A photovoltaic system, power supply system and insulation fault detection method

Abstract

This application discloses a photovoltaic system, a power supply system, and an insulation fault detection method. The positive and negative output terminals of a first DC / DC circuit are connected to a positive DC bus and a neutral bus, respectively. The positive and negative output terminals of a second DC / DC circuit are connected to the first and second input terminals of a negative voltage circuit, respectively. The first and second output terminals of the negative voltage circuit are used to connect to the neutral bus and a negative DC bus, respectively. The negative output terminal of the second DC / DC circuit is used to connect to the neutral bus. An insulation impedance detection circuit is connected between the bus and ground. The bus includes a positive DC bus, a neutral bus, or a negative DC bus. The insulation impedance detection circuit includes at least a switch. The negative DC bus is connected to the neutral bus through an electrical component or a voltage source. The controller obtains the insulation impedance based on the voltage to ground of the corresponding bus before and after the switch is closed, and determines whether an insulation fault exists in the photovoltaic system based on the insulation impedance, thereby providing timely protection.

Description

Technical Field

[0001] This application relates to the field of photovoltaic power generation technology, and in particular to a photovoltaic system, a power supply system, and a method for detecting insulation faults. Background Technology

[0002] Photovoltaic power generation converts solar energy into electrical energy. A typical photovoltaic system includes a photovoltaic array and a power conversion circuit. Since the photovoltaic array outputs direct current (DC) and the AC power grid outputs alternating current (AC), an inverter is needed to convert the DC output of the photovoltaic array into AC power and feed it back to the AC power grid.

[0003] In actual operation, photovoltaic systems may experience insulation faults. When an insulation fault occurs, it is generally necessary to detect it in time and control the inverter to stop operating in order to prevent the insulation fault from spreading and affecting the operation of the entire photovoltaic system.

[0004] However, existing insulation fault detection methods are all designed for traditional single DC bus photovoltaic systems, and cannot achieve comprehensive insulation fault detection for dual DC bus photovoltaic systems. Summary of the Invention

[0005] This application provides a photovoltaic system, a power supply system, and an insulation fault detection method, which can realize the insulation fault detection of a photovoltaic system with dual DC buses.

[0006] This application provides a photovoltaic system that differs from traditional unipolar photovoltaic systems. This photovoltaic system includes three buses: a DC positive bus, a neutral bus, and a DC negative bus. The neutral bus can be an exposed line or a single potential, provided that the potentials of the neutral buses on the photovoltaic side and the inverter side are consistent. The DC bus voltage includes both positive and negative voltages. The photovoltaic system includes: a first DC / DC circuit, a second DC / DC circuit, a negative voltage circuit, an insulation resistance detection circuit, and a controller. The input terminals of the first and second DC / DC circuits are respectively connected to their corresponding photovoltaic strings. The positive and negative output terminals of the first DC / DC circuit are respectively connected to the positive DC bus and the neutral bus. The positive and negative output terminals of the second DC / DC circuit are respectively connected to the first and second input terminals of the negative voltage circuit, and the first and second output terminals of the negative voltage circuit are respectively connected to the neutral bus and the negative DC bus. The negative output terminal of the second DC / DC circuit is connected to the neutral bus. The insulation resistance detection circuit is connected between the bus and ground. The bus includes: a positive DC bus, a neutral bus, or a negative DC bus. The insulation resistance detection circuit includes at least a switch. The negative DC bus is connected to the neutral bus through an electrical component or a voltage source. The controller obtains the insulation resistance based on the voltage to ground of the corresponding bus before and after the switch is closed, and detects whether there is an insulation fault in the photovoltaic system based on the insulation resistance.

[0007] The photovoltaic system provided in this application includes an insulation impedance detection circuit. This circuit can be connected between any one of the three busbars and ground. To comprehensively detect the insulation impedance of the photovoltaic system, the DC negative busbar is equivalent to the neutral busbar, meaning the DC negative busbar is connected to the neutral busbar via a voltage source or electrical component, forming a conductive path between them. Since the insulation impedance detection circuit includes a switch, the voltage to ground of the busbar connected to the circuit is obtained before and after the switch is closed. Based on the two voltage readings and Thevenin's law, an equation containing voltage and resistance is obtained. Solving this equation yields the insulation impedance. This insulation impedance is the comprehensive impedance of the photovoltaic system to ground. Therefore, based on this impedance, it can be determined whether the photovoltaic system has an insulation fault. Typically, when an insulation fault occurs in the photovoltaic system, the insulation impedance to ground decreases. Therefore, the insulation impedance can be compared with a preset threshold. When the insulation impedance is less than the preset threshold, it indicates an insulation fault in the photovoltaic system, and protection should be implemented promptly.

[0008] In one possible implementation, the controller uses Thevenin's law to set up equations based on the bus voltage to ground before the switch is closed and the bus voltage to ground after the switch is closed. Solving the equations yields the insulation impedance. When the insulation impedance is less than a preset threshold, it is determined that there is an insulation fault in the photovoltaic system, and insulation protection can be performed in a timely manner.

[0009] In one possible implementation, for the sake of hardware circuit simplicity, the insulation impedance detection circuit includes at least a switch and a resistor connected in series. In this embodiment, the specific positional relationship between the switch and the resistor is not limited; for example, the switch can be close to ground, or the resistor can be close to ground. Since the resistance value in the insulation impedance detection circuit is known, the bus voltage to ground is measured once before the switch is closed and once after the switch is closed. Based on Thevenin's law, the equations for the equivalent circuit are established, where the resistance and the two measured voltages are known quantities. Solving the equations yields the unknown insulation impedance.

[0010] In one possible implementation, the electrical components include at least one of the following: a resistor, a relay, an IGBT, a MOSFET, an inductor, or a diode.

[0011] In one possible implementation, to simplify the circuit and reduce its cost, the electrical components can be implemented using diodes, namely: a first diode; the anode of the first diode is connected to the DC negative bus, and the cathode of the first diode is connected to the neutral bus. This achieves the existence of a current path between the DC negative bus and the neutral bus. Due to the unidirectional conduction characteristic of the diode, the current is unidirectional, and it can flow from the DC negative bus to the neutral bus, but it cannot flow from the neutral bus to the DC negative bus.

[0012] In one possible implementation, the insulation resistance detection circuit is connected between the DC positive bus and ground; the first end of the insulation resistance detection circuit is connected to the DC positive bus, and the second end of the insulation resistance detection circuit is connected to the positive output terminal of the second DC / DC circuit. Both the first and second ends of the insulation resistance detection circuit are grounded through a series switch and a resistor; the controller is used to obtain the insulation resistance based on the ground voltage and resistance of the DC positive bus before and after the switch is closed.

[0013] In one possible implementation, to avoid the influence of the DC positive bus on the first input terminal of the negative voltage circuit, the insulation impedance detection circuit further includes: a first isolation circuit; the first terminal of the first isolation circuit is connected to the second terminal of the insulation impedance detection circuit, and the second terminal of the first isolation circuit is grounded through a series resistor and a switch; the first isolation circuit includes at least one of the following: a resistor, a relay, an IGBT, a MOSFET, an inductor, or a diode.

[0014] In one possible implementation, the first isolation circuit includes a second diode; the anode of the second diode is connected to the second terminal of the insulation resistance detection circuit, and the cathode of the second diode is grounded through a series resistor and a switch. Due to the unidirectional conduction characteristic of the second diode, and because the cathode of the second diode is close to the DC positive bus, the high voltage of the DC positive bus will not be applied to the first input terminal of the negative voltage circuit through the second diode.

