the first current value and is not further described here.

[0132] In another possible implementation, after determining the first and second voltage values, the control circuit 1 obtains the first and second current values ​​collected by the current sensor in the conversion circuit 1. The control circuit 1 can then determine the second impedance to ground of the conversion circuit 1 based on the first and second voltage values, first and second current values ​​corresponding to the conversion circuit 1. This effectively improves the accuracy of insulation impedance detection in the photovoltaic power generation system.

[0133] Specifically, the second impedance to ground of the conversion circuit 1 determined by the control circuit 1 conforms to the following formula:

[0134]

[0135] Among them, R i is the second impedance to ground of the conversion circuit 1, is the first current value flowing through the current limiting resistor in the conversion circuit 1 at time t0; is the second current value flowing through the current limiting resistor in the conversion circuit 1 at time t1; is the first voltage value corresponding to the conversion circuit 1, is the second voltage value corresponding to the conversion circuit 1.

[0136] It should be understood that the process of other control circuits determining the second impedance to ground of the conversion circuit connected thereto is similar to the process of the control circuit 1 determining the second impedance to ground of the conversion circuit 1 itself, and will not be repeated here.

[0137] Corresponding to embodiment 1, Figure 10 A method for determining the insulation resistance of a system provided in an embodiment of the present application can be applied to Figure 9 The data collector in the photovoltaic power generation system shown in FIG. 1 specifically includes the following steps:

[0138] S1001: The data collector obtains the ground voltage of the negative bus of the DC circuit where each conversion circuit is located and the current flowing through the current limiting resistor in each conversion circuit.

[0139] Specifically, the data collector obtains the ground voltage of the negative bus of the DC circuit 1 where the conversion circuit 1 is located, and obtains the ground voltage of the negative bus of the DC circuit 2 where the conversion circuit 2 is located. Similarly, the data collector can obtain the ground voltage of the negative bus of the DC circuit N where the conversion circuit N is located.

[0140] Exemplarily, the voltage to ground of the negative bus of the DC circuit 1 acquired by the data collector may specifically include a first voltage value at time t0 and a second voltage value at time t1; wherein, time t0 and time t1 are separated by a preset time length. It should be understood that the preset time length may be a fixed value or dynamically adjusted according to the operating conditions of the photovoltaic power generation system in an actual environment. For example, the preset time length may be 1 minute. The first voltage value is determined by the control circuit 1 at time t0 after the conversion circuit 1 performs the first voltage adjustment, and the second voltage value may be determined by the control circuit 1 at time t1 after the conversion circuit 1 performs the second voltage adjustment.

[0141] It should be understood that there are multiple ways for the data collector to obtain the first voltage value and the second voltage value, including but not limited to the following two:

[0142] Mode 1: The data collector receives the first voltage value and the second voltage value corresponding to the conversion circuit 1 through the control circuit 1.

[0143] Method 2: The data collector receives, through the control circuit 1, a first voltage between the positive bus and the negative bus of the DC circuit 1 collected at time t0 by the sampling circuit 1 corresponding to the conversion circuit 1, and a second voltage of the positive bus to ground collected at time t0 by the receiving sampling circuit 1; the data collector determines a first voltage value based on the first voltage and the second voltage; similarly, the data collector can also determine the second voltage value based on a third voltage between the positive bus and the negative bus collected at time t1 by the sampling circuit 1 and a fourth voltage of the positive bus to ground.

[0144] It should be understood that the specific implementation method of the data collector obtaining the ground voltage of the negative bus of the DC circuit where other conversion circuits are located is similar to the specific implementation method of obtaining the ground voltage of the negative bus corresponding to the conversion circuit 1, which will not be repeated here.

[0145] There are multiple ways to implement the data collector to obtain the current flowing through the current-limiting resistor in each conversion circuit.

[0146] The following takes the conversion circuit 1 as an example to introduce a method in which the data collector obtains the current flowing through the current-limiting resistor in the conversion circuit 1 .

[0147] In one possible embodiment, the data collector can receive the third voltage value of the adjustable power supply 1 in the conversion circuit at time t0 and the fourth voltage value at time t1 from the control circuit 1, and determine the first current value flowing through the current limiting resistor at time t0 based on the first voltage value, the third voltage value and the resistance value of the pre-stored current limiting resistor; and determine the second current value flowing through the current limiting resistor at time t1 based on the second voltage value, the fourth voltage value and the resistance value of the current limiting resistor.

