Impedance detection method and photovoltaic system

Abstract

An impedance detection method (800, 900, 1000, 1100) and a photovoltaic system (400, 500, 1200, 1300, 1400, 1500, 1600) are provided to help reduce the complexity and cost of impedance detection. It includes: sampling the voltage between the DC bus and the ground (PE) at the first time point and the second time point respectively to obtain the first voltage value (U1) and the second voltage value (U2); sampling the leakage current (I rcd ) on the DC bus at the first time point and the second time point respectively to obtain the first current value (I rcd1 ) and the second current value (I rcd2 ); based on the difference between the first voltage value (U1) and the second voltage value (U2), and the difference between the first current value (I rcd1 ) and the second current value (I rcd2 ), the insulation impedance value (R pv ) of the junction box (1, 2, …, M, 240) is calculated to determine whether the impedance of the junction box (1, 2, …, M, 240) is abnormal.

Description

Technical Field

[0001] This application relates to the field of electronics, and more specifically, to an impedance detection method and a photovoltaic system. Background Technology

[0002] In a distributed inverter grid-connected power generation system, multiple combiner boxes are typically connected in parallel to the inverter's DC bus via a direct-current-to-direct-current (DC-DC) boost circuit. When the insulation impedance of a photovoltaic string in a combiner box to ground is low, the inverter detects through its insulation impedance detection circuit that the system's insulation impedance does not meet safety regulations and needs to shut down. This will cause all combiner boxes connected in parallel to the inverter's DC bus to fail to work, resulting in a loss of power generation from the inverter.

[0003] Currently, different DC cabinets can be connected in series with DC switches. The insulation impedance of the system can be detected individually by controlling the opening and closing of the DC switches. The DC switch of the combiner box that is detecting normal operation can be closed, and the DC switch of the combiner box that is detecting abnormal operation can be opened.

[0004] However, the above method requires the use of DC contactors to control the opening and closing of the switch, which is costly and complex to control. Summary of the Invention

[0005] This application provides an impedance detection method and a photovoltaic system that can achieve abnormal detection of junction box insulation impedance with simple operation and low cost.

[0006] Firstly, an impedance detection method is provided, applied to a photovoltaic system. The photovoltaic system includes multiple combiner boxes and an inverter. The input terminals of the multiple combiner boxes are respectively connected to photovoltaic strings, and the output terminals of the multiple combiner boxes are connected to the inverter via a DC bus. Each combiner box includes at least one DC switch and at least one DC-DC boost unit. The input terminal of the DC switch is connected to the photovoltaic strings, the output terminal of the DC switch is connected to the input terminal of the DC-DC boost unit, and the output terminal of the DC-DC boost unit is connected to the DC bus. The method includes:

[0007] The voltage between the DC bus and the ground wire (protecting earthing, PE) is sampled at a first time point and a second time point respectively to obtain a first voltage value and a second voltage value; the leakage current on the DC bus is sampled at the first time point and the second time point respectively to obtain a first current value and a second current value; based on the difference between the first voltage value and the second voltage value, and the difference between the first current value and the second current value, the insulation impedance value of the combiner box is calculated to determine whether the impedance of the combiner box is abnormal.

[0008] It should be understood that the combiner box in the embodiments of this application has a voltage control function and can connect to multiple parallel photovoltaic strings, which are obtained by connecting at least one photovoltaic cell in series.

[0009] The embodiments of this application can obtain the first voltage value and the second voltage value between the DC bus and the ground wire, as well as the first current value and the second current value corresponding to the first voltage value and the second voltage value, by sampling. This allows the impedance of each combiner box to the ground PE to be calculated, thereby locating the impedance anomaly of a specific combiner box. This helps to reduce the complexity and cost of impedance detection and improve the efficiency of impedance detection.

[0010] In conjunction with the first aspect, in some implementations of the first aspect, the photovoltaic system further includes a power supply unit, one end of which is grounded and the other end is connected to a DC bus. The power supply unit is in an off state at the first time point and in an operating state at the second time point.

[0011] In this embodiment, the voltage between the negative DC bus BUS- and the ground PE (hereinafter referred to as BUS- / PE) and the leakage current on the DC bus are sampled at the first time point when the power supply unit is in the off state. Then, the BUS- / PE voltage and the leakage current on the DC bus are sampled at the second time point when the power supply unit is in the working state. In this way, by changing the switching state of the power supply unit, the change of the BUS- / PE voltage and the change of the DC bus current in each combiner box can be obtained.

[0012] In conjunction with the first aspect, in some implementations of the first aspect, before obtaining the second voltage value and the second current value, the power supply unit is closed, so that the power supply unit is in a working state; the voltage between the DC bus and the ground wire is adjusted to the first preset voltage through the power supply unit.

[0013] It should be understood that the first voltage value and the first current value in the embodiments of this application are obtained by sampling when the power supply unit is in the off state, and the second voltage value and the second current value are obtained by sampling when the power supply unit is in the working state.

[0014] In this embodiment, when the power supply unit is in operation, the BUS- / PE voltage can first be adjusted to a first preset voltage. After the first preset voltage stabilizes, it is sampled to obtain a second voltage value and a second current. This allows for accurate calculation of the insulation impedance value of the combiner box to ground, improving the accuracy of impedance detection.

[0015] In conjunction with the first aspect, in some implementations of the first aspect, the photovoltaic system further includes a power supply unit, one end of which is grounded and the other end is connected to a DC bus. The power supply unit is in operation at both the first time point and the second time point.

[0016] In this embodiment, the BUS- / PE voltage and leakage current on the DC bus are sampled twice while the power supply unit is in operation. This allows for sampling at two different time points when the power supply unit is in operation to obtain two different BUS- / PE voltages and two different leakage currents on the DC bus, thus providing information on the changes in BUS- / PE voltage and DC bus current for each combiner box.

[0017] In conjunction with the first aspect, in some implementations of the first aspect, before obtaining the first voltage value and the first current value, the power supply unit is closed, so that the power supply unit is in a working state; the voltage between the DC bus and the ground wire is adjusted to the second preset voltage through the power supply unit.

[0018] It should be understood that the first voltage value and the first current value in the embodiments of this application are obtained by sampling when the power supply unit is in the working state.

[0019] In this embodiment of the application, when the power supply unit is in operation, the BUS- / PE voltage can first be adjusted to a second preset voltage. After the second preset voltage stabilizes, it is sampled to obtain a first voltage value and a first current value. This allows for accurate calculation of the insulation impedance value of the combiner box to ground, improving the accuracy of impedance detection.

[0020] In conjunction with the first aspect, in some implementations of the first aspect, after a first preset duration, the voltage between the DC bus and the ground wire is adjusted to a third preset voltage by the power supply unit.

[0021] It should be understood that the second voltage value and the second current value in the embodiments of this application are obtained by sampling when the power supply unit is in the working state.

[0022] In this embodiment, when the power supply unit is in operation, the BUS- / PE voltage can first be adjusted to a third preset voltage. After the third preset voltage stabilizes, it is sampled to obtain a second voltage value and a second current value. This allows for accurate calculation of the insulation impedance value of the combiner box to ground, improving the accuracy of impedance detection.

[0023] In conjunction with the first aspect, in some implementations of the first aspect, if it is determined that the impedance of the combiner box is abnormal, the maximum power tracking point (MPPT) voltage corresponding to the photovoltaic string in the combiner box is adjusted; the MPPT voltage is sampled at the third and fourth time points respectively to obtain the first MPPT voltage value and the second MPPT voltage value; the voltage between the DC bus and the ground wire is sampled at the third and fourth time points respectively to obtain the third voltage value and the fourth voltage value; based on the first MPPT voltage value, the second MPPT voltage value, the third voltage value, and the fourth voltage value, the insulation impedance value of the MPPT voltage is calculated to determine whether the impedance of the photovoltaic string is abnormal.

[0024] Furthermore, in this embodiment of the application, after determining that a junction box has an impedance abnormality, it can pinpoint which MPPT in the junction box has an impedance abnormality to ground, thus making the positioning more accurate and efficient.

[0025] In conjunction with the first aspect, in some implementations of the first aspect, before obtaining the first MPPT voltage and the third voltage value, the MPPT voltage is adjusted to a fourth preset voltage by the DC-DC boost unit.

