A sampling circuit, a branch insulation impedance detection circuit and method

Abstract

This invention relates to the field of inverter technology and provides a sampling circuit, a branch insulation impedance detection circuit, and a method. The sampling circuit for branch insulation impedance detection, when the insulation impedance of the string inverter to ground is abnormal, is connected to the output terminal of any PV branch connected to the string inverter. It is used to adjust the impedance of the output terminal of that PV branch to ground to obtain the corresponding sampling voltage of the output terminal of that PV branch to ground. This invention can accurately locate PV branches with abnormal insulation impedance, improve detection efficiency, and reduce maintenance costs.

Description

Technical Field

[0001] This invention belongs to the field of inverter technology, and particularly relates to a sampling circuit, a branch insulation impedance detection circuit and method. Background Technology

[0002] Currently, string photovoltaic inverters with multi-channel MPPT (Maximum Power Point Tracking) controllers are increasingly widely used. However, photovoltaic modules are affected by factors such as weather, which may lead to equipment aging and changes in their insulation resistance to ground. These changes in insulation resistance can cause safety hazards. For example, excessively low insulation resistance can generate large leakage currents, resulting in electric shock risks, grid connection safety accidents, and personal injury and property damage.

[0003] In related technologies, the impedance to ground at the positive terminal BUS+, the negative terminal BUS-, or the midpoint BUS_M of the busbar is changed to obtain the voltage between BUS+, BUS-, or BUS_M and ground, thereby determining whether the insulation impedance of the prototype system to ground is abnormal. However, the current solution cannot determine the insulation impedance of each PV branch, cannot accurately detect abnormal PV branches for timely repair, and the detection effect is unsatisfactory.

[0004] Therefore, there is an urgent need in this field to solve the technical problem of accurately detecting abnormal PV branches. Summary of the Invention

[0005] This invention provides a sampling circuit for branch insulation impedance detection, aiming to solve the problem of accurately detecting abnormal PV branches.

[0006] The present invention is implemented as follows: a sampling circuit for detecting the insulation impedance of a branch circuit is provided. When the insulation impedance of the string inverter to ground is abnormal, the sampling circuit is connected to the output terminal of any PV branch connected to the string inverter to adjust the impedance of the output terminal of the any PV branch to ground, so as to obtain the sampling voltage of the output terminal of the corresponding PV branch to ground.

[0007] Furthermore, the sampling circuit includes a first impedance adjustment sub-circuit and / or a second impedance adjustment sub-circuit;

[0008] The first impedance adjustment sub-circuit is connected between the positive output terminal of any PV branch and ground to increase the impedance between the positive output terminal and ground;

[0009] The second impedance adjustment sub-circuit is connected between the negative output terminal of any of the PV branches and ground, and is used to increase the impedance between the negative output terminal and ground.

[0010] Furthermore, the sampling circuit further includes: a first voltage equalization sub-circuit and a second voltage equalization sub-circuit;

[0011] The first voltage equalization sub-circuit is connected between the positive output terminal of any PV branch and ground, and the second voltage equalization sub-circuit is connected between the negative output terminal of any PV branch and ground. The first voltage equalization sub-circuit and the second voltage equalization sub-circuit are used to equalize the voltage of the positive output terminal and the negative output terminal relative to ground.

[0012] Furthermore, the first impedance adjustment sub-circuit includes a first resistor and a first switch; wherein, one end of the first resistor is connected to the positive output terminal of any PV branch, the other end of the first resistor is connected to one end of the first switch, and the other end of the first switch is grounded, and the impedance between the positive output terminal of the PV branch and ground is adjusted by closing or opening the first switch.

[0013] The second impedance adjustment sub-circuit includes a second resistor and a second switch; wherein, one end of the second resistor is grounded, the other end of the second resistor is connected to one end of the second switch, and the other end of the second switch is connected to the negative output terminal of any PV branch, and the impedance between the negative output terminal of the PV branch and ground is adjusted by closing or opening the second switch.

[0014] Furthermore, the first voltage equalization sub-circuit includes at least one resistor, and the second voltage equalization sub-circuit includes at least one resistor.

[0015] The at least one resistor in the first voltage equalization sub-circuit is connected between the positive output terminal of any PV branch and ground, and the at least one resistor in the second voltage equalization sub-circuit is connected between the negative output terminal of any PV branch and ground.

[0016] Furthermore, the first voltage equalization sub-circuit includes a third resistor and a fourth resistor. One end of the third resistor is connected to the positive output terminal of any PV branch, the other end of the third resistor is connected to one end of the fourth resistor, and the other end of the fourth resistor is grounded.

