Direct current impedance detection circuit of photovoltaic system and photovoltaic system

Abstract

The utility model relates to a DC impedance detection circuit of a photovoltaic system and the photovoltaic system, and the DC impedance detection circuit is provided with an insulation impedance circuit and an inversion controller, the first end of the insulation impedance circuit is connected with a bus of the photovoltaic system, and the second end of the insulation impedance circuit is connected with a ground end. The inverter controller is connected with control ends of each photovoltaic unit circuit and the insulation impedance circuit in the photovoltaic system, when the insulation impedance circuit is in a first state, the ground end and the positive electrode end of the bus are conducted to form a first loop, and when the insulation impedance circuit is in a second state, the ground end and the negative electrode end of the bus are conducted to form a second loop. The inverter controller is used for controlling the state of the insulation impedance circuit and determining the insulation impedance of the photovoltaic system according to the difference between the first current relation of the photovoltaic unit circuit in the first loop and the second current relation of the photovoltaic unit circuit in the second loop. And the convenience of direct-current impedance detection of the photovoltaic system is improved.

Description

Technical Field

[0001] The present application relates to the field of power electronics technology, and in particular to a direct current impedance detection circuit of a photovoltaic system and a photovoltaic system. Background Art

[0002] Clean energy applications represented by photovoltaic power generation and electrochemical energy storage systems are becoming more and more widespread. However, new energy photovoltaic systems are generally placed outdoors. Affected by weather factors such as dust, rain and snow, the insulation impedance to the ground on the DC side of the photovoltaic system will change.

[0003] When the insulation impedance on the DC side is too low, it is easy to cause electric shock hazard. Therefore, the insulation impedance of the photovoltaic system must be tested. Utility Model Content

[0004] Based on this, it is necessary to provide a simple and convenient DC impedance detection circuit for a photovoltaic system and a photovoltaic system.

[0005] In the first aspect, the present application provides a DC impedance detection circuit of a photovoltaic system, wherein the photovoltaic system includes a plurality of photovoltaic unit circuits; wherein the negative poles of each of the photovoltaic unit circuits are connected to each other, and the DC impedance detection circuit includes: an insulation impedance circuit, wherein the first end of the insulation impedance circuit is connected to the bus of the photovoltaic system, and the second end of the insulation impedance circuit is connected to the ground end, and when the insulation impedance circuit is in a first state, the ground end is connected to the positive end of the bus to form a first loop, and when the insulation impedance circuit is in a second state, the ground end is connected to the negative end of the bus to form a second loop; an inverter controller, respectively connected to the control end of each of the photovoltaic unit circuits and the insulation impedance circuit, for controlling the state of the insulation impedance circuit, and determining the insulation impedance of the photovoltaic system according to the difference between the first current relationship of the photovoltaic unit circuit in the first loop and the second current relationship of the photovoltaic unit circuit in the second loop.

[0006] In one embodiment, the insulation impedance circuit includes: a resistor, a first end of the resistor is connected to the ground; a switch component is respectively connected to the inverter controller, the positive end of the busbar of the photovoltaic system, the negative end of the busbar, and the second end of the resistor, wherein when the switch component conducts the path between the positive end of the busbar and the resistor, the insulation impedance circuit is in the first state; when the switch component conducts the path between the negative end of the busbar and the resistor, the insulation impedance circuit is in the second state.

[0007] In one embodiment, the switch component includes: a first relay and a second relay; wherein the control end of the first relay is connected to the inverter controller, the first end of the first relay is connected to the positive end of the bus, the second end of the first relay is respectively connected to the second end of the resistor and the second end of the second relay, the first end of the second relay is connected to the negative end of the bus, and the control end of the second relay is connected to the inverter controller.

[0008] In one embodiment, the switch component includes: a first switch tube and a second switch tube; wherein the control end of the first switch tube is connected to the inverter controller, the first end of the first switch tube is connected to the positive end of the bus, the second end of the first switch tube is respectively connected to the second end of the resistor and the second end of the second switch tube, the first end of the second switch tube is connected to the negative end of the bus, and the control end of the second switch tube is connected to the inverter controller.

