Inverter with multi-functional circuit and method for ISO detection, PID repair, and nighttime power supply

Abstract

This invention discloses a multifunctional circuit for an inverter integrating ISO detection, PID repair, and nighttime power supply, as well as a method for implementing ISO detection, PID compensation, and nighttime power supply functions in a photovoltaic inverter based on this circuit. This invention incorporates multiple unidirectional conducting devices and switching devices, and achieves ISO detection, PID compensation, and nighttime power supply functions in the photovoltaic inverter on the same circuit by controlling the states of the switching devices. Therefore, the advantage of this invention is that it proposes a multifunctional composite circuit integrating ISO insulation impedance detection, PID repair, and nighttime bus power supply required by a photovoltaic inverter. Using the circuit provided by this invention, different functions can be achieved at different stages of inverter operation based on the different device control logics within the circuit.

Description

Technical Field

[0001] This invention relates to a multifunctional composite circuit that integrates multiple functions required by a photovoltaic inverter, and a method for realizing ISO detection, PID repair, and nighttime power supply based on the multifunctional composite circuit. Background Technology

[0002] With the large-scale development of photovoltaic power plants, people have gradually recognized the impact of the PID effect of photovoltaic modules on the power generation efficiency of power plants. Previously, when power plants were adapted to PID repair functions, it was necessary to add a separate PID repair function box or select a PID repair function board. Based on the current application requirements of string inverters, the PID repair function, which was previously an optional feature for users, is increasingly becoming a standard feature of inverters. The previous method of using optional PID repair function boxes or boards to implement PID repair was not only costly but also required additional wiring work, making maintenance relatively complex. To improve the utilization rate of photovoltaic inverters, it has been proposed to use SVG compensation at night. This requires an external power supply to power the inverter's DC bus for startup. Therefore, the bus needs to be charged at night. This function also requires certain control circuits and control logic, increasing system complexity. Summary of the Invention

[0003] The technical problem this invention aims to solve is that: the original method of using an optional PID repair function box or function board to implement the PID repair function is not only costly, but also requires an additional amount of wiring work, making maintenance relatively complex; using the inverter for SVG compensation at night requires charging the bus through the power supply at night, and this function also requires certain control circuits and control logic, increasing system complexity.

[0004] To solve the above-mentioned technical problems, one technical solution of the present invention is to provide a multi-functional circuit for an inverter that integrates ISO detection, PID repair, and nighttime power supply. The circuit is characterized by including a unidirectional conducting device 1, a unidirectional conducting device 2, a unidirectional conducting device 3, a unidirectional conducting device 4, and a switching device 6 with two pairs of ports. One pair of ports of the switching device 6 is defined as port 1 and port 2, and the other pair of ports of the switching device 6 is defined as port 3 and port 4.

[0005] The current inflow terminal of unidirectional conduction device one and the current outflow terminal of unidirectional conduction device three are connected to the BUS+ port of the DC bus of the photovoltaic inverter; the current inflow terminal of unidirectional conduction device two and the current outflow terminal of unidirectional conduction device four are connected to the BUS- port of the DC bus of the photovoltaic inverter.

[0006] The current output terminals of unidirectional conducting device one and unidirectional conducting device two are connected to one end of switching device one; the other end of switching device one is connected to port two of switching device six and one end of switching device four; port one of switching device six is ​​connected to the negative terminal of the controllable DC power supply; the other end of switching device four is connected to one end of resistor device R1.

[0007] The current inflow terminals of unidirectional conducting device three and unidirectional conducting device four are connected to one end of switching device three; the other end of switching device three is connected to port four of switching device six and one end of switching device two; port three of switching device six is ​​connected to the positive terminal of the controllable DC power supply; the other end of switching device two is connected to one end of resistor device R2.

[0008] The other end of resistor R1 is connected to the other end of resistor R2 and then connected to the grounding terminal PE of the photovoltaic inverter.

