Photovoltaic inverter insulation resistance detection circuit and photovoltaic system

Abstract

The utility model provides a photovoltaic inverter insulation resistance detection circuit and a photovoltaic system. The photovoltaic inverter insulation resistance detection circuit comprises a positive detection circuit and a negative detection circuit. The input end of the positive detection circuit is connected with a bus anode BUS +; the input end of the negative detection circuit is connected with a bus cathode BUS-; the output ends of the positive detection circuit and the negative detection circuit are grounded; the positive detection circuit comprises a first sampling resistor, a first relay, a first leakage current adjusting resistor, a second relay and a second leakage current adjusting resistor; the negative detection circuit comprises a second sampling resistor, a third relay, a third leakage current adjusting resistor, a fourth relay and a fourth leakage current adjusting resistor; wherein the leakage current adjusting resistor is connected in parallel with the corresponding relay. The detection circuit in the application comprises two relays, the contact distance meets the safety standard, and the system safety is improved. The relay is connected in parallel with the leakage current adjusting resistor, thereby preventing detection failure caused by faults of any relay in the positive and negative detection circuits, ensuring timely discovery of insulation problems, and avoiding fault expansion.

Description

TECHNICAL FIELD

[0001] The utility model relates to photovoltaic power generation technical field especially, it relates to a kind of photovoltaic inverter insulation impedance detection circuit and photovoltaic system. BACKGROUND

[0002] In modern power electronic energy equipment field, especially photovoltaic inverter and energy storage inverter, ground insulation impedance detection module has extremely key position, and it belongs to safety regulation circuit module.

[0003] Taking photovoltaic inverter as an example, its operation process involves strict safety detection link.When photovoltaic inverter detects the input voltage of battery panel and the output voltage of power grid reach operation requirement, only then consider entering grid-connected stage.However, before grid connection, to ensure compliance with safety regulation requirements, the insulation impedance between the primary live circuit of photovoltaic inverter and inverter housing (housing connects ground) must be accurately detected.Only when the insulation impedance meets the established requirement, inverter can start inverting procedure, and output power realizes grid-connected operation.The core significance of this detection process is to ensure the electrical safety of personnel accessible area on inverter, to prevent electric shock and other safety accidents caused by insulation failure.If fault occurs in the detection process of current photovoltaic inverter insulation impedance detection circuit, it may cause detection failure, so it is necessary to improve the stability of detection circuit. SUMMARY

[0004] The utility model provides a kind of photovoltaic inverter insulation impedance detection circuit to solve how the problem of improving the stability of inverter insulation impedance detection circuit.

[0005] Firstly, the utility model provides a kind of photovoltaic inverter insulation impedance detection circuit, comprising: positive detection circuit and negative detection circuit;

[0006] The input end of the positive detection circuit is connected with bus positive pole BUS+;The input end of the negative detection circuit is connected with bus negative pole BUS-;The output end of the positive detection circuit and the negative detection circuit is grounded;

[0007] The positive detection circuit includes first sampling resistor, first relay, first leakage current adjusting resistor, second relay and second leakage current adjusting resistor;The negative detection circuit includes second sampling resistor, third relay, third leakage current adjusting resistor, fourth relay and fourth leakage current adjusting resistor;Wherein, leakage current adjusting resistor is connected in parallel with corresponding relay.

[0008] Secondly, the utility model provides a kind of photovoltaic system, comprising: photovoltaic assembly, DC / DC converter, DC / AC inverter, control circuit and the photovoltaic inverter insulation impedance detection circuit of the first aspect or any implementation manner of the first aspect.

[0009] The photovoltaic assembly, the DC / DC converter and the DC / AC inverter are connected in sequence.

[0010] The DC / AC inverter comprises a positive output end and a negative output end; the positive output end is connected with the input end of the positive detection circuit; and the negative output end is connected with the input end of the negative detection circuit.

[0011] The control circuit is connected with the photovoltaic inverter insulation impedance detection circuit, and is used for controlling the on-off of the first relay and the second relay.

[0012] In a possible implementation, the control circuit is connected with the DC / AC inverter, and is used for controlling the DC / AC inverter to enter a protection mode when detecting an abnormal leakage current.