[0148] The data collector determines the first current value flowing through the current-limiting resistor in the conversion circuit 1 at time t0 based on the first voltage value, the third voltage value, and the pre-stored resistance value of the current-limiting resistor. Specifically, the process can be as follows: if the first voltage value is U1, the third voltage value is U3, and the current-limiting resistor is R0, then the first current value is I1 = (U1-U3) / R0. The control circuit 1 determines the second current value in a similar manner to the process for determining the first current value, and will not be further described here.

[0149] In another possible implementation, the data collector may receive, through the control circuit 1 , a first current value collected at time t0 and a second current value collected at time t1 by the current sensor in the conversion circuit 1 .

[0150] S1002: The data collector determines a first ground impedance of the photovoltaic power generation system according to the ground voltage of the negative bus of the DC circuit where all the conversion circuits are located and the current flowing through the current limiting resistor in each conversion circuit.

[0151] Specifically, the data collector determines the first ground impedance of the photovoltaic power generation system based on the ground voltage of the negative bus corresponding to conversion circuit 1, the ground voltage of the negative bus corresponding to conversion circuit 2,..., the ground voltage of the negative bus corresponding to conversion circuit N, and the current flowing through the current limiting resistor in each conversion circuit 1-conversion circuit N.

[0152] Taking N as 2 as an example, in a possible implementation, when the voltage to ground of the negative bus of the DC circuit where the conversion circuit 1 is located determined by the control circuit 1 includes a first voltage value and a second voltage value, and the voltage to ground of the negative bus of the DC circuit where the conversion circuit 2 is located determined by the control circuit 2 includes a first voltage value and a second voltage value, the data collector can determine the first impedance to ground of the photovoltaic power generation system based on the first voltage value and the second voltage value determined by the control circuit 1 and the first voltage value and the second voltage value determined by the control circuit 2, as well as the first current value and the second current value of the current limiting resistor flowing through the conversion circuit 1 and the first current value and the second current value of the current limiting resistor in the conversion circuit 2.

[0153] In one possible implementation, the data collector determines the first ground impedance of the photovoltaic power generation system based on the first voltage value and the second voltage value corresponding to each conversion circuit, which may conform to the following formula:

[0154]

[0155] Wherein, Rx is the first impedance to ground of the photovoltaic power generation system, i is an integer greater than or equal to 1; N is the number of conversion circuits in the photovoltaic power generation system; is the first current value flowing through the current-limiting resistor in the i-th conversion circuit at time t0; is the second current value flowing through the current-limiting resistor in the i-th group of conversion circuits at time t1; is the first voltage value of the negative bus of the DC circuit where the i-th conversion circuit is located, is the second voltage value of the negative bus of the DC circuit where the i-th conversion circuit is located.

[0156] For example, in combination with the conversion circuit 1 and the conversion circuit 2, the first voltage value of the conversion circuit 1 is The first current value is The second voltage value is The second current value is The first voltage value of the conversion circuit 2 is The first current value is The second voltage value is The second current value is Then the first impedance to ground is

[0157] In this embodiment, the data collector uses the ratio of the average value of the ground voltage of the negative bus of the DC circuit where the conversion circuit 1 is located and the ground voltage of the negative bus of the DC circuit where the conversion circuit 2 is located to the sum of the current value flowing through the current limiting resistor in the conversion circuit 1 and the current value flowing through the current limiting resistor in the conversion circuit 1 as the first ground impedance of the photovoltaic power generation system, effectively improving the accuracy of the determined first ground impedance.

[0158] Corresponding to embodiment 2, Figure 11 Another method for determining the insulation resistance of a system provided in the embodiment of the present application can be applied to Figure 9 The data collector in the photovoltaic power generation system shown in FIG. 1 specifically includes the following steps:

[0159] S1101: The data collector receives the second ground impedance of all conversion circuits.

[0160] In a possible implementation, the data collector is in communication connection with all control circuits in the photovoltaic power generation system, and the data collector receives the second impedance to ground of all conversion circuits through all control circuits.