[0017] The second voltage equalization sub-circuit includes a fifth resistor R5 and a sixth resistor R6. One end of the fifth resistor is grounded, and the other end of the fifth resistor is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to the negative output terminal of any PV branch.

[0018] Furthermore, the first voltage equalization sub-circuit includes a third resistor and a fourth resistor. One end of the third resistor is connected to the positive output terminal of any PV branch, the other end of the third resistor is connected to one end of the fourth resistor, and the other end of the fourth resistor is grounded.

[0019] The second voltage equalization sub-circuit includes a fifth resistor R5 and a sixth resistor R6. One end of the fifth resistor is grounded, and the other end of the fifth resistor is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to the negative output terminal of any PV branch.

[0020] The first impedance adjustment sub-circuit includes a first resistor and a first switch; wherein, one end of the first resistor is connected to the positive output terminal of any PV branch, the other end of the first resistor is connected to one end of the first switch, and the other end of the first switch is connected between the third resistor and the fourth resistor.

[0021] The second impedance adjustment sub-circuit includes a second resistor and a second switch; wherein, one end of the second resistor is grounded, the other end of the second resistor is connected to one end of the second switch, and the other end of the second switch is connected between the fifth resistor and the sixth resistor.

[0022] Furthermore, the resistance values ​​of the third resistor and the fifth resistor are equal, and the resistance values ​​of the fourth resistor and the sixth resistor are equal.

[0023] This invention also provides a branch insulation impedance detection circuit, comprising:

[0024] The aforementioned sampling circuit; and

[0025] A control logic circuit, connected to the sampling circuit, is used to obtain the sampling voltage of the output terminal of any PV branch relative to ground when adjusting the impedance of the output terminal of any PV branch to ground, determine the insulation impedance of any PV branch based on different sampling voltages and the output voltage of any PV branch, and determine whether the insulation impedance of any PV branch is abnormal based on a preset threshold.

[0026] This invention also provides a method for detecting branch insulation impedance, characterized in that it is implemented based on the aforementioned branch insulation impedance detection circuit, and the method includes:

[0027] If it is determined that the insulation impedance of the string inverter to ground is abnormal, each rotary switch of the string inverter is closed in turn, and the insulation impedance of the string inverter to ground is determined again.

[0028] If it is determined again that the insulation impedance of the string inverter to ground is abnormal, the sampling circuit is connected to the output terminal of the PV branch corresponding to the currently closed rotary switch, and the impedance of the output terminal of the PV branch to ground is adjusted to obtain the corresponding sampling voltage of the output terminal to ground.

[0029] The insulation impedance of the PV branch is determined based on different sampling voltages and the output voltage of the PV branch.

[0030] The insulation impedance of the PV branch is determined based on a preset threshold to determine whether an abnormality has occurred.

[0031] Furthermore, determining the insulation impedance of the PV branch based on different sampling voltages and the output voltage of the PV branch includes:

[0032] The first voltage of the negative output terminal of the PV branch to ground when the first switch is closed and the second switch is open, the second voltage of the negative output terminal of the PV branch to ground when the first switch is open and the second switch is closed, and the output voltage of the PV branch are obtained. The insulation impedance of the PV branch is calculated based on the first voltage, the second voltage and the output voltage.

[0033] Furthermore, the insulation impedance of the PV branch, calculated based on the first voltage, the second voltage, and the output voltage, is obtained using the following formula:

[0034]

[0035] Where R represents the insulation impedance of the PV branch, Req0 represents the equivalent resistance of the positive output terminal of the PV branch to ground, Req1 represents the equivalent resistance of the negative output terminal of the PV branch to ground, and intermediate variables... G is determined based on the first voltage, the second voltage, and the output voltage of the PV branch.

[0036] Furthermore, the step of determining whether the insulation impedance of the PV branch is abnormal based on a preset threshold includes:

[0037] If the insulation impedance of the PV branch does not reach the preset threshold, it is determined that the insulation impedance of the PV branch is abnormal.

[0038] The beneficial effects achieved by this invention are as follows:

[0039] In the event of abnormal insulation impedance of a string inverter to ground, this invention further connects a sampling circuit to the output terminal of any PV branch connected to the string inverter. Since the sampling circuit may adjust the impedance of the output terminal of the PV branch to ground, it can obtain different sampling voltages of the output terminal of the PV branch to ground. Based on the different sampling voltages and the output voltage of the PV branch, the insulation impedance of the PV branch can be accurately determined, thereby accurately locating the PV branch with abnormal insulation impedance, improving detection efficiency and reducing maintenance costs. Attached Figure Description

[0040] Figure 1 This is a block diagram of an insulation impedance detection scheme provided by existing technology;