[0009] Preferably, it also includes a detection circuit for detecting the DC bus voltage V2 of the photovoltaic inverter, the PE voltage V1 of the DC bus BUS+ port of the photovoltaic inverter to the ground terminal of the photovoltaic inverter, the PE voltage V3 of the DC bus BUS- port of the photovoltaic inverter to the ground terminal of the photovoltaic inverter, and controlling the DC power supply output voltage V4.

[0010] Preferably, the unidirectional conducting device one, unidirectional conducting device two, unidirectional conducting device three and unidirectional conducting device four are switching devices controlled by a photovoltaic inverter controller.

[0011] Preferably, the unidirectional conducting device one, unidirectional conducting device two, unidirectional conducting device three, unidirectional conducting device four, the switching device one, the switching device two, the switching device three, the switching device four, the switching device five, the switching device six, the resistor device R1, and the resistor device R2 are single devices or a group of devices composed of multiple single devices.

[0012] Preferably, the first, second, third, fourth, fifth, and sixth switching devices are high-voltage reed relays.

[0013] Preferably, the first unidirectional conducting device, the second unidirectional conducting device, the third unidirectional conducting device, and the fourth unidirectional conducting device are high-voltage diodes or diodes connected in series.

[0014] Preferably, the first unidirectional conducting device, the second unidirectional conducting device, the third unidirectional conducting device, and the fourth unidirectional conducting device are relays.

[0015] Another technical solution of the present invention provides a method for realizing the ISO detection function of a photovoltaic inverter using the aforementioned multifunctional circuit integrating ISO detection, PID repair, and nighttime power supply, characterized in that the sixth switching device is in the open state, with each pair of its ports not connected, and the second and third unidirectional conducting devices are in the off state, comprising the following steps:

[0016] Step 1: The photovoltaic inverter controller controls switch device 1 and switch device 4 to be turned on, while switch device 2 and switch device 3 are turned off. At this time:

[0017] The detected DC bus voltage V2 of the photovoltaic inverter is denoted as V. bus The detected voltage V1 between the DC bus BUS+ port of the photovoltaic inverter and the PE ground terminal of the photovoltaic inverter is recorded as V. b The input voltage of n photovoltaic cells is denoted as V. pv1 V pv2 ,……,V pvn Then we have:

[0018]

[0019] In the formula, R x1 R x2 ... R xn R represents the insulation resistance between the positive output terminals PV1+, PV2+, ..., PVn+ of the n photovoltaic cells and the ground terminal PE of the photovoltaic inverter. z This indicates the insulation resistance between the negative output terminal PV- of the photovoltaic cell or the DC bus BUS- port of the photovoltaic inverter and the grounding terminal PE of the photovoltaic inverter.

[0020] Step 2: The photovoltaic inverter controller turns on switching devices one and four, and switching devices two and three also turn on. At this time, the detected DC bus voltage V2 of the photovoltaic inverter remains unchanged, still V. bus The detected voltage V1 between the DC bus BUS-port of the photovoltaic inverter and the PE terminal of the photovoltaic inverter is denoted as V. c Then we have:

[0021]

[0022] Step 3: The photovoltaic inverter controller disconnects switch device 1, switch device 2, switch device 3, switch device 4, switch device 5, and switch device 6. The photovoltaic inverter controller then determines the location of the device based on the detected values ​​of V2 and V6. c The insulation resistance G was calculated. x As shown in the following formula:

[0023]

[0024] When designing the inverter multifunctional circuit as described in claim 1, which integrates ISO detection, PID repair, and nighttime power supply, R1 = R1.

[0025] Another technical solution of the present invention provides a method for implementing PID compensation function in the above-mentioned inverter with a multi-functional circuit integrating ISO detection, PID repair, and nighttime power supply, characterized by comprising the following steps:

[0026] Keep the following switching devices open: Switch 1, Switch 2, Switch 3, Switch 4, Switch 5, and Switch 6.