[0009] In one embodiment, the insulation impedance circuit further includes: a third relay, wherein the third relay is connected in series in the path between the ground terminal and the switch component.

[0010] In one embodiment, the insulation impedance circuit further includes: an inductor, wherein the inductor is connected in series in a path between the ground terminal and the switch component.

[0011] In one embodiment, the insulation impedance includes branch insulation impedance; each of the photovoltaic unit circuits includes a plurality of parallel photovoltaic unit branches, and the DC impedance detection circuit also includes: a current detection circuit, which is respectively connected to the target pole of each of the photovoltaic unit branches, and is used to detect the branch current of the target pole of each of the photovoltaic unit branches; the inverter controller is also connected to the current detection circuit, and is used to control the DC side insulation impedance circuit to be in a target state and each of the branch currents satisfies the target current relationship, and determines that the branch insulation impedance of the target pole of the photovoltaic unit branch fails; wherein the target current relationship includes the relationship between the branch currents of each of the photovoltaic unit branches when the branch insulation impedance of the photovoltaic unit branch fails and each of the photovoltaic unit branches in the corresponding photovoltaic unit circuit forms a discharge circuit.

[0012] In one embodiment, the target pole of the photovoltaic unit branch is positive, and the target state is the second state; the target pole of the photovoltaic unit branch is negative, and the target state is the first state.

[0013] In one embodiment, the current detection circuit includes a plurality of current sensors; wherein at least one current sensor is correspondingly arranged for each photovoltaic unit branch.

[0014] In a second aspect, the present application further provides a photovoltaic system, comprising: a plurality of photovoltaic unit circuits and a DC impedance detection circuit of the photovoltaic system as described in any one of the embodiments of the present application; wherein the negative poles of each of the photovoltaic unit circuits are connected to each other.

[0015] The DC impedance detection circuit and photovoltaic system of the present application are provided by setting an insulation impedance circuit and an inverter controller, wherein the first end of the insulation impedance circuit is connected to the busbar of the photovoltaic system, the second end of the insulation impedance circuit is connected to the ground end, the inverter controller is respectively connected to each photovoltaic unit circuit and the control end of the insulation impedance circuit in the photovoltaic system, when the insulation impedance circuit is in the first state, the ground end is connected to the positive end of the busbar to form a first loop, when the insulation impedance circuit is in the second state, the ground end is connected to the negative end of the busbar to form a second loop, the inverter controller is used to control the state of the insulation impedance circuit, and determine the insulation impedance of the photovoltaic system according to the difference between the first current relationship of the photovoltaic unit circuit in the first loop and the second current relationship of the photovoltaic unit circuit in the second loop. The present application forms different conduction loops in the photovoltaic system by setting an insulation impedance circuit to disturb the photovoltaic system, thereby determining the insulation impedance of the photovoltaic system by the difference between the first current relationship corresponding to the connection structure of the photovoltaic unit circuit in the first loop and the second current relationship corresponding to the connection structure of the photovoltaic unit circuit in the second loop, and then judging whether the photovoltaic system has a whole machine-to-ground insulation impedance fault according to the value of the insulation impedance. The DC impedance detection circuit of the present application has a simple structure, which improves the simplicity of DC impedance detection of the photovoltaic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the conventional technology, the drawings required for use in the embodiments or the conventional technology descriptions are briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative work.

