An insulation impedance detection circuit, method and related apparatus

Abstract

The application discloses an insulation impedance detection circuit, which comprises an impedance matching circuit and a controller. The impedance matching circuit comprises at least two switches and a plurality of matching resistors. The plurality of matching resistors are connected between a positive bus and a negative bus. The switches are connected in parallel at two ends of part of the resistors. The ground is connected between the plurality of matching resistors and between two ends of the switches. At least one different matching resistor exists between the at least two switches in parallel. The controller is used for controlling the corresponding switch to act when a first impedance between the positive bus and the ground is less than an impedance threshold value, so that part of the matching resistors are connected in parallel with a second impedance between the negative bus and the ground, thereby reducing the impedance between the negative bus and the ground. When the second impedance is less than the impedance threshold value, the corresponding switch is controlled to act, so that part of the matching resistors are connected in parallel with the first impedance, thereby reducing the impedance between the positive bus and the ground. The scheme can match the impedance between the negative bus and the ground or match the impedance between the positive bus and the ground, so that the insulation impedance can be accurately detected.

Description

Technical Field

[0001] This application relates to the field of insulation fault technology, specifically to an insulation impedance detection circuit, method, and related device. Background Technology

[0002] In a power supply system, the DC side may experience ground insulation failure due to various reasons such as dust, rain, and snow. When a ground insulation failure occurs, the leakage current may cause an electric shock hazard.

[0003] However, when a ground insulation fault occurs on the DC side of the power supply system, there may be a small positive busbar to ground impedance or a small negative busbar to ground impedance, which makes the insulation impedance detected by the traditional insulation impedance detection circuit inaccurate. Summary of the Invention

[0004] In view of this, this application provides an insulation resistance detection circuit, method and related apparatus that can accurately detect insulation resistance.

[0005] To solve the above problems, the technical solution provided in this application is as follows:

[0006] This application provides an insulation impedance detection circuit, including: an impedance matching circuit and a controller, wherein the impedance matching circuit includes: at least two switches and multiple matching resistors;

[0007] The plurality of matching resistors are connected between the positive bus and the negative bus, the switch is connected in parallel across the two ends of a portion of the resistors, and ground is connected between the plurality of matching resistors and between the two ends of the switch; at least two switches connected in parallel have at least one different matching resistor.

[0008] The controller is configured to, when the first impedance of the positive busbar to ground is less than an impedance threshold, control a corresponding switch to connect a portion of the matching resistor in parallel with the second impedance of the negative busbar to ground, thereby reducing the impedance of the negative busbar to ground; and when the second impedance is less than the impedance threshold, control a corresponding switch to connect a portion of the matching resistor in parallel with the first impedance, thereby reducing the impedance of the positive busbar to ground.

[0009] One possible implementation is that the impedance matching circuit includes: a first switch, a second switch, and m matching resistors; where m is an integer greater than 3.

[0010] m matching resistors are connected in series between the positive busbar and the negative busbar; m1 matching resistors are connected in series between ground and the positive busbar; m2 matching resistors are connected in series between ground and the negative busbar, where m = m1 + m2; m1 and m2 are integers greater than or equal to 1; the first switch is connected in parallel with at least two of the m matching resistors, and when the first switch is on, at least one matching resistor is connected between the positive busbar and ground or at least one matching resistor is connected between the negative busbar and ground; the second switch is connected in parallel with at least two of the m matching resistors, and when the second switch is on, at least one matching resistor is connected between the positive busbar and ground or at least one matching resistor is connected between the negative busbar and ground; the resistors connected in parallel with the first switch and the resistors connected in parallel with the second switch are at least different.

[0011] One possible implementation is that m is an even number greater than 3, m1 is equal to m2, or m1 is not equal to m2.

[0012] One possible implementation is that m is an odd number greater than 3, and m1 is not equal to m2.

[0013] In one possible implementation, there are four matching resistors, namely a first resistor, a second resistor, a third resistor, and a fourth resistor;

[0014] The first end of the first resistor is connected to the positive busbar, the second end of the first resistor is connected to the first end of the second resistor, the second end of the second resistor is connected to the first end of the third resistor, the second end of the third resistor is connected to the first end of the fourth resistor, and the second end of the fourth resistor is connected to the negative busbar; the second end of the second resistor is grounded, the two ends of the first switch are respectively connected to the second end of the first resistor and the second end of the fourth resistor, and the two ends of the second switch are respectively connected to the first end of the first resistor and the second end of the third resistor.

[0015] In one possible implementation, the controller is configured to control the first switch to turn on and the second switch to turn off when the first impedance of the positive busbar to ground is less than an impedance threshold, thereby reducing the impedance of the negative busbar to ground; and to control the first switch to turn off and the second switch to turn on when the second impedance is less than the impedance threshold, thereby reducing the impedance of the positive busbar to ground.

[0016] One possible implementation further includes: an impedance disturbance circuit and a voltage sampling circuit; the first terminal of the impedance disturbance circuit is connected to the positive bus, the second terminal of the impedance disturbance circuit is connected to the negative bus, and the third terminal of the impedance disturbance circuit is grounded; the impedance disturbance circuit includes at least a disturbance switch and a disturbance resistor.

[0017] The controller is used to control the disturbance switch to change the resistance of the positive busbar to ground and to the negative busbar to ground.

[0018] The voltage sampling circuit is used to collect the voltage to ground corresponding to the impedance disturbance circuit before and after the impedance disturbance circuit is disturbed after the impedance matching circuit is completed. The voltage to ground includes the voltage to ground of the positive bus or the voltage between ground and the negative bus.

[0019] The controller is also configured to obtain the insulation impedance based on the voltage to ground, the matching resistor, and the disturbance resistor.

[0020] In one possible implementation, the impedance matching circuit further includes: a variable resistor, wherein the m1 matching resistors are connected in series with the variable resistor between ground and the positive bus, and the m2 matching resistors are connected in series with the variable resistor between ground and the negative bus; the controller is used to change the resistance value of the variable resistor.