[0027] When the compensation voltage is set to PV- positive bias, PV- is the negative electrode of the photovoltaic cell:

[0028] Step 101: The optical inverter controller controls the switching device three and the switching device four to be turned on, and causes the switching device one and the switching device two to be turned off;

[0029] Step 102: Close the switching device six, so that the two pairs of ports of the switching device six are connected;

[0030] Step 103: Control the output of the controllable DC power supply to set the compensation bias voltage V. ref At this time, the unidirectional conducting device three is in the off state, the switching device one and the switching device two are in the open state, and a positive voltage V4 is added between the DC bus BUS- port of the photovoltaic inverter and the grounding terminal PE of the photovoltaic inverter to achieve the PID repair effect.

[0031] When the compensation voltage is set to a negative bias of PV+, PV+ is the positive electrode of the photovoltaic cell:

[0032] Step 201: The optical inverter controller controls the first and second switching devices to be turned on, and causes the third and fourth switching devices to be turned off;

[0033] Step 202: Close the switching device six, so that the two pairs of ports of the switching device six are connected;

[0034] Step 203: Control the output of the controllable DC power supply to set the compensation bias voltage V. ref At this time, the second unidirectional conducting device is in the off state, the third and fourth switching devices are in the open state, and a negative voltage V4 is added between the DC bus BUS+ port of the photovoltaic inverter and the grounding terminal PE of the photovoltaic inverter to achieve PID repair.

[0035] Another technical solution of the present invention provides a method for realizing the nighttime power supply function by integrating the above-mentioned inverter with ISO detection, PID repair, and nighttime power supply multifunctional circuit, characterized by comprising the following steps:

[0036] Step 301: Close the sixth switch device to make the two pairs of ports of the sixth switch device conduct, close the first switch device and the third switch device, and open the fourth switch device and the second switch device;

[0037] Step 302: Use the controllable DC power supply to output the required DC voltage V4 to charge the DC bus of the photovoltaic inverter, thereby enabling the photovoltaic inverter controller to operate in the SVG reactive power compensation state.

[0038] Step 303: After the photovoltaic inverter controller starts working, disconnect the first, second, third, fourth, fifth, and sixth switching devices. The multi-functional circuit is in standby mode. At this time, the second and third unidirectional conducting devices are in the on state, the first and fourth unidirectional conducting devices are in the off state, and the fourth switching device and the second switching device are in the off state. Apply a negative voltage V4 between the BUS+ and BUS- ports of the photovoltaic inverter to achieve nighttime power supply.

[0039] This invention proposes a multifunctional composite circuit that integrates ISO insulation impedance detection, PID repair, and nighttime bus power supply required by photovoltaic inverters. By using the circuit provided by this invention, different functions can be achieved at different stages of inverter operation based on the control logic of different devices in the circuit. Attached Figure Description

[0040] Figure 1 The circuit topology of the present invention is illustrated in the figure. For a unidirectional conducting device, the current can only flow from port 1 marked in the figure to port 2. For a switching device, ports 3 and 4 marked in the figure can be interchanged.

[0041] Figure 2 The circuit topology for ISO insulation resistance testing is illustrated.

[0042] Figure 3 for Figure 2 A simplified diagram;

[0043] Figure 4 and Figure 5 for Figure 1 A simplified circuit diagram for implementing PID compensation.

[0044] Figure 6for Figure 1 A simplified circuit diagram for providing nighttime power supply.

[0045] Figure 7 It indicated Figure 1 Replacement schemes for the circuit shown;

[0046] Figure 8 It indicated Figure 1 One feasible implementation of the circuit shown;

[0047] Figure 9 It indicated Figure 1 Another feasible implementation of the circuit shown. Detailed Implementation

[0048] The present invention will be further illustrated below with reference to specific embodiments. It should be understood that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Furthermore, it should be understood that after reading the teachings of this invention, those skilled in the art can make various alterations or modifications to the invention, and these equivalent forms also fall within the scope defined by the appended claims.

[0049] like Figure 1 As shown, the circuit topology of the inverter integrated with ISO detection, PID repair, and nighttime power supply disclosed in this embodiment consists of: unidirectional conducting devices Da, Db, Dc, and Dd; switching devices K1, K2, K3, K4, K5, and K6; resistive devices R1 and R2; and a DC power supply LPS1 with adjustable output. The devices described above can be single devices or groups of devices that perform similar functions. For example, the unidirectional conducting devices Da, Db, Dc, and Dd can be multiple unidirectional conducting devices (such as diodes) connected in series, or they can be logic-controllable unidirectional conducting switches (such as relays, MOSFETs, IGBTs, SCRs, etc.); the switching devices K1, K2, K3, K4, K5, and K6 can be multiple switching devices (such as relays, MOSFETs, IGBTs, etc.) connected in series; and the resistive devices R1 and R2 can also be multiple resistors connected in series.