[0041] Figure 2 This is a block diagram of a sampling circuit for branch insulation impedance detection provided in an embodiment of the present invention;

[0042] Figure 3 This is an example of a sampling circuit provided in an embodiment of the present invention;

[0043] Figure 4 This is another example of a sampling circuit provided in the embodiments of the present invention;

[0044] Figure 5 This is another example of a sampling circuit provided in the embodiments of the present invention;

[0045] Figure 6 This is another example of a sampling circuit provided in the embodiments of the present invention;

[0046] Figure 7 These are examples of high-impedance circuits and differential circuits provided in embodiments of the present invention;

[0047] Figure 8 This is an example of a voltage sampling circuit provided in an embodiment of the present invention;

[0048] Figure 9 This is a flowchart of the branch insulation impedance detection method provided in the embodiment of the present invention. Detailed Implementation

[0049] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0050] An insulation resistance detection scheme is provided in the prior art, such as Figure 1 As shown, this method uses the impedance of the positive terminal BUS+, the negative terminal BUS-, or the midpoint BUS_M of the busbar to ground to obtain the voltage between BUS+, BUS-, or BUS_M and ground, thereby determining whether the insulation impedance of the prototype system to ground is abnormal. However, the current solution cannot determine the insulation impedance of each PV branch, cannot accurately detect abnormal PV branches for timely repair, and the detection effect is unsatisfactory.

[0051] In cases where the insulation impedance of a string inverter to ground is abnormal, this invention further connects a sampling circuit to the output terminal of any PV branch connected to the string inverter. This adjusts the impedance of the PV branch's output terminal to ground and obtains a sampling voltage at that PV branch's output terminal to ground. Based on different sampling voltages and the output voltage of the PV branch, the insulation impedance of the PV branch can be determined, and it can be judged whether the insulation impedance of the PV branch is abnormal. The sampling circuit, branch insulation impedance detection circuit, and method of this invention can obtain different sampling voltages at the output terminal of the PV branch to ground by adjusting the insulation impedance of the PV branch, thereby accurately locating PV branches with abnormal insulation impedance, improving detection efficiency, and reducing maintenance costs.

[0052] Example 1

[0053] This embodiment provides a sampling circuit for branch insulation impedance detection. When the insulation impedance of the string inverter to ground is abnormal, the sampling circuit is connected to the output terminal of any PV branch connected to the string inverter to adjust the impedance of the output terminal of the PV branch to ground in order to obtain the corresponding sampling voltage of the output terminal of the PV branch to ground.

[0054] It should be understood that abnormal insulation impedance of a string inverter to ground can be achieved using existing technologies, which will not be described in detail here. This embodiment is a scheme for detecting the insulation impedance of a branch circuit when the overall insulation impedance of the string inverter to ground is abnormal, thereby identifying the PV branch with abnormal insulation impedance.

[0055] like Figure 2 As shown, the sampling circuit for branch insulation impedance detection provided in this embodiment is connected to the positive output terminal PV+ and the negative output terminal PV- of any PV branch connected to the string inverter. It should be noted that PV+ and PV- can refer to... Figure 2 The positive and negative output terminals of any PV branch, such as PV2+ and PV2-, can be connected to a control logic circuit to determine the insulation impedance of the PV branch based on different sampling voltages and the output voltage of the PV branch, and to determine whether the insulation impedance of the PV branch is abnormal, thereby improving detection efficiency and reducing maintenance costs.

[0056] In this embodiment, when the insulation impedance of the string inverter to ground is abnormal, a sampling circuit is connected to the output terminal of any PV branch connected to the string inverter to adjust the impedance of the output terminal of the PV branch to ground, thereby obtaining the sampling voltage of the output terminal of the PV branch to ground. The different sampling voltages obtained after adjustment are used to realize the insulation impedance detection of the PV branch, providing a calculation basis for determining the insulation impedance of the PV branch.

[0057] Example 2

[0058] Based on Example 1, such as Figure 3 As shown, the sampling circuit for branch insulation impedance detection includes a first impedance adjustment sub-circuit 201 and / or a second impedance adjustment sub-circuit 202.

[0059] The first impedance adjustment sub-circuit 201 is connected between the positive output terminal PV+ of any PV branch and ground, and is used to increase the impedance between the positive output terminal PV+ and ground.

[0060] The second impedance adjustment sub-circuit 202 is connected between the negative output terminal PV- of the PV branch and ground, and is used to increase the impedance between the negative output terminal PV- and ground.