[0021] This application also provides a photovoltaic system, including a power circuit and the insulation resistance detection circuit described above; the insulation resistance detection circuit is connected to the DC side of the power circuit and is used to detect the insulation resistance of the DC side of the power circuit.

[0022] This application also provides a method for detecting insulation impedance, wherein the impedance matching circuit includes at least two switches and multiple matching resistors; the impedance matching circuit is used to perform impedance matching before insulation detection.

[0023] The method includes:

[0024] When the first impedance of the positive busbar to ground is less than the impedance threshold, the corresponding switch is controlled to operate, so that part of the matching resistor is connected in parallel with the second impedance of the negative busbar to ground, thereby reducing the impedance of the negative busbar to ground; when the second impedance is less than the impedance threshold, the corresponding switch is controlled to operate, so that part of the matching resistor is connected in parallel with the first impedance, thereby reducing the impedance of the positive busbar to ground.

[0025] In one possible implementation, the impedance matching circuit includes a first switch and a second switch, and the matching resistor includes a first resistor, a second resistor, a third resistor, and a fourth resistor; a first terminal of the first resistor is connected to the positive busbar, a second terminal of the first resistor is connected to the first terminal of the second resistor, a second terminal of the second resistor is connected to the first terminal of the third resistor, a second terminal of the third resistor is connected to the first terminal of the fourth resistor, and a second terminal of the fourth resistor is connected to the negative busbar; a second terminal of the second resistor is grounded, and the two terminals of the first switch are respectively connected to the second terminals of the first resistor and the fourth resistor, and the two terminals of the second switch are respectively connected to the first terminals of the first resistor and the second terminals of the third resistor; when the first impedance of the positive busbar to ground is less than an impedance threshold, the first switch is turned on and the second switch is turned off, thereby reducing the impedance of the negative busbar to ground;

[0026] When the second impedance is less than the impedance threshold, the first switch is turned off and the second switch is turned on, thereby reducing the impedance of the positive busbar to ground.

[0027] One possible implementation is that the impedance disturbance circuit includes at least a disturbance switch and a disturbance resistor;

[0028] After impedance matching is performed by the impedance matching circuit, the following is also included:

[0029] The disturbance switch is controlled to change the resistance of the positive busbar to ground and the resistance of the negative busbar to ground; the ground voltages before and after the disturbance of the impedance disturbance circuit are collected, and the ground voltages include the voltage between the positive busbar and ground or the voltage between ground and the negative busbar.

[0030] The insulation impedance is obtained based on the voltage to ground, the matching resistor, and the disturbance resistor.

[0031] This application also provides a control device, including a processor and a memory, wherein the memory is used to store programs, instructions or code, and the processor is used to execute the programs, instructions or code in the memory to complete the insulation impedance detection method described above.

[0032] This application also provides a computer-readable storage medium storing a computer program, which is loaded by a processor to execute the insulation impedance detection method described above.

[0033] This application provides an insulation impedance detection circuit that adds an impedance matching circuit to the sampling circuit to actively match the impedance of the positive busbar to ground or the impedance of the negative busbar to ground. When the first impedance of the positive busbar to ground is less than the impedance threshold, the impedance of the negative busbar to ground needs to be lowered. Therefore, a matching resistor is connected in parallel between the negative busbar and ground. Similarly, when the second impedance of the negative busbar to ground is less than the impedance threshold, the impedance of the positive busbar to ground needs to be lowered. Therefore, a matching resistor is connected in parallel between the positive busbar and ground. This makes the voltage sampled by the sampling circuit more accurate, thereby calculating the accurate insulation impedance and promptly identifying insulation faults. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of a photovoltaic system;

[0035] Figure 2 A schematic diagram of an insulation resistance detection circuit provided in an embodiment of this application;

[0036] Figure 3 A schematic diagram of another insulation resistance detection circuit provided in an embodiment of this application;

[0037] Figure 4A for Figure 3 An equivalent schematic diagram of the impedance matching circuit provided in the embodiment shown;

[0038] Figure 4B for Figure 3 Another equivalent schematic diagram of the impedance matching circuit provided in the illustrated embodiment;

[0039] Figure 5 A schematic diagram of another impedance matching circuit provided in an embodiment of this application;

[0040] Figure 6 A schematic diagram of another insulation resistance detection circuit provided in an embodiment of this application;

[0041] Figure 7 A schematic diagram of another insulation resistance detection circuit provided in an embodiment of this application;

[0042] Figure 8 for Figure 7 The embodiment shown provides an equivalent diagram of an insulation impedance detection circuit;

[0043] Figure 9 for Figure 7 An equivalent diagram of another insulation resistance detection circuit provided in the illustrated embodiment;

[0044] Figure 10A A schematic diagram of another insulation resistance detection circuit provided in an embodiment of this application;

[0045] Figure 10Bfor Figure 10A The equivalent diagram of the corresponding insulation resistance detection circuit;

[0046] Figure 11 A flowchart illustrating an insulation impedance detection method provided in this application embodiment;

[0047] Figure 12 A flowchart illustrating yet another method for detecting insulation impedance provided in this application embodiment;

[0048] Figure 13 This is a schematic diagram of a control device provided in an embodiment of this application. Detailed Implementation

[0049] To enable those skilled in the art to better understand and implement the technical solutions provided in the embodiments of this application, the application scenarios will be described below in conjunction with the accompanying drawings.

[0050] The insulation impedance detection circuit provided in this application is used to detect the DC side insulation impedance to ground in a power supply system. It does not specifically limit the type of power supply system. For example, it can be a photovoltaic system, where the photovoltaic panel may have a ground insulation fault.

[0051] See Figure 1 The figure shows a schematic diagram of a photovoltaic system.

[0052] Taking a photovoltaic system as an example, the insulation resistance between the positive busbar PV+ and the ground PE is represented by R+, and the insulation resistance between the negative busbar PV- and the ground PE is represented by R-.