[0015] In one possible implementation, to better isolate the DC positive bus from the first input terminal of the negative voltage circuit, the insulation resistance detection circuit further includes: a second isolation circuit; the first terminal of the second isolation circuit is connected to the first terminal of the insulation resistance detection circuit, and the second terminal of the second isolation circuit is connected to ground through a resistor and a switch in series; the second isolation circuit includes at least one of the following: a resistor, a relay, an IGBT, a MOSFET, an inductor, or a diode.

[0016] In one possible implementation, for ease of implementation and cost savings, the second isolation circuit further includes a third diode; the anode of the third diode is connected to the first terminal of the insulation resistance detection circuit, and the cathode of the third diode is grounded through a series resistor and a switch. Due to the unidirectional conduction characteristic of the third diode, and because the anode of the third diode is connected to the DC positive bus, and the cathode of the third diode is close to the first input terminal of the negative voltage circuit, the voltage at the first input terminal of the negative voltage circuit will not affect the DC positive bus.

[0017] The insulation impedance detection circuit provided in this application embodiment can be connected not only between the DC positive bus and ground, but also between the DC negative bus and ground, or between the neutral bus and ground. The obtained insulation impedance can characterize the insulation status of the photovoltaic system.

[0018] In one possible implementation, the insulation resistance detection circuit is connected between the DC negative bus and ground; the first end of the insulation resistance detection circuit is connected to the DC negative bus, and the second end of the insulation resistance detection circuit is grounded through a switch and a resistor connected in series; the controller is used to obtain the insulation resistance based on the ground voltage and resistance of the DC negative bus before and after the switch is closed.

[0019] In one possible implementation, the insulation impedance detection circuit is connected between the neutral bus and ground; the first end of the insulation impedance detection circuit is connected to the neutral bus, and the second end of the insulation impedance detection circuit is grounded through a switch and a resistor connected in series; the controller is used to obtain the insulation impedance based on the neutral bus's voltage to ground and resistance before and after the switch is closed.

[0020] In one possible implementation, the first DC / DC circuit, the second DC / DC circuit, the negative voltage circuit, and the insulation resistance detection circuit are integrated in a DC combiner box.

[0021] In one possible implementation, the system further includes: a first inverter and a second inverter; the first input terminal and the second input terminal of the first inverter are respectively used to connect to the DC positive bus and the neutral bus; the first input terminal and the second input terminal of the second inverter are respectively used to connect to the neutral bus and the DC negative bus.

[0022] The above is an introduction using a photovoltaic system as an example. The insulation impedance detection circuit provided in this application embodiment can also be applied to other similar power systems including three busbars, such as other new energy fields, including wind power generation, hydropower generation, etc., or it can also be used in energy storage systems. The advantages of the various technical solutions in the above photovoltaic system are also applicable to the following power systems, and will not be repeated here.

[0023] This application embodiment also provides a power supply system including: an insulation impedance detection circuit and a controller; the insulation impedance detection circuit is connected between a bus and ground, the bus including: a DC positive bus, a neutral bus, or a DC negative bus; wherein, the DC positive bus and the neutral bus correspond to a first DC power supply, and the neutral bus and the DC negative bus correspond to a second DC power supply; the insulation impedance detection circuit includes at least a switch; the DC negative bus is connected to the neutral bus through an electrical component or a voltage source; the controller is used to obtain the insulation impedance based on the voltage to ground of the corresponding bus before and after the switch is closed, and to detect whether there is an insulation fault in the power supply system based on the insulation impedance.

[0024] In one possible implementation, the circuit further includes: a first DC / DC circuit, a second DC / DC circuit, and a negative voltage circuit; the input terminal of the first DC / DC circuit is used to connect to a first DC power supply; the input terminal of the second DC / DC circuit is used to connect to a second DC power supply; the positive output terminal and the negative output terminal of the first DC / DC circuit are used to connect to a positive DC bus and a neutral bus, respectively; the positive output terminal and the negative output terminal of the second DC / DC circuit are used to connect to the first input terminal and the second input terminal of the negative voltage circuit, respectively; the first output terminal and the second output terminal of the negative voltage circuit are used to connect to the neutral bus and the negative DC bus, respectively; and the negative output terminal of the second DC / DC circuit is used to connect to the neutral bus.

[0025] In one possible implementation, the insulation resistance detection circuit is connected between the DC positive bus and ground; the first end of the insulation resistance detection circuit is connected to the DC positive bus, and the second end of the insulation resistance detection circuit is connected to the positive output terminal of the second DC / DC circuit. Both the first and second ends of the insulation resistance detection circuit are grounded through a series switch and a resistor; the controller is used to obtain the insulation resistance based on the ground voltage and resistance of the DC positive bus before and after the switch is closed.

[0026] In one possible implementation, the insulation resistance detection circuit is connected between the DC negative bus and ground; the first end of the insulation resistance detection circuit is connected to the DC negative bus, and the second end of the insulation resistance detection circuit is grounded through a switch and a resistor connected in series; the controller is used to obtain the insulation resistance based on the ground voltage and resistance of the DC negative bus before and after the switch is closed.

[0027] In one possible implementation, the insulation impedance detection circuit is connected between the neutral bus and ground; the first end of the insulation impedance detection circuit is connected to the neutral bus, and the second end of the insulation impedance detection circuit is grounded through a switch and a resistor connected in series; the controller is used to obtain the insulation impedance based on the neutral bus's voltage to ground and resistance before and after the switch is closed.

[0028] Based on the photovoltaic system and DC power supply provided in the above embodiments, this application also provides an insulation fault detection method for a photovoltaic system. The photovoltaic system includes: a first DC / DC circuit, a second DC / DC circuit, a negative voltage circuit, an insulation impedance detection circuit, and a controller; the input terminal of the first DC / DC circuit is used to connect to the corresponding photovoltaic string; the input terminal of the second DC / DC circuit is used to connect to the corresponding photovoltaic string; the positive output terminal and negative output terminal of the first DC / DC circuit are respectively used to connect to the positive DC bus and the neutral bus; the positive output terminal and negative output terminal of the second DC / DC circuit are respectively connected to the first input terminal and the second input terminal of the negative voltage circuit, and the first output terminal and the second output terminal of the negative voltage circuit are respectively used to connect to the neutral bus and the negative DC bus; the negative output terminal of the second DC / DC circuit is used to connect to the neutral bus; the insulation impedance detection circuit is connected between the bus and ground, and the bus includes: a positive DC bus, a neutral bus, or a negative DC bus; the insulation impedance detection circuit includes at least a switch; the negative DC bus is connected to the neutral bus through an electrical component or a voltage source;

[0029] The method includes: obtaining the voltage to ground of the busbar before the switch is closed; obtaining the voltage to ground of the busbar after the switch is closed; obtaining the insulation impedance based on the voltage to ground of the busbar before the switch is closed and the voltage to ground of the busbar after the switch is closed; and detecting whether there is an insulation fault in the photovoltaic system based on the insulation impedance.