[0017] Figure 1 This is a structural example diagram of a photovoltaic system in one embodiment;

[0018] Figure 2 is a schematic structural diagram of a DC impedance detection circuit of a photovoltaic system in one embodiment;

[0019] Figure 3 is a schematic structural diagram of an insulation impedance circuit in one embodiment;

[0020] Figure 4a is an equivalent schematic diagram of a current loop of an insulation impedance circuit in a first state in one embodiment;

[0021] Figure 4b is an equivalent schematic diagram of a current loop of an insulation impedance circuit in a second state in one embodiment;

[0022] Figure 5 is a schematic structural diagram of an insulation impedance circuit in another embodiment;

[0023] Figure 6 is a schematic structural diagram of an insulation impedance circuit in another embodiment;

[0024] Figure 7 is a schematic structural diagram of an insulation impedance circuit in another embodiment;

[0025] Figure 8 is a schematic structural diagram of a photovoltaic system in another embodiment;

[0026] Fig. 9 is a schematic structural diagram of a current detection circuit in one embodiment;

[0027] Fig.10 is an equivalent schematic diagram of a current loop when a photovoltaic unit branch fails in one embodiment;

[0028] Fig.11 is a structural schematic diagram of a current detection circuit in another embodiment;

[0029] Fig.12 FIG. 4 is an equivalent schematic diagram of a current loop when a photovoltaic unit branch fails in another embodiment.

[0030] Description of reference numerals:

[0031] 10. Photovoltaic unit circuit; 11. Photovoltaic unit branch; 20. DC transformer; 30. Inverter; 40. Insulation impedance circuit; 41. Switch component; 51. Current sensor; 511. First current sensor; 512. Second current sensor; 513. Third current sensor. DETAILED DESCRIPTION

[0032] In order to facilitate understanding of the present application, the present application will be described more fully below with reference to the relevant drawings. Embodiments of the present application are provided in the drawings. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. On the contrary, the purpose of providing these embodiments is to make the disclosure of the present application more thorough and comprehensive.

[0033] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those commonly understood by those skilled in the art to which this application belongs. The terms used herein in the specification of this application are only for the purpose of describing specific embodiments and are not intended to limit this application.

[0034] It is understood that the terms "first", "second", etc. used in this application may be used herein to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish a first element from another element. For example, without departing from the scope of this application, a first resistor may be referred to as a second resistor, and similarly, a second resistor may be referred to as a first resistor. Both the first resistor and the second resistor are resistors, but they are not the same resistor.

[0035] It can be understood that the “connection” in the following embodiments should be understood as “electrical connection”, “communication connection”, etc. if the connected circuits, modules, units, etc. have electrical signals or data transmission between each other.

[0036] It can be understood that “at least one” means one or more, “plurality” means two or more, and “at least part of an element” means part or all of an element.

[0037] When used herein, the singular forms "a", "an", and "said / the" may also include plural forms, unless the context clearly indicates otherwise. It should also be understood that the terms "include / comprise" or "have" and the like specify the presence of stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not exclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. At the same time, the term "and / or" used in this specification includes any and all combinations of the relevant listed items.

[0038] Please refer to Figure 1 The photovoltaic system of the present application includes a plurality of photovoltaic unit circuits 10, wherein the negative poles of the photovoltaic unit circuits 10 are connected to each other.

[0039] The photovoltaic unit may include a single photovoltaic panel, a photovoltaic string formed by connecting multiple photovoltaic panels in series, and a photovoltaic array composed of multiple photovoltaic strings. The present application does not impose any specific restrictions on the type of photovoltaic unit.

[0040] As an example, the photovoltaic system may also include multiple DC transformers (also referred to as DC-DC converters) 20, bus capacitors C and inverters (also referred to as DC-AC converters) 30; wherein each photovoltaic unit circuit 10 is correspondingly connected to a DC transformer 20, and the DC power generated by each photovoltaic unit circuit 10 is boosted by the DC transformer 20 and then converted into AC power by the inverter 30.

[0041] For the problems existing in the background technology, please refer to Figure 2The present application provides a DC impedance detection circuit for a photovoltaic system, including: an insulation impedance circuit 40 and an inverter controller (not shown). The first end of the insulation impedance circuit 40 is connected to the busbar of the photovoltaic system, the second end of the insulation impedance circuit 40 is connected to the ground, and the inverter controller is respectively connected to each photovoltaic unit circuit 10 and the control end of the insulation impedance circuit 40.