[0013] The utility model provides a photovoltaic inverter insulation impedance detection circuit and photovoltaic system, and this detection circuit is constituted by positive detection circuit and negative detection circuit. The input end of positive detection circuit is connected with bus positive pole BUS+, and the input end of negative detection circuit is connected with bus negative pole BUS-, and the output end of positive detection circuit and negative detection circuit is all grounded. The two detection circuits are symmetrical in structure, and include sampling resistance, two relays and two leakage current adjusting resistance. The leakage current adjusting resistance is connected in parallel at the two ends of relay. In the detection process, the impedance of BUS+ and BUS- relative to the ground can be changed by controlling the on-off state of relay, and then leakage current is measured. The insulation impedance value calculated according to Ohm's law is compared with the preset threshold value to judge whether there is a problem of insulation performance decline. The positive detection circuit and negative detection circuit in the application are equipped with two relays, and the contact spacing conforms to the safety specification, thereby enhancing the safety of the system. In addition, the leakage current adjusting resistance is connected in parallel with each relay, which can prevent any relay in the positive and negative detection circuits from causing detection failure due to failure, improve the stability of detection effect, and ensure that the problem of insulation performance decline can be found in time. Once the insulation performance decline is detected, the system will control the inverter to enter the protection mode and prohibit starting, thereby preventing further expansion of the fault. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical scheme in the embodiments of the utility model, the following will briefly introduce the drawings needed to be used in the embodiments or prior art description, and obviously, the drawings in the following description are only some embodiments of the utility model, and for those skilled in the art, other drawings can also be obtained according to these drawings without paying the creative labor.

[0015] Figure 1It is the structure schematic view of the photovoltaic inverter insulation impedance detection circuit provided by an embodiment of the utility model.

[0016] Figure 2 It is the structure schematic view of the photovoltaic inverter insulation impedance detection circuit provided by another embodiment of the utility model.

[0017] Figure 3 It is the structure schematic view of the photovoltaic inverter insulation impedance detection circuit provided by another embodiment of the utility model.

[0018] Figure 4 It is the structure schematic view of the photovoltaic inverter insulation impedance detection circuit provided by another embodiment of the utility model.

[0019] Figure 5 It is the structure schematic view of the photovoltaic inverter insulation impedance detection circuit provided by another embodiment of the utility model.

[0020] Figure 6 It is the structure schematic view of the photovoltaic system provided by an embodiment of the utility model. Specific embodiments

[0021] In order to make the personnel in the technical field better understand the scheme, the technical solutions in the scheme embodiments will be clearly described below in combination with the drawings in the scheme embodiments. Obviously, the described embodiments are part of the embodiments of the scheme, rather than all the embodiments. Based on the embodiments in the scheme, all other embodiments obtained by the person skilled in the art without creative labor should belong to the protection scope of the scheme.

[0022] The term "includes" and other any variants in the specification and claims of the scheme and the above-mentioned drawings means "includes but is not limited to", and is intended to cover the non-exclusive inclusion, and is not limited to the examples listed in the text. In addition, the terms "first" and "second" are used to distinguish different objects, rather than to describe a specific order.

[0023] The implementation of the utility model will be described in detail below in combination with specific drawings:

[0024] Figure 1 It is the structure schematic view of the photovoltaic inverter insulation impedance detection circuit provided by an embodiment of the utility model. Referring to Figure 1 The photovoltaic inverter insulation impedance detection circuit comprises a positive detection circuit and a negative detection circuit.

[0025] The input end of the positive detection circuit is connected with the positive bus BUS+, and the input end of the negative detection circuit is connected with the negative bus BUS-; the output ends of the positive detection circuit and the negative detection circuit are grounded.

[0026] The positive detection circuit comprises a first sampling resistor R1, a first relay RLY1, a first leakage current adjusting resistor R1', a second relay RLY2 and a second leakage current adjusting resistor R2'; the negative detection circuit comprises a second sampling resistor R2, a third relay RLY3, a third leakage current adjusting resistor R3', a fourth relay RLY4 and a fourth leakage current adjusting resistor R4'; wherein the leakage current adjusting resistor is connected in parallel with the corresponding relay.

[0027] As shown in Figure 1 , the first leakage current adjusting resistor R1' is connected in parallel with the first relay RLY1, the second leakage current adjusting resistor R2' is connected in parallel with the second relay RLY2, the third leakage current adjusting resistor R3' is connected in parallel with the third relay RLY3, and the fourth leakage current adjusting resistor R4' is connected in parallel with the fourth relay RLY4.