[0030] As can be seen from the above technical solutions, the embodiments of this application have the following advantages:

[0031] Since the photovoltaic system provided in this application embodiment includes a DC positive bus, a neutral bus, and a DC negative bus, it is necessary to detect the insulation condition of the DC positive bus, the DC negative bus, and the photovoltaic array. However, traditional insulation impedance detection circuits cannot comprehensively detect insulation faults in this multi-bus photovoltaic system. Therefore, to comprehensively detect insulation faults in the photovoltaic system provided in this application embodiment, this application embodiment provides an insulation fault detection method. This method involves connecting an insulation impedance detection circuit between any one of the three buses and ground. The three buses include: the DC positive bus L+, the neutral bus M, and the DC negative bus L-. Furthermore, an auxiliary circuit can connect the DC negative bus L- to the neutral bus M, forming a closed circuit between them. This ensures that the insulation impedance detection circuit can also detect the insulation condition of the DC negative bus L- to ground. The auxiliary circuit includes at least electrical components or a voltage source. The insulation impedance detection circuit includes at least a switch. The insulation status of the photovoltaic system can be obtained based on the voltage to ground of the corresponding busbars before and after the switch is closed. Specifically, insulation faults in the primary photovoltaic array, such as those on the DC positive busbar L+ and the DC negative busbar L-, will affect the insulation impedance. Therefore, the photovoltaic system provided in this application embodiment can comprehensively detect insulation faults. Attached Figure Description

[0032] Figure 1 A schematic diagram of a photovoltaic system provided in an embodiment of this application;

[0033] Figure 2 A schematic diagram of yet another photovoltaic system provided in this application embodiment;

[0034] Figure 3 A schematic diagram of another photovoltaic system provided in the embodiments of this application;

[0035] Figure 4 A schematic diagram of another photovoltaic system provided in the embodiments of this application;

[0036] Figure 5 A schematic diagram of yet another photovoltaic system provided in this application embodiment;

[0037] Figure 6 A schematic diagram of yet another photovoltaic system provided in this application embodiment;

[0038] Figure 7 A Thevenin equivalent circuit diagram when the switch is open is provided in an embodiment of this application;

[0039] Figure 8 A Thevenin equivalent circuit diagram for a switch when closed is provided in an embodiment of this application;

[0040] Figure 9 A schematic diagram of yet another photovoltaic system provided in this application embodiment;

[0041] Figure 10 A schematic diagram of yet another photovoltaic system is provided for the embodiments of this application;

[0042] Figure 11 A schematic diagram of another photovoltaic system provided in the embodiments of this application;

[0043] Figure 12 A schematic diagram of a power supply system provided in an embodiment of this application;

[0044] Figure 13 A schematic diagram of another power supply system provided in an embodiment of this application;

[0045] Figure 14 A schematic diagram of yet another power supply system provided in an embodiment of this application;

[0046] Figure 15 A schematic diagram of another power supply system provided in the embodiments of this application;

[0047] Figure 16This is a flowchart of an insulation fault detection method for a photovoltaic system provided in an embodiment of this application. Detailed Implementation

[0048] The terms "first," "second," etc., used in the following description are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature specified with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this application, unless otherwise stated, "multiple" means two or more.

[0049] Furthermore, in this application, directional terms such as "upper" and "lower" may be defined relative to the orientation in which the components are schematically placed in the accompanying drawings. It should be understood that these directional terms can be relative concepts, used for relative description and clarification, and can change accordingly depending on the orientation in which the components are placed in the accompanying drawings.

[0050] In this application, unless otherwise expressly specified and limited, the term "connection" should be interpreted broadly. For example, "connection" can be a fixed connection, a detachable connection, or an integral part; it can be a direct connection or an indirect connection through an intermediate medium. Furthermore, the term "coupled" can refer to a method of electrical connection for signal transmission. "Coupled" can be a direct electrical connection or an indirect electrical connection through an intermediate medium.

[0051] Photovoltaic System Examples

[0052] To enable those skilled in the art to better understand the technical solutions provided in the embodiments of this application, a photovoltaic system provided in the embodiments of this application is described below.

[0053] See Figure 1 The figure is a schematic diagram of a photovoltaic system provided in an embodiment of this application.

[0054] This application relates to a photovoltaic system. Unlike traditional monopolar photovoltaic systems, the photovoltaic system provided in this application includes three buses: a positive DC bus L+, a neutral bus M, and a negative DC bus L-. The neutral bus M can be an exposed wire or a virtual potential; that is, the DC-side neutral bus M and the AC input-side neutral bus M only need to have the same potential. It is not necessary for the DC-side and AC-side M to be physically connected. This photovoltaic system includes three DC buses: a positive DC bus L+, a neutral bus M, and a negative DC bus L-.

[0055] For example, if the voltage of L+ is +1500V and the voltage of L- is -1500V, then the voltage rating of this photovoltaic system is ±1500V. However, the voltage after L+ and L- are connected in series is 3000V. Therefore, the photovoltaic system provided in this application embodiment can be subject to a 1500V safety standard, thereby reducing the voltage withstand requirements for the power transistors in the power converter and inverter.

[0056] The input terminal of the power converter 200 is used to connect to the photovoltaic array 100. The first output terminal of the power converter 200 is connected to the first terminal of the DC positive bus L+. The second output terminal of the power converter 200 is connected to the first terminal of the neutral bus M. The third output terminal of the power converter 200 is connected to the first terminal of the DC negative bus L-.

[0057] Furthermore, the photovoltaic system provided in this application embodiment includes at least two inverters: a first inverter 107 and a second inverter 108.

[0058] The first input terminal of the first inverter 107 is connected to the second terminal of the DC positive bus L+, and the second input terminal of the first inverter 107 is connected to the second terminal of the neutral bus M.

[0059] The first input terminal of the second inverter 108 is connected to the second terminal of the neutral bus M, and the second input terminal of the second inverter 108 is connected to the second terminal of the DC negative bus L-.

[0060] Figure 1 The photovoltaic system shown can reduce the voltage drop across power devices, which is beneficial for the selection of power devices.

[0061] In actual operation, the distance between the power converter and the subsequent inverter may be relatively far. Therefore, the power loss on the power cable corresponding to the DC bus is relatively large. In order to improve power generation efficiency, it is necessary to minimize this loss. Figure 1 The corresponding total voltage of the DC bus is 3000V. The higher the voltage, the lower the current, which can reduce the loss on the DC bus.

[0062] The following is combined with Figure 2 A schematic diagram of another photovoltaic system provided in the embodiments of this application is briefly introduced.

[0063] See Figure 2 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0064] The photovoltaic system provided in this embodiment includes three buses: a positive DC bus L+, a neutral bus M, and a negative DC bus L-. The voltage between the positive DC bus L+ and the neutral bus M is 1500V, and the voltage between the negative DC bus L- and the neutral bus M is -1500V.

[0065] The photovoltaic system provided in this application embodiment includes a first DC / DC circuit 103, a second DC / DC circuit 104, and a negative voltage circuit 106. The input terminal of the first DC / DC circuit 103 is connected to a first photovoltaic array PV1, and the output terminal of the first DC / DC circuit 103 is connected to the positive DC bus L+ and the neutral bus M. The input terminal of the second DC / DC circuit 104 is connected to a second photovoltaic array PV2, and the output terminal of the second DC / DC circuit 104 is connected to the neutral bus M and the negative DC bus L-.

[0066] The output voltage of a typical photovoltaic array is positive. Therefore, the output voltage of the second DC / DC circuit 104 is also positive. Thus, a negative voltage circuit 106 is needed to convert the positive voltage output by the DC / DC circuit 104 into a negative voltage to supply the neutral bus M and the DC negative bus L-. For example, one implementation of the negative voltage circuit 106 can be a Buck-Boost circuit, or other circuit topologies; no specific limitations are made in this embodiment.

[0067] In addition, the connection method of the first inverter 107 and the second inverter 108 to the three buses is the same as... Figure 1 The same applies, so I won't repeat it here.