[0061] Figure 3 In this diagram, the equivalent resistance of the positive output terminal PV+ to ground is denoted as Req0, and the equivalent resistance of the negative output terminal PV- to ground is denoted as Req1. The positive output terminal PV+ of the PV branch is connected to one end of the equivalent resistance Req0, and the other end of the equivalent resistance Req0 is grounded; the negative output terminal PV- is connected to one end of the equivalent resistance Req1, and the other end of the equivalent resistance Req1 is grounded. The insulation impedance of the PV branch needs to be obtained through these two equivalent resistances and the output voltage of the PV branch. These two equivalent resistances are unknowns, while the output voltage of the PV branch can be measured. In this embodiment, different data on the impedance between the output terminal and ground and the sampling voltage are obtained by changing the impedance between the output terminal and ground. Based on the different sampling voltages, the insulation impedance of the PV branch can be further determined.

[0062] In some cases, the sampling circuit may include a first impedance adjustment sub-circuit 201 and a second impedance adjustment sub-circuit 202. The impedance between the positive output terminal PV+ and ground and the impedance between the negative output terminal PV- and ground are adjusted by the first impedance adjustment sub-circuit 201 and the second impedance adjustment sub-circuit 202, respectively. This allows the two sets of impedances between the output terminals and ground and the corresponding sampling voltages to be obtained. Based on the different sampling voltages, the insulation impedance of the PV branch can be further determined.

[0063] In other cases, the sampling circuit may include only the first impedance adjustment sub-circuit 201 or the second impedance adjustment sub-circuit 202. When only one impedance adjustment sub-circuit is included, the impedance between the output terminal and ground can also be obtained, and different data of the impedance between the output terminal and ground and the sampling voltage can be obtained. Based on the different sampling voltages, the insulation impedance of the PV branch can be further determined.

[0064] In this embodiment, the impedance between the output terminal of the PV branch and ground is changed by the first impedance adjustment sub-circuit and / or the second impedance adjustment sub-circuit, so as to obtain different sampling voltages corresponding to different impedances. In this way, the insulation impedance of the PV branch can be further determined based on the different sampling voltages, thereby realizing the insulation impedance detection of the PV branch.

[0065] Example 3

[0066] Based on Example 2, such as Figure 3 As shown, the sampling circuit for branch insulation impedance detection also includes: a first voltage equalization sub-circuit 203 and a second voltage equalization sub-circuit 204.

[0067] The first voltage equalization sub-circuit 203 is connected between the positive output terminal PV+ of any PV branch and ground, and the second voltage equalization sub-circuit 204 is connected between the negative output terminal PV- of the PV branch and ground. The first voltage equalization sub-circuit 203 and the second voltage equalization sub-circuit 204 are used to equalize the voltage of the positive output terminal and the negative output terminal relative to ground.

[0068] In this embodiment, by using two voltage equalization sub-circuits, the voltage between the positive output terminal and ground of the PV branch and the voltage between the negative output terminal and ground can be made symmetrical, thus achieving a balanced effect.

[0069] Example 4

[0070] Based on Example 2, such as Figure 3 As shown, the first impedance adjustment sub-circuit 201 includes a first resistor R1 and a first switch SW1; wherein, one end of the first resistor R1 is connected to the positive output terminal PV+ of any PV branch, the other end of the first resistor R1 is connected to one end of the first switch SW1, and the other end of the first switch SW1 is grounded. The impedance between the positive output terminal of the PV branch and ground is adjusted by closing or opening the first switch SW1. For example, closing the first switch SW1 increases the impedance between the positive output terminal PV+ of the PV branch and ground.

[0071] The second impedance adjustment sub-circuit 202 includes a second resistor R2 and a second switch SW2. One end of the second resistor R2 is grounded, and the other end of the second resistor R2 is connected to one end of the second switch SW2. The other end of the second switch SW2 is connected to the negative output terminal PV- of the PV branch. The impedance between the negative output terminal of the PV branch and ground is adjusted by closing or opening the second switch SW2. For example, closing the second switch SW2 increases the impedance between the negative output terminal PV- of the PV branch and ground.

[0072] In the first impedance adjustment sub-circuit 201 and the second impedance adjustment sub-circuit 202, closing or opening the switch can connect the corresponding resistor, thereby increasing the impedance of the corresponding line. Taking the first impedance adjustment sub-circuit 201 as an example, closing the first switch SW1 allows the first resistor R1 to be connected, thereby increasing the impedance between the positive output terminal PV+ and ground. When the first switch SW1 is opened, it returns to the state where only the first voltage equalization sub-circuit 203 is connected. Similarly, taking the second impedance adjustment sub-circuit 202 as an example, closing the second switch SW2 allows the second resistor R2 to be connected, thereby increasing the impedance between the negative output terminal PV- and ground.