[0026] In this embodiment, the MPPT voltage is first adjusted to a fourth preset voltage. After the fourth preset voltage stabilizes, it is sampled to obtain the first MPPT voltage and the third voltage value. This allows for accurate calculation of the insulation impedance value of the MPPT voltage to ground, improving the accuracy of impedance detection.

[0027] In conjunction with the first aspect, in some implementations of the first aspect, after a second preset duration, the MPPT voltage is adjusted to a fifth preset voltage by the DC-DC boost unit.

[0028] In this embodiment, the MPPT voltage is first adjusted to a fifth preset voltage. After the fifth preset voltage stabilizes, it is sampled to obtain the second MPPT voltage and the fourth voltage value. This allows for accurate calculation of the insulation impedance value of the MPPT voltage to ground, improving the accuracy of impedance detection.

[0029] In conjunction with the first aspect, in some implementations of the first aspect, the power supply unit includes at least one of a relay, a resistor, a diode, or a DC power supply.

[0030] It should be understood that the aforementioned resistor can be an output resistor, and the relay can be an output relay. The relay is used to control the opening and closing of the power supply unit, so as to control whether the power supply unit is in an open state or an operating state.

[0031] Secondly, a photovoltaic system is provided, including multiple combiner boxes, an inverter, and an impedance detection device. The input terminals of the multiple combiner boxes are respectively connected to a photovoltaic string. The multiple combiner boxes are connected to the inverter via a DC bus. Each combiner box includes at least one DC switch and at least one DC-DC boost unit. The input terminal of the DC switch is connected to the photovoltaic string, the output terminal of the DC switch is connected to the input terminal of the DC-DC boost unit, and the output terminal of the DC-DC boost unit is connected to the DC bus.

[0032] The impedance detection device is used to: sample the voltage between the DC bus and the ground wire at a first time point and a second time point respectively to obtain a first voltage value and a second voltage value; and sample the leakage current on the DC bus at the first time point and a second time point respectively to obtain a first current value and a second current value; and calculate the insulation impedance value of the combiner box based on the difference between the first voltage value and the second voltage value, and the difference between the first current value and the second current value, so as to determine whether the impedance of the combiner box is abnormal.

[0033] In conjunction with the second aspect, in some implementations of the second aspect, the photovoltaic system further includes a power supply unit, one end of which is grounded and the other end is connected to a DC bus. The power supply unit is in an off state at the first time point and in an operating state at the second time point.

[0034] In conjunction with the second aspect, in some implementations of the second aspect, the impedance detection device is used to: close the power supply unit before obtaining the second voltage value and the second current value, so that the power supply unit is in an operating state; and adjust the voltage between the DC bus and the ground wire to a first preset voltage.

[0035] In conjunction with the second aspect, in some implementations of the second aspect, the photovoltaic system further includes a power supply unit, one end of which is grounded and the other end is connected to a DC bus, and the power supply unit is in operation at both the first time point and the second time point.

[0036] In conjunction with the second aspect, in some implementations of the second aspect, the impedance detection device is used to: close the power supply unit before obtaining the first voltage value and the first current value, so that the power supply unit is in an operating state; and adjust the voltage between the DC bus and the ground wire to a second preset voltage.

[0037] In conjunction with the second aspect, in some implementations of the second aspect, the impedance detection device is used to: adjust the voltage between the DC bus and the ground wire to a third preset voltage after a first preset time period.

[0038] In conjunction with the second aspect, in some implementations of the second aspect, the impedance detection device is used to: if it is determined that the impedance of the combiner box is abnormal, adjust the maximum power tracking point (MPPT) voltage corresponding to the photovoltaic string in the combiner box; sample the MPPT voltage at a third time point and a fourth time point respectively to obtain a first MPPT voltage value and a second MPPT voltage value; and sample the voltage between the DC bus and the ground wire at the third time point and the fourth time point respectively to obtain a third voltage value and a fourth voltage value; and calculate the insulation impedance value of the MPPT voltage based on the first MPPT voltage value, the second MPPT voltage value, the third voltage value, and the fourth voltage value to determine whether the impedance of the photovoltaic string is abnormal.

[0039] In conjunction with the second aspect, in some implementations of the second aspect, the impedance detection device is used to: adjust the MPPT voltage to a fourth preset voltage before obtaining the first MPPT voltage and the third voltage value.

[0040] In conjunction with the second aspect, in some implementations of the second aspect, the impedance detection device is used to: adjust the MPPT voltage to a fifth preset voltage after a second preset time period.

[0041] In conjunction with the second aspect, in some implementations of the second aspect, the power supply unit includes at least one of a relay, a resistor, a diode, or a DC power supply.

[0042] Thirdly, an impedance detection device is provided. This impedance detection device can be an electronic device, or a chip or chip system within an electronic device. The impedance detection device can include a sensor detection unit and a processing unit, and the sensor detection unit can be a residual current device (RCD) sensor.

[0043] When the impedance detection device is an electronic device, the processing unit may be a processor. The impedance detection device may also include a storage unit, which may be a memory. The storage unit stores instructions, and the processing unit executes the instructions stored in the storage unit to cause the electronic device to implement an impedance detection method described in the first aspect or any possible implementation thereof.

[0044] When the impedance detection device is a chip or chip system within an electronic device, the processing unit can be a processor. The processing unit executes instructions stored in the storage unit to cause the electronic device to implement an impedance detection method described in the first aspect or any possible implementation of the first aspect. The storage unit can be a storage unit within the chip (e.g., a register, cache, etc.) or a storage unit located outside the chip within the electronic device (e.g., a read-only memory, random access memory, etc.).

[0045] Fourthly, an impedance detection device is provided, including at least one processor and an interface. The interface is used to provide program instructions or data to the at least one processor, which executes the program instructions to cause the impedance detection device to perform the method in any of the possible implementations of the first aspect described above.

[0046] Optionally, the impedance detection device in the fourth aspect described above may further include a memory. The processor can call a program in the memory. Furthermore, the memory may be integrated with the processor, or the memory may be separate from the processor.

[0047] In the specific implementation process, the memory can be a non-transitory memory, such as read-only memory (ROM), which can be integrated with the processor on the same chip or set on different chips. The embodiments of this application do not limit the type of memory or the way the memory and processor are set.

[0048] It should be understood that the relevant data interaction process, such as sending indication information, can be the process of outputting indication information from the processor, and receiving capability information can be the process of the processor receiving input capability information. Specifically, the processed output data can be output to the transmitter, and the input data received by the processor can come from the receiver. Here, the transmitter and receiver can be collectively referred to as a transceiver.

[0049] Fifthly, a chip or chip system is provided, the chip or chip system including at least one processor and a communication interface, the communication interface and at least one processor being interconnected via a line, the at least one processor being used to run computer programs or instructions to perform the method in any possible implementation of the first aspect above.

[0050] In a sixth aspect, a computer program product is provided, comprising: a computer program (also referred to as code or instructions) that, when executed, causes a computer to perform the method in any of the possible implementations of the first aspect described above.

[0051] In a seventh aspect, a computer-readable storage medium is provided that stores a computer program (also referred to as code or instructions) that, when executed on a computer, causes the computer to perform the methods in any of the possible implementations of the first aspect described above. Attached Figure Description

[0052] Figure 1 This is a circuit topology diagram of a photovoltaic system provided in an embodiment of this application;

[0053] Figure 2 This is a schematic diagram of the internal circuitry of a combiner box provided in an embodiment of this application;

[0054] Figure 3 This is a circuit topology diagram of another photovoltaic system provided in the embodiments of this application;

[0055] Figure 4 This is a circuit topology diagram of another photovoltaic system provided in the embodiments of this application;

[0056] Figure 5 This is another circuit topology diagram of a photovoltaic system provided in the embodiments of this application;

[0057] Figure 6 This is a schematic diagram of a combiner box Thevenin equivalent circuit provided in an embodiment of this application;

[0058] Figure 7 This is a schematic diagram of a multi-machine parallel Thevenin equivalent circuit provided in an embodiment of this application;

[0059] Figure 8 This is a schematic flowchart of an impedance detection method provided in an embodiment of this application;

[0060] Figure 9 This is a schematic flowchart of another impedance detection method provided in the embodiments of this application;

[0061] Figure 10 This is a schematic flowchart of another impedance detection method provided in the embodiments of this application;

[0062] Figure 11 This is a schematic flowchart of another impedance detection method provided in the embodiments of this application;

[0063] Figure 12 This is another circuit topology diagram of a photovoltaic system provided in the embodiments of this application;

[0064] Figure 13 This is another circuit topology diagram of a photovoltaic system provided in the embodiments of this application;

[0065] Figure 14 This is another circuit topology diagram of a photovoltaic system provided in the embodiments of this application;

[0066] Figure 15 This is another circuit topology diagram of a photovoltaic system provided in the embodiments of this application;

[0067] Figure 16 This is another circuit topology diagram of a photovoltaic system provided in the embodiments of this application;

[0068] Figure 17 This is a schematic block diagram of an impedance detection device provided in an embodiment of this application;

[0069] Figure 18 This is a schematic block diagram of another impedance detection device provided in the embodiments of this application. Detailed Implementation

[0070] The technical solutions in this application will now be described with reference to the accompanying drawings.