[0068] Since the photovoltaic system provided in this application embodiment includes a DC positive bus, a neutral bus, and a DC negative bus, it is necessary to detect the insulation condition of the DC positive bus, the DC negative bus, and the photovoltaic array. However, traditional insulation impedance detection circuits cannot comprehensively detect insulation faults in this multi-bus photovoltaic system. Therefore, to comprehensively detect insulation faults in the photovoltaic system provided in this application embodiment, this application embodiment provides an insulation fault detection method. This method involves connecting an insulation impedance detection circuit between any one of the three buses and ground. The three buses include: the DC positive bus L+, the neutral bus M, and the DC negative bus L-. Furthermore, an auxiliary circuit can connect the DC negative bus L- to the neutral bus M, forming a closed circuit between them. This ensures that the insulation impedance detection circuit can also detect the insulation condition of the DC negative bus L- to ground. The auxiliary circuit includes at least electrical components or a voltage source. The insulation impedance detection circuit includes at least a switch. The insulation status of the photovoltaic system can be obtained based on the voltage to ground of the corresponding busbars before and after the switch is closed. Specifically, insulation faults in the primary photovoltaic array, such as those on the DC positive busbar L+ and the DC negative busbar L-, will affect the insulation impedance. Therefore, the photovoltaic system provided in this application embodiment can comprehensively detect insulation faults.

[0069] The following section will continue using a photovoltaic system, which includes two DC / DC circuits and a negative voltage circuit, as an example.

[0070] See Figure 3 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0071] The photovoltaic system provided in this application includes: a first DC / DC circuit 103, a second DC / DC circuit 104, a negative voltage circuit 106, an insulation resistance detection circuit 105, and a controller (not shown in the figure).

[0072] The input terminal of the first DC / DC circuit 103 is used to connect to the corresponding photovoltaic string; the input terminal of the second DC / DC circuit 104 is used to connect to the corresponding photovoltaic string.

[0073] The positive and negative output terminals of the first DC / DC circuit 103 are used to connect the positive DC bus L+ and the neutral bus M, respectively.

[0074] The positive and negative output terminals of the second DC / DC circuit 104 are connected to the first and second input terminals of the negative voltage circuit 106, respectively. The first and second output terminals of the negative voltage circuit 106 are used to connect the neutral bus M and the DC negative bus L-, respectively. The negative output terminal of the second DC / DC circuit 104 is used to connect the neutral bus M.

[0075] The insulation resistance detection circuit 105 is connected between the busbar and ground. The busbar includes at least one of the following: a DC positive busbar L+, a neutral busbar M, or a DC negative busbar L-. The insulation resistance detection circuit 105 includes at least a switch. The DC negative busbar L- is connected to the neutral busbar M through an electrical component or a voltage source.

[0076] This application does not specifically limit the specific implementation of the switch in the insulation impedance detection circuit 105. For example, it can be a relay or other switching device that can control its opening and closing. The state of the switch can be controlled by a controller, that is, the controller controls the opening and closing of the switch.

[0077] The controller is used to obtain the insulation impedance based on the bus voltage to ground before and after the switch is closed, and to determine whether there is an insulation fault in the photovoltaic system based on the insulation impedance.

[0078] Figure 3 The insulation resistance detection circuit 105 is connected between the DC positive bus L+ and the ground PE as an example. Therefore, the insulation resistance can be obtained by obtaining the voltage of the DC positive bus L+ to ground before and after the switch in the insulation resistance detection circuit 105 is closed.

[0079] The auxiliary circuit 109 is used to connect the DC negative bus L- to the neutral bus M, so that a conductive path is formed between the DC negative bus L- and PV- or the neutral bus M. It should be noted that the formation of a conductive path here does not mean that the DC negative bus L- and the neutral bus M have the same potential, but rather that there is a potential difference between them.

[0080] The auxiliary circuit 109 may include at least an electrical component or a voltage source. For example, the electrical component may include at least one of the following: a resistor, a relay, an IGBT, a MOSFET, an inductor, or a diode. For example, the electrical component may include a diode, with its anode connected to the DC negative bus L- and its cathode connected to the neutral bus M. That is, the DC negative bus L- can form a conduction path to the neutral bus M, thereby converting the ground insulation impedance of the DC negative bus L- to the equivalent ground insulation impedance of the neutral bus through the diode.

[0081] The location of the insulation resistance detection circuit 105 is not limited in the embodiments of this application. For example, when the photovoltaic system includes a DC combiner box, the insulation resistance detection circuit 105 can be located in the DC combiner box.

[0082] The photovoltaic system provided in this application includes an insulation impedance detection circuit. This circuit can be connected between any one of the three busbars and ground. To comprehensively detect the insulation impedance of the photovoltaic system, the DC negative busbar is equivalent to the neutral busbar, meaning the DC negative busbar is connected to the neutral busbar via a voltage source or electrical component, forming a conductive path between them. Since the insulation impedance detection circuit includes a switch, the voltage to ground of the busbar connected to the circuit is obtained before and after the switch is closed. Based on the two voltage readings and Thevenin's law, an equation containing voltage and resistance is obtained. Solving this equation yields the insulation impedance. This insulation impedance is the comprehensive impedance of the photovoltaic system to ground. Therefore, based on this impedance, it can be determined whether the photovoltaic system has an insulation fault. Typically, when an insulation fault occurs in the photovoltaic system, the insulation impedance to ground decreases. Therefore, the insulation impedance can be compared with a preset threshold. When the insulation impedance is less than the preset threshold, it indicates an insulation fault in the photovoltaic system, and protection should be implemented promptly.

[0083] See Figure 4 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0084] The photovoltaic system provided in this embodiment includes a DC combiner box 1000 and a DC switch 102. A first DC / DC circuit 103 and a second DC / DC circuit 104 are respectively connected to a first photovoltaic array PV1 and a second photovoltaic array PV2 via the DC switch 102. The DC switch 102 can be disconnected when needed, for example, when a fault occurs in the photovoltaic system, the DC switch 102 disconnects, thereby disconnecting the photovoltaic arrays from the DC / DC circuits and providing protection. This embodiment does not specifically limit the specific implementation of the DC switch 102; for example, it can be a relay or other types of switches.

[0085] For ease of control, the controller can also be located in the DC combiner box 1000. The controller can control the operation of the first DC / DC circuit 103, the second DC / DC circuit 104 and the negative voltage circuit 106.

[0086] To help those skilled in the art better understand the principle of photovoltaic system insulation fault detection provided in the embodiments of this application, the following is combined with... Figure 5 A detailed explanation is provided. In the following embodiments of this application, the first DC / DC circuit 103 and the second DC / DC circuit 104 are used as examples of boost circuits. It should be understood that the first DC / DC circuit 103 and the second DC / DC circuit 104 can also be other forms of DC-DC converter circuits, and no specific limitation is made in the embodiments of this application.

[0087] See Figure 5 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0088] In the photovoltaic system provided in this application embodiment, the DC negative bus L- is connected to the neutral bus M through electrical components. Taking the auxiliary circuit including electrical components as an example for ease of explanation, and to simplify the circuit structure and reduce the overall cost of the photovoltaic system, the electrical component can be a first diode D1.

[0089] The anode of the first diode D1 is connected to the DC negative bus, and the cathode of the first diode D1 is connected to the neutral bus M.

[0090] The insulation resistance detection circuit 105 is connected between the DC positive bus L+ and ground PE.

[0091] The first terminal of the insulation resistance detection circuit 105 is connected to the DC positive bus L+, and the second terminal of the insulation resistance detection circuit 105 is connected to the positive output terminal of the second DC / DC circuit 104. Both the first and second terminals of the insulation resistance detection circuit 105 are grounded through a series switch K1 and a resistor R1. In this embodiment, the specific positional relationship between the series switch K1 and the resistor R1 is not limited. For example, the switch K1 can be close to the ground PE, or the resistor R1 can be close to the ground PE.

[0092] The controller is used to obtain the insulation impedance based on the DC positive bus L+ voltage to ground PE before and after the switch K1 is closed, i.e., the two voltages and the resistance.