[0073] It should be understood that the sampling circuit may include both the first impedance adjustment sub-circuit 201 and the second impedance adjustment sub-circuit 202, or it may include only the first impedance adjustment sub-circuit 201 or the second impedance adjustment sub-circuit 202, for example, Figure 4 The sampling circuit shown only includes the first impedance adjustment sub-circuit 201.

[0074] In this embodiment, an impedance adjustment sub-circuit structure with a series resistor and switch is adopted. The impedance between the output terminal and ground is adjusted by closing or opening the switch to obtain different sampling voltages, which are used to determine the insulation impedance of the PV branch.

[0075] Example 5

[0076] Based on Example 4, such as Figure 3 As shown, the first voltage equalization sub-circuit 203 includes at least one resistor, and the second voltage equalization sub-circuit 204 includes at least one resistor.

[0077] At least one resistor in the first voltage equalization sub-circuit 203 is connected between the positive output terminal PV+ of any PV branch and ground, and at least one resistor in the second voltage equalization sub-circuit 204 is connected between the negative output terminal PV- of the PV branch and ground.

[0078] It should be understood that in other implementations, the first voltage equalization sub-circuit 203 / second voltage equalization sub-circuit 204 may include one resistor, two resistors, three resistors, four resistors, etc. By setting the resistance value, the voltage of the negative output terminal PV- of the PV branch to ground and the voltage of the positive output terminal PV+ of the PV branch to ground can be balanced.

[0079] In this embodiment, a resistor is used to implement the voltage equalization sub-circuit. By setting the resistance value of at least one resistor in the two voltage equalization sub-circuits, the voltage between the positive output terminal and ground of the PV branch and the voltage between the negative output terminal and ground can be made symmetrical, thus achieving the effect of equalization.

[0080] Example 6

[0081] Based on Example 5, such as Figure 3 As shown, the first voltage equalization sub-circuit 203 includes a third resistor R3 and a fourth resistor R4. One end of the third resistor R3 is connected to the positive output terminal PV+ of any PV branch, and the other end of the third resistor R3 is connected to one end of the fourth resistor R4. The other end of the fourth resistor R4 is grounded.

[0082] The second voltage equalization sub-circuit 204 includes a fifth resistor R5 and a sixth resistor R6. One end of the fifth resistor R5 is grounded, and the other end of the fifth resistor R5 is connected to one end of the sixth resistor R6. The other end of the sixth resistor R6 is connected to the negative output terminal PV- of the PV branch.

[0083] Preferably, the resistance values ​​of the third resistor R3 and the fifth resistor R5 are equal, and the resistance values ​​of the fourth resistor R4 and the sixth resistor R6 are equal. When R3 = R5 and R4 = R6, the voltage between the positive output terminal and ground and the voltage between the negative output terminal and ground of the PV branch can be symmetrical.

[0084] In this embodiment, by setting two resistors in series between the positive output terminal PV+ and ground, and between the negative output terminal PV- and ground, the voltage between the positive output terminal and ground and the voltage between the negative output terminal and ground of the PV branch can be made symmetrical by setting the resistance values ​​of these four resistors, thus achieving a balanced effect.

[0085] Example 7

[0086] Based on the aforementioned embodiment three, as Figure 5 As shown, the first voltage equalization sub-circuit 203 includes a third resistor R3 and a fourth resistor R4. One end of the third resistor R3 is connected to the positive output terminal PV+ of any PV branch, and the other end of the third resistor R3 is connected to one end of the fourth resistor R4. The other end of the fourth resistor R4 is grounded.

[0087] The second voltage equalization sub-circuit 204 includes a fifth resistor R5 and a sixth resistor R6. One end of the fifth resistor R5 is grounded, and the other end of the fifth resistor R5 is connected to one end of the sixth resistor R6. The other end of the sixth resistor R6 is connected to the negative output terminal PV- of the PV branch.

[0088] The first impedance adjustment sub-circuit 201 includes a first resistor R1 and a first switch SW1; wherein, one end of the first resistor R1 is connected to the positive output terminal PV+ of the PV branch, the other end of the first resistor R1 is connected to one end of the first switch SW1, and the other end of the first switch SW1 is connected between the third resistor R3 and the fourth resistor R4.

[0089] The second impedance adjustment sub-circuit 202 includes a second resistor R2 and a second switch SW2; wherein, one end of the second resistor R2 is grounded, the other end of the second resistor R2 is connected to one end of the second switch SW2, and the other end of the second switch SW2 is connected between the fifth resistor R5 and the sixth resistor R6.