[0042] When the insulation impedance circuit 40 is in the first state, the ground terminal is connected to the positive terminal BUS+ of the busbar to form a first loop. When the insulation impedance circuit is in the second state, the ground terminal is connected to the negative terminal BUS- of the busbar to form a second loop.

[0043] The inverter controller (not shown) is connected to the control end of each photovoltaic unit circuit 10 and the insulation impedance circuit 40, respectively, and is used to control the state of the insulation impedance circuit 40, and determine the insulation impedance of the photovoltaic system according to the difference between the first current relationship of the photovoltaic unit circuit 10 in the first loop and the second current relationship of the photovoltaic unit circuit 10 in the second loop.

[0044] The first current relationship includes the current relationship of the current loop formed by the photovoltaic system and the insulation impedance circuit 40 when the insulation impedance circuit 40 constitutes the first loop, and the second current relationship includes the current relationship of the current loop formed by the photovoltaic system and the insulation impedance circuit 40 when the insulation impedance circuit 40 constitutes the second loop. As an example, when the insulation impedance point circuit 40 is in the first state, the ground terminal and the positive terminal BUS+ of the busbar are connected to form the first loop, and the first current relationship can be obtained according to the circuit connection relationship between the first loop and the photovoltaic unit circuit 10. Similarly, the second current relationship can be obtained according to the circuit connection relationship between the second loop and the photovoltaic unit circuit 10. The relationship formula containing the insulation impedance can be obtained according to the difference between the first current relationship and the second current relationship, and the value of the insulation impedance is determined according to the relationship formula.

[0045] As an example, the inverter controller can reuse the maximum power point tracking (MPPT) controller in the photovoltaic system, thereby avoiding the addition of additional devices and improving the simplicity of the detection circuit.

[0046] In the above embodiment, an insulation impedance circuit 40 and an inverter controller are provided, wherein a first end of the insulation impedance circuit 40 is connected to the busbar of the photovoltaic system, and a second end of the insulation impedance circuit 40 is connected to the ground end, and the inverter controller is respectively connected to each photovoltaic unit circuit 10 in the photovoltaic system and a control end of the insulation impedance circuit 40. When the insulation impedance circuit 40 is in a first state, the ground end is connected to the positive end of the busbar to form a first loop. When the insulation impedance circuit 40 is in a second state, the ground end is connected to the negative end of the busbar to form a second loop. The inverter controller is used to control the state of the insulation impedance circuit 40, and to determine the insulation impedance of the photovoltaic system according to the difference between the first current relationship of the photovoltaic unit circuit 10 in the first loop and the second current relationship of the photovoltaic unit circuit 10 in the second loop. The present application sets an insulation impedance circuit 40 to form different conduction loops in the photovoltaic system, disturbing the photovoltaic system, thereby determining the insulation impedance of the photovoltaic system through the difference between a first current relationship corresponding to the connection structure of the photovoltaic unit circuit 10 in the first loop and a second current relationship corresponding to the connection structure of the photovoltaic unit circuit 10 in the second loop, and then judging whether there is an insulation impedance fault of the photovoltaic system to the ground based on the value of the insulation impedance. The DC impedance detection circuit of the present application has a simple structure, which improves the simplicity of DC impedance detection of the photovoltaic system.

[0047] In one embodiment, please refer to Figure 3 The insulation impedance circuit includes: a resistor R and a switch component 41; wherein the first end of the resistor R is connected to the ground, and the switch component 41 is respectively connected to the inverter controller, the positive terminal BUS+ of the busbar of the photovoltaic system, the negative terminal BUS- of the busbar, and the second end of the resistor R.

[0048] As an example, the resistance value of the resistor R is greater than or equal to 1 kilo-ohm, which improves the safety of the DC impedance detection circuit.