[0053] When an insulation fault occurs on the DC side, it is equivalent to connecting a smaller impedance Rx in parallel with the insulation impedance R+ or R-. Figure 1 Taking the impedance Rx connected in parallel with the insulation impedance R- as an example. Since the voltage between the positive busbar PV+ and the ground PE plus the voltage between the ground PE and the negative busbar PV- equals the voltage between the positive busbar PV+ and the negative busbar PV-, when the impedance Rx is small enough, it becomes very difficult for the sampling circuit to sample the voltage between the ground PE and the negative busbar PV-, especially when the DC busbar voltage fluctuates, which will lead to inaccurate insulation impedance calculations.

[0054] To address the above technical issues, this application provides an insulation impedance detection circuit that adds an impedance matching circuit to the sampling circuit to actively disturb the positive busbar-to-ground impedance or the negative busbar-to-ground impedance, thereby making the voltage sampled by the sampling circuit more accurate, and thus calculating the accurate insulation impedance to promptly identify insulation faults.

[0055] To make the above-mentioned objectives, features and advantages of this application more apparent and understandable, the embodiments of this application will be further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0056] See Figure 2 The figure is a schematic diagram of an insulation impedance detection circuit provided in an embodiment of this application.

[0057] The insulation impedance detection circuit provided in this application includes an impedance matching circuit 100 and a controller (not shown in the figure). The impedance matching circuit 100 includes at least two switches and multiple matching resistors.

[0058] The insulation impedance detection circuit in this embodiment is described using a photovoltaic system as an example. An impedance matching circuit 100 is connected to the DC / AC side of the inverter circuit. The first terminal of the impedance matching circuit 100 is connected to the positive bus PV+, the second terminal is connected to the negative bus PV-, and the third terminal is grounded to PE. It should be understood that the insulation impedance detection circuit provided in this embodiment can control the switch in the impedance matching circuit 100 according to the connection position of the impedance Rx, causing the impedance matching circuit 100 to lower the impedance of the positive bus PV+ to ground PE, or lower the impedance of the negative bus PV- to ground PE. Figure 2 The diagram below illustrates the case where impedance Rx is connected in parallel with insulation impedance R-.

[0059] Multiple matching resistors are connected between the positive and negative busbars, a switch is connected in parallel across some of the resistors, and ground is connected between the multiple matching resistors and between the two ends of the switch; at least two switches connected in parallel have at least one different matching resistor.

[0060] The controller is used to control the corresponding switch action when the first impedance of the positive busbar to ground is less than the impedance threshold, so that part of the matching resistor is connected in parallel with the second impedance of the negative busbar to ground, thereby reducing the impedance of the negative busbar to ground; when the second impedance is less than the impedance threshold, the controller controls the corresponding switch action to connect part of the matching resistor in parallel with the first impedance, thereby reducing the impedance of the positive busbar to ground.

[0061] The impedance matching circuit provided in this application embodiment can achieve impedance matching between the positive busbar and ground, as well as impedance matching between the negative busbar and ground.

[0062] This application does not specifically limit the method of obtaining the first and second impedances. The first and second impedances can be obtained directly or indirectly characterized by other parameters. For example, the first impedance can be characterized by sampling the voltage between the positive busbar and ground, and the second impedance can be characterized by sampling the voltage between ground and the negative busbar. Under normal circumstances, the voltage between the positive busbar and ground and the voltage between the negative busbar and ground should be symmetrical and almost equal. If the voltage between the positive busbar and ground is greater than the voltage between the negative busbar and ground, it indicates that the impedance between the negative busbar and ground is smaller, i.e., the second impedance is smaller. If the voltage between the positive busbar and ground is less than the voltage between the negative busbar and ground, it indicates that the impedance between the positive busbar and ground is smaller, i.e., the first impedance is smaller. For example, when the voltage between the positive busbar and ground is less than a voltage threshold, it is equivalent to the first impedance being less than an impedance threshold. Only when the first impedance is less than the impedance threshold is it necessary to lower the impedance between the negative busbar and ground. Therefore, a matching resistor is connected in parallel between the negative busbar and ground. Similarly, when the absolute value of the voltage between the negative busbar and ground is less than a voltage threshold, it is equivalent to the second impedance being less than an impedance threshold. When the second impedance is less than the impedance threshold, it is necessary to reduce the impedance of the positive bus to ground. Therefore, a matching resistor is connected in parallel between the positive bus and ground.

[0063] When the first impedance is greater than or equal to the impedance threshold, and the second impedance is greater than or equal to the impedance threshold, the impedance matching circuit does not need to be connected to the power supply system, and there is no need to match the impedance.

[0064] The circuit provided in this application embodiment includes an impedance matching circuit comprising: a first switch, a second switch, and m matching resistors; where m is an integer greater than 3.

[0065] m matching resistors are connected in series between the positive and negative busbars, m1 matching resistors are connected in series between ground and the positive busbar, and m2 matching resistors are connected in series between ground and the negative busbar, where m = m1 + m2; m1 and m2 are integers greater than or equal to 1; the first switch is connected in parallel with at least two of the m matching resistors, and when the first switch is on, at least one matching resistor is connected between the positive busbar and ground or at least one matching resistor is connected between the negative busbar and ground; the second switch is connected in parallel with at least two of the m matching resistors, and when the second switch is on, at least one matching resistor is connected between the positive busbar and ground or at least one matching resistor is connected between the negative busbar and ground; the resistors connected in parallel with the first switch and the resistors connected in parallel with the second switch are at least different.

[0066] The insulation resistance detection circuit provided in this application embodiment, wherein m can be an even number or an odd number. For example, when m is an even number greater than 3, m1 equals m2, or m1 does not equal m2. For example, if m is 4, then m1 is 2 and m2 is 2, meaning that two matching resistors can be connected in series between the positive busbar and ground, and two resistors can be connected in series between ground and the negative busbar. If cost is not a concern, a larger number of matching resistors can be connected, meaning m can also be a larger even number. For example, if m is 6, then m1 is 3 and m2 is 3, meaning that three matching resistors can be connected in series between the positive busbar and ground, and three resistors can be connected in series between ground and the negative busbar. When m1 is not equal to m2, for example, m1 is 2 and m2 is 4.