[0028] In the specific implementation process, before the inverter starts, a voltage is applied to the ground through BUS+ and BUS- on the DC side, and the leakage current is measured by changing the impedance of BUS+ to ground and BUS- to ground through the relay attraction. According to Ohm's law, the insulation impedance value can be calculated, and if it is lower than the set threshold, the inverter enters the protection mode, which prohibits starting and sends an alarm. After the inverter starts, the AC component on the AC side is collected during system operation, and the average value of the AC component is calculated. If it is lower than the set threshold, the inverter enters the protection mode.

[0029] As shown in Figure 1 , when the relay is closed, the leakage current adjusting resistor is short-circuited, and when the relay is opened, the leakage current adjusting resistor is short-circuited. The leakage current adjusting resistor is connected to the circuit, so as to measure the leakage current by changing the impedance of BUS+ to ground and BUS- to ground through the relay attraction. The positive detection circuit and the negative detection circuit each comprise two relays, the second relay RLY2 and the first relay RLY1 form a redundant backup, and the fourth relay RLY4 and the third relay RLY3 form a redundant backup. When any one of the first relay RLY1 or the second relay RLY2 has a sticking fault, the other relay can be engaged, and when any one of the third relay RLY3 or the fourth relay RLY4 has a sticking fault, the other relay can be engaged, thereby adjusting the impedance between BUS+ and ground and BUS- and ground to detect the leakage current. This mechanism can identify potential insulation problems in the circuit in a timely manner, ensuring that the photovoltaic inverter can operate stably and safely even under complex working conditions. This significantly improves the fault tolerance performance and reliability of the entire system, providing a solid guarantee for efficient conversion and stable transmission of photovoltaic energy.

[0030] The insulation impedance detection circuit of this photovoltaic inverter enables 24 / 7 monitoring before and after inverter startup, allowing for real-time detection of potential problems and timely identification of reduced insulation performance, thus preventing further escalation of faults. It reduces false alarms and unnecessary downtime, avoids erroneous alarms caused by environmental fluctuations, and ensures stable system operation. Furthermore, it helps extend equipment lifespan, reduce maintenance costs, and improve the overall efficiency and reliability of the power generation system.

[0031] This invention provides an insulation impedance detection circuit for a photovoltaic inverter and a photovoltaic system. The detection circuit consists of a positive detection circuit and a negative detection circuit. The input terminal of the positive detection circuit is connected to the positive bus BUS+, while the input terminal of the negative detection circuit is connected to the negative bus BUS-. The output terminals of both the positive and negative detection circuits are grounded. These two detection circuits are structurally symmetrical, each including a sampling resistor, two relays, and two leakage current regulating resistors. The leakage current regulating resistors are connected in parallel across the two ends of the relays. During the detection process, by controlling the on / off state of the relays, the impedance of BUS+ and BUS- relative to ground can be changed, thereby measuring the leakage current. The insulation impedance value calculated according to Ohm's law is compared with a preset threshold to determine whether there is a problem with decreased insulation performance. Both the positive and negative detection circuits in this application are equipped with two relays, and their contact spacing complies with safety specifications, thereby enhancing system safety. Furthermore, each relay is connected in parallel with a leakage current regulating resistor, which prevents detection failure due to a fault in either the positive or negative detection circuit, improves the stability of the detection effect, and ensures timely detection of insulation performance degradation. Once a decrease in insulation performance is detected, the system will control the inverter to enter protection mode, prohibiting startup and thus preventing the fault from escalating further.

[0032] In different embodiments, the structures of the first relay RLY1, the second relay RLY2, the third relay RLY3, and the fourth relay RLY4 are different, as shown below. Figure 1 and Figure 2 As shown.

[0033] In one possible implementation, such as Figure 1 As shown, each relay includes three contacts.

[0034] As in the above embodiment, a corresponding leakage current regulating resistor is connected in parallel between the second and third contacts of each relay. Furthermore, when the second and third contacts of each relay are connected, the corresponding leakage current regulating resistor is short-circuited; when the first and second contacts of each relay are connected, the corresponding leakage current regulating resistor is connected in series in the circuit.

[0035] The second contact of the first relay RLY1 is connected to the first sampling resistor; the third contact of the first relay RLY1 is connected to the third contact of the second relay RLY2.

[0036] The second contact of the third relay RLY3 is connected with the second sampling resistor; the third contact of the second relay RLY2 is connected with the third contact of the fourth relay RLY4.