[0093] For example, when switch K1 is open (before it closes), the DC positive bus L+ is not grounded to PE through switch K1 and resistor R1; that is, the branch formed by R1 and K1 in series is not conductive. At this time, the voltage between the DC positive bus L+ and PE is obtained. When switch K1 is closed, the branch formed by R1 and K1 in series becomes conductive, and the DC positive bus L+ is grounded to PE through switch K1 and resistor R1. The voltage between the DC positive bus L+ and PE is then obtained. Since the impedance of the DC positive bus L+ to ground changes before and after switch K1 is turned on (because resistor R1 is connected to the system after K1 is turned on), it will affect the impedance of L+ to ground. Since R1 is known, the insulation impedance of the photovoltaic system can be obtained through equations, thereby determining whether an insulation fault has occurred in the photovoltaic system. For example, if the obtained insulation impedance is less than a preset threshold, it indicates that an insulation fault exists in the photovoltaic system. The inverter with the insulation fault should be shut down to prevent the fault from spreading.

[0094] To avoid the influence of the DC positive bus L+ on the first input terminal of the negative voltage circuit 106, the insulation resistance detection circuit 105 provided in this application embodiment may further include: a first isolation circuit G1;

[0095] The first terminal of the first isolation circuit G1 is connected to the second terminal of the insulation impedance detection circuit 105, and the second terminal of the first isolation circuit G1 is grounded through a series resistor R and a switch K1.

[0096] The embodiments of this application do not limit the specific implementation of the first isolation circuit G1, as long as it can isolate the DC positive bus L+ from the first input terminal of the negative voltage circuit 106. For example, the first isolation circuit G1 may include at least one of the following: a resistor, a relay, an insulated gate bipolar transistor (IGBT), a metal oxide semiconductor field-effect transistor (MOS), an inductor, or a diode.

[0097] In addition, in order to better isolate the DC positive bus L+ from the first input terminal of the negative voltage circuit 106, the insulation resistance detection circuit 105 may also include a second isolation circuit G2.

[0098] The first terminal of the second isolation circuit G2 is connected to the first terminal of the insulation impedance detection circuit 105, and the second terminal of the second isolation circuit G2 is connected to ground through a resistor and a switch connected in series.

[0099] Similar to the first isolation circuit G1, the embodiments of this application do not specifically limit the implementation of the second isolation circuit G2. For example, the second isolation circuit G2 may include at least one of the following: a resistor, a relay, an IGBT transistor, a MOSFET, an inductor, or a diode.

[0100] This embodiment uses a DC switch including a first DC switch S1 and a second DC switch S2 as an example. The first DC / DC circuit 103 is connected to the first photovoltaic array PV1 via the first DC switch S1, and the second DC / DC circuit 104 is connected to the second photovoltaic array PV2 via the second DC switch S2.

[0101] See Figure 6 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0102] This embodiment describes the specific implementation of the first isolation circuit and the second isolation circuit. For convenience and simplicity, and to save circuit costs, in one possible implementation, the first isolation circuit G1 may include: the second diode D2.

[0103] The anode of the second diode D2 is connected to the second terminal of the insulation resistance detection circuit 105, and the cathode of the second diode D2 is grounded through the series resistor R1 and the switch K1.

[0104] Due to the unidirectional conduction characteristic of the second diode D2, and because the cathode of the second diode D2 is close to the DC positive bus L+, the high voltage of the DC positive bus L+ will not be applied to the first input terminal of the negative voltage circuit 106 through the second diode D2.

[0105] To facilitate circuit implementation and save costs, the second isolation circuit G2 may include a third diode D3;

[0106] The anode of the third diode D3 is connected to the first terminal of the insulation resistance detection circuit 105, and the cathode of the third diode D3 is grounded through the series resistor R1 and the switch K1.

[0107] Due to the unidirectional conduction characteristic of the third diode D3, and because the anode of the third diode D3 is connected to the DC positive bus L+, and the cathode of the third diode D3 is close to the first input terminal of the negative voltage circuit 106, the voltage at the first input terminal of the negative voltage circuit 106 will not affect the DC positive bus L+.

[0108] In summary, the embodiments of this application achieve bidirectional isolation between the first input terminal of the negative voltage circuit 106 and the DC positive bus L+ through the second diode D2 and the third diode D3, so that the two do not affect each other.

[0109] The following is combined with Figure 7 and Figure 8Analyze the specific methods for insulation impedance testing.

[0110] See Figure 7 The figure is a Thevenin equivalent circuit diagram provided in an embodiment of this application when the switch is open.

[0111] The insulation resistance detection circuit provided in this application embodiment can be based on Thevenin's law. When the switch in the insulation resistance detection circuit is open, Thevenin's law can be used to equate the DC positive bus L+ to ground PE to... Figure 7 The circuit shown.

[0112] Among them, the DC positive bus L+ can be equivalent to a voltage source and an impedance connected in series, U represents the equivalent voltage source, Rx represents the equivalent impedance of the photovoltaic system to ground PE, and U1 represents the voltage of the DC positive bus L+ to ground.

[0113] See Figure 8 The figure is a Thevenin equivalent circuit diagram of a switch when closed, provided in an embodiment of this application.

[0114] and Figure 7 correspond, Figure 8 Indicates switch Figure 6 The equivalent circuit diagram is shown when switch K1 is closed. When switch K1 is closed, resistor R1 is connected to the circuit, that is, the DC positive bus L+ is grounded through resistor R1.

[0115] The following is a summary Figure 7 and Figure 8 Formulate equations to obtain Rx.

[0116] First, by Figure 7 In the circuit shown, since there is an open circuit between the DC positive bus L+ and PE, U = U1.

[0117] Depend on Figure 8 In the circuit shown, U = Ux + U2, where Ux = Rx * I, U2 = R1 * I, and I is the current flowing through R1 and Rx.

[0118] Therefore, by combining the above formulas, we can obtain Rx = [(U1-U2)*R1] / U2.

[0119] Since the value of R1 is known, U1 and U2 can be detected. Therefore, the value of Rx can be obtained. By comparing the value of Rx with a preset threshold, if Rx is less than the preset threshold, it indicates that an insulation fault has occurred in the photovoltaic system. Rx is the parallel value of the insulation resistance of PV+ and PV- to PE on one side of the photovoltaic array, and the insulation resistance of the DC positive bus L+ and DC negative bus L- to PE. Therefore, in the photovoltaic system provided in this application embodiment, when an insulation fault is detected in the photovoltaic system, it may be an insulation fault of the DC positive bus L+, an insulation fault of the DC negative bus L- to ground, or an insulation fault of the photovoltaic array side to ground.

[0120] It should be understood that U1 and U2 can be obtained through a voltage detection circuit. Generally, photovoltaic systems are equipped with a voltage detection circuit for the bus voltage.

[0121] The above embodiments describe the insulation resistance detection circuit connected between the DC positive bus and ground. The following describes the case where the insulation resistance detection circuit is connected between the neutral bus and ground, with reference to the accompanying drawings.

[0122] See Figure 9 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0123] The insulation detection circuit 105 in the photovoltaic system provided in this application embodiment is connected between the neutral bus M and the ground PE. Similar to the above embodiments, the insulation detection circuit 105 includes a resistor R1 and a switch K1 connected in series.