[0067] Alternatively, m can be an odd number greater than 3, in which case m1 is not equal to m2. For example, m is 5, m1 is 2, and m2 is 3. The order can also be reversed, with m1 being 3 and m2 being 2, and so on.

[0068] The following describes a specific implementation method with reference to the attached diagram, for example, where m is 4, m1 is 2, and m2 is 2.

[0069] See Figure 3 The figure is a schematic diagram of another insulation impedance detection circuit provided in the embodiment of this application.

[0070] The insulation impedance detection circuit provided in this application embodiment includes an impedance matching circuit 100 comprising four matching resistors and two switches. The four matching resistors are a first resistor R5, a second resistor R6, a third resistor R7, and a fourth resistor R8.

[0071] The first end of the first resistor R5 is connected to the positive busbar PV+. The second end of the first resistor R5 is connected to the first end of the second resistor R6. The second end of the second resistor R6 is connected to the first end of the third resistor R7. The second end of the third resistor R7 is connected to the first end of the fourth resistor R8. The second end of the fourth resistor R8 is connected to the negative busbar PV-. The second end of the second resistor R6 is grounded to PE. The two ends of the first switch K1 are connected to the second ends of the first resistor R5 and the fourth resistor R8, respectively. The two ends of the second switch K2 are connected to the first end of the first resistor R5 and the second end of the third resistor R7, respectively.

[0072] from Figure 3 It can be seen that the two ends of the first switch K1 and the two ends of the second switch K2 are wrapped around the ground PE, that is, the ground PE is located between the two ends of the first switch K1, and the ground PE is also located between the two ends of the second switch K2.

[0073] The specific working principle is as follows: the controller (not shown in the figure) is used to control the first switch K1 to be turned on and the second switch K2 to be turned off when the first impedance of the positive busbar PV+ to ground PE is less than the impedance threshold, thereby reducing the impedance of the negative busbar PV- to ground PE; when the second impedance is less than the impedance threshold, it controls the first switch K1 to be turned off and the second switch K2 to be turned on, thereby reducing the impedance of the positive busbar PV+ to ground PE.

[0074] The insulation impedance detection circuit provided in this application embodiment can achieve matching of both the positive busbar to ground impedance and the negative busbar to ground impedance.

[0075] See Figure 4A The figure is an equivalent schematic diagram of the impedance matching circuit provided in the embodiment of this application.

[0076] In this embodiment, a small impedance is applied between the negative busbar PV- and the ground PE, which causes the sampled value of the negative busbar PV- to the ground PE to be too small. Therefore, it is necessary to lower the impedance of the positive busbar PV+ to the ground PE, thereby increasing the sampled value of the negative busbar PV- to the ground PE, so as to calculate the accurate insulation impedance.

[0077] correspond Figure 3 In this impedance matching circuit, the controller needs to close the second switch K2 and open the first switch K1. The equivalent connection relationship of the impedance matching circuit is as follows: Figure 4A As shown, the fourth resistor R8 is connected between the positive busbar PV+ and the negative busbar PV-. The first resistor R5 and the second resistor R6 are connected in series and then connected in parallel with the third resistor R7 between the positive busbar PV+ and ground PE.

[0078] from Figure 4A As can be seen, a matching resistor is connected between the positive busbar PV+ and the ground PE, which can reduce the impedance between the positive busbar PV+ and the ground PE, so that the impedance of the negative busbar PV- to the ground PE is small, and the impedance of the positive busbar PV+ to the ground PE is also small. The difference between the two should be as small as possible, which can improve the sampling value of the negative busbar PV- to the ground PE, such as the sampling voltage, thereby improving the accuracy of the insulation impedance.

[0079] The following describes how impedance matching circuits can reduce the impedance of the negative busbar to ground.

[0080] See Figure 4B This figure is another equivalent schematic diagram of the impedance matching circuit provided in the embodiment of this application.

[0081] In this embodiment, a small impedance is applied between the positive busbar PV+ and the ground PE, which causes the sampled value of the positive busbar PV+ to the ground PE to be too small. Therefore, it is necessary to lower the impedance of the negative busbar PV- to the ground PE, thereby increasing the sampled value of the positive busbar PV+ to the ground PE, so as to calculate the accurate insulation impedance.

[0082] correspond Figure 3 In this impedance matching circuit, the controller needs to open the second switch K2 and close the first switch K1. The equivalent connection relationship of the impedance matching circuit is as follows: Figure 4B As shown, the first resistor R5 is connected between the positive busbar PV+ and the negative busbar PV-. The third resistor R7 and the fourth resistor R8 are connected in series and then connected in parallel with the second resistor R6 between the negative busbar PV- and ground PE.

[0083] from Figure 4B As can be seen, a matching resistor is connected between the negative busbar PV- and the ground PE, which can reduce the impedance between the negative busbar PV- and the ground PE, so that the impedance of the negative busbar PV- to the ground PE is small, and the impedance of the positive busbar PV+ to the ground PE is also small. The difference between the two should be as small as possible, which can improve the sampling value of the negative busbar PV- to the ground PE, such as the sampling voltage, thereby improving the accuracy of the insulation impedance.

[0084] The insulation matching circuit described above is based on an example with four matching resistors. It should be understood that it can also include more resistors, such as five or six. The following section, with reference to the attached diagram, describes the implementation method including six matching resistors.

[0085] See Figure 5 This figure is a schematic diagram of another impedance matching circuit provided in an embodiment of this application.

[0086] The insulation impedance detection circuit provided in this embodiment includes an impedance matching circuit 100 comprising 6 matching resistors and 2 switches. The 6 matching resistors are the first resistor R5, the second resistor R6, the third resistor R7, the fourth resistor R8, the eleventh resistor R11, and the twelfth resistor R12.