[0050] One-way conductors: Port 1 of Da and Port 2 of Dc are connected to the DC bus BUS+ of the photovoltaic inverter; Port 1 of Db and Port 2 of Dd are connected to the DC bus BUS- of the photovoltaic inverter. Ports 2 of resistors R1 and R2 are interconnected and then connected to the photovoltaic inverter's ground terminal PE. Port 2 of Da and Port 2 of Db are interconnected and then connected to Port 4 of switch K1. Port 1 of Dc and Port 1 of Dd are interconnected and then connected to Port 4 of switch K3. Port 3 of switch K1 is connected to the photovoltaic inverter's ground terminal PE via switch K4 and resistor R1. Port 3 of switch K3 is connected to the photovoltaic inverter's ground terminal PE via switch K2 and resistor R2. Port 3 of switching device K1 is connected to the negative terminal (-) of controllable DC power supply LPS1 via terminal 3 of switching device K6. Port 3 of switching device K3 is connected to the positive terminal (+) of controllable DC power supply LPS1 via terminal 6 of switching device K6. A dedicated detection circuit is required to detect the inverter's DC bus voltage V2; DC bus BUS+ to PE voltage V1; DC bus BUS- to ground voltage V3; and controllable DC power supply LPS1 output voltage V4. The inverter controller analyzes the current operating stage and inverter user settings to configure different switching device (K1, K2, K3, K4, K5, K6) turn-on and turn-off logic, enabling functions such as inverter ISO insulation resistance detection, PID repair, and nighttime power supply.

[0051] In the circuit topology described above, the unidirectional conducting devices Da, Db, Dc, and Dd use high-voltage diodes or diodes connected in series, and the switching devices K1, K2, K3, K4, K5, and K6 use high-voltage reed relays. Therefore, Figure 8 The circuit topology described above.

[0052] In the circuit topology described above, the unidirectional conducting devices Da, Db, Dc, and Dd use relays Ka, Kb, Kc, and Kd, respectively, to achieve unidirectional conduction characteristics based on software logic control. The switching devices K1, K2, K3, K4, K5, and K6 still use high-voltage reed relays. Therefore, Figure 9 The circuit topology described above.

[0053] Figure 1 The specific methods for implementing inverter ISO insulation resistance detection, PID repair, and nighttime power supply functions in the circuit shown are as follows:

[0054] 1) Method for implementing ISO testing functions

[0055] When the inverter is powered on, an ISO insulation resistance test needs to be performed before operation. During this time, all contacts of the switching device K6 remain open. Figure 2 As shown, Figure 2 The voltage at point A shown is greater than that at BUS-. Figure 2 The voltage at point B shown is less than BUS+, and the unidirectional conducting devices Db and Dc are in the off state. Therefore, when the circuit operates in ISO insulation resistance detection mode, the simplified circuit is as follows: Figure 3 As shown.

[0056] The ISO insulation testing function is implemented as follows:

[0057] Step 1: The inverter controller turns on switching devices K1 and K4, and turns off switching devices K2 and K3. At this time, the bus voltage V2 is detected and recorded as V. bus The insulation voltage between the BUS and PE is V1, denoted as V. b The input voltage of each PV channel is denoted as V. pv1 V pv2 ,……,V pvn According to Kirchhoff's laws, the following relationship can be derived:

[0058]

[0059] In the formula R x1 R x2 ... R xn R represents the insulation resistance between the positive output terminals PV1+, PV2+, ..., PVn+ of the n photovoltaic cells and the ground terminal PE of the photovoltaic inverter. z This indicates the insulation resistance between the negative output terminal PV- of the photovoltaic cell or the DC bus BUS- port of the photovoltaic inverter and the grounding terminal PE of the photovoltaic inverter.