[0090] It should be understood that the sampling circuit in this embodiment can be as follows: Figure 5 The circuit shown includes both a first impedance adjustment sub-circuit 201 and a second impedance adjustment sub-circuit 202. Alternatively, it may include only the first impedance adjustment sub-circuit 201 or the second impedance adjustment sub-circuit 202, for example. Figure 6 The sampling circuit shown only includes the first impedance adjustment sub-circuit 201.

[0091] Taking the first impedance adjustment sub-circuit 201 as an example, when the first switch SW1 is closed, the first resistor R1 is connected, causing the impedance between the positive output terminal PV+ of the PV branch and ground to change. When the first switch SW1 is open, the impedance between the positive output terminal PV+ of the PV branch and ground returns to the state when the first voltage equalization sub-circuit 203 is connected. The second impedance adjustment sub-circuit 202 is similar and will not be described in detail.

[0092] In this embodiment, an impedance adjustment sub-circuit structure with a series resistor and switch is adopted. By closing or opening the switch, the impedance between the output terminal and ground is adjusted, and different sampling voltages can be obtained to determine the insulation impedance of the PV branch.

[0093] Example 8

[0094] This embodiment provides a branch insulation impedance detection circuit, including:

[0095] Any of the sampling circuits provided in the foregoing embodiments; and

[0096] The control logic circuit is connected to the sampling circuit. When the impedance of the output terminal of any PV branch to ground is adjusted, the sampling voltage of the corresponding output terminal of the PV branch to ground is obtained. Based on the different sampling voltages and the output voltage of the PV branch, the insulation impedance of the PV branch is determined, and based on a preset threshold, it is determined whether the insulation impedance of the PV branch is abnormal.

[0097] In practical applications, the control logic circuit can be a control IC, such as a microcontroller or DSP. This embodiment does not impose any limitations on this.

[0098] In the sampling circuit of the aforementioned embodiment, the sampling point of the negative output terminal PV- of the PV branch is denoted as A, and the sampling point of the ground (casing) is denoted as B. The sampling voltage of the negative output terminal PV- of the PV branch to ground is high voltage. The connection between the control logic circuit and the sampling circuit can be achieved as follows: Figure 7The high-impedance circuit 701 and differential circuit 702 shown are used to implement the control logic circuit. The control logic circuit connects A and B through two high-resistance resistors in the high-impedance circuit 701, equalizing the high voltage through high resistance. The high voltage signal is then sent to the differential circuit 702, which outputs a low-voltage signal to the corresponding pin of the control IC to determine the insulation impedance of the PV branch. The two high-resistance resistors can have a resistance of 56MΩ. The differential circuit 702 can be a differential circuit composed of an operational amplifier and its surrounding circuitry; the operational amplifier can be a TLV90641. In some implementations, the high-impedance circuit 701 and differential circuit 702 can be part of the sampling circuit in the aforementioned embodiments, or they can be independent of the sampling circuit and control logic circuit.

[0099] When obtaining the sampling voltage of the output terminal of the corresponding PV branch to ground, different sampling voltages are measured through the aforementioned high-impedance circuit 701 and differential circuit 702. Furthermore, the output voltage of the PV branch can be measured by a high-voltage sensor or by a voltage sampling circuit. Specifically, the measurement is performed by a high-voltage sensor or a voltage sampling circuit. For example, the voltage sampling circuit could be... Figure 8 The voltage sampling circuit shown is connected to the negative output terminal PV- and the positive output terminal PV+ of the PV branch to obtain the voltage between the negative output terminal PV- and the positive output terminal PV+, which is the output voltage of the PV branch.

[0100] In this embodiment, when the insulation impedance of the string inverter to ground is abnormal, a sampling circuit is connected to the output terminal (positive output terminal PV+, negative output terminal PV-) of any PV branch connected to the string inverter. When the impedance of the output terminal of any PV branch to ground is adjusted by the sampling circuit, the control logic circuit can obtain the sampling voltage of the corresponding output terminal (negative output terminal PV-) to ground of that PV branch. Based on different sampling voltages and the output voltage of that PV branch, the insulation impedance of that PV branch is determined, and a preset threshold is used to determine whether the insulation impedance of that PV branch is abnormal. This allows for accurate identification of PV branches with abnormal insulation impedance, improving detection efficiency and reducing maintenance costs.

[0101] Example 9

[0102] This embodiment provides a branch insulation impedance detection method, implemented based on the branch insulation impedance detection circuit of the aforementioned embodiment. The branch insulation impedance detection method of this embodiment is as follows: Figure 9 As shown, it includes:

[0103] Step S901: If it is determined that the insulation impedance of the string inverter to ground is abnormal, close each rotary switch of the string inverter in turn, and determine again whether the insulation impedance of the string inverter to ground is abnormal.