[0087] The first end of the first resistor R5 is connected to the positive busbar PV+. The second end of the first resistor R5 is connected to the first end of the second resistor R6. The second end of the second resistor R6 is connected to the first end of the third resistor R7. The second end of the third resistor R7 is connected to the first end of the fourth resistor R8. The second end of the fourth resistor R8 is connected to the first end of the eleventh resistor R11. The second end of the eleventh resistor R11 is connected to the first end of the twelfth resistor R12. The second end of the twelfth resistor R12 is connected to the negative busbar PV-. The second end of the third resistor R7 is grounded. The two ends of the first switch K1 are connected to the second ends of the second resistor R6 and the eleventh resistor R11, respectively. The two ends of the second switch K2 are connected to the second ends of the first resistor R5 and the fourth resistor R8, respectively.

[0088] from Figure 5It can be seen that the two ends of the first switch K1 and the two ends of the second switch K2 are wrapped around the ground PE, that is, the ground PE is located between the two ends of the first switch K1, and the ground PE is also located between the two ends of the second switch K2.

[0089] The specific working principle is as follows: the controller (not shown in the figure) is used to control the first switch K1 to open and the second switch K2 to open when the first impedance of the positive busbar PV+ to ground PE is less than the impedance threshold, thereby reducing the impedance of the negative busbar PV- to ground PE; when the second impedance is less than the impedance threshold, it controls the first switch K1 to open and the second switch K2 to open, thereby reducing the impedance of the positive busbar PV+ to ground PE.

[0090] Understandably, when the impedance matching circuit 100 includes 6 matching resistors and 2 switches, the 2 switches can also be... Figure 3 The structure shown is not described in detail here; in addition, for other impedance matching circuits, their structure and working principle can be referred to the above examples, and will not be listed one by one.

[0091] The insulation impedance detection circuit provided in this application embodiment can achieve matching of both the positive busbar to ground impedance and the negative busbar to ground impedance.

[0092] To improve the accuracy of insulation impedance detection, the insulation impedance detection circuit provided in this application embodiment may further include an impedance disturbance circuit, which can realize the disturbance of the positive busbar-to-ground voltage or the negative busbar-to-ground voltage. The following is a detailed description in conjunction with the accompanying drawings.

[0093] See Figure 6 The figure is a schematic diagram of another insulation impedance detection circuit provided in the embodiment of this application.

[0094] In addition to the impedance matching circuit 100, the insulation impedance detection circuit provided in this application embodiment may also include: an impedance disturbance circuit 200 and a voltage sampling circuit (not shown in the figure); the first end of the impedance disturbance circuit 200 is connected to the positive bus PV+, the second end of the impedance disturbance circuit 200 is connected to the negative bus PV-, and the third end of the impedance disturbance circuit 200 is grounded to PE; the impedance disturbance circuit 200 includes at least a disturbance switch and a disturbance resistor.

[0095] The controller is used to control the operation of the disturbance switch to change the resistance between the positive busbar PV+ and the ground PE, and to change the resistance between the negative busbar PV- and the ground PE.

[0096] It should be understood that after the impedance disturbance circuit 200 causes disturbance, it can change the voltage of the positive busbar to ground and the voltage of the negative busbar to ground. This can cause the voltage to ground to change before and after the disturbance switch is activated, so that the insulation impedance can be solved by setting up equations and improving the accuracy of the insulation impedance.

[0097] The voltage sampling circuit is used to collect the voltage to ground before and after the impedance disturbance circuit is disturbed after the impedance matching circuit has been activated. The voltage to ground includes the voltage between the positive bus and the ground or the voltage between the ground and the negative bus.

[0098] The controller is also used to obtain the insulation impedance based on the voltage to ground, matching resistance, and disturbance resistance.

[0099] This application does not specifically limit the implementation of the impedance disturbance circuit, but the impedance disturbance circuit includes at least a resistor and a switch. A specific implementation is described below with reference to the accompanying drawings.

[0100] See Figure 7 The figure is a schematic diagram of another insulation resistance detection circuit provided in an embodiment of this application.

[0101] The impedance disturbance circuit provided in this application embodiment includes four resistors and two switches as an example. Specifically, the impedance disturbance circuit 200 includes: a fifth disturbance resistor R1, a sixth disturbance resistor R2, a seventh disturbance resistor R3, and an eighth disturbance resistor R4. The two switches are the third switch K3 and the fourth switch K4.

[0102] The first end of the fifth disturbance resistor R1 is connected to the positive bus PV+. The second end of the fifth disturbance resistor R1 is connected to the first end of the sixth disturbance resistor R2. The second end of the sixth disturbance resistor R2 is connected to the first end of the seventh disturbance resistor R3. The second end of the seventh disturbance resistor R3 is connected to the first end of the eighth disturbance resistor R4. The second end of the eighth disturbance resistor R4 is connected to the negative bus PV-. The second end of the sixth disturbance resistor R2 is grounded. The two ends of the fourth switch K4 are connected to the second ends of the fifth disturbance resistor R1 and the eighth disturbance resistor R4, respectively. The two ends of the third switch K3 are connected to the first ends of the fifth disturbance resistor R1 and the seventh disturbance resistor R3, respectively.

[0103] from Figure 7 It can be seen that the two ends of the third switch K3 and the two ends of the fourth switch K4 are wrapped around the ground PE, that is, the ground PE is located between the two ends of the third switch K3, and at the same time, the ground PE is located between the two ends of the fourth switch K4.

[0104] The working principle of the insulation impedance detection circuit provided in the embodiments of this application is described below with reference to the accompanying drawings.

[0105] See Figure 8 The figure is an equivalent diagram of an insulation impedance detection circuit provided in an embodiment of this application.

[0106] See Figure 9 This figure is an equivalent diagram of another insulation impedance detection circuit provided in an embodiment of this application.