[0161] Exemplarily, the data collector receives the second impedance to ground of the conversion circuit 1 itself through the control circuit 1 , and the data collector receives the second impedance to ground of the conversion circuit 2 itself through the control circuit 2 .

[0162] S1102: The data collector determines the first impedance to ground of the photovoltaic power generation system based on the second impedance to ground of all conversion circuits.

[0163] In a possible implementation, the data collector determines the first impedance to ground of the photovoltaic power generation system based on the second impedance to ground of all conversion circuits, which may conform to the following formula:

[0164]

[0165] Wherein, i is an integer greater than or equal to 1; Rx is the impedance to ground, N is the number of conversion circuits in the photovoltaic power generation system, and Ri is the second impedance to ground of the i-th conversion circuit.

[0166] Taking N equal to 2 as an example, the data logger can determine the first impedance to ground of the photovoltaic power generation system based on the second impedance to ground of conversion circuit 1 and the second impedance to ground of conversion circuit 2. Assuming that the second impedance to ground of conversion circuit 1 is R1 and the second impedance to ground of conversion circuit 2 is R2, the first impedance to ground of the photovoltaic power generation system is R3 = (R1*R2) / (R1+R2).

[0167] In this embodiment, the data collector determines the first ground impedance of the photovoltaic power generation system based on the second ground impedance of all conversion circuits in the photovoltaic power generation system, effectively improving the accuracy of ground impedance detection of the photovoltaic power generation system.

[0168] It should be noted that the specific process of the first control circuit in the above embodiment 3 calculating the first impedance to ground of the photovoltaic power generation system based on the second impedance to ground of all the conversion circuits in the photovoltaic power generation system is similar to Figure 11The specific process of the data collector calculating the first ground impedance of the photovoltaic power generation system based on the second ground impedance of all conversion circuits in the photovoltaic power generation system is similar and will not be repeated here.

[0169] In one possible embodiment, Figure 9 Each conversion circuit in the photovoltaic power generation system shown may also include an inverter circuit, each inverter circuit is arranged between at least one photovoltaic string and the power grid in the photovoltaic power generation system, a DC circuit is provided between each inverter circuit and at least one photovoltaic string, and an AC circuit is provided between each inverter circuit and the power grid; and each inverter circuit also has a coupling function, so when the inverter circuit is not operating, the first impedance to ground is the impedance to ground of at least one DC circuit; when the inverter circuit is operating, the first impedance to ground is the parallel impedance value of the impedance to ground of at least one DC circuit and the impedance to ground of at least one AC circuit; and then the data collector can determine the impedance to ground of at least one AC circuit based on the impedance to ground of at least one DC circuit and the parallel impedance value.

[0170] For example, the impedance to ground of all DC circuits in the photovoltaic power generation system is R1; the impedance to ground of the entire photovoltaic power generation system (the parallel impedance value of the DC circuit and the AC circuit) is R2. According to the parallel resistance formula R2=R1 / / R3, the impedance to ground of all AC circuits in the photovoltaic power generation system can be determined.

[0171] In this embodiment, the data collector can determine the ground impedance of all DC circuits in the photovoltaic power generation system, as well as the parallel impedance of all DC circuits and all AC circuits based on the operating status of the inverter circuit, and further determine the ground impedance of the AC circuits. This allows for better insulation impedance testing of the DC and AC circuits in the photovoltaic power generation system, further enhancing the safety of the photovoltaic power generation system.

[0172] In one possible implementation, each inverter circuit is connected to a control circuit, so that the data collector can send control instructions to the inverter circuit through the control circuit to control the operation and shutdown of the inverter circuit. For example, inverter circuit 1 in conversion circuit 1 is connected to control circuit 1, so that the data collector can send control instructions to inverter circuit 1 through control circuit 1 to control the operation and shutdown of inverter circuit 1.

[0173] In this embodiment, by controlling the operation of the inverter device in each conversion circuit within each photovoltaic power generation system, the impedance to ground of all AC circuits in the photovoltaic power generation system can be indirectly determined from the impedance to ground of all DC circuits in the photovoltaic power generation system and the overall impedance to ground of the photovoltaic power generation system. This allows for better insulation impedance testing of the DC and AC circuits in the photovoltaic power generation system, effectively improving the safety of the photovoltaic power generation system.