[0124] The controller can obtain the insulation impedance of the photovoltaic system based on the neutral bus M-to-ground voltage and resistance R1 before and after switch K1 is closed. It should be understood that when the insulation impedance detection circuit is connected between the neutral bus M and ground PE, the specific method for obtaining the insulation impedance can still use Thevenin's law, as described above. Figure 7 and Figure 8 The details of the process will not be repeated here. After obtaining the insulation impedance, the controller can determine whether an insulation fault has occurred in the photovoltaic system. When the obtained insulation impedance is less than a preset threshold, it indicates that an insulation fault has occurred in the photovoltaic system. At this time, the controller can control both the first DC switch S1 and the second DC switch S2 to open, thereby disconnecting the photovoltaic array from the DC / DC circuit. Additionally, the controller can also control the two DC / DC circuits to stop working, thus shutting down the two inverters connected downstream.

[0125] Figure 9 This section describes the case where the insulation resistance detection circuit is connected between the neutral busbar and ground. The following section will combine... Figure 10 This section describes the situation where the insulation resistance detection circuit is connected between the DC negative bus and ground.

[0126] See Figure 10 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0127] The insulation detection circuit 105 in the photovoltaic system provided in this application embodiment is connected between the DC negative bus L- and ground PE. Similar to the above embodiment, the insulation detection circuit 105 includes a resistor R1 and a switch K1 connected in series.

[0128] The controller can obtain the insulation impedance of the photovoltaic system based on the DC negative bus L- to ground voltage and resistance R1 before and after switch K1 is closed. It should be understood that when the insulation impedance detection circuit is connected between the DC negative bus L- and ground PE, the specific method for obtaining the insulation impedance can still use Thevenin's law, as described above. Figure 7 and Figure 8 The details of the process will not be repeated here. After obtaining the insulation impedance, the controller can determine whether an insulation fault has occurred in the photovoltaic system. When the obtained insulation impedance is less than a preset threshold, it indicates that an insulation fault has occurred in the photovoltaic system. At this time, the controller can control both the first DC switch S1 and the second DC switch S2 to open, thereby disconnecting the photovoltaic array from the DC / DC circuit. Additionally, the controller can also control the two DC / DC circuits to stop working, thus shutting down the two inverters connected downstream.

[0129] The above describes the connection of the three busbars to the insulation detection circuit. It should be understood that each of the three busbars corresponds to one of the two inverters. Specifically, the DC positive busbar L+ is connected to insulation detection circuit 105 as an example. (See also...) Figure 11 This figure is a schematic diagram of another photovoltaic system provided in an embodiment of this application.

[0130] The photovoltaic system provided in this application embodiment further includes: a first inverter 107 and a second inverter 108;

[0131] The first input terminal and the second input terminal of the first inverter 107 are used to connect the DC positive bus L+ and the neutral bus M, respectively.

[0132] The first and second input terminals of the second inverter 108 are used to connect the neutral bus M and the DC negative bus L-, respectively.

[0133] For example, the voltage at the input terminal of the first inverter 107 is 0V-1500V, the voltage at the input terminal of the second inverter 108 is -1500V-0V, and the voltage level of the entire photovoltaic system is 3000V.

[0134] Power System Implementation Examples

[0135] Based on the photovoltaic system provided in the above embodiments, this application also provides a power supply system. The difference between this power supply system and the photovoltaic system above is that it does not limit the type of DC power supply. For example, the DC power supply can be any new energy source, such as a photovoltaic array, which can be a DC power supply generated by wind power generation, a DC power supply generated by hydropower generation, or a DC power supply generated by energy storage batteries. As long as the power supply system includes three buses, it can form positive voltage and negative voltage.

[0136] See Figure 12 The figure is a schematic diagram of a power supply system provided in an embodiment of this application.

[0137] The power supply system provided in this embodiment includes: an insulation resistance detection circuit 105 and a controller (not shown in the figure).

[0138] The insulation resistance detection circuit 105 is connected between the busbar and ground. The busbar includes a DC positive busbar L+, a neutral busbar M, or a DC negative busbar L-. The DC positive busbar L+ and the neutral busbar correspond to the first DC power supply 201, and the neutral busbar M and the DC negative busbar L- correspond to the second DC power supply 202.

[0139] Figure 12 The following is an example of how the insulation resistance detection circuit 105 is connected between the DC positive bus L+ and ground PE.

[0140] The insulation resistance detection circuit 105 includes at least a switch; the DC negative bus L- is connected to the neutral bus M through an electrical component or voltage source, meaning there is a certain potential difference between the DC negative bus L- and the neutral bus M. The auxiliary circuit 109 connects the DC negative bus L- to the neutral bus M, forming a conductive path between the DC negative bus L- and PV- or the neutral bus M. It should be noted that forming a conductive path here does not mean that the DC negative bus L- and the neutral bus M have the same potential, but rather that there is a potential difference between them. For example, L- and M can be connected through an auxiliary circuit, which can include at least an electrical component or voltage source. For example, the electrical component can include at least one of the following: a resistor, a relay, an IGBT, a MOSFET, an inductor, or a diode. For example, electrical components may include diodes. The anode of the diode is connected to the DC negative bus L-, and the cathode of the diode can be connected to the neutral bus M. That is, the DC negative bus L- can form a conduction path to the neutral bus M, thereby converting the ground insulation impedance of the DC negative bus L- to the ground insulation impedance of the neutral bus through the diode.

[0141] This application does not specifically limit the specific implementation of the switch in the insulation impedance detection circuit 105. For example, it can be a relay or other switching device that can control its opening and closing. The state of the switch can be controlled by a controller, that is, the controller controls the opening and closing of the switch.

[0142] The controller is used to obtain the insulation impedance based on the bus voltage to ground before and after the switch is closed. An insulation impedance less than a preset threshold indicates an insulation fault in the power system. The specific method by which the controller obtains the insulation impedance can be found in the description of the photovoltaic system embodiment, and will not be repeated here.

[0143] The following is combined with Figure 13 This application describes a specific implementation of a power supply system provided in an embodiment of the present application. It may also include a power conversion circuit, which includes: a first DC / DC circuit 103, a second DC / DC circuit 104, and a negative voltage circuit 106.

[0144] The input terminal of the first DC / DC circuit 103 is used to connect to the first DC power supply 201; the input terminal of the second DC / DC circuit 104 is used to connect to the second DC power supply 202.

[0145] The positive and negative output terminals of the first DC / DC circuit 103 are used to connect the positive DC bus L+ and the neutral bus M, respectively.

[0146] The positive and negative output terminals of the second DC / DC circuit 104 are connected to the first and second input terminals of the negative voltage circuit 106, respectively. The first and second output terminals of the negative voltage circuit 106 are used to connect the neutral bus M and the DC negative bus, respectively. The negative output terminal of the second DC / DC circuit 104 is used to connect the neutral bus M.

[0147] The following is an example of the insulation resistance detection circuit 105 connected between the DC positive bus L+ and ground PE.

[0148] The first terminal of the insulation resistance detection circuit 105 is connected to the DC positive bus L+, and the second terminal of the insulation resistance detection circuit 105 is connected to the positive output terminal of the second DC / DC circuit 104. Both the first and second terminals of the insulation resistance detection circuit 105 are grounded through a series switch and a resistor.

[0149] The controller is used to obtain the insulation impedance based on the ground voltage and resistance of the DC positive bus L+ before and after the switch is closed. For the specific method of obtaining the impedance, please refer to the description of the photovoltaic system embodiment, which will not be repeated here.

[0150] Once the controller obtains the insulation impedance, it can determine whether an insulation fault has occurred in the power system. When the obtained insulation impedance is less than a preset threshold, it indicates an insulation fault in the power system. In this case, the controller can disconnect both the first and second DC power supplies from the power conversion circuit, for example, disconnecting the DC power supplies from the DC / DC circuit. Additionally, the controller can also stop the two DC / DC circuits from operating and shut down the two inverters connected downstream.

[0151] See Figure 14 This figure is a schematic diagram of another power supply system provided in an embodiment of this application.