[0049] In which, when the switch component 41 conducts the path between the positive terminal BUS+ of the bus and the resistor R, the insulation impedance circuit is in the first state; when the switch component 41 conducts the path between the negative terminal BUS- of the bus and the resistor R, the insulation impedance circuit is in the second state.

[0050] As an example, the switch assembly may include a single-pole double-throw switch and an electromagnetic coil, and the conduction or closing of the electromagnetic coil is controlled by the inverter controller, thereby controlling the closing direction of the single-pole double-throw switch.

[0051] As an example, see Figure 4a Assuming that the photovoltaic system includes two photovoltaic unit circuits, when the insulation impedance circuit is in the first state, the equivalent schematic diagram of the circuit connection relationship between the photovoltaic unit circuit and the first loop is as follows Figure 4a As shown, the first current relationship can be determined according to the equivalent schematic diagram of the circuit connection relationship:

[0052] (1)

[0053] Wherein, V1 is the voltage between the positive terminal PV1+ of photovoltaic unit circuit 1 and the negative terminal PV- of photovoltaic unit circuit, V2 is the voltage between the positive terminal PV2+ of photovoltaic unit circuit 2 and the negative terminal PV- of photovoltaic unit circuit, V - is the voltage between the ground terminal and the negative terminal PV- of the photovoltaic unit circuit when the insulation impedance circuit is in the first state, R1m is the insulation impedance of the positive terminal of the photovoltaic unit circuit 1 to the ground, R2m is the insulation impedance of the positive terminal of the photovoltaic module 2 to the ground, and Rn is the insulation impedance of the negative terminal of the photovoltaic unit circuit to the ground;

[0054] When the insulation impedance circuit is in the second state, please refer to Figure 4b The equivalent schematic diagram of the connection relationship between the photovoltaic unit circuit and the second loop circuit is as follows Figure 4b As shown, the second current relationship can be determined according to the equivalent schematic diagram of the circuit connection relationship:

[0055] (2)

[0056] Among them, V - ‘ is the voltage between the ground terminal and the negative terminal PV- of the photovoltaic unit circuit when the insulation impedance circuit is in the second state;

[0057] The difference between formula (1) and formula (2) is:

[0058] (3)

[0059] According to the definition of the insulation resistance of the photovoltaic system to the ground, the insulation resistance of the photovoltaic system to the ground R iso satisfy:

[0060] (4)

[0061] According to formula (3) and formula (4), the insulation resistance Riso can be determined as:

[0062] .

[0063] In the above embodiment, when the switch component 41 switches on the path between the positive terminal BUS+ of the busbar and the resistor R, the first current relationship is determined according to the circuit connection relationship between the first loop and the photovoltaic unit circuit, and when the switch component 41 switches on the path between the negative terminal BUS- of the busbar and the resistor R, the second current relationship is determined according to the circuit connection relationship between the second loop and the photovoltaic unit circuit, and then a relationship formula including the insulation impedance is obtained according to the difference between the first current relationship and the second current relationship, the insulation impedance is determined according to the relationship formula, and then it is determined whether there is a fault in the insulation impedance of the entire photovoltaic system to the ground according to the value of the insulation impedance.

[0064] In one embodiment, please refer to Figure 5 The switch component includes: a first relay K1 and a second relay K2.

[0065] Among them, the control end of the first relay K1 is connected to the inverter controller, the first end of the first relay K1 is connected to the positive terminal BUS+ of the bus, the second end of the first relay K1 is respectively connected to the second end of the resistor R and the second end of the second relay K2, the first end of the second relay K2 is connected to the negative terminal BUS- of the bus, and the control end of the second relay K2 is connected to the inverter controller.

[0066] As an example, when the insulation impedance circuit is in the first state, K1 is closed, K2 is disconnected, and the path between the positive terminal BUS+ of the bus and the resistor R is in a conductive state, forming a first loop; when the insulation impedance circuit is in the second state, K1 is disconnected, K2 is closed, and the path between the negative terminal BUS- of the bus and the resistor R is in a conductive state, forming a second loop.