[0174] In a possible embodiment, the data collector can also send an array insulation impedance detection command to each control circuit, so that each control circuit can determine the ground voltage of the negative bus of the DC current of the conversion circuit connected to it according to the detection command.

[0175] Optionally, the detection command may further include a preset period, so that the control circuit 1 can periodically determine the voltage of the negative bus to ground corresponding to the conversion circuit 1. The preset period in the detection command may be a fixed value or a value dynamically adjusted according to the actual operating state of the photovoltaic power generation system, and the embodiments of the present application do not specifically limit this. For example, the preset period may be 5 minutes or 9 minutes. In this way, the control circuit 1 can periodically determine the voltage of the negative bus to ground according to the detection command from the data collector, thereby realizing periodic detection of the ground impedance of the photovoltaic power generation system, and effectively ensuring the safe operation of the photovoltaic power generation system.

[0176] In one possible embodiment, the data collector can also output an alarm message when it determines that the first ground impedance of the photovoltaic power generation system is less than a first preset value. Specifically, the data collector can display an alarm message or emit an audible alarm stating, "The system's ground impedance has failed. Please pay attention to safety." This can prompt operation and maintenance personnel to take appropriate measures, effectively improving the safety of the photovoltaic power generation system.

[0177] It should be understood that the above embodiments or implementation methods in each embodiment can be used in combination.

[0178] Those skilled in the art will appreciate that the embodiments of the present application can be provided as methods, systems, or computer program products. Therefore, the present application can adopt the form of a complete hardware embodiment, a complete software embodiment, or an embodiment in combination with software and hardware. Moreover, the present application can adopt the form of a computer program product implemented on one or more computer-usable storage media (including but not limited to magnetic disk storage, CD-ROM, optical storage, etc.) that contain computer-usable program code.

[0179] The present application is described with reference to the flowcharts and / or block diagrams of the methods, devices (systems), and computer program products according to the present application. It should be understood that each process and / or block in the flowchart and / or block diagram, as well as the combination of processes and / or blocks in the flowchart and / or block diagram, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, a special-purpose computer, an embedded processor, or other programmable data processing device to produce a machine, so that the instructions executed by the processor of the computer or other programmable data processing device generate instructions for implementing the processes in the flowchart and / or block diagram. Figure 1a process or multiple processes and / or boxes Figure 1 A device that provides the functions specified in a block or multiple blocks.

[0180] These computer program instructions may also be stored in a computer readable memory that can direct a computer or other programmable data processing device to work in a specific manner, so that the instructions stored in the computer readable memory produce an article of manufacture comprising an instruction device, which implements the process Figure 1 a process or multiple processes and / or boxes Figure 1 The function specified in one or more boxes.

[0181] These computer program instructions can also be loaded onto a computer or other programmable data processing device so that a series of operational steps are executed on the computer or other programmable device to produce a computer-implemented process, thereby providing the instructions executed on the computer or other programmable device for implementing the process. Figure 1 a process or multiple processes and / or boxes Figure 1 A step that specifies a function in one or more boxes.

[0182] Obviously, those skilled in the art may make various changes and modifications to this application without departing from the spirit and scope of this application. Thus, if these modifications and variations of this application fall within the scope of the claims of this application and their equivalents, this application is intended to include these modifications and variations.

Claims

1. A photovoltaic power generation system, characterized in that: The system comprises at least one conversion circuit and at least one control circuit, wherein each control circuit is connected to each conversion circuit in a one-to-one correspondence; each conversion circuit is connected to the positive terminal of at least one photovoltaic string via a positive bus of a DC circuit, and each conversion circuit is connected to the negative terminal of at least one photovoltaic string via a negative bus of the DC circuit; Each of the conversion circuits is configured to adjust the voltage of the negative terminal or the positive terminal of the at least one photovoltaic string to ground at least twice; Each of the control circuits is configured to determine the voltage of the negative bus to ground during at least two adjustments by the conversion circuit to which it is connected to the voltage of the negative terminal or the positive terminal of the at least one photovoltaic string to ground; The voltage of the negative bus to ground is used to determine the first impedance to ground of the photovoltaic power generation system.