[0107] Figure 8 The impedance matching circuit in the circuit applies a small impedance to the negative busbar PV- and ground PE, and needs to reduce the impedance of the positive busbar PV+ and ground PE. That is, the second switch K2 is closed and the first switch K1 is open.

[0108] Figure 8 The impedance disturbance circuit in the example is described with the third switch K3 closed and the fourth switch K4 open.

[0109] Figure 9 The impedance disturbance circuit in the example is described with the third switch K3 open and the fourth switch K4 closed.

[0110] Setting: When the insulation resistance R- and parallel resistance Rx are very small, the impedance disturbance circuit 200 operates; when the third switch K3 is closed and the fourth switch K4 is open, the voltage between ground PE and negative busbar PV- is V-, and the voltage between positive busbar PV+ and negative busbar PV- is V; when the fourth switch K2 is open and the third switch K3 is closed, the voltage between ground PE and negative busbar PV- is V. - ′ The voltage between the positive busbar PV+ and the negative busbar PV- is V. ′ .

[0111] Depend on Figure 8 and Figure 9 The following equation can be obtained:

[0112]

[0113] The insulation resistances R- and R+ can be solved separately;

[0114]

[0115] It should be understood that by substituting formula (3) into formula (1), the insulation impedance R- can be solved, that is, by substituting the insulation impedance R+ into formula (1), the insulation impedance R- can be solved; according to Riso=R+||R-, the insulation impedance Riso can be solved.

[0116] The impedance matching circuit described above uses two switches as an example. The following describes the implementation method involving three switches.

[0117] For example, the impedance matching circuit 100 further includes: a variable resistor, m1 matching resistors connected in series with the variable resistor between ground PE and positive busbar PV+, and m2 matching resistors connected in series with the variable resistor between ground PE and negative busbar PV-; a controller is used to change the resistance value of the variable resistor. The variable resistor can be obtained by connecting a resistor and a switch in series. The controller can control the switching on and off of the switch to enable or disable the resistor, thereby changing the external resistance value presented by the variable resistor.

[0118] See Figure 10A The figure is a schematic diagram of another impedance matching circuit provided in an embodiment of this application.

[0119] The impedance matching circuit includes four matching resistors, two switches, and a variable resistor. The four matching resistors are resistor R5, resistor R6, resistor R7, and resistor R8. The two switches are switch K1 and switch K2. The variable resistor includes resistor R9 and switch K5.

[0120] The first terminal of the first resistor R5 is connected to the positive busbar PV+. The second terminal of the first resistor R5 is connected to the first terminal of the second resistor R6. The second terminal of the second resistor R6 is connected to the first terminal of the third resistor R7. The second terminal of the third resistor R7 is connected to the first terminal of the fourth resistor R8. The second terminal of the fourth resistor R8 is connected to the negative busbar PV-. The second terminal of the second resistor R6 is grounded through the ninth resistor R9. The two terminals of the second switch K2 are connected to the first terminals of the first resistor R5 and the second terminals of the third resistor R7, respectively. The two terminals of the first switch K1 are connected to the second terminals of the first resistor R5 and the second terminals of the fourth resistor R8, respectively. The fifth switch K5 is connected in parallel across the ninth resistor R9.

[0121] When the fifth switch K5 is closed, it is equivalent to Figure 3 The corresponding implementation method.

[0122] When the fifth switch K5 is open, the second switch K2 is open, and the equivalent circuit of the first switch K1 being open is as follows: Figure 10B The left-hand diagram shows the equivalent circuit where, when the fifth switch K5 is open, the second switch K2 is open and the first switch K1 is closed, as shown in the diagram below. Figure 10B As shown in the right-hand figure, relative Figure 3 In terms of the corresponding implementation method, it can be seen that its impedance matching resistance range varies more (relying on the fifth switch K5 to switch the ninth resistor R9 into or out of the circuit).

[0123] The above is just an illustrative example; more resistors and more switches can be used for impedance matching, which will not be elaborated here.

[0124] Based on the insulation impedance detection circuit provided in the above embodiments, this application also provides a photovoltaic system.

[0125] The photovoltaic system provided in this application includes a power circuit and the insulation resistance detection circuit described in the above embodiments. The insulation resistance detection circuit is connected to the DC side of the power circuit and is used to detect the insulation resistance of the DC side of the power circuit. This application does not specifically limit the type of power circuit; for example, the power circuit can be a DC / AC inverter circuit. The above embodiments are described using the example of the insulation resistance detection circuit being connected to the DC side of the DC / AC inverter. It should be understood that the power circuit can include a series-connected DC / DC and DC / AC inverter, and the insulation resistance detection circuit is connected to the DC side of the DC-DC inverter connected to the photovoltaic string.

[0126] Based on the insulation impedance detection circuit and photovoltaic system provided in the above embodiments, this application also provides an insulation impedance detection method, which will be described in detail below with reference to the accompanying drawings.

[0127] See Figure 11 The figure is a flowchart of an insulation impedance detection method provided in an embodiment of this application.

[0128] The insulation impedance detection method provided in this application includes an impedance matching circuit comprising at least two switches and multiple matching resistors; the impedance matching circuit is used to perform impedance matching before insulation detection; the method includes:

[0129] S101: When the first impedance of the positive busbar to ground is less than the impedance threshold, control the corresponding switch to make part of the matching resistor parallel with the second impedance of the negative busbar to ground, so as to reduce the impedance of the negative busbar to ground.

[0130] S102: When the second impedance is less than the impedance threshold, control the corresponding switch to make part of the matching resistor parallel with the first impedance, so as to reduce the impedance of the positive bus to ground.

[0131] This application provides a method for detecting insulation impedance. An impedance matching circuit is added to the sampling circuit to actively disturb the positive busbar to ground impedance or the negative busbar to ground impedance, thereby making the voltage sampled by the sampling circuit more accurate, and then calculating the accurate insulation impedance to promptly identify insulation faults.