[0071] To facilitate a clear description of the technical solutions in the embodiments of this application, the following points will be explained first.

[0072] First, in the embodiments shown below, the terms and English abbreviations, such as photovoltaic panel, combiner box, etc., are exemplary examples given for ease of description and should not constitute any limitation on this application. This application does not preclude the possibility of defining other terms that can achieve the same or similar functions in existing or future agreements.

[0073] Second, in the embodiments shown below, the terms "first," "second," and various numerical designations are merely for descriptive convenience and are not intended to limit the scope of the embodiments of this application. For example, they distinguish different voltage values ​​or different time points.

[0074] Third, "at least one" means one or more, while "more than one" means two or more. "And / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can mean: A alone, A and B simultaneously, or B alone, where A and B can be singular or plural. The character " / " generally indicates that the preceding and following related objects are in an "or" relationship. "At least one of the following" or similar expressions refer to any combination of these items, including any combination of single or plural items. For example, at least one of a, b, and c can mean: a, or b, or c, or a and b, or a and c, or b and c, or a, b, and c, where a, b, and c can be single or multiple.

[0075] The embodiments of this application can be applied to distributed inverter multi-machine grid-connected power generation systems (hereinafter also referred to as photovoltaic systems). For example, Figure 1 This is a circuit topology diagram of a photovoltaic system provided in an embodiment of this application. For example... Figure 1As shown, M combiner boxes are connected in parallel to the inverter's DC bus. Each combiner box is connected to a photovoltaic panel, which is an array composed of multiple photovoltaic strings connected in parallel. After the combiner boxes collect the DC current, they output it to the inverter, which performs maximum power point tracking (MPPT) control. The inverter then outputs the inverted AC power to a transformer (e.g., a split-type transformer). Finally, the transformer transforms the AC voltage and transmits it to the AC grid to meet the load's power demand.

[0076] It should be understood that the photovoltaic string is composed of multiple photovoltaic cells with lower voltage connected in series, which can increase the voltage several times over; while the photovoltaic panel composed of multiple photovoltaic strings connected in parallel can increase the current several times over when the voltage is the same.

[0077] In the aforementioned photovoltaic system, the inverter is mainly used to realize MPPT control and inverter functions. The medium-voltage switch is connected to the inverter and can be used to open, close, control, and protect electrical equipment during the power generation, transmission, and distribution processes of the system.

[0078] In photovoltaic inverter technology, most photovoltaic inverter grid-connected power generation technical standards have safety provisions, requiring that the insulation resistance value of the combiner box to the ground be tested before grid-connected power generation, and the detected insulation resistance value be compared with the minimum impedance value required by the standard to determine whether the insulation resistance value of the combiner box to the ground meets the safety grid connection requirements.

[0079] It should be understood that impedance includes resistance and reactance. Generally, impedance is a complex number, with resistance and reactance forming the real and imaginary parts of the complex number, respectively. The insulation impedance of a combiner box to ground may be a purely resistive value, or it may contain inductive or capacitive reactance.

[0080] exist Figure 1 In this circuit, the insulation impedance detection circuit is connected to the inverter's DC bus to detect whether the insulation impedance of the M combiner boxes to ground is abnormal. When the inverter detects an abnormality in the insulation impedance of one or more of the M combiner boxes to ground through the insulation detection circuit, a shutdown operation is required. This will cause all combiner boxes connected in parallel to the inverter's DC bus to malfunction, resulting in a loss of power generation.

[0081] Figure 2 A schematic diagram of an internal circuit 200 of a combiner box according to an embodiment of this application is shown. Figure 2 As shown, circuit 200 includes a DC switch 220 and a DC / DC boost circuit 230. The photovoltaic panel 210 is connected to one end of the DC switch 220 in the combiner box 240, and the other end of the DC switch 220 is connected to the DC / DC boost circuit 230.

[0082] Among them, the photovoltaic panel 210 is composed of N photovoltaic modules connected in series and parallel. The photovoltaic cell can use the photoelectric conversion principle to convert the sun's radiation into electrical energy through semiconductor materials. Compared with ordinary batteries, photovoltaic cells are more energy-efficient and environmentally friendly.

[0083] The DC switch 220 is a circuit protection device, generally composed of conductive parts, arc extinguishing parts, operating and rotating parts, etc. It can perform opening and closing operations, and play a protective tripping role in short circuit, overload, and reverse current.

[0084] The DC / DC boost circuit 230 is a commonly used circuit in DC / DC converters, which can increase the voltage. Typically, in order to achieve maximum power point tracking (MPPT), the inverter needs to use a DC / DC converter in the front stage to convert the changing photovoltaic (PV) voltage into a stable output voltage for the subsequent inverter to perform DC-AC operation.

[0085] In one possible implementation, the above can be controlled by using a controllable on / off switch. Figure 1 Each junction box shown was tested individually. Figure 3 This is a circuit topology diagram of another photovoltaic system provided in an embodiment of this application. For example... Figure 3 As shown, multiple DC power supplies are connected in series with a controllable on / off switch S, which is connected to the combiner box. Alternatively, multiple DC power supplies and the controllable on / off switch S can be integrated inside the combiner box. It should be understood that... Figure 3 The combiner box is not shown. When testing the insulation impedance of the combiner box to ground, each combiner box can be tested individually by controlling the opening and closing of switch S. Normal closing is detected, and abnormal opening is detected, ensuring that the abnormality of one combiner box will not cause other parts of the machine to malfunction.

[0086] Among the above possible implementations, a DC controller is required to control the connection and disconnection of switch S. However, DC controllers are costly, large in size, and complex to control, making them difficult to commercialize.

[0087] In view of this, embodiments of this application provide an impedance detection method and a photovoltaic system. By adding a power supply unit and a sensor detection unit to the combiner box, abnormal insulation impedance detection of the combiner box can be achieved with simple operation and low cost. At the same time, by adjusting the MPPT voltage, it is possible to further detect which photovoltaic string has an abnormal impedance to the ground. This enables rapid and accurate repair of abnormal components of the grid-connected inverter, which helps to reduce the loss of power generation.

[0088] For example, Figure 4 This is a circuit topology diagram of another photovoltaic system 400 provided in an embodiment of this application. For example... Figure 4As shown, the photovoltaic system 400 includes M combiner boxes (combiner box 1, combiner box 2, ..., combiner box M) connected in parallel to the inverter. For example, combiner box 1 connects to N parallel photovoltaic strings, combiner box 2 connects to Q parallel photovoltaic strings, ..., combiner box M connects to P parallel photovoltaic strings. The values ​​of N, Q, and P are all greater than or equal to 1, and the values ​​of N, Q, and P can be the same, different, or all the same; this application does not impose any restrictions on these values.

[0089] exist Figure 4 In this embodiment, the M combiner boxes are connected to the inverter in parallel. It should be understood that the M combiner boxes can also be connected to the inverter in series, or in a combination of parallel and series connections. The number of photovoltaic strings connected to each combiner box can be the same or different, and this embodiment does not impose any restrictions.

[0090] This application embodiment does not use a DC contactor to control the controllable on / off switch, but uses the DC switch built into the inverter. This simplifies operation, saves costs, and is easy to commercialize.