[0037] In another possible implementation, as shown in FIG. 2, each relay includes six contacts. Among them, each relay is composed of two parts A and B. Figure 2

[0038] The second contact and the third contact of each relay are connected in parallel with the corresponding leakage current adjusting resistor; when the second contact and the third contact of each relay are connected, the corresponding leakage current adjusting resistor is short-circuited; when the first contact and the second contact of each relay are connected, the corresponding leakage current adjusting resistor is connected in series in the circuit; the second contact of the first relay RLY1 is connected with the first sampling resistor; the second contact of the third relay RLY3 is connected with the second sampling resistor;

[0039] The positive detection circuit further includes a fifth leakage current adjusting resistor R5' and a sixth leakage current adjusting resistor R6'; the negative detection circuit further includes a seventh leakage current adjusting resistor R7' and an eighth leakage current adjusting resistor R8'.

[0040] The fourth contact and the fifth contact of the first relay RLY1 are connected in parallel with the fifth leakage current adjusting resistor R5'; the fourth contact and the fifth contact of the second relay RLY2 are connected in parallel with the sixth leakage current adjusting resistor R6'; the third contact of the second relay RLY2 is connected with the fifth contact of the first relay RLY1; the second contact of the second relay RLY2 is connected with the fifth contact; the third contact and the fourth contact of the first relay RLY1 are connected;

[0041] The fourth contact and the fifth contact of the third relay RLY3 are connected in parallel with the seventh leakage current adjusting resistor R7'; the fourth contact and the fifth contact of the fourth relay RLY4 are connected in parallel with the eighth leakage current adjusting resistor R8'; the third contact of the fourth relay RLY4 is connected with the fifth contact of the third relay RLY3; the third contact and the fifth contact of the fourth relay RLY4 are connected.

[0042] In the embodiment, each relay adopts the structure of six contacts, compared with the structure of three contacts, the creepage distance between the contacts is further increased, and the phenomenon of creepage caused by too close distance is effectively avoided.

[0043] On the basis of the foregoing embodiment, in a possible implementation, the resistance values of the corresponding resistors in the positive detection circuit and the negative detection circuit are the same.

[0044] ​In the embodiment, when the system is well insulated, the electrical parameters (such as current and voltage) of the positive and negative detection circuits are symmetrical. By comparing the detection results of the positive and negative detection circuits, common-mode interference can be effectively eliminated. For example, electromagnetic interference in the external environment may affect the detection circuit, but the interference affects the positive and negative detection circuits to approximately the same extent. By comparing the differences between the two to calculate the insulation impedance, the influence of interference on the detection result can be reduced, thereby improving the accuracy of detection. On the other hand, by using the detection results of the two detection circuits to solve the equation, the insulation impedance value is calculated to determine whether the system has failed.

[0045] In a possible implementation, as shown in Figure 3 Each leakage current adjusting resistor includes a plurality of voltage dividing resistors connected in series.

[0046] In the implementation, first, the total resistance value range required is roughly estimated according to Ohm's law (I = U / R, where I is the current, U is the voltage, and R is the resistance) and the expected leakage current adjusting range. For example, when the power supply voltage is fixed at 5V, the total resistance Rtotal1 = U / I = 5V / 1u.A = 5M2 is calculated when the leakage current I = 1u.A, and Rtotal2 = 5V / 10u.A = 500k2 is calculated when the leakage current I = 10u.A.

[0047] In the embodiment, each leakage current adjusting resistor includes a plurality of voltage dividing resistors connected in series

[0048] In a possible implementation, as shown in Figure 4 Each sampling resistor includes a plurality of voltage dividing resistors connected in series.

[0049] Taking two resistors as an example, there are resistors R1 and R2. First, R1 and R2 are connected end to end to form a series combination, and the equivalent resistance of the series combination is assumed to be Rseries = R1 × R2. Then the series combination is connected in parallel with an external circuit, which means that the voltage across the series combination is equal to the voltage across the other branch connected in parallel. From the circuit connection, the current is divided into two paths at the parallel node, one path flows through the series resistor combination, and the other path flows through the other branch connected in parallel. Inside the series resistor combination, the current first flows through R1 and then flows through R2. According to the characteristic that the current is equal everywhere in a series circuit, the currents through R1 and R2 are the same. In terms of voltage distribution, there is voltage division inside the series resistor combination.