[0067] In one embodiment, please refer to Figure 6 The switch component includes: a first switch tube S1 and a second switch tube S2.

[0068] Among them, the control end of the first switch tube S1 is connected to the inverter controller, the first end of the first switch tube S1 is connected to the positive terminal BUS+ of the bus, the second end of the first switch tube S1 is respectively connected to the second end of the resistor R and the second end of the second switch tube S2, the first end of the second switch tube S2 is connected to the negative terminal BUS- of the bus, and the control end of the second switch tube S2 is connected to the inverter controller. As an example, the first switch tube may include a field effect tube or a transistor, and the switch tube in the photovoltaic system may be reused to reduce the complexity of the DC impedance detection circuit structure.

[0069] In one embodiment, please continue to refer to Figure 6 The insulation impedance circuit also includes: a third relay K3, and the third relay K3 is connected in series in the path between the ground terminal and the switch component.

[0070] In the above embodiment, by providing the third relay K3, it is possible to prevent the resistor R from affecting the performance of the photovoltaic system when the photovoltaic system is connected to the grid.

[0071] In one embodiment, please refer to Figure 7 The insulation impedance circuit also includes: an inductor L, which is connected in series in the path between the ground terminal and the switch component.

[0072] As an example, the inductor L can reuse the inductor in the photovoltaic system to avoid adding additional devices. At the same time, the inductor L can reduce current impact and protect the photovoltaic system and the DC impedance detection circuit.

[0073] In one embodiment, please refer to Figure 8 Each photovoltaic unit circuit in the photovoltaic system includes a plurality of parallel photovoltaic unit branches 11; the insulation impedance includes the branch insulation impedance; the DC impedance detection circuit also includes: a current detection circuit (not shown), and the current detection circuit is respectively connected to the target pole and the inverter controller of each photovoltaic unit branch 11.

[0074] The current detection circuit is used to detect the branch current of the target pole of each photovoltaic unit branch.

[0075] Wherein, the branch insulation impedance is the insulation impedance of the photovoltaic unit branch 11 to the ground. The branch current is the current flowing through the photovoltaic unit branch 11. The target pole includes a positive pole or a negative pole. As an example, the current detection circuit may include a current sampling circuit, and the branch current of each photovoltaic unit branch 11 is detected through a sampling resistor.

[0076] In one embodiment, please refer to Fig. 9 The current detection circuit includes a plurality of current sensors 51 ; wherein, at least one current sensor 51 is correspondingly arranged for each photovoltaic unit branch 11 .

[0077] The circuit sensor 51 may be a current sensor in the photovoltaic system. As an example, the current sensor may be disposed at at least one of the positive electrode of the photovoltaic unit branch 11 or the negative electrode of the photovoltaic unit branch 11 .

[0078] The inverter controller is also used to control the DC side insulation impedance circuit to be in a target state and the branch currents of each branch satisfy the target current relationship, and determine that the branch insulation impedance of the target pole of the photovoltaic unit branch 11 fails; wherein the target current relationship includes the relationship between the branch currents of each photovoltaic unit branch 11 when the branch insulation impedance of the photovoltaic unit branch 11 fails and each photovoltaic unit branch 11 in the corresponding photovoltaic unit circuit forms a discharge loop.

[0079] In one embodiment, the target state may include a first state and a second state; wherein, if the target pole of the photovoltaic unit branch is positive, the target state is the second state; if the target pole of the photovoltaic unit branch is negative, the target state is the first state.