[0091] For ease of description, the following analysis uses combiner box 1 as an example. The circuit structure and analysis process of the other combiner boxes are the same as those of combiner box 1. For example, Figure 5 This is a circuit topology diagram of another photovoltaic system 500 provided in the embodiments of this application. The photovoltaic system 500 is described using the combiner box 1 in the photovoltaic system 400 as an example.

[0092] like Figure 5 As shown, in the photovoltaic system 500, N photovoltaic strings are connected to the input terminal of combiner box 1. Combiner box 1 includes N DC switches 401, N DC-DC boost units 402, and an impedance detection device 403. The input terminal of each DC switch 401 is connected to the photovoltaic strings, the output terminal of each DC switch 401 is connected to the input terminal of each DC-DC boost unit 402, the output terminal of each DC-DC boost unit 402 is connected to the input terminal of the impedance detection device, and the output terminal of the impedance detection device is connected to the DC bus.

[0093] Optionally, the photovoltaic system 500 includes a power supply unit 404, one end of which is grounded and the other end is connected to a DC bus.

[0094] The impedance detection device 403 includes a sensor detection unit and a processing unit. The sensor detection unit can be a current sensor, an RCD sensor, or a resistor. It should be understood that the impedance detection device 403 can be located inside or outside the combiner box, and this embodiment of the application does not impose any limitations on this.

[0095] The impedance detection device is used to: sample the voltage between the DC bus and the ground wire at a first time point and a second time point respectively to obtain a first voltage value and a second voltage value; and sample the leakage current on the DC bus at the first time point and a second time point respectively to obtain a first current value and a second current value; and calculate the insulation impedance value of the combiner box based on the difference between the first voltage value and the second voltage value, and the difference between the first current value and the second current value, so as to determine whether the impedance of the combiner box is abnormal.

[0096] Optionally, the photovoltaic system 500 further includes a power supply unit 404, one end of which is grounded and the other end is connected to a DC bus. The power supply unit is in an off state at the first time point and in an operating state at the second time point.

[0097] Optionally, the impedance detection device is used to: close the power supply unit before obtaining the second voltage value and the second current value, so that the power supply unit is in working state; and adjust the voltage between the DC bus and the ground wire to the first preset voltage.

[0098] Optionally, the photovoltaic system also includes a power supply unit, one end of which is grounded and the other end is connected to a DC bus. The power supply unit is in operation at both the first time point and the second time point.

[0099] Optionally, the impedance detection device is used to: close the power supply unit before obtaining the first voltage value and the first current value, so that the power supply unit is in working state; and adjust the voltage between the DC bus and the ground wire to the second preset voltage.

[0100] Optionally, the impedance detection device is used to adjust the voltage between the DC bus and the ground wire to a third preset voltage after a first preset time period.

[0101] Optionally, the impedance detection device is used to: if it is determined that the impedance of the combiner box is abnormal, adjust the maximum power tracking point (MPPT) voltage corresponding to the photovoltaic string in the combiner box; sample the MPPT voltage at a third time point and a fourth time point respectively to obtain a first MPPT voltage value and a second MPPT voltage value; and sample the voltage between the DC bus and the ground wire at the third time point and the fourth time point respectively to obtain a third voltage value and a fourth voltage value; and calculate the insulation impedance value of the MPPT voltage based on the first MPPT voltage value, the second MPPT voltage value, the third voltage value, and the fourth voltage value to determine whether the impedance of the photovoltaic string is abnormal.

[0102] Optionally, the impedance detection device is used to adjust the MPPT voltage to a fourth preset voltage before obtaining the first MPPT voltage and the third voltage value.

[0103] Optionally, the impedance detection device is used to adjust the MPPT voltage to a fifth preset voltage after a second preset time period.

[0104] Optionally, the power supply unit includes at least one of a relay, a resistor, a diode, or a DC power supply.

[0105] exist Figure 5 middle, I bus1+ I is the current on the positive DC bus BUS+. bus1- I is the current on the negative DC bus BUS-. DC1 This refers to the output current of the power supply unit. MPPT1, MPPT2...MPPT N Represents the MPPT voltage corresponding to the N photovoltaic strings, R po1 R represents the insulation resistance value of the first MPPT positive voltage to ground. ne1 R represents the insulation resistance of the first MPPT negative voltage to ground. po2 R represents the insulation resistance value of the second MPPT positive voltage to ground. ne2 This represents the insulation resistance value of the second MPPT negative voltage to ground; and so on, R poN R represents the insulation resistance of the Nth MPPT positive voltage to ground. neN This represents the insulation resistance value of the Nth MPPT negative voltage to ground.

[0106] In this embodiment, the current sensor can sense information about the measured current, such as I. bus1 + and I bus1- It can also transform the detected current information into standard electrical signals or other forms of information for output.

[0107] The leakage current sensor can detect the signals output by the sensors in each branch in real time. When the insulation of the branch is normal, the current flowing through the leakage current sensor is the same in magnitude but opposite in direction, and its output signal is zero. When the branch is grounded, the leakage current sensor has a differential current flowing through it, and its output signal is not zero.

[0108] For example, discrete devices can be used to sample I. bus1 + and I bus1- and I bus1 + and I bus1- Subtract to obtain the leakage current I rcd .

[0109] For example, a precision resistor is typically connected in series in the current loop, and the sampled current value is calculated based on the voltage difference across the resistor.

[0110] As an optional embodiment, the power supply unit 404 includes at least one of a relay, a resistor, a diode, or a DC power supply.

[0111] In this embodiment, relay K is an output relay, which is an automatic switch that uses a small current to control a large current. It is used in circuits for automatic adjustment, safety protection, and circuit switching. In this embodiment, the power supply unit can be turned off by disconnecting relay K, or turned on by closing relay K.

[0112] In the embodiments of this application, the resistor R0 is the output resistor, which refers to the Thevenin equivalent resistance seen from the output terminal of the amplifier. The amplifier can be equivalent to a signal source with internal resistance R0.

[0113] The DC power supply is an adjustable DC power supply, with one end connected to ground via a resistor and the other end connected to either the positive DC bus BUS+ or the negative DC bus BUS-, providing a stable current to the load. For example, this adjustable DC power supply can be a flyback power supply or a forward power supply, etc., and this application does not impose any limitations on this embodiment.

[0114] According to Thevenin's theorem, the combiner box can be viewed from the negative DC bus BUS- and the ground wire PE (BUS- / PE terminals), and the result is as follows: Figure 6 The Thevenin equivalent circuit of the combiner box shown can be represented by a voltage source U. oc and a resistor R x Series connection, resistor R x The equivalent resistance R of the photovoltaic panel side of the combiner box to the ground pv (That is, the insulation impedance value of the combiner box to the ground) and the parallel resistance R of the inverter system to the ground. s I rcd This is the sampling current of the sensor detection unit.

[0115] Furthermore, when M combiner boxes are connected in parallel, applying Thevenin's theorem, we can obtain the following... Figure 7 The Thevenin equivalent circuit for multiple machines in parallel is shown.

[0116] exist Figure 7 Middle,U oc R is the equivalent voltage source for the internal circuit. x1 R x2 ...R xM Let I represent the equivalent resistance of the first, second, ..., Mth combiner boxes, respectively. r1 I r2 ...I rM These represent the leakage currents in the first, second, ..., Mth combiner boxes, respectively, DC1, DC2, ... DC... MThese represent the adjustable DC power supplies in the first, second...Mth combiner boxes, respectively. K represents the output relay, and R0 represents the output resistor.

[0117] The embodiments of this application are based on, as follows: Figure 6 The Thevenin equivalent circuit shown analyzes the insulation impedance of the combiner box. By changing the BUS- / PE voltage through the power supply unit, and by analyzing the changes in the BUS- / PE voltage and the RCD leakage current sensor in the combiner box, the insulation impedance of each combiner box to ground can be calculated, thereby determining whether the insulation impedance of the combiner box is abnormal. The following will combine... Figure 8 , Figure 9 and Figure 10 The specific impedance detection methods are described in detail.

[0118] It should be understood that the steps and / or processes of the impedance detection method in the embodiments of this application can be performed by an impedance detection device, which can be integrated into the photovoltaic system described in this application, or can be used as a standalone device to perform the steps and / or processes of the impedance detection method through a detection interface. This application does not impose any limitations on this.