[0050] Therefore, when the load current of other parts of the circuit instantaneously increases, causing the power supply voltage to drop slightly, the voltage drop across the series voltage dividing circuit is much smaller than that of other circuits directly connected to the power supply without voltage dividing stabilization measures. This helps maintain the normal operation of subsequent circuit modules (such as signal acquisition circuits, control circuits, etc.) connected to it, avoiding misoperation or performance degradation caused by voltage fluctuations.

[0051] In this embodiment, the structure of the series voltage dividing resistor in parallel with the external circuit has good compatibility and can be easily connected with various circuit modules of different functions. The flexibility of the circuit structure facilitates expansion, and the number and parameters of the series voltage dividing resistors can be increased or adjusted according to actual needs. If more different levels of voltage division are required, other resistors can be further connected in series based on the existing series combination, or the resistance value of the voltage dividing resistor can be adjusted to achieve more accurate voltage division. The scalability of this circuit enables it to adapt to the changing technical requirements and application scenarios, providing convenient conditions for the upgrading and optimization of circuit systems.

[0052] In one possible implementation, as shown in Figure 5 each voltage dividing resistor is connected in parallel with one or more backup resistors.

[0053] When each voltage dividing resistor is connected in parallel with one or more backup resistors, a layer of redundancy protection is added to the circuit. Under normal circumstances, when a voltage dividing resistor is connected in parallel with a backup resistor, the voltage dividing resistor has little effect on the operation of the voltage dividing circuit. This is because the characteristics of parallel resistors make the equivalent resistance after parallel connection similar to that when they exist alone, so the voltage division value can be maintained near the designed value. However, if the voltage dividing resistor fails due to some reason, the parallel backup resistor will start working at this time. Although the equivalent resistance after parallel connection changes, it can still maintain a certain degree of voltage division function, preventing the entire voltage dividing circuit from failing due to voltage dividing resistor failure, thereby ensuring that the subsequent circuit modules connected to it can continue to operate.

[0054] In this embodiment, each voltage dividing resistor is connected in parallel with one or more resistors, which can improve system stability.

[0055] In one possible implementation, it further includes a bus support capacitor connected in parallel between BUS+ and BUS-.

[0056] The bus support capacitor is connected in parallel between BUS+ and BUS-, stabilizing the voltage, suppressing fluctuations, improving electromagnetic compatibility, and reducing the probability of failure. It quickly responds to load changes, enhances circuit transient performance, reduces startup time, and protects components from high voltage damage. The capacitor can also limit voltage spikes, protect circuit components, extend life, reduce maintenance costs, and improve system stability and reliability.

[0057] In a possible implementation, the positive detection circuit and the ground end are further connected in parallel with a first impedance; and the negative detection circuit and the ground end are further connected in parallel with a second impedance.

[0058] In the embodiment, the first impedance and the second impedance guarantee that the system reaches the best detection performance and circuit stability, and ensure that the entire circuit system can accurately monitor the relevant voltage, current or signal parameters, and provide reliable data support for subsequent control and processing links.

[0059] Figure 6 is a structural schematic diagram of a photovoltaic system according to an embodiment of the present application. The present application provides a photovoltaic system, comprising: a photovoltaic module PV, a DC / DC converter, a DC / AC inverter, a control circuit (not shown in the figure) and the photovoltaic inverter insulation impedance detection circuit provided by any one of the preceding embodiments.

[0060] The photovoltaic module PV, the DC / DC converter and the DC / AC inverter are connected in sequence.

[0061] The DC / AC inverter comprises a positive output end and a negative output end; the positive output end is connected with the input end of the positive detection circuit; and the negative output end is connected with the input end of the negative detection circuit.

[0062] The control circuit is connected with the photovoltaic inverter insulation impedance detection circuit, and is used for controlling the on-off of the first relay RLY1 and the second relay RLY2.

[0063] In a possible implementation, the control circuit is connected with the DC / AC inverter, and is used for controlling the DC / AC inverter to enter a protection mode when detecting an abnormal leakage current.

[0064] Specifically, the control circuit controls the relay to be attracted when starting, to be disconnected during the measurement process, and to be attracted again after the measurement.

[0065] The above embodiments are only used to illustrate the technical solutions of the present application, but not to limit the same; although the present application has been described in detail with reference to the foregoing embodiments, it should be understood by those skilled in the art that the technical solutions recorded in the foregoing embodiments can be modified, or some technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the present application.