2. The photovoltaic power generation system according to claim 1, wherein: The photovoltaic power generation system further includes a data collector, which is respectively connected to each of the control circuits for communication; Each of the control circuits is further configured to send the negative bus voltage to ground determined by the control circuit to the data collector; the data collector is configured to determine the first ground impedance of the photovoltaic power generation system based on the negative bus voltage to ground determined by at least one of the control circuits; or Each of the control circuits is further configured to calculate the second impedance to ground of the conversion circuit to which it is connected based on the determined voltage to ground of the negative bus, and to send the second impedance to ground to the data collector; the data collector is configured to determine the first impedance to ground of the photovoltaic power generation system based on the second impedance to ground of at least one of the conversion circuits.

3. The photovoltaic power generation system according to claim 2, wherein: The photovoltaic power generation system further includes at least one sampling circuit, each sampling circuit being connected to the positive bus and / or the negative bus; each sampling circuit being connected to each conversion circuit in a one-to-one correspondence; each conversion circuit further includes at least one boost circuit, each boost circuit being connected to the output end of a photovoltaic string; Each of the boost circuits is further configured to, when it is determined that the output power of the at least one photovoltaic string is lower than a preset value, increase the DC voltage generated by the at least one photovoltaic string and then transmit it to the power grid in the photovoltaic power generation system; Each of the sampling circuits is configured to sample, based on the first voltage range, the increased value of the DC voltage and a current value of the voltage to ground of the negative terminal or the positive terminal of the at least one photovoltaic string; Each of the conversion circuits, when used to adjust the voltage of the negative terminal or the positive terminal of the at least one photovoltaic string to ground at least twice, is specifically used to: The method further comprises: receiving the increased value of the DC voltage and the current value of the voltage to ground from the sampling circuit connected thereto; and adjusting the voltage to ground of the negative terminal or the positive terminal of the at least one photovoltaic string at least twice based on the increased value of the DC voltage and the current value of the voltage to ground.

4. The photovoltaic power generation system according to claim 3, wherein: Each of the sampling circuits is connected to each of the control circuits in a one-to-one correspondence; when each of the sampling circuits is connected to the negative bus, each of the control circuits, when used to determine the voltage of the negative bus relative to ground, is specifically used to: The sampling circuit connected thereto is controlled to sample the voltage of the negative bus to ground based on a second voltage range; wherein the second voltage range is smaller than the first voltage range.

5. The photovoltaic power generation system according to claim 4, characterized in that: Each of the sampling circuits is connected to each of the control circuits in a one-to-one correspondence; when each of the sampling circuits is connected to the positive bus and the negative bus, respectively, each of the control circuits, when used to determine the voltage of the negative bus relative to ground, is specifically configured to: controlling the connected sampling circuit to sample a first voltage of the positive bus relative to ground and a second voltage between the positive bus and the negative bus based on a second voltage range; wherein the second voltage range is smaller than the first voltage range; The difference between the first voltage and the second voltage is determined as the voltage of the negative bus to ground.

6. The photovoltaic power generation system according to any one of claims 3 to 5, characterized in that: Each of the conversion circuits specifically includes a current-limiting resistor connected in series between the positive bus or the negative bus and a ground line; the voltage of the negative bus to ground includes a first voltage value determined by the control circuit at time t0 and a second voltage value determined at time t1; wherein the time t0 is separated from the time t1 by a preset time length; The data collector determines the first ground impedance of the photovoltaic power generation system according to the ground voltage of at least one of the negative buses, and the first ground impedance conforms to the following formula: ； Wherein, Rx is the first impedance to ground, i is an integer greater than or equal to 1; N is the number of the conversion circuits; is the first current value flowing through the current limiting resistor in the i-th conversion circuit at time t0; is the second current value flowing through the current limiting resistor in the i-th conversion circuit at time t1; The first voltage value determined by the i-th control circuit, the The second voltage value is determined for the i-th control circuit.