[0119] For example, Figure 8 This is a schematic flowchart of an impedance detection method 800 provided in an embodiment of this application. Method 800 includes the following steps:

[0120] S801 samples the voltage between the DC bus and the ground wire at the first time point and the second time point respectively to obtain the first voltage value and the second voltage value.

[0121] In this embodiment of the application, the sensor detection unit in the impedance detection device can be used for sampling. The sensor detection unit can be a differential resistor. The differential resistor can be used to sample the BUS- / PE voltage of the combiner box to obtain the first voltage value U1 and the second voltage value U2.

[0122] For example, a voltage sensor can also be used to sample the BUS- / PE voltage of the combiner box to obtain a first voltage value U1 and a second voltage value U2.

[0123] S802 samples the leakage current on the DC bus at the first time point and the second time point respectively to obtain the first current value and the second current value.

[0124] In this embodiment, an RCD leakage current sensor can be used to sample the leakage current on the DC bus to obtain a first current value I. rcd1 Second current value I rcd2 .

[0125] S803, based on the difference between the first voltage value and the second voltage value, and the difference between the first current value and the second current value, calculate the insulation resistance value of the combiner box to determine whether the impedance of the combiner box is abnormal.

[0126] In the embodiments of this application, I rcd1 and I rcd2 It can be represented as follows:

[0127] I rcd1 =(U oc -U1) / R x

[0128] I rcd2 =(U oc -U2) / R x

[0129] By combining the two formulas above, the equivalent impedance R can be obtained. x , means as follows:

[0130] R x =(U1-U2) / (I rcd1 -I rcd2 )

[0131] Furthermore, based on the equivalent resistance R x and the internal resistance R of the inverter system to the ground s The insulation resistance value R of the combiner box to the ground can be obtained. pv , means as follows:

[0132] R pv =(R x ×R s ) / (R s -R x )

[0133] Since the insulation impedance standard for a normal inverter is not less than Upv_max / (30mA), therefore, when R pv When the value is less than Upv_max / (30mA), a low insulation resistance alarm can be reported.

[0134] It should be understood that Upv_max is the maximum voltage value of the inverter grid-connected power generation system. Depending on the system, there are generally two voltage levels. For example, the value of Upv_max can be 1500V or 1100V.

[0135] It should be understood that U1 in the above text is not equal to U2, I rcd1 Not equal to I rcd2 U1 and U2 are limited by Upv_max. Depending on the system, U1 is less than 1100V or 1500V, and similarly, U2 is less than 1100V or 1500V.

[0136] In this embodiment, two different voltage values ​​and two different current values ​​are obtained by sampling through a sensor detection unit. Based on the changes in voltage and current values, it can be determined whether the insulation impedance of the combiner box to the ground is abnormal. This helps to reduce the complexity of operation and lower costs.

[0137] This application provides two different logic implementations for S801 and S802, which are described below in conjunction with... Figure 9 and Figure 10 Provide a detailed description.

[0138] For example, Figure 9 This is a schematic flowchart of another impedance detection method 900 provided in this application embodiment. In method 900, the power supply unit is in an off state at a first time point and in an operating state at a second time point. It should be understood that the power supply unit in this embodiment is an adjustable DC power supply, and the relay K is an output relay. Method 900 includes the following steps:

[0139] S901, M combiner box outputs in parallel.

[0140] S902, relay K is disconnected, and the adjustable DC power supply is turned off.

[0141] In this embodiment, the DC output relay K is not energized, and the power supply to the combiner box is in the off state at the first time point.

[0142] S903, each combiner box samples the BUS- / PE voltage U1, and the RCD leakage current sensor samples the leakage current I. rcd1 .

[0143] In this embodiment, at the first time point, each combiner box samples the BUS- / PE voltage U1 based on the differential resistor and obtains the DC leakage current I using an RCD leakage current sensor. rcd1 .

[0144] S904, relay K is closed, the adjustable DC power supply is working, and the adjustable DC power supply controls the BUS- / PE voltage to U2.

[0145] S905, each combiner box samples the BUS- / PE voltage U2, and the RCD leakage current sensor samples the leakage current I. rcd2 .

[0146] In this embodiment of the application, before obtaining the second voltage value and the second current value, the power supply unit is closed, so that the power supply unit is in working state; the voltage between the DC bus and the ground wire is adjusted to the first preset voltage through the power supply unit.

[0147] In this embodiment, when the DC output relay K is energized, the BUS- / PE voltage is first controlled to a first preset voltage using an adjustable DC power supply. After the first preset voltage stabilizes, it is sampled to obtain U2.

[0148] In this embodiment of the application, the BUS- / PE voltage and leakage current are sampled at a second time point to obtain U2 and I. rcd2 At this second time point, the adjustable DC power supply is in operation.

[0149] It should be understood that the first preset voltage is U2, the second voltage value is the sampled U2, and the second current value is the sampled I. rcd2 .

[0150] S906, based on U1, U2, I rcd1 and I rcd2 Calculate the insulation resistance value of the combiner box to the ground PE.

[0151] The calculation method in this application embodiment has been described in S703 and will not be repeated here.

[0152] In this embodiment, the BUS- / PE voltage can be sampled once before the inverter is connected to the grid, and then sampled again during the inverter's grid connection process to determine impedance anomalies. This can save power and detect whether the impedance of the combiner box is abnormal in a timely manner.

[0153] The above method 800 samples the adjustable DC power supply when it is in the off state and when it is in the working state, respectively, to obtain U1 and U2, I rcd1 and I rcd2 The following will combine Figure 10 This section details another logic for implementing S801 and S802.

[0154] For example, Figure 10 This is a schematic flowchart of another impedance detection method 1000 provided in this application embodiment. In method 1000, the power supply unit is in an operating state at both the first and second time points. It should be understood that the power supply unit in this embodiment is an adjustable DC power supply, and the relay K is an output relay. Method 1000 includes the following steps:

[0155] S1001, M combiner box outputs in parallel.

[0156] S1002, relay K is closed, the adjustable DC power supply is working, and the adjustable DC power supply controls the BUS- / PE voltage to U1.

[0157] Before obtaining the first voltage value and the first current value, the power supply unit is closed in this embodiment of the application, so that the power supply unit is in working state; the voltage between the DC bus and the ground wire is adjusted to the second preset voltage through the power supply unit.

[0158] In this embodiment, when the DC output relay K is energized, the BUS- / PE voltage is first controlled to a second preset voltage using an adjustable DC power supply. After the second preset voltage stabilizes, it is sampled again at a first time point to obtain U1.

[0159] S1003, each combiner box samples the BUS- / PE voltage U1, and the RCD leakage current sensor samples the leakage current I. rcd1 .

[0160] It should be understood that in the embodiments of this application, the second preset voltage is U1, the first voltage value is the sampled U1, and the first current value is the sampled I. rcd1 .

[0161] S1004, relay K is closed, the adjustable DC power supply is working, and the adjustable DC power supply controls the BUS- / PE voltage to U2.

[0162] In this embodiment of the application, before obtaining the second voltage value and the second current value, after a first preset time period, the voltage between the DC bus and the ground wire is adjusted to a third preset voltage by the power supply unit.

[0163] In this embodiment, when the DC output relay K is energized, the BUS- / PE voltage is first controlled to a third preset voltage using an adjustable DC power supply. After the third preset voltage stabilizes, it is sampled again at a second time point to obtain U2.

[0164] After the adjustable DC power supply controls the BUS- / PE voltage to U1 for the first time, it can adjust the BUS- / PE voltage a second time after a first preset time. The first preset time can be 5s, 10s or any other time. This application embodiment does not limit this.

[0165] For example, in the process of adjusting the BUS- / PE voltage from U1 to U2, the voltage change can be gradually controlled to adjust to U2, or it can be directly adjusted to U2. This application does not limit this.

[0166] S1005, each combiner box samples the BUS- / PE voltage U2, and the RCD leakage current sensor samples the leakage current I. rcd2 .

[0167] It should be understood that in the embodiments of this application, the third preset voltage is U2, the second voltage value is the sampled U2, and the second current value is the sampled I. rcd2 .

[0168] S1006, based on U1, U2, I rcd1 and I rcd2 Calculate the insulation resistance value of the combiner box to the ground PE.