Claims

1. A photovoltaic inverter insulation impedance detection circuit, characterized by, Comprising: positive detection circuit and negative detection circuit; the input end of the positive detection circuit is connected with the positive bus BUS+; the input end of the negative detection circuit is connected with the negative bus BUS-; the output end of the positive detection circuit and the negative detection circuit is grounded; the positive detection circuit comprises a first sampling resistor, a first relay, a first leakage current adjusting resistor, a second relay and a second leakage current adjusting resistor; the negative detection circuit comprises a second sampling resistor, a third relay, a third leakage current adjusting resistor, a fourth relay and a fourth leakage current adjusting resistor; wherein the leakage current adjusting resistor is connected in parallel with the corresponding relay.

2. The photovoltaic inverter insulation impedance detection circuit of claim 1, wherein, Each relay comprises three contacts; the second contact and the third contact of each relay are connected in parallel with the corresponding leakage current adjusting resistor; when the second contact and the third contact of each relay are connected, the corresponding leakage current adjusting resistor is short-circuited; when the first contact and the second contact of each relay are connected, the corresponding leakage current adjusting resistor is connected in series in the circuit; the second contact of the first relay is connected with the first sampling resistor; the third contact of the first relay is connected with the third contact of the second relay; the second contact of the third relay is connected with the second sampling resistor; the third contact of the second relay is connected with the third contact of the fourth relay.

3. The photovoltaic inverter insulation impedance detection circuit of claim 1, wherein, Each relay comprises six contacts; the second contact and the third contact of each relay are connected in parallel with the corresponding leakage current adjusting resistor; when the second contact and the third contact of each relay are connected, the corresponding leakage current adjusting resistor is short-circuited; when the first contact and the second contact of each relay are connected, the corresponding leakage current adjusting resistor is connected in series in the circuit; the second contact of the first relay is connected with the first sampling resistor; the second contact of the third relay is connected with the second sampling resistor; the positive detection circuit further comprises a fifth leakage current adjusting resistor and a sixth leakage current adjusting resistor; the negative detection circuit further comprises a seventh leakage current adjusting resistor and an eighth leakage current adjusting resistor; the fourth contact and the fifth contact of the first relay are connected in parallel with the fifth leakage current adjusting resistor; the fourth contact and the fifth contact of the second relay are connected in parallel with the sixth leakage current adjusting resistor; the third contact of the second relay is connected with the fifth contact of the first relay; the second contact of the second relay is connected with the fifth contact; the third contact and the fourth contact of the first relay are connected; the fourth contact and the fifth contact of the third relay are connected in parallel with the seventh leakage current adjusting resistor; the fourth contact and the fifth contact of the fourth relay are connected in parallel with the eighth leakage current adjusting resistor; the third contact of the fourth relay is connected with the fifth contact of the third relay; the third contact and the fifth contact of the fourth relay are connected.

4. The photovoltaic inverter insulation impedance detection circuit of claim 1 or 3, wherein, Each leakage current adjusting resistor comprises a plurality of voltage dividing resistors connected in series; wherein each voltage dividing resistor is connected in parallel with one or more resistors.

5. The photovoltaic inverter insulation impedance detection circuit of claim 1 or 3, wherein, Each sampling resistor comprises a plurality of voltage dividing resistors connected in series; wherein each voltage dividing resistor is connected in parallel with one or more resistors.

6. The photovoltaic inverter insulation impedance detection circuit of claim 1, wherein, Further comprising a bus support capacitor connected in parallel between the BUS+ and the BUS-.

7. The photovoltaic inverter insulation impedance detection circuit of claim 1, wherein, The positive detection circuit and the ground end are also connected in parallel with a first impedance; the negative detection circuit and the ground end are also connected in parallel with a second impedance.

8. A photovoltaic system characterized by, The application relates to a photovoltaic inverter insulation impedance detection circuit. The photovoltaic component, the DC / DC converter and the DC / AC inverter are sequentially connected. The DC / AC inverter comprises a positive output end and a negative output end; the positive output end is connected with the input end of the positive detection circuit; the negative output end is connected with the input end of the negative detection circuit. The control circuit is connected with the photovoltaic inverter insulation impedance detection circuit, and is used for controlling the on-off of the first relay and the second relay. The control circuit is connected with the DC / AC inverter, and is used for controlling the DC / AC inverter to enter a protection mode when detecting an abnormal leakage current.

9. The photovoltaic system of claim 8, wherein, ​

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