[0132] In one possible implementation, the impedance matching circuit includes a first switch and a second switch, and matching resistors including a first resistor, a second resistor, a third resistor, and a fourth resistor. The first terminal of the first resistor is connected to the positive busbar; the second terminal of the first resistor is connected to the first terminal of the second resistor; the second terminal of the second resistor is connected to the first terminal of the third resistor; the second terminal of the third resistor is connected to the first terminal of the fourth resistor; and the second terminal of the fourth resistor is connected to the negative busbar. The second terminal of the second resistor is grounded. The two terminals of the first switch are connected to the second terminals of the first and fourth resistors, respectively, and the two terminals of the second switch are connected to the first terminals of the first and third resistors, respectively. When the first impedance of the positive busbar to ground is less than an impedance threshold, the first switch is turned on, and the second switch is turned off, reducing the impedance of the negative busbar to ground. When the second impedance is less than the impedance threshold, the first switch is turned off, and the second switch is turned on, reducing the impedance of the positive busbar to ground.

[0133] See Figure 12 The figure is a flowchart of another insulation impedance detection method provided in the embodiments of this application.

[0134] To improve the accuracy of insulation impedance detection, the insulation impedance detection circuit provided in this application embodiment also includes an impedance disturbance circuit, which can realize the disturbance of the positive busbar-to-ground voltage or the negative busbar-to-ground voltage. The following is a detailed description in conjunction with the accompanying drawings.

[0135] One possible implementation is that the insulation impedance detection circuit includes, in addition to the impedance matching circuit, an impedance disturbance circuit; the impedance disturbance circuit includes at least a disturbance switch and a disturbance resistor.

[0136] To facilitate understanding, a complete procedure for testing insulation resistance is described below.

[0137] S1001: When the first impedance of the positive busbar to ground is less than the impedance threshold, control the corresponding switch in the impedance matching circuit to make part of the matching resistors parallel with the second impedance of the negative busbar to ground, so as to reduce the impedance of the negative busbar to ground.

[0138] S1002: When the second impedance is less than the impedance threshold, control the corresponding switch action in the impedance matching circuit to connect part of the matching resistor in parallel with the first impedance, so as to reduce the impedance of the positive bus to ground.

[0139] As described in the above embodiments, determining whether the first impedance and the second impedance are less than the impedance threshold can be achieved by detecting the negative bus voltage to ground and the positive bus voltage to ground, which will not be elaborated further here.

[0140] S1003: After the impedance matching circuit completes its operation, the disturbance switch in the control impedance disturbance circuit is activated to change the resistance of the positive busbar to ground and the resistance of the negative busbar to ground.

[0141] S1004: Collects the voltage to ground before and after the impedance disturbance circuit disturbance. The voltage to ground includes the voltage between the positive bus and the ground or the voltage between the ground and the negative bus.

[0142] S1005: Obtain the insulation impedance based on the voltage to ground, matching resistance, and disturbance resistance.

[0143] The insulation impedance detection method provided in this application first uses an impedance matching circuit to change the impedance of the positive busbar to ground or the impedance of the negative busbar to ground, and then uses an impedance perturbation circuit to achieve impedance perturbation, and collects the voltage to ground before and after the perturbation. This can ensure that the collected signal is more accurate, and thus obtain a more accurate insulation impedance.

[0144] In one possible implementation, see Figure 13 The figure is a schematic diagram of a control device provided in an embodiment of this application.

[0145] The control device may include a memory 1011 and a processor 1012. The processor 1012 may be connected to the power converter and can drive the switches in the various power conversion circuits of the power converter. For example... Figure 13 As shown, the memory can be random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (Electronic Programmable ROM), registers, hard disks, removable disks, etc.

[0146] The memory 1011 can store computer instructions. When the computer instructions stored in the memory 1011 are executed by the processor 1012, the processor 1012 can be used to execute the control method of the power converter. The memory 1011 can also store data, such as preset ranges, preset thresholds, and other information involved in the above embodiments.

[0147] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented in software, it can be implemented, in whole or in part, as a computer program product. A computer program product includes one or more computer instructions. When the computer program instructions are loaded and executed on a computer, all or part of the flow or function according to the embodiments of this application is generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape) or a semiconductor medium (e.g., solid-state disk (SSD)).

[0148] This application also provides a readable storage medium for storing the methods provided in the above embodiments. Examples include random access memory (RAM), flash memory, read-only memory (ROM), EPROM, non-volatile read-only memory (EPROM), registers, hard disks, removable disks, or any other form of storage medium in the art.

[0149] It should be noted that the various embodiments in this specification are described in a progressive manner, with each embodiment focusing on the differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. Regarding the methods disclosed in the embodiments, since they correspond to the product embodiments disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to in the description of the product embodiments.

[0150] The above description of the disclosed embodiments enables those skilled in the art to make or use this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An insulation resistance detection circuit, characterized in that, include: An impedance matching circuit and a controller, wherein the impedance matching circuit includes at least two switches and multiple matching resistors; The plurality of matching resistors are connected between the positive bus and the negative bus, the switch is connected in parallel across the two ends of a portion of the resistors, and ground is connected between the plurality of matching resistors and between the two ends of the switch; at least two switches connected in parallel have at least one different matching resistor. The controller is configured to, when the first impedance of the positive busbar to ground is less than an impedance threshold, control a corresponding switch to connect a portion of the matching resistor in parallel with the second impedance of the negative busbar to ground, thereby reducing the impedance of the negative busbar to ground; and when the second impedance is less than the impedance threshold, control a corresponding switch to connect a portion of the matching resistor in parallel with the first impedance, thereby reducing the impedance of the positive busbar to ground.