[0169] This embodiment of the application can sample the BUS- / PE voltage twice online during the grid-connected operation of the inverter to determine impedance anomalies. In this way, only the BUS- / PE voltage needs to be adjusted to obtain two different voltage values. The operation is simple and can more effectively locate the combiner box where the anomaly has occurred.

[0170] It should be understood that the method for detecting the insulation impedance of combiner boxes described above can be used to test multiple combiner boxes in parallel, which is beneficial to improving testing efficiency.

[0171] The above text combined Figures 8 to 10 This paper describes in detail a method for detecting abnormal insulation impedance of a combiner box to ground. In actual testing, because the combiner box connects to multiple photovoltaic strings, this embodiment can also accurately detect which specific photovoltaic string in the combiner box has low insulation impedance to ground. The following will combine... Figure 11 This document details methods for detecting abnormalities in photovoltaic (PV) strings.

[0172] For example, Figure 11 This is a schematic flowchart of another impedance detection method 1100 provided in this application embodiment. Method 1100 includes the following steps:

[0173] S801 samples the voltage between the DC bus and the ground wire at the first time point and the second time point respectively to obtain the first voltage value and the second voltage value.

[0174] S802 samples the leakage current on the DC bus at the first time point and the second time point respectively to obtain the first current value and the second current value.

[0175] S803, based on the difference between the first voltage value and the second voltage value, and the difference between the first current value and the second current value, calculate the insulation resistance value of the combiner box to determine whether the impedance of the combiner box is abnormal.

[0176] S1110, If it is determined that the impedance of the combiner box is abnormal, the maximum power tracking point (MPPT) voltage corresponding to the photovoltaic string in the combiner box is adjusted.

[0177] S1120, the MPPT voltage is sampled at the third time point and the fourth time point respectively to obtain the first MPPT voltage value and the second MPPT voltage value.

[0178] It should be understood that the adjustable DC power supply is in operation at both the third and fourth time points.

[0179] S1130 samples the voltage between the DC bus and the ground wire at the third and fourth time points, respectively, to obtain the third voltage value and the fourth voltage value.

[0180] S1140, based on the first MPPT voltage value, the second MPPT voltage value, the third voltage value, and the fourth voltage value, calculates the insulation resistance value of the MPPT voltage to determine whether the impedance of the photovoltaic string is abnormal.

[0181] This embodiment of the application, by adjusting the MPPT voltage, can calculate the insulation resistance value R of the MPPT voltage to ground for each photovoltaic string based on two different sampled MPPT voltage values. po and R ne , where R po R is the insulation resistance value of the positive pair of the MPPT voltage. ne The insulation resistance value of the negative pair of the MPPT voltage can be used to detect the photovoltaic string corresponding to the MPPT voltage with low insulation resistance. This method is simple to operate, and the detection results are efficient, accurate, and easy to implement.

[0182] As an optional embodiment, before obtaining the first MPPT voltage value and the third voltage value, the MPPT voltage is adjusted to a fourth preset voltage by a DC-DC boost unit.

[0183] As an optional embodiment, before obtaining the second MPPT voltage value and the fourth voltage value, the MPPT voltage can be adjusted to the fifth preset voltage through the DC-DC boost unit after a second preset time period.

[0184] In this embodiment, for combiner boxes with insulation impedance problems, the voltage change of each MPPT can be controlled sequentially by the internal DC-DC boost unit, thereby calculating the insulation impedance R of the positive and negative terminals of each MPPT to ground. po and R ne This helps to accurately locate which photovoltaic string has an abnormal insulation impedance in the case of parallel operation of the combiner box, ensuring normal grid connection.

[0185] The following analysis uses the first photovoltaic string as an example to analyze the insulation impedance value of the MPPT voltage to ground. Firstly, a DC-DC boost unit is used to control the MPPT voltage corresponding to the photovoltaic string to the fourth preset voltage U. pv11 The BUS- / PE voltage is obtained as U. 11 Then control the MPPT voltage to the fifth preset voltage U. pv12 The BUS- / PE voltage is obtained as U.12 Then, the insulation resistance R of the MPPT voltage to the ground PE corresponding to a single photovoltaic string can be solved according to the following set of equations. po1 and R ne1 :

[0186] U 11 =(U pv11 ×R ne1 ) / (R po1 +R ne1 )

[0187] U 12 =(U pv12 ×R ne1 ) / (R po1 +R ne1 )

[0188] In the above formula, U is known. 11 U 12 U pv11 And U pv12 Therefore, R can be solved. po1 and R ne1 Because the negative terminals of multiple MPPTs are connected in parallel, it is impossible to distinguish which specific MPPT voltage negative terminal has an abnormal insulation resistance to ground. However, the positive terminals of the MPPTs can be distinguished. Therefore, when R... po1 If the impedance is below a safety threshold, the insulation impedance of the first photovoltaic string can be determined to be abnormal. For example, this safety threshold can be 50 kΩ.

[0189] It should be understood that for combiner boxes with abnormal insulation impedance, the insulation impedance value of the MPPT voltage to ground of other photovoltaic strings is tested one by one. The testing method is the same as the method described above, and will not be repeated here.

[0190] Optionally, after S1140, if an abnormal insulation impedance is detected in a combiner box within the photovoltaic system, a command is sent to the monitoring board in the inverter. This command indicates that the combiner box has low insulation impedance, and the input DC switch of the combiner box with low insulation impedance trips. Other combiner boxes with normal insulation impedance can then be connected to the grid. Furthermore, back-end personnel can receive low insulation impedance alarms via an application (APP) for timely fault repair.

[0191] In the above Figure 4 and Figure 5 In the circuit, the impedance detection device is connected to the DC bus, and the output terminal of the power supply unit 404 is connected to the negative DC bus. However, it should be understood that the connection positions of the sensor detection unit 403 and the power supply unit 404 in the circuit can be changed. The following example still uses combiner box 1. Figures 12 to 16This paper introduces five different circuit topology transformation forms for photovoltaic systems.

[0192] In photovoltaic systems 1200, 1300, 1400, 1500, and 1600, for example, combiner box 1 includes N DC switches, N DC-DC boost units, an impedance detection device, and a power supply unit.

[0193] It should be understood that although the circuit structure has changed, the impedance detection methods 800, 900, 1000 and 1100 described in the embodiments of this application can still be applied to any one of circuits 1200, 1300, 1400, 1500 or 1600, and this application does not impose any restrictions on them.

[0194] like Figure 12 As shown, in the photovoltaic system 1200, the input terminal of the DC switch is connected to the photovoltaic string, and the output terminal is connected to the input terminal of the DC-DC boost unit. The output terminal of the DC-DC boost unit is connected to the input terminal of the impedance detection device, and the output terminal of the impedance detection device is connected to the DC bus and located inside the power supply unit.

[0195] Unlike the power supply unit in photovoltaic system 500 which is connected to the negative DC bus BUS-, the power supply unit in circuit 1200 is connected to the positive DC bus BUS+.

[0196] like Figure 13 As shown, in circuit 1300, the input terminal of the DC switch is connected to the photovoltaic string, and the output terminal is connected to the input terminal of the DC-DC boost unit, the output terminal of which is connected to the DC bus.

[0197] Unlike the photovoltaic system 500, where the power supply unit is connected to the negative DC bus BUS- and the impedance detection device is connected to the DC bus inside the power supply unit, the photovoltaic system 1300 has the power supply unit connected to the positive DC bus BUS+ and the impedance detection device connected to the DC bus outside the power supply unit.

[0198] like Figure 14 As shown, in the photovoltaic system 1400, the input terminal of the DC switch is connected to the photovoltaic string, the output terminal is connected to the input terminal of the impedance detection device, the output terminal of the impedance detection device is connected to the input terminal of the DC-DC boost unit, and the output terminal of the DC-DC boost unit is connected to the DC bus.

[0199] Unlike the photovoltaic system 500, where the power supply unit is connected to the negative DC bus BUS- and the impedance detection device is connected to the DC bus inside the power supply unit, the photovoltaic system 1400 has the power supply unit connected to the positive DC bus BUS+ and the impedance detection device connected between the DC switch and the DC-DC boost unit.