7. The photovoltaic power generation system according to claim 6, characterized in that: Each of the conversion circuits further includes an adjustable power supply, one end of the adjustable power supply being connected to the negative bus or the positive bus, and the other end being connected to the ground line via the current-limiting resistor; the adjustable power supply being configured to adjust the voltage of the negative terminal or the positive terminal of the at least one photovoltaic string relative to the ground at least twice; Each sampling circuit is further configured to collect a third voltage value of the adjustable power supply in the conversion circuit connected thereto at time t0, and collect a fourth voltage value of the adjustable power supply in the conversion circuit connected thereto at time t1, and send the third voltage value and the fourth voltage value to the control circuit connected thereto; Before being used to determine the first ground impedance of the photovoltaic power generation system, the data collector is further used to: receiving, from each of the control circuits, the third voltage value and the fourth voltage value of the adjustable power supply in the conversion circuit connected thereto; Determine the first current value flowing through the current limiting resistor at time t0 based on the first voltage value, the third voltage value and the pre-stored resistance value of the current limiting resistor; and determine the second current value flowing through the current limiting resistor at time t1 based on the second voltage value, the fourth voltage value and the resistance value of the current limiting resistor.

8. The photovoltaic power generation system according to claim 6, wherein: Each of the conversion circuits further includes an adjustable power supply and a current sensor; one end of the adjustable power supply is connected to the negative bus or the positive bus, and the other end is grounded through the current limiting resistor; the current sensor is arranged between the adjustable power supply and the negative bus or the positive bus, or the current sensor is arranged in the adjustable power supply; The adjustable power supply is used to adjust the voltage of the negative terminal or the positive terminal of the at least one photovoltaic string to ground at least twice; Before the data collector is used to determine the first ground impedance of the photovoltaic power generation system, the current sensor is used to sample the first current value at time t0 and the second current value at time t1, and send the first current value and the second current value to the control circuit connected to the conversion circuit; The data collector is further configured to receive, from the control circuit, the first current value and the second current value collected by the current sensor in each of the conversion circuits.

9. The photovoltaic power generation system according to any one of claims 3 to 5, characterized in that: Each of the conversion circuits specifically includes a current-limiting resistor connected in series between the positive bus or the negative bus and a ground line; the voltage of the negative bus to ground includes a first voltage value determined by the control circuit at time t0 and a second voltage value determined at time t1; wherein the time t0 is separated from the time t1 by a preset time length; Each of the control circuits calculates the second impedance to ground of the conversion circuit connected thereto according to the determined voltage to ground of the negative bus, which conforms to the following formula: ； Among them, the R i is the second ground impedance of the i-th conversion circuit, is the first current value flowing through the current limiting resistor in the i-th conversion circuit at time t0; is the second current value flowing through the current limiting resistor in the i-th conversion circuit at time t1; The first voltage value determined by the i-th control circuit, The second voltage value is determined for the i-th control circuit.

10. The photovoltaic power generation system according to claim 9, characterized in that: The first impedance to ground determined by the data collector according to the second impedance to ground of at least one of the conversion circuits complies with the following formula: ； Wherein, i is an integer greater than or equal to 1; R x is the first impedance to ground, is the number of the conversion circuits, the R i is the second impedance to ground of the i-th conversion circuit.

11. The photovoltaic power generation system according to claim 10, wherein: Each of the conversion circuits further includes an adjustable power supply, one end of the adjustable power supply being connected to the negative bus or the positive bus, and the other end being connected to the ground line via the current-limiting resistor; the adjustable power supply being configured to adjust the voltage of the negative terminal or the positive terminal of the at least one photovoltaic string relative to the ground at least twice; Each sampling circuit is further configured to collect a third voltage value of the adjustable power supply in the conversion circuit connected thereto at time t0, and collect a fourth voltage value of the adjustable power supply in the conversion circuit connected thereto at time t1, and send the third voltage value and the fourth voltage value to the control circuit connected thereto; Each of the control circuits is further configured to: receiving the third voltage value and the fourth voltage value of the adjustable power supply in the conversion circuit connected thereto; Determine the first current value flowing through the current limiting resistor at time t0 based on the first voltage value, the third voltage value and the pre-stored resistance value of the current limiting resistor; and determine the second current value flowing through the current limiting resistor at time t1 based on the second voltage value, the fourth voltage value and the resistance value of the current limiting resistor.