[0080] As an example, please refer to Fig. 9 and Fig.10 , the current sensor can be set at the positive electrode of the photovoltaic unit branch to detect the branch current of the positive electrode of each photovoltaic unit branch, and the second relay K2 is closed. Assuming that the branch insulation impedance R1 of the positive electrode of photovoltaic unit branch 1 fails, the positive electrode of each photovoltaic unit branch forms a path to the ground, which can be formed as follows Fig.10 The current loop shown (the direction of the arrow is the current direction), in which the DC current generated by the photovoltaic unit branch 1 does not pass through the current sensor, the DC current generated by the photovoltaic unit branch 2 passes through the second current sensor 512 and the first current sensor 511 in sequence, and the DC current generated by the photovoltaic unit branch 3 passes through the third current sensor 513 and the first current sensor 511 in sequence. According to the connection relationship of the circuit, when the first branch current ipv1 detected by the first current sensor 511 is equal to the sum of the second branch current ipv2 detected by the second current sensor 512 and the third branch current ipv3 detected by the third current sensor 513, it is determined that the branch insulation impedance of the positive pole of the photovoltaic unit branch 1 is faulty.

[0081] As an example, see Fig.11 and Fig.12 , the current sensor can be set at the negative pole of the photovoltaic unit branch to detect the branch current of the negative pole of each photovoltaic unit branch, and the first relay K1 is closed. Assuming that the branch insulation impedance R2 of the negative pole of photovoltaic unit branch 1 fails, the negative pole of each photovoltaic unit branch forms a path to the ground, which can form the following Fig.12 The current loop shown (the direction of the arrow is the current direction), in which the DC current generated by the photovoltaic unit branch 1 does not pass through the current sensor, the DC current generated by the photovoltaic unit branch 2 passes through the third current sensor 513 and the second current sensor 512 in sequence, and the DC current generated by the photovoltaic unit branch 3 passes through the third current sensor 513 and the first current sensor 511 in sequence. According to the connection relationship of the circuit, when the third branch current ipv3 detected by the third current sensor 513 is equal to the sum of the second branch current ipv2 detected by the third current sensor 512 and the first branch current ipv1 detected by the first current sensor 511, it is determined that the branch insulation impedance of the negative pole of the photovoltaic unit branch 1 is faulty.

[0082] In the above embodiment, the failure of the branch insulation impedance of the positive or negative electrode of the photovoltaic unit branch can be determined based on the relationship between the branch currents detected by each current sensor, thereby realizing the detection of the photovoltaic unit branch, improving the simplicity of DC impedance detection of the photovoltaic system, and current sensors and the like can reuse the current sensors in the photovoltaic system, reducing the cost of the DC impedance detection circuit of the photovoltaic system.

[0083] In one embodiment, the present application further provides a photovoltaic system, comprising: a plurality of photovoltaic unit circuits and a DC impedance detection circuit of the photovoltaic system of any one of the embodiments of the present application; wherein the negative poles of each photovoltaic unit circuit are connected to each other.

[0084] Wherein, the DC impedance detection circuit is connected to the photovoltaic system and is used to detect the insulation impedance of the photovoltaic system.

[0085] In the description of this specification, the description with reference to the terms "some embodiments", "other embodiments", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present application. In this specification, the schematic description of the above terms does not necessarily refer to the same embodiment or example.

[0086] The technical features of the above-described embodiments may be arbitrarily combined. To make the description concise, not all possible combinations of the technical features in the above-described embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0087] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of the present application. It should be pointed out that, for a person of ordinary skill in the art, several variations and improvements can be made without departing from the concept of the present application, and these all belong to the protection scope of the present application. Therefore, the protection scope of the present application shall be subject to the attached claims.