[0200] like Figure 15 As shown, in the photovoltaic system 1500, the input terminal of the impedance detection device is connected to the photovoltaic string, the output terminal is connected to the input terminal of the DC switch, the output terminal of the DC switch is connected to the input terminal of the DC-DC boost unit, and the output terminal of the DC-DC boost unit is connected to the DC bus.

[0201] Unlike the photovoltaic system 500, where the power supply unit is connected to the negative DC bus BUS- and the impedance detection device is connected to the DC bus inside the power supply unit, the photovoltaic system 500 has the power supply unit connected to the positive DC bus BUS+ and the impedance detection device connected before the DC switch.

[0202] like Figure 16 As shown, in circuit 1600, the input terminal of the DC switch is connected to the photovoltaic string, and the output terminal is connected to the input terminal of the DC-DC boost unit. The output terminal of the DC-DC boost unit is connected to the input terminal of the impedance detection device, and the output terminal of the impedance detection device is connected to the DC bus and located inside the power supply unit.

[0203] Unlike the photovoltaic system 500, where the power supply unit is located inside the combiner box and connected to the negative DC bus BUS-, the photovoltaic system 1600 has its power supply unit located inside the inverter and connected to the negative DC bus BUS-.

[0204] It should be understood that the circuit conversion methods in the photovoltaic system 500 and photovoltaic systems 1200 to 1600 can also be combined with each other.

[0205] Optionally, based on the photovoltaic system 500, the impedance detection device can be connected to the DC bus outside the power supply unit in conjunction with the connection method of the photovoltaic system 1300.

[0206] Optionally, based on the photovoltaic system 500, the impedance detection device can be connected between the DC switch and the DC / DC boost unit in conjunction with the connection method of the photovoltaic system 1400.

[0207] Optionally, based on the photovoltaic system, the impedance detection device can be connected before the DC switch in conjunction with the connection method of the photovoltaic system.

[0208] Optionally, based on the photovoltaic system 1600, the impedance detection device can be connected between the DC switch and the DC / DC boost unit in conjunction with the connection method of the photovoltaic system 1400.

[0209] Optionally, based on the photovoltaic system 1600, the impedance detection device can be connected before the DC switch in the same way as the photovoltaic system 1500.

[0210] It should be understood that there may be other possible combinations, and the embodiments of this application are not limited herein.

[0211] The above text combines Figures 8 to 11 The impedance detection method according to the embodiments of this application is described in detail below, in conjunction with... Figure 17 and Figure 18 The impedance detection device according to embodiments of this application is described in detail.

[0212] Figure 17 A schematic block diagram of an impedance detection device 1700 according to an embodiment of this application is shown. The device 1700 includes a sampling module 1710 and a processing module 1720. The sampling module 1710 is equivalent to the sensor detection unit in the photovoltaic system described above, and the processing module 1720 is equivalent to the processing unit in the photovoltaic system described above.

[0213] The sampling module 1710 is used to: sample the voltage between the DC bus and the ground wire at a first time point and a second time point respectively to obtain a first voltage value and a second voltage value; and sample the leakage current on the DC bus at the first time point and the second time point respectively to obtain a first current value and a second current value; the processing module 1720 is used to: calculate the insulation impedance value of the combiner box based on the difference between the first voltage value and the second voltage value, and the difference between the first current value and the second current value, so as to determine whether the impedance of the combiner box is abnormal.

[0214] Optionally, the photovoltaic system also includes a power supply unit, one end of which is grounded and the other end is connected to a DC bus. The power supply unit is in an off state at a first time point and in an operating state at a second time point.

[0215] Optionally, the processing module 1720 is configured to: close the power supply unit to put the power supply unit into operation before obtaining the second voltage value and the second current value; and adjust the voltage between the DC bus and the ground wire to a first preset voltage.

[0216] Optionally, the photovoltaic system also includes a power supply unit, one end of which is grounded and the other end is connected to the DC bus. The power supply unit is in operation at both the first and second time points.

[0217] Optionally, the processing module 1720 is configured to: close the power supply unit to put the power supply unit into operation before obtaining the first voltage value and the first current value; and adjust the voltage between the DC bus and the ground wire to a second preset voltage.

[0218] Optionally, the processing module 1720 is configured to: after a first preset duration, adjust the voltage between the DC bus and the ground wire to a third preset voltage.

[0219] Optionally, the processing module 1720 is used to: if it is determined that the impedance of the combiner box is abnormal, adjust the maximum power tracking point (MPPT) voltage corresponding to the photovoltaic string in the combiner box; the sampling module 1710 is used to: sample the MPPT voltage at the third time point and the fourth time point respectively to obtain the first MPPT voltage value and the second MPPT voltage value; the sampling module 1710 is also used to: sample the voltage between the DC bus and the ground wire at the third time point and the fourth time point respectively to obtain the third voltage value and the fourth voltage value; the processing module 1720 is also used to: calculate the insulation impedance value of the MPPT voltage based on the first MPPT voltage value, the second MPPT voltage value, the third voltage value and the fourth voltage value to determine whether the impedance of the photovoltaic string is abnormal.

[0220] Optionally, before obtaining the first MPPT voltage and the third voltage value, the processing module 1720 is used to: adjust the MPPT voltage to a fourth preset voltage.

[0221] Optionally, the processing module 1720 is configured to: adjust the MPPT voltage to a fifth preset voltage after a second preset duration.

[0222] Optionally, the power supply unit includes at least one of a relay, a resistor, a diode, or a DC power supply.

[0223] It should be understood that the device 1700 here is embodied in the form of a functional module. The term "module" here can refer to an application-specific integrated circuit (ASIC), electronic circuitry, a processor (e.g., a shared processor, a proprietary processor, or a group processor, etc.) and memory for executing one or more software or firmware programs, integrated logic circuitry, and / or other suitable components supporting the described functions. In an alternative example, those skilled in the art will understand that the device 1700 can be an electronic device, or a chip or chip system within an electronic device, or the functions of an electronic device or a chip or chip system within an electronic device can be integrated into the device 1700. The device 1700 can be used to perform various processes and / or steps in the above method embodiments and any impedance detection method; to avoid repetition, these will not be described further here.

[0224] The aforementioned device 1700 has the function of implementing the corresponding steps performed by the impedance detection device in the above method; the above function can be implemented by hardware or by hardware executing corresponding software. The hardware or software includes one or more modules corresponding to the above function.

[0225] In the embodiments of this application, Figure 17The device 1700 in the text can also be a chip or a chip system, such as a system on chip (SoC).

[0226] Figure 18 A schematic block diagram of another impedance detection device 1800 provided in an embodiment of this application is shown. The device 1800 includes a processor 1810, a transceiver 1820, and a memory 1830. The processor 1810, transceiver 1820, and memory 1830 communicate with each other via internal interconnection. The memory 1830 stores instructions, and the processor 1810 executes the instructions stored in the memory 1830 to control the transceiver 1820 to transmit and / or receive signals.

[0227] It should be understood that device 1800 may specifically be the impedance detection device in the above embodiments, or the function of the impedance detection device in the above embodiments may be integrated into device 1800. Device 1800 may be used to execute the various steps and / or processes corresponding to the impedance detection device in the above method embodiments. Optionally, the memory 1830 may include read-only memory and random access memory, and provide instructions and data to the processor. A portion of the memory may also include non-volatile random access memory. For example, the memory may also store device type information. The processor 1810 may be used to execute instructions stored in the memory, and when the processor executes the instructions, the processor may execute the various steps and / or processes corresponding to the impedance detection device in the above method embodiments.

[0228] It should be understood that, in the embodiments of this application, the processor 1810 may be a central processing unit (CPU), or it may be other general-purpose processors, digital signal processors (DSPs), application-specific integrated circuits (ASICs), field-programmable gate arrays (FPGAs), or other programmable logic devices, discrete gate or transistor logic devices, discrete hardware components, etc. The general-purpose processor may be a microprocessor or any conventional processor.

[0229] In implementation, each step of the above method can be completed by integrated logic circuits in the processor's hardware or by instructions in software. The steps of the method disclosed in the embodiments of this application can be directly manifested as execution by a hardware processor, or as a combination of hardware and software modules within the processor. The software modules can reside in random access memory, flash memory, read-only memory, programmable read-only memory, electrically erasable programmable memory, registers, or other mature storage media in the art. This storage medium is located in memory, and the processor executes the instructions in the memory, combining them with its hardware to complete the steps of the above method. To avoid repetition, detailed descriptions are omitted here.