[0104] Step S902: If it is determined again that the insulation impedance of the string inverter to ground is abnormal, the sampling circuit is connected to the output terminal of the PV branch corresponding to the currently closed rotary switch, and the impedance of the output terminal of the PV branch to ground is adjusted to obtain the corresponding sampling voltage of the output terminal to ground.

[0105] Step S903: Determine the insulation impedance of the PV branch based on different sampling voltages and the output voltage of the PV branch;

[0106] Step S904: Determine whether the insulation impedance of the PV branch is abnormal based on a preset threshold.

[0107] In practice, string inverters contain multiple rotary switches, each corresponding to at least one MPPT and at least one PV branch. In some cases, any PV branch may also be connected to other PV branches. When the string inverter self-test determines that its insulation impedance to ground is abnormal, if the PV branch with the abnormality cannot be identified, all PV branches need to be inspected, and specific instruments are required for inspection at specific time periods (such as at night), resulting in low detection efficiency and high maintenance costs. The method used in this embodiment does not require consideration of time periods, and the detection circuit structure is simple and easy to implement.

[0108] Specifically, when an abnormal insulation impedance of the string inverter to ground is determined, all rotary switches are opened, and then each rotary switch of the string inverter is closed in turn. The insulation impedance of the string inverter to ground is checked again to determine which rotary switch corresponds to the abnormal PV branch. When a rotary switch is closed and the abnormal insulation impedance of the string inverter to ground is confirmed again, the PV branch corresponding to the currently closed rotary switch is determined to be abnormal. A sampling circuit is connected to the output terminal of any PV branch corresponding to that rotary switch, and the impedance of the output terminal of that PV branch to ground is adjusted to obtain the corresponding negative output terminal sampling voltage to ground. Based on different sampling voltages and the output voltage of that PV branch, the insulation impedance of that PV branch is determined. Finally, based on a preset threshold, it can be determined whether the insulation impedance of that PV branch is abnormal. The preset threshold can be set according to actual needs, for example, 50K.

[0109] It should be understood that there may be more than one PV branch malfunctioning. Each time one rotary switch is closed, the remaining rotary switches are opened.

[0110] by Figure 2For example, a string inverter contains multiple rotary switches 1...n / 2, each corresponding to two MPPTs. For instance, rotary switch 1 corresponds to MPPT1 and MPPT2, and rotary switch 1 corresponds to four PV branches—PV1, PV2, PV3, and PV4. The positive output terminal PV1+ and negative output terminal PV1- of PV1 are connected to the positive output terminal PV2+ and negative output terminal PV2- of PV2, respectively. When rotary switch 1 is closed, if the insulation impedance of the string inverter to ground is again determined to be abnormal, then at least one of the PV branches PV1, PV2, PV3, and PV4 corresponding to rotary switch 1 has an abnormal detection impedance. A sampling circuit is connected to the output terminal of any PV branch corresponding to rotary switch 1 to adjust the impedance of that PV branch's output terminal to ground. It should be noted that when the sampling circuit is connected between the connection point of PV1 and PV2 and rotary switch 1, the insulation impedance of the two PV branches PV1 and PV2 can be determined. The same applies to PV3 and PV4, and will not be elaborated further.

[0111] In this embodiment, a branch insulation impedance detection circuit with a simple structure and easy implementation is used to detect the insulation impedance of the PV branch connected to the corresponding rotary switch when the insulation impedance of the string inverter to ground is determined to be abnormal. This can accurately identify the PV branch with abnormal insulation impedance, improve detection efficiency, and reduce maintenance costs.

[0112] Example 10

[0113] When the branch insulation impedance detection circuit includes the sampling circuit provided in Embodiment Six, the insulation impedance of the PV branch is determined based on different sampling voltages and the output voltage of the PV branch, including:

[0114] The first voltage of the negative output terminal PV- to ground of the PV branch when the first switch SW1 is closed and the second switch SW2 is open, the second voltage of the negative output terminal PV- to ground of the PV branch when the first switch SW1 is open and the second switch SW2 is closed, and the output voltage of the PV branch are obtained. The insulation impedance of the PV branch is calculated based on the first voltage, the second voltage and the output voltage.

[0115] The sampling point at the negative output terminal PV- of the PV branch is denoted as A, and the sampling point at the ground (casing) is denoted as B. Figure 3 and Figure 4 To explain:

[0116] by Figure 3When the state of the first switch SW1 is "ON" (closed) and the state of the second switch SW2 is "OFF" (open), the sampled voltage (first voltage) at points A and B is Va, and the output voltage of the PV branch is V1. Based on the fact that the inflow current and the outflow current are equal, we can obtain the relationship a):

[0117]

[0118] When the state of the first switch SW1 is "OFF" (open) and the state of the second switch SW2 is "ON" (closed), the sampled voltage (second voltage) at points A and B is Vb, and the output voltage of the PV branch is V1. Based on the fact that the inflow current and the outflow current are equal, we can obtain the relationship b):

[0119]

[0120] If R1 = R2, R3 = R5, and R4 = R6, then relation c) can be obtained from relations a) to b).