[0060] Step 2: The inverter controller turns on switching devices K1 and K4, and also turns on switching devices K2 and K3. At this time, the bus voltage V2 should remain unchanged and still be recorded as V. bus The insulation voltage V1 between the BUS and PE is denoted as V. c The voltage of each PV input channel is denoted as V. pv1 V pv2 ,……,V pvn According to Kirchhoff's laws, the following relationship can be derived:

[0061]

[0062] Step 3: Disconnect all switching devices. The inverter controller will then detect the V... b V c The insulation impedance is calculated based on voltage, and the calculation method is as follows:

[0063] When designing the circuit, R1 = R2. Based on equations (1) and (2), we obtain the following equation (3):

[0064]

[0065] The insulation resistance G can be derived from equation (3). x The expression is shown in equation (4) below.

[0066]

[0067] (ii) PID compensation function implementation method

[0068] When the inverter needs to implement PID repair, all switching devices K1, K2, K3, K4, K5, and K6 should be disconnected before compensation. The inverter controller can configure the user-set inverter parameters: compensation voltage direction, compensation bias voltage magnitude V. ref The inverter controller controls the switching devices and the output voltage V4 of the controllable DC power supply LPS1.

[0069] When the compensation voltage direction is set to PV-forward bias, a positive voltage needs to be applied between BUS- and PE. Therefore, the inverter controller needs to first turn on switching devices K3 and K4, and turn off switching devices K1 and K2, then turn on switching device K6, and finally control the DC power supply LPS1 to output the set compensation bias voltage V. ref At this time, the unidirectional conducting device Dc is in the off state, and the switching devices K1 and K2 are in the open state. The simplified circuit is as follows: Figure 4 As shown, the dashed arrow represents the circuit's operating current loop, meaning that a positive voltage V4 is added between BUS- and PE to achieve PID repair.

[0070] When the compensation voltage direction is set to PV+ negative bias, a negative voltage needs to be added between BUS+ and PE. Therefore, the inverter controller needs to first turn on switching devices K1 and K2, and turn off switching devices K3 and K4, then turn on switching device K6, and finally control the DC power supply LPS1 to output the set compensation bias voltage V. ref At this time, the unidirectional conducting device Db is in the off state, and switches K3 and K4 are in the open state. The simplified circuit is as follows: Figure 5 As shown, the dashed arrow represents the circuit's operating current loop, meaning that a negative voltage V4 is added between BUS+ and PE to achieve PID repair.

[0071] (III) Methods for Implementing Nighttime Power Supply Function

[0072] When the photovoltaic inverter is operating at night, the photovoltaic panels cannot supply DC power to the inverter, and the inverter controller cannot operate at night. In this case, it is necessary to first close switching devices K6, K1, and K3, and open switching devices K4 and K2. Then, use the external power supply LPS1 to output the required DC voltage V4 to charge the inverter's DC bus, thereby enabling the inverter controller to operate in SVG reactive power compensation mode. After the inverter starts operating, all switching devices are disconnected, and the circuit provided by this invention is in standby mode. When the circuit provided by this invention is operating in this mode, unidirectional conducting devices Db and Dc are in the ON state, Da and Dd are in the OFF state, and switching devices K4 and K2 are in the OFF state. The simplified circuit is as follows: Figure 6 As shown, the dashed arrow represents the circuit's operating current loop, meaning the circuit adds a negative voltage V4 between BUS+ and BUS- to provide power at night.

[0073] Figure 1 In the scheme shown, the unidirectional conduction device can achieve its unidirectional conduction characteristic by using a switching device controlled by an inverter controller. That is, as... Figure 7 , Figure 9 In this context, the unidirectional conduction switch can be replaced with a switching device, and its on / off characteristics can be controlled accordingly in the logic described above to achieve switching between different functions. For example... Figure 7 As shown, the unidirectional conducting devices Da, Db, Dc, and Dd are replaced by switching devices Ka, Kb, Kc, and Kd.