[0230] Those skilled in the art will recognize that the modules and algorithm steps of the various examples described in conjunction with the embodiments disclosed herein can be implemented in electronic hardware, or a combination of computer software and electronic hardware. Whether these functions are implemented in hardware or software depends on the specific application and design constraints of the technical solution. Those skilled in the art can use different methods to implement the described functions for each specific application, but such implementation should not be considered beyond the scope of this application.

[0231] Those skilled in the art will understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and modules described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0232] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of modules is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple modules or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be through some interfaces; the indirect coupling or communication connection between apparatuses or modules may be electrical, mechanical, or other forms.

[0233] The modules described as separate components may or may not be physically separate. The components shown as modules may or may not be physical modules; that is, they may be located in one place or distributed across multiple network modules. Some or all of the modules can be selected to achieve the purpose of this embodiment according to actual needs. Furthermore, the functional modules in the various embodiments of this application may be integrated into one processing module, or each module may exist physically separately, or two or more modules may be integrated into one module.

[0234] If the aforementioned functions are implemented as software functional modules and sold or used as independent products, they can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or a portion of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

[0235] The above description is merely a specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. An impedance detection method, characterized in that, This invention is applied to a photovoltaic system, which includes multiple combiner boxes and an inverter. The input terminals of the multiple combiner boxes are respectively connected to a photovoltaic string, and the output terminals of the multiple combiner boxes are connected to the inverter via a DC bus. The N photovoltaic strings are connected to the combiner box, which includes N DC switches and N DC-DC boost units. The input terminals of the DC switches are connected to the photovoltaic strings, the output terminals of the DC switches are connected to the input terminals of the DC-DC boost units, and the output terminals of the DC-DC boost units are connected to the DC bus. The method includes: The voltage between the DC bus and the ground wire is sampled at the first time point and the second time point respectively to obtain the first voltage value and the second voltage value; The leakage current on the DC bus is sampled at the first time point and the second time point respectively to obtain the first current value and the second current value; Based on the difference between the first voltage value and the second voltage value, and the difference between the first current value and the second current value, after determining that the insulation resistance value of the combiner box is less than the insulation resistance threshold, the insulation resistance of the combiner box is indicated to be abnormal.

2. The method according to claim 1, characterized in that, The photovoltaic system also includes a power supply unit, one end of which is grounded and the other end is connected to the DC bus. The power supply unit is in an off state at the first time point and in an operating state at the second time point.

3. The method according to claim 2, characterized in that, Before obtaining the second voltage value and the second current value, the method further includes: Close the power supply unit to put it into operation. The power supply unit adjusts the voltage between the DC bus and the ground wire to a first preset voltage.

4. The method according to claim 1, characterized in that, The photovoltaic system also includes a power supply unit, one end of which is grounded and the other end is connected to the DC bus. The power supply unit is in operation at both the first time point and the second time point.

5. The method according to claim 4, characterized in that, Before obtaining the first voltage value and the first current value, the method further includes: Close the power supply unit to put it into operation. The power supply unit adjusts the voltage between the DC bus and the ground wire to a second preset voltage.

6. The method according to claim 5, characterized in that, Before obtaining the second voltage value and the second current value, the method further includes: After a first preset time period, the voltage between the DC bus and the ground wire is adjusted to a third preset voltage by the power supply unit.

7. The method according to any one of claims 1 to 6, characterized in that, The method further includes: If the impedance of the combiner box is determined to be abnormal, the maximum power tracking point (MPPT) voltage corresponding to the photovoltaic string in the combiner box is adjusted. The MPPT voltage is sampled at the third and fourth time points respectively to obtain the first MPPT voltage value and the second MPPT voltage value; The voltage between the DC bus and the ground wire is sampled at the third time point and the fourth time point, respectively, to obtain the third voltage value and the fourth voltage value. Based on the first MPPT voltage value, the second MPPT voltage value, the third voltage value, and the fourth voltage value, the insulation impedance value of the MPPT voltage is calculated to determine whether the impedance of the photovoltaic string is abnormal.

8. The method according to claim 7, characterized in that, Before obtaining the first MPPT voltage value and the third voltage value, the method further includes: The MPPT voltage is adjusted to the fourth preset voltage by the DC-DC boost unit.

9. The method according to claim 8, characterized in that, Before obtaining the second MPPT voltage value and the fourth voltage value, the method further includes: After a second preset duration, the MPPT voltage is adjusted to a fifth preset voltage by the DC-DC boost unit.

10. The method according to any one of claims 2 to 6, characterized in that, The power supply unit includes at least one of a relay, a resistor, a diode, or a DC power supply.

11. A photovoltaic system, characterized in that, The system includes multiple combiner boxes, an inverter, and an impedance detection device. The input terminals of the multiple combiner boxes are respectively connected to photovoltaic strings, and the output terminals of the multiple combiner boxes are connected to the inverter via a DC bus. N photovoltaic strings are connected to the combiner boxes. Each combiner box includes N DC switches and N DC-DC boost units. The input terminals of the DC switches are connected to the photovoltaic strings, the output terminals of the DC switches are connected to the input terminals of the DC-DC boost units, the output terminals of the DC-DC boost units are connected to the input terminals of the impedance detection devices, and the output terminals of the impedance detection devices are connected to the DC bus. The impedance detection device is used to: sample the voltage between the DC bus and the ground wire at a first time point and a second time point respectively to obtain a first voltage value and a second voltage value; and to sample the leakage current on the DC bus at the first time point and the second time point respectively to obtain a first current value and a second current value. Based on the difference between the first voltage value and the second voltage value, and the difference between the first current value and the second current value, after determining that the insulation resistance value of the combiner box is less than the insulation resistance threshold, the insulation resistance of the combiner box is indicated to be abnormal.

12. The photovoltaic system according to claim 11, characterized in that, The photovoltaic system also includes a power supply unit, one end of which is grounded and the other end is connected to the DC bus. The power supply unit is in an off state at the first time point and in an operating state at the second time point.

13. The photovoltaic system according to claim 12, characterized in that, The impedance detection device is used for: Before obtaining the second voltage value and the second current value, the power supply unit is closed, so that the power supply unit is in the working state; Adjust the voltage between the DC bus and the ground wire to a first preset voltage.

14. The photovoltaic system according to claim 11, characterized in that, The photovoltaic system also includes a power supply unit, one end of which is grounded and the other end is connected to the DC bus. The power supply unit is in operation at both the first time point and the second time point.

15. The photovoltaic system according to claim 14, characterized in that, The impedance detection device is used for: Before obtaining the first voltage value and the first current value, the power supply unit is closed, so that the power supply unit is in the working state; Adjust the voltage between the DC bus and the ground wire to the second preset voltage.

16. The photovoltaic system according to claim 15, characterized in that, The impedance detection device is used for: After a first preset time period, the voltage between the DC bus and the ground wire is adjusted to a third preset voltage.

17. The photovoltaic system according to any one of claims 11 to 16, characterized in that, The impedance detection device is used for: If the impedance of the combiner box is determined to be abnormal, the maximum power tracking point (MPPT) voltage corresponding to the photovoltaic string in the combiner box is adjusted. The MPPT voltage is sampled at the third and fourth time points respectively to obtain the first MPPT voltage value and the second MPPT voltage value; Furthermore, the voltage between the DC bus and the ground wire is sampled at the third time point and the fourth time point respectively to obtain the third voltage value and the fourth voltage value; Based on the first MPPT voltage value, the second MPPT voltage value, the third voltage value, and the fourth voltage value, the insulation impedance value of the MPPT voltage is calculated to determine whether the impedance of the photovoltaic string is abnormal.

18. The photovoltaic system according to claim 17, characterized in that, The impedance detection device is used for: Before obtaining the first MPPT voltage and the third voltage value, the MPPT voltage is adjusted to a fourth preset voltage.

19. The photovoltaic system according to claim 18, characterized in that, The impedance detection device is used for: After the second preset duration, the MPPT voltage is adjusted to the fifth preset voltage.

20. The photovoltaic system according to any one of claims 12 to 16, characterized in that, The power supply unit includes at least one of a relay, a resistor, a diode, or a DC power supply.

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