[0152] The power supply system provided in this embodiment is described using the example of the insulation impedance detection circuit 105 connected between the DC negative bus L- and ground PE.

[0153] The first terminal of the insulation resistance detection circuit 105 is connected to the DC negative bus L-, and the second terminal of the insulation resistance detection circuit 105 is grounded through a switch and a resistor connected in series.

[0154] The controller is used to obtain the insulation impedance based on the ground voltage and resistance of the corresponding DC negative bus before and after the switch is closed. For the specific method of obtaining the impedance, please refer to the description of the photovoltaic system embodiment, which will not be repeated here.

[0155] See Figure 15 This figure is a schematic diagram of another power supply system provided in an embodiment of this application.

[0156] In the power supply system provided in this embodiment, the insulation impedance detection circuit 105 is connected between the neutral bus M and the ground PE.

[0157] The first terminal of the insulation resistance detection circuit 105 is connected to the neutral bus M, and the second terminal of the insulation resistance detection circuit 105 is grounded through a switch and a resistor connected in series.

[0158] The controller is used to obtain the insulation impedance based on the ground voltage and resistance of the neutral bus before and after the switch is closed. For the specific method of obtaining the impedance, please refer to the description of the photovoltaic system embodiment, which will not be repeated here.

[0159] Method Implementation Examples

[0160] Based on the photovoltaic system provided in the above embodiments, this application also provides a method for detecting insulation faults in a photovoltaic system, which will be described in detail below with reference to the accompanying drawings.

[0161] See Figure 14 The figure is a flowchart of an insulation fault detection method for a photovoltaic system provided in an embodiment of this application.

[0162] The insulation fault detection method for photovoltaic systems provided in this application embodiment is applicable to the photovoltaic system described in any of the above embodiments. The photovoltaic system includes: a first DC / DC circuit, a second DC / DC circuit, a negative voltage circuit, an insulation impedance detection circuit, and a controller. The input terminal of the first DC / DC circuit is used to connect to the corresponding photovoltaic string. The input terminal of the second DC / DC circuit is used to connect to the corresponding photovoltaic string. The positive and negative output terminals of the first DC / DC circuit are respectively used to connect to the positive DC bus and the neutral bus. The positive and negative output terminals of the second DC / DC circuit are respectively connected to the first and second input terminals of the negative voltage circuit. The first and second output terminals of the negative voltage circuit are respectively used to connect to the neutral bus and the negative DC bus. The negative output terminal of the second DC / DC circuit is used to connect to the neutral bus. The insulation impedance detection circuit is connected between the bus and ground. The bus includes: a positive DC bus, a neutral bus, or a negative DC bus. The insulation impedance detection circuit includes at least a switch. The negative DC bus is connected to the neutral bus through an electrical component or a voltage source.

[0163] The method includes:

[0164] S1201: Obtain the voltage to ground of the busbar before the switch is closed; that is, obtain the voltage to ground of the busbar when the switch is open. For example, when the insulation detection circuit is connected between the DC positive busbar and ground, obtain the voltage to ground of the DC positive busbar when the switch is open.

[0165] S1202: Obtain the voltage to ground of the bus after the switch is closed; for example, obtain the voltage to ground of the DC positive bus after the switch is closed.

[0166] S1203: The insulation resistance is obtained based on the busbar voltage to ground before and after the switch is closed; see details for further information. Figure 7 and Figure 8 The corresponding description is that the insulation resistance can be obtained using Thevenin's law.

[0167] S1204: An insulation resistance less than a preset threshold indicates an insulation fault in the photovoltaic system.

[0168] When an insulation fault occurs in a photovoltaic system, the insulation resistance decreases. Therefore, the insulation resistance can be compared with a preset threshold. When the insulation resistance is less than the preset threshold, it indicates that there is an insulation fault in the photovoltaic system.

[0169] Insulation impedance is the parallel value of the insulation impedance of the photovoltaic array to the PE and the insulation impedance of the DC positive bus L+ and the DC negative bus L- to the PE. Therefore, in the photovoltaic system provided in this application embodiment, when an insulation fault is detected in the photovoltaic system, it may be an insulation fault of the DC positive bus L+, an insulation fault of the DC negative bus L- to ground, or an insulation fault to ground occurring on one side of the photovoltaic array.

[0170] Since the photovoltaic system provided in this application embodiment includes a DC positive bus, a neutral bus, and a DC negative bus, it is necessary to detect the insulation condition of the DC positive bus, the DC negative bus, and the photovoltaic array. However, traditional insulation impedance detection circuits cannot comprehensively detect insulation faults in this multi-bus photovoltaic system. Therefore, to comprehensively detect insulation faults in the photovoltaic system provided in this application embodiment, this application embodiment provides an insulation fault detection method. This method involves connecting an insulation impedance detection circuit between any one of the three buses and ground. The three buses include: a DC positive bus L+, a neutral bus M, and a DC negative bus L-. An auxiliary circuit can connect the DC negative bus L- to the neutral bus M, forming a closed circuit between them. This ensures that the insulation impedance detection circuit can also detect the insulation condition of the DC negative bus L- to ground. The auxiliary circuit includes at least electrical components or a voltage source. The insulation impedance detection circuit includes at least a switch. The insulation status of the photovoltaic system can be obtained based on the voltage to ground of the corresponding busbars before and after the switch is closed. Specifically, insulation faults in the primary photovoltaic array, such as those on the DC positive busbar L+ and the DC negative busbar L-, will affect the insulation impedance. Therefore, the insulation detection method for photovoltaic systems provided in this application can comprehensively detect insulation faults.

[0171] It should be understood that in this application, "at least one (item)" means one or more, and "more than" means two or more. "And / or" is used to describe the relationship between related objects, indicating that three relationships can exist. For example, "A and / or B" can represent three cases: only A exists, only B exists, and both A and B exist simultaneously, 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 (item) 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 (item) of a, b, or c can represent: a, b, c, "a and b", "a and c", "b and c", or "a and b and c", where a, b, and c can be single or multiple.

[0172] The above-described embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of this application.

Claims

1. A photovoltaic system, characterized in that, include: The circuit consists of a first DC / DC circuit, a second DC / DC circuit, a negative voltage circuit, an insulation resistance detection circuit, and a controller. The input terminal of the first DC / DC circuit is used to connect to the corresponding photovoltaic string; the input terminal of the second DC / DC circuit is used to connect to the corresponding photovoltaic string. The positive and negative output terminals of the first DC / DC circuit are used to connect to the positive DC bus and the neutral bus, respectively. The positive and negative output terminals of the second DC / DC circuit are respectively connected to the first and second input terminals of the negative voltage circuit. The first and second output terminals of the negative voltage circuit are respectively used to connect to the neutral bus and the DC negative bus. The negative output terminal of the second DC / DC circuit is used to connect to the neutral bus. The insulation impedance detection circuit is connected between the busbar and ground, and the busbar includes: the DC positive busbar, the neutral busbar, or the DC negative busbar; The insulation impedance detection circuit includes at least a switch; the DC negative bus is connected to the neutral bus via an electrical component or a voltage source. The controller is used to obtain the insulation impedance based on the ground voltage of the bus before and after the switch is closed, and to detect whether there is an insulation fault in the photovoltaic system based on the insulation impedance.

2. The photovoltaic system according to claim 1, characterized in that, The controller is specifically used to obtain the insulation impedance based on the bus voltage to ground before the switch is closed and the bus voltage to ground after the switch is closed. The insulation impedance being less than a preset threshold indicates that the photovoltaic system has an insulation fault.

3. The photovoltaic system according to claim 1 or 2, characterized in that, The insulation impedance detection circuit includes at least the switch and resistor connected in series.