12. The photovoltaic power generation system according to claim 10, wherein: Each of the conversion circuits further includes an adjustable power supply and a current sensor; one end of the adjustable power supply is connected to the negative bus or the positive bus, and the other end is grounded through the current limiting resistor; the current sensor is arranged between the adjustable power supply and the negative bus or the positive bus, or the current sensor is arranged in the adjustable power supply; The adjustable power supply is used to adjust the voltage of the negative terminal or the positive terminal of the at least one photovoltaic string to ground at least twice; Before the control circuit is used to calculate the second ground impedance of the conversion circuit connected thereto, the current sensor is used to sample the first current value at time t0 and the second current value at time t1, and send the first current value and the second current value to the control circuit connected to the conversion circuit; The control circuit is further configured to receive the first current value and the second current value.

13. The photovoltaic power generation system according to any one of claims 2 to 5, 7, 8 or 10 to 12, characterized in that: Each of the conversion circuits further includes an inverter circuit, each of the inverter circuits being arranged between the at least one photovoltaic string and the power grid in the photovoltaic power generation system, the DC circuit being between each of the inverter circuits and the at least one photovoltaic string, and the AC circuit being between each of the inverter circuits and the power grid; When the inverter circuit is not running, the first impedance to ground is the impedance to ground of at least one of the DC circuits; When the inverter circuit is running, the first impedance to ground is a parallel impedance value of the impedance to ground of at least one of the DC circuits and the impedance to ground of at least one of the AC circuits; The data collector is further configured to determine the impedance to ground of at least one of the AC circuits based on the impedance to ground of at least one of the DC circuits and the parallel impedance value.

14. A method for determining the insulation resistance of a system, characterized in that: A data collector is used in a photovoltaic power generation system, wherein the photovoltaic power generation system further comprises at least one control circuit and at least one conversion circuit, each of the control circuits being connected to each of the conversion circuits in a one-to-one correspondence; the data collector is respectively connected to each of the control circuits in a communication manner; and the method comprises: The data collector receives the ground voltage of the negative bus of the DC circuit where the conversion circuit connected to it is located, determined by each control circuit; the data collector determines the first ground impedance of the photovoltaic power generation system based on the ground voltage of at least one of the negative buses; or, The data collector receives the second ground impedance of the conversion circuit itself determined by each control circuit to which it is connected, where the second ground impedance is calculated by the control circuit based on the ground voltage of the negative bus of the DC circuit where the conversion circuit is located; the data collector determines the first ground impedance of the photovoltaic power generation system based on the second ground impedance of at least one of the conversion circuits.

15. The method according to claim 14, wherein Each of the conversion circuits includes a current-limiting resistor connected in series between the positive bus or the negative bus of the DC circuit in which the conversion circuit is located and the ground line; the voltage of the negative bus to ground includes a first voltage value determined by the conversion circuit at time t0 and a second voltage value determined at time t1; wherein the time t0 is separated from the time t1 by a preset time length; The data collector determines the first ground impedance of the photovoltaic power generation system according to the ground voltage of at least one of the negative buses, specifically including: The data collector receives a third voltage value of the adjustable power supply in each of the conversion circuits at the time t0 and a fourth voltage value at the time t1; determines a first current value flowing through the current limiting resistor at the time t0 based on the first voltage value, the third voltage value, and the pre-stored resistance value of the current limiting resistor; and determines a second current value flowing through the current limiting resistor at the time t1 based on the second voltage value, the fourth voltage value, and the resistance value of the current limiting resistor; or The data collector receives a first current value flowing through the current limiting resistor collected by the current sensor in each of the conversion circuits at the time t0, and a second current value flowing through the current limiting resistor collected at the time t1; The data collector determines the first ground impedance of the photovoltaic power generation system based on the first current value, the second current value, the first voltage value, and the second voltage value corresponding to each conversion circuit.

16. The method according to claim 14 or 15, characterized in that There is at least one AC circuit between at least one inverter circuit included in the at least one conversion circuit and the power grid in the photovoltaic power generation system; the at least one inverter circuit corresponds one-to-one to the at least one AC circuit; when the at least one inverter circuit is not in operation, the first impedance to ground is the impedance to ground of the at least one DC circuit; when the at least one inverter circuit is in operation, the first impedance to ground is the parallel impedance value of the impedance to ground of the at least one DC circuit and the impedance to ground of the at least one AC circuit; The method further comprises: The data collector determines the impedance to ground of the at least one AC circuit based on the impedance to ground of the at least one DC circuit and the parallel impedance value.

Images