2. The circuit according to claim 1, characterized in that, The impedance matching circuit includes: a first switch, a second switch, and m matching resistors; m is an integer greater than 3; m matching resistors are connected in series between the positive busbar and the negative busbar; m1 matching resistors are connected in series between ground and the positive busbar; m2 matching resistors are connected in series between ground and the negative busbar, where m = m1 + m2; m1 and m2 are integers greater than or equal to 1; the first switch is connected in parallel with at least two of the m matching resistors, and when the first switch is on, at least one matching resistor is connected between the positive busbar and ground or at least one matching resistor is connected between the negative busbar and ground; the second switch is connected in parallel with at least two of the m matching resistors, and when the second switch is on, at least one matching resistor is connected between the positive busbar and ground or at least one matching resistor is connected between the negative busbar and ground; the resistors connected in parallel with the first switch and the resistors connected in parallel with the second switch are at least different.

3. The circuit according to claim 2, characterized in that, The m is an even number greater than 3, the m1 is equal to the m2, or the m1 is not equal to the m2.

4. The circuit according to claim 2, characterized in that, The m is an odd number greater than 3, and the m1 is not equal to the m2.

5. The circuit according to claim 3, characterized in that, The matching resistors are four in number: a first resistor, a second resistor, a third resistor, and a fourth resistor. The first end of the first resistor is connected to the positive busbar, the second end of the first resistor is connected to the first end of the second resistor, the second end of the second resistor is connected to the first end of the third resistor, the second end of the third resistor is connected to the first end of the fourth resistor, and the second end of the fourth resistor is connected to the negative busbar; the second end of the second resistor is grounded, the two ends of the first switch are respectively connected to the second end of the first resistor and the second end of the fourth resistor, and the two ends of the second switch are respectively connected to the first end of the first resistor and the second end of the third resistor.

6. The circuit according to claim 5, characterized in that, The controller is configured to control the first switch to turn on and the second switch to turn off when the first impedance of the positive busbar to ground is less than an impedance threshold, thereby reducing the impedance of the negative busbar to ground; and to control the first switch to turn off and the second switch to turn on when the second impedance is less than the impedance threshold, thereby reducing the impedance of the positive busbar to ground.

7. The circuit according to any one of claims 1-6, characterized in that, Also includes: An impedance disturbance circuit and a voltage sampling circuit are provided; the first terminal of the impedance disturbance circuit is connected to the positive bus, the second terminal of the impedance disturbance circuit is connected to the negative bus, and the third terminal of the impedance disturbance circuit is grounded; the impedance disturbance circuit includes at least a disturbance switch and a disturbance resistor. The controller is used to control the disturbance switch to change the resistance of the positive busbar to ground and the resistance of the negative busbar to ground. The voltage sampling circuit is used to collect the voltage to ground corresponding to the impedance disturbance circuit before and after the impedance disturbance circuit is disturbed after the impedance matching circuit is completed. The voltage to ground includes the voltage to ground of the positive bus or the voltage between ground and the negative bus. The controller is also configured to obtain the insulation impedance based on the voltage to ground, the matching resistor, and the disturbance resistor.

8. The circuit according to claim 2, characterized in that, The impedance matching circuit further includes: a variable resistor, wherein the m1 matching resistors are connected in series with the variable resistor between ground and the positive bus, and the m2 matching resistors are connected in series with the variable resistor between ground and the negative bus; the controller is used to change the resistance value of the variable resistor.

9. A photovoltaic system, characterized in that, Includes a power circuit and an insulation resistance detection circuit as described in any one of claims 1-8; The insulation impedance detection circuit is connected to the DC side of the power circuit and is used to detect the insulation impedance of the DC side of the power circuit.

10. A method for detecting insulation resistance, characterized in that, The impedance matching circuit includes at least two switches and multiple matching resistors; the impedance matching circuit is used to perform impedance matching before insulation testing. The method includes: When the first impedance of the positive busbar to ground is less than the impedance threshold, the corresponding switch is controlled to operate, so that part of the matching resistor is connected in parallel with the second impedance of the negative busbar to ground, thereby reducing the impedance of the negative busbar to ground; when the second impedance is less than the impedance threshold, the corresponding switch is controlled to operate, so that part of the matching resistor is connected in parallel with the first impedance, thereby reducing the impedance of the positive busbar to ground.

11. The method according to claim 10, characterized in that, The impedance matching circuit includes a first switch and a second switch, and the matching resistor includes a first resistor, a second resistor, a third resistor, and a fourth resistor; the first end of the first resistor is connected to the positive busbar, the second end of the first resistor is connected to the first end of the second resistor, the second end of the second resistor is connected to the first end of the third resistor, the second end of the third resistor is connected to the first end of the fourth resistor, and the second end of the fourth resistor is connected to the negative busbar; the second end of the second resistor is grounded, and the two ends of the first switch are respectively connected to the second ends of the first resistor and the fourth resistor, and the two ends of the second switch are respectively connected to the first ends of the first resistor and the second ends of the third resistor; When the first impedance of the positive busbar to ground is less than the impedance threshold, the first switch is turned on and the second switch is turned off to reduce the impedance of the negative busbar to ground. When the second impedance is less than the impedance threshold, the first switch is turned off and the second switch is turned on, thereby reducing the impedance of the positive busbar to ground.

12. The method according to claim 10 or 11, characterized in that, An impedance disturbance circuit includes at least a disturbance switch and a disturbance resistor; After impedance matching is performed by the impedance matching circuit, the following is also included: The disturbance switch is controlled to change the resistance of the positive busbar to ground and the resistance of the negative busbar to ground; the ground voltages before and after the disturbance of the impedance disturbance circuit are collected, and the ground voltages include the voltage between the positive busbar and ground or the voltage between ground and the negative busbar. The insulation impedance is obtained based on the voltage to ground, the matching resistor, and the disturbance resistor.

13. A control device, characterized in that, It includes a processor and a memory, the memory being used to store programs, instructions, or code, and the processor being used to execute the programs, instructions, or code in the memory to perform the insulation impedance detection method as described in any one of claims 10-12.

14. A computer-readable storage medium, characterized in that, The device contains a computer program that is loaded by a processor to execute the insulation impedance detection method as described in any one of claims 10-12.

Images