4. The photovoltaic system according to any one of claims 1-3, characterized in that, The electrical components include at least one of the following: resistor, relay, IGBT, MOSFET, inductor, or diode.

5. The photovoltaic system according to claim 4, characterized in that, The electrical component includes: a first diode; The anode of the first diode is connected to the DC negative bus, and the cathode of the first diode is connected to the neutral bus.

6. The photovoltaic system according to any one of claims 1-5, characterized in that, The insulation impedance detection circuit is connected between the DC positive bus and ground. The first end of the insulation impedance detection circuit is connected to the DC positive bus, and the second end of the insulation impedance detection circuit is connected to the positive output terminal of the second DC / DC circuit. Both the first and second ends of the insulation impedance detection circuit are grounded through the switch and resistor connected in series. The controller is used to obtain the insulation impedance based on the ground voltage of the DC positive bus and the resistance before and after the switch is closed.

7. The photovoltaic system according to claim 6, characterized in that, The insulation impedance detection circuit further includes: a first isolation circuit; The first terminal of the first isolation circuit is connected to the second terminal of the insulation impedance detection circuit, and the second terminal of the first isolation circuit is grounded through a series resistor and the switch; The first isolation circuit includes at least one of the following: a resistor, a relay, an IGBT, a MOSFET, an inductor, or a diode.

8. The photovoltaic system according to claim 7, characterized in that, The first isolation circuit includes: a second diode; The anode of the second diode is connected to the second terminal of the insulation resistance detection circuit, and the cathode of the second diode is grounded through a series resistor and a switch.

9. The photovoltaic system according to any one of claims 6-8, characterized in that, The insulation impedance detection circuit further includes: a second isolation circuit; The first terminal of the second isolation circuit is connected to the first terminal of the insulation impedance detection circuit, and the second terminal of the second isolation circuit is connected to ground through a resistor in series with the switch; The second isolation circuit includes at least one of the following: a resistor, a relay, an IGBT, a MOSFET, an inductor, or a diode.

10. The photovoltaic system according to claim 9, characterized in that, The second isolation circuit also includes: a third diode; The anode of the third diode is connected to the first terminal of the insulation resistance detection circuit, and the cathode of the third diode is grounded through the series resistor and switch.

11. The photovoltaic system according to any one of claims 1-5, characterized in that, The insulation impedance detection circuit is connected between the DC negative bus and ground. The first end of the insulation impedance detection circuit is connected to the DC negative bus, and the second end of the insulation impedance detection circuit is grounded through a switch and a resistor connected in series. The controller is used to obtain the insulation impedance based on the ground voltage of the DC negative bus and the resistance before and after the switch is closed.

12. The photovoltaic system according to any one of claims 1-5, characterized in that, The insulation impedance detection circuit is connected between the neutral busbar and ground. The first end of the insulation impedance detection circuit is connected to the neutral bus, and the second end of the insulation impedance detection circuit is grounded through a switch and a resistor connected in series. The controller is used to obtain the insulation impedance based on the ground voltage of the neutral bus and the resistance before and after the switch is closed.

13. The photovoltaic system according to any one of claims 1-12, characterized in that, The first DC / DC circuit, the second DC / DC circuit, the negative voltage circuit, and the insulation resistance detection circuit are integrated in a DC combiner box.

14. The photovoltaic system according to any one of claims 1-13, characterized in that, Also includes: First inverter and second inverter; The first input terminal and the second input terminal of the first inverter are respectively used to connect the DC positive bus and the neutral bus; The first input terminal and the second input terminal of the second inverter are respectively used to connect the neutral bus and the DC negative bus.

15. A power supply system, characterized in that, include: Insulation resistance detection circuit and controller; The insulation impedance detection circuit is connected between the busbar and ground. The busbar includes a positive DC busbar, a neutral busbar, or a negative DC busbar. The positive DC busbar and the neutral busbar correspond to a first DC power supply, and the neutral busbar and the negative DC busbar correspond to a second DC power supply. The insulation impedance detection circuit includes at least a switch; the DC negative bus is connected to the neutral bus via an electrical component or a voltage source. The controller is used to obtain the insulation impedance based on the ground voltage of the bus before and after the switch is closed, and to detect whether there is an insulation fault in the power system based on the insulation impedance.

16. The power supply system according to claim 15, characterized in that, Also includes: First DC / DC circuit, second DC / DC circuit, and negative voltage circuit; The input terminal of the first DC / DC circuit is used to connect to the first DC power supply; The input terminal of the second DC / DC circuit is used to connect to the second DC power supply; The positive and negative output terminals of the first DC / DC circuit are respectively used to connect the positive DC bus and the neutral bus; The positive and negative output terminals of the second DC / DC circuit are respectively connected to the first and second input terminals of the negative voltage circuit. The first and second output terminals of the negative voltage circuit are respectively used to connect to the neutral bus and the DC negative bus. The negative output terminal of the second DC / DC circuit is used to connect to the neutral bus.

17. The power supply system according to claim 16, characterized in that, The insulation impedance detection circuit is connected between the DC positive bus and ground. The first end of the insulation impedance detection circuit is connected to the DC positive bus, and the second end of the insulation impedance detection circuit is connected to the positive output terminal of the second DC / DC circuit. Both the first and second ends of the insulation impedance detection circuit are grounded through the switch and resistor connected in series. The controller is used to obtain the insulation impedance based on the ground voltage of the DC positive bus and the resistance before and after the switch is closed.

18. The power supply system according to claim 15 or 16, characterized in that, The insulation impedance detection circuit is connected between the DC negative bus and ground. The first end of the insulation impedance detection circuit is connected to the DC negative bus, and the second end of the insulation impedance detection circuit is grounded through a switch and a resistor connected in series. The controller is used to obtain the insulation impedance based on the ground voltage of the DC negative bus and the resistance before and after the switch is closed.

19. The power supply system according to claim 15 or 16, characterized in that, The insulation impedance detection circuit is connected between the neutral busbar and ground. The first end of the insulation impedance detection circuit is connected to the neutral bus, and the second end of the insulation impedance detection circuit is grounded through a switch and a resistor connected in series. The controller is used to obtain the insulation impedance based on the ground voltage of the neutral bus and the resistance before and after the switch is closed.

20. A method for detecting insulation faults in a photovoltaic system, characterized in that, The photovoltaic system includes: a first DC / DC circuit, a second DC / DC circuit, a negative voltage circuit, an insulation resistance detection circuit, and a controller; the input terminal of the first DC / DC circuit is used to connect to the corresponding photovoltaic string; the input terminal of the second DC / DC circuit is used to connect to the corresponding photovoltaic string; the positive and negative output terminals of the first DC / DC circuit are respectively used to connect to the positive DC bus and the neutral bus; the positive and negative output terminals of the second DC / DC circuit are respectively connected to the first and second input terminals of the negative voltage circuit, and the first and second output terminals of the negative voltage circuit are respectively used to connect to the neutral bus and the negative DC bus; the negative output terminal of the second DC / DC circuit is used to connect to the neutral bus; the insulation resistance detection circuit is connected between the bus and ground, and the bus includes: the positive DC bus, the neutral bus, or the negative DC bus; the insulation resistance detection circuit includes at least a switch; the negative DC bus is connected to the neutral bus through an electrical component or a voltage source; The method includes: Obtain the voltage to ground of the busbar before the switch is closed; Obtain the voltage to ground of the busbar after the switch is closed; The insulation resistance is obtained based on the busbar voltage to ground before the switch is closed and the busbar voltage to ground after the switch is closed. The insulation impedance is used to detect whether there is an insulation fault in the photovoltaic system.

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