Claims

1. A multi-functional circuit for inverter set ISO detection, PID repair, and night power supply, characterized in that, The circuit topology of the multifunctional circuit comprises a unidirectional conducting device one, a unidirectional conducting device two, a unidirectional conducting device three, a unidirectional conducting device four, and a switching device six with two pairs of ports, one pair of ports of the switching device six is defined as port one and port two, and the other pair of ports of the switching device six is defined as port three and port four; The current inflow end of the unidirectional conducting device one and the current outflow end of the unidirectional conducting device three are connected to the photovoltaic inverter DC bus BUS+ port; the current inflow end of the unidirectional conducting device two and the current outflow end of the unidirectional conducting device four are connected to the photovoltaic inverter DC bus BUS- port; The current outflow end of the unidirectional conducting device one and the current outflow end of the unidirectional conducting device two are connected to one end of the switching device one; the other end of the switching device one is connected to port two of the switching device six and one end of the switching device four; port one of the switching device six is connected to the negative end of the controllable DC power supply; the other end of the switching device four is connected to one end of the resistor device R1; The current inflow end of the unidirectional conducting device three and the current inflow end of the unidirectional conducting device four are connected to one end of the switching device three; the other end of the switching device three is connected to port four of the switching device six and one end of the switching device two; port three of the switching device six is connected to the positive end of the controllable DC power supply; the other end of the switching device two is connected to one end of the resistor device R2; The other end of the resistor device R1 and the other end of the resistor device R2 are connected to the photovoltaic inverter ground PE.

2. The multi-functional circuit for an inverter as described in claim 1, integrating ISO detection, PID repair, and nighttime power supply, is characterized in that... It also includes a detection circuit for detecting the DC bus voltage V2 of the photovoltaic inverter, the voltage V1 between the photovoltaic inverter DC bus BUS+ port and the photovoltaic inverter ground PE, the voltage V3 between the photovoltaic inverter DC bus BUS- port and the photovoltaic inverter ground PE, and the output voltage V4 of the controllable DC power supply.

3. The multi-functional circuit for an inverter as described in claim 1, integrating ISO detection, PID repair, and nighttime power supply, is characterized in that... The unidirectional conducting device one, the unidirectional conducting device two, the unidirectional conducting device three, and the unidirectional conducting device four are switching devices controlled by the photovoltaic inverter controller.

4. The multi-functional circuit for an inverter as described in claim 1, integrating ISO detection, PID repair, and nighttime power supply, is characterized in that... The unidirectional conducting device one, the unidirectional conducting device two, the unidirectional conducting device three, the unidirectional conducting device four, the switching device one, the switching device two, the switching device three, the switching device four, the switching device six, the resistor device R1, and the resistor device R2 are single devices or device groups composed of multiple single devices.

5. The multi-functional circuit for an inverter as described in claim 1, integrating ISO detection, PID repair, and nighttime power supply, is characterized in that... The switching device one, the switching device two, the switching device three, the switching device four, and the switching device six are high-voltage dry reed relays.

6. The multi-functional circuit for an inverter as described in claim 1, integrating ISO detection, PID repair, and nighttime power supply, is characterized in that... The unidirectional conducting device one, the unidirectional conducting device two, the unidirectional conducting device three, and the unidirectional conducting device four are high-voltage diodes or diode strings in series.

7. The multi-functional circuit for an inverter as described in claim 1, integrating ISO detection, PID repair, and nighttime power supply, is characterized in that... The unidirectional conducting device one, the unidirectional conducting device two, the unidirectional conducting device three, and the unidirectional conducting device four are relays.