Claims

1. A DC impedance detection circuit for a photovoltaic system, characterized in that: The photovoltaic system includes a plurality of photovoltaic unit circuits; wherein the negative electrodes of the photovoltaic unit circuits are connected to each other and to the negative end of the busbar of the photovoltaic system, and the positive electrodes of the photovoltaic unit circuits are connected to the positive end of the busbar of the photovoltaic system, and the DC impedance detection circuit includes: an insulation impedance circuit, wherein a first end of the insulation impedance circuit is connected to a busbar of the photovoltaic system, and a second end of the insulation impedance circuit is connected to a ground end. When the insulation impedance circuit is in a first state, the ground end is connected to the positive end of the busbar to form a first loop. When the insulation impedance circuit is in a second state, the ground end is connected to the negative end of the busbar to form a second loop. An inverter controller is respectively connected to the control end of each photovoltaic unit circuit and the insulation impedance circuit, and is used to control the state of the insulation impedance circuit and determine the insulation impedance of the photovoltaic system according to the difference between the first current relationship of the photovoltaic unit circuit in the first loop and the second current relationship of the photovoltaic unit circuit in the second loop.

2. The DC impedance detection circuit according to claim 1, characterized in that: The insulation impedance circuit comprises: A resistor, wherein a first end of the resistor is connected to a ground terminal; The switch component is respectively connected to the inverter controller, the positive terminal of the busbar of the photovoltaic system, the negative terminal of the busbar, and the second end of the resistor, wherein: When the switch assembly conducts the path between the positive terminal of the busbar and the resistor, the insulation impedance circuit is in the first state; When the switch assembly switches on the path between the negative terminal of the busbar and the resistor, the insulation impedance circuit is in the second state.

3. The DC impedance detection circuit according to claim 2, characterized in that: The switch component includes: a first relay and a second relay; wherein the control end of the first relay is connected to the inverter controller, the first end of the first relay is connected to the positive end of the bus, the second end of the first relay is respectively connected to the second end of the resistor and the second end of the second relay, the first end of the second relay is connected to the negative end of the bus, and the control end of the second relay is connected to the inverter controller.

4. The DC impedance detection circuit according to claim 2, characterized in that: The switch component includes: a first switch tube and a second switch tube; wherein the control end of the first switch tube is connected to the inverter controller, the first end of the first switch tube is connected to the positive end of the bus, the second end of the first switch tube is respectively connected to the second end of the resistor and the second end of the second switch tube, the first end of the second switch tube is connected to the negative end of the bus, and the control end of the second switch tube is connected to the inverter controller.

5. The DC impedance detection circuit according to any one of claims 2 to 4, characterized in that: The insulation impedance circuit also includes: A third relay is connected in series on the path between the ground terminal and the switch component.

6. The DC impedance detection circuit according to any one of claims 2 to 4, characterized in that: The insulation impedance circuit also includes: An inductor is connected in series in a path between the ground terminal and the switch component.

7. The DC impedance detection circuit according to claim 1, characterized in that: The insulation impedance includes branch insulation impedance; each of the photovoltaic unit circuits includes a plurality of photovoltaic unit branches connected in parallel, and the DC impedance detection circuit further includes: A current detection circuit is connected to the target pole of each photovoltaic unit branch, and is used to detect the branch current of the target pole of each photovoltaic unit branch; The inverter controller is also connected to the current detection circuit, and is used to control the DC side insulation impedance circuit to be in a target state and each branch current satisfies a target current relationship, and determine that the branch insulation impedance of the target pole of the photovoltaic unit branch has a fault; wherein the target current relationship includes the relationship between the branch currents of each photovoltaic unit branch when the branch insulation impedance of the photovoltaic unit branch fails and each photovoltaic unit branch in the corresponding photovoltaic unit circuit forms a discharge loop.

8. The DC impedance detection circuit according to claim 7, characterized in that: The target pole of the photovoltaic unit branch is positive, and the target state is the second state; The target pole of the photovoltaic unit branch is the negative pole, and the target state is the first state.

9. The DC impedance detection circuit according to claim 8, characterized in that: The current detection circuit includes a plurality of current sensors; wherein at least one current sensor is correspondingly arranged for each photovoltaic unit branch.

10. A photovoltaic system, characterized in that: include: A plurality of photovoltaic unit circuits and a DC impedance detection circuit for a photovoltaic system according to any one of claims 1 to 9; wherein the negative poles of the photovoltaic unit circuits are connected to each other.

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