8. A method for implementing the ISO detection function of a photovoltaic inverter by a multifunctional circuit with ISO detection, PID repair, and night power supply according to claim 1, characterized in that, The switching device six is in an open state, and each pair of ports is not connected, the unidirectional conducting device two and the unidirectional conducting device three work in a cut-off state, comprising the following steps: First step: the switching device one and the switching device four are turned on by the photovoltaic inverter controller, and the switching device two and the switching device three are turned off, at this time: Let the detected DC bus voltage V2 of the photovoltaic inverter be denoted as V bus ; let the detected photovoltaic inverter DC bus BUS-port-to-photovoltaic inverter ground PE voltage V1 be denoted as V b , the voltage of n-path photovoltaic cell input be denoted as V pv1 , pv2 , ……, V pvn , then there is: wherein R x1 , R x2 , …, R xn respectively represent the insulation impedance between the positive output terminals PV1+, PV2+, …, PVn+ of the n photovoltaic cells and the ground terminal PE of the photovoltaic inverter, R z represents the insulation impedance between the negative output terminal PV- of the photovoltaic cell or the DC bus BUS- port of the photovoltaic inverter and the ground terminal PE of the photovoltaic inverter; Second step: the photovoltaic inverter controller controls the switch device one and the switch device four to be on, and the switch device two and the switch device three are also on, at this time, the detected photovoltaic inverter DC bus voltage V2 remains unchanged, still V bus ; the detected photovoltaic inverter DC bus BUS-port-to-photovoltaic inverter ground PE voltage V1 is recorded as V c , then: Third step: the photovoltaic inverter controller disconnects the switching device one, the switching device two, the switching device three, the switching device four, the switching device six, and the photovoltaic inverter controller disconnects the switching device five according to the detected V b , V c The insulation impedance G x is calculated as shown in the following formula: When designing the inverter set ISO detection, PID repair, night power supply multifunctional circuit as claimed in claim 1, R1=R2.

9. The method for realizing the PID compensation function of the multi-functional circuit of the ISO detection, PID repair and night power supply of the inverter set according to claim 1, characterized in that, The method comprises the following steps: The first switch device, the second switch device, the third switch device, the fourth switch device and the sixth switch device are kept off; When the compensation voltage direction is set as PV- positive bias, PV- is the negative electrode of the photovoltaic cell: Step 101, the light inverter controller controls the third switch device and the fourth switch device to be on, and the first switch device and the second switch device to be off; Step 102, the sixth switch device is closed, so that the two pairs of ports of the sixth switch device are on; Step 103, control the controllable DC power supply to output a compensation bias voltage V ref At this time, the unidirectional conducting device works in the off state, the switch device one and the switch device two work in the off state, and a positive voltage V4 is added between the photovoltaic inverter DC bus BUS-port and the photovoltaic inverter ground PE to achieve the PID repair effect. When the compensation voltage direction is set as PV+ negative bias, PV+ is the positive electrode of the photovoltaic cell: Step 201, the light inverter controller controls the first switch device and the second switch device to be on, and the third switch device and the fourth switch device to be off; Step 202, the sixth switch device is closed, so that the two pairs of ports of the sixth switch device are on; Step 203, control the controllable direct current power supply to output a compensation bias voltage V ref At this time, the unidirectional conducting device two works in the cutoff state, the switch device three and the switch device four work in the open state, and a negative voltage V4 is added between the photovoltaic inverter DC bus BUS+ port and the photovoltaic inverter ground PE to achieve the PID repair effect.

10. A method for implementing night power supply function by the multi-functional circuit of claim 1, wherein the ISO detection, PID repair and night power supply of the inverter set, characterized in that, The method comprises the following steps: Step 301, the sixth switch device is closed, so that the two pairs of ports of the sixth switch device are on, the first switch device and the third switch device are closed, and the fourth switch device and the second switch device are off; Step 302, the required DC voltage V4 is output by using the controllable DC power supply, the photovoltaic inverter DC bus is charged, and then the photovoltaic inverter controller works in the SVG reactive power compensation state; Step 303, after the photovoltaic inverter controller works, the first switch device, the second switch device, the third switch device, the fourth switch device and the sixth switch device are disconnected, and the multifunctional circuit is in standby state, at this time, the second unidirectional conduction device and the third unidirectional conduction device are in the on state, the first unidirectional conduction device and the fourth unidirectional conduction device are in the off state, and the fourth switch device and the second switch device are in the off state, a negative voltage V4 is added between the photovoltaic inverter DC bus BUS+ port and the photovoltaic inverter DC bus BUS- port, so as to achieve the night power supply effect.

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