[0121]

[0122] remember The insulation impedance of the PV branch is calculated based on the first voltage, the second voltage, and the output voltage, using the following formula:

[0123]

[0124] Where R represents the insulation impedance of the PV branch, Req0 represents the equivalent resistance of the positive output terminal of the PV branch to ground, Req1 represents the equivalent resistance of the negative output terminal of the PV branch to ground, and intermediate variables... Va represents the first voltage, Vb represents the second voltage, V1 represents the third voltage, R1 represents the fourth voltage, R3 represents the third voltage, and R4 represents the fourth voltage.

[0125] by Figure 4 When the first switch SW1 is in the "OFF" (open) state, the sampled voltage (first voltage) at points A and B is Va, and the output voltage of the PV branch is V1. Based on the fact that the inflow current and the outflow current are equal, we can obtain the relationship d):

[0126]

[0127] When the first switch SW1 is in the "ON" (closed) state, the sampled voltage (second voltage) between points A and B is Vb, and the output voltage of the PV branch is V1. Based on the fact that the inflow current and the outflow current are equal, the relationship e) can be obtained:

[0128]

[0129] If R3 = R5 and R4 = R6, relation f) can be obtained from relations d) to e).

[0130]

[0131] remember The insulation impedance of the PV branch is calculated based on the first voltage, the second voltage, and the output voltage, using the following formula:

[0132]

[0133] Where R represents the insulation impedance of the PV branch, Req0 represents the equivalent resistance of the positive output terminal of the PV branch to ground, Req1 represents the equivalent resistance of the negative output terminal of the PV branch to ground, and intermediate variables... Va represents the first voltage, Vb represents the second voltage, V1 represents the third voltage, R1 represents the fourth voltage, R3 represents the third voltage, and R4 represents the fourth voltage.

[0134] In this embodiment, based on the branch insulation impedance detection circuit, the first voltage of the negative output terminal PV- to ground of the PV branch when the first switch SW1 is closed and the second switch SW2 is open, the second voltage of the negative output terminal PV- to ground of the PV branch when the first switch SW1 is open and the second switch SW2 is closed, and the output voltage of the PV branch are obtained. The insulation impedance of the PV branch can be calculated, thereby identifying the PV branch with insulation abnormality and enabling timely maintenance.

[0135] Example 11

[0136] Based on Example 9, the insulation impedance of the PV branch is determined to be abnormal based on a preset threshold, including:

[0137] If the insulation impedance of the PV branch does not reach the preset threshold, it is determined that the insulation impedance of the PV branch is abnormal.

[0138] It should be understood that if the insulation impedance of the PV branch reaches a preset threshold, then the insulation impedance of the PV branch is considered to be normal. The preset threshold can be set according to actual needs, for example, 50KΩ.

[0139] The sampling circuit, branch insulation impedance detection circuit, and method provided in this invention, when the insulation impedance of the string inverter to ground is abnormal, further connect a sampling circuit to the output terminal of any PV branch connected to the string inverter. Since the sampling circuit may adjust the impedance of the output terminal of the PV branch to ground, different sampling voltages of the output terminal of the PV branch to ground can be obtained. Based on the different sampling voltages and the output voltage of the PV branch, the insulation impedance of the PV branch can be accurately determined, thereby accurately locating the PV branch with abnormal insulation impedance. This invention has a simple structure and low cost. It can be used as a black box for detection circuits, independent of the string inverter, and can determine the insulation impedance status of all string branches. It can quickly locate the abnormal insulation impedance point of a certain PV branch, avoid repeated manual investigation, improve detection efficiency, and the solution is simple and practical. The investigation does not affect the user's power generation. It is easy to carry and transport, and reduces maintenance costs.

[0140] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A branch insulation impedance detection circuit, characterized in that, include: The sampling circuit for branch insulation impedance detection, when the insulation impedance of the string inverter to ground is abnormal, is connected to the output terminal of any PV branch connected to the string inverter, and is used to adjust the impedance of the output terminal of the PV branch to ground to obtain the corresponding sampling voltage of the output terminal of the PV branch to ground. Based on the different sampling voltages and the output voltage of the PV branch, the insulation impedance of the PV branch is determined, and whether the insulation impedance of the PV branch is abnormal is determined based on a preset threshold. A control logic circuit is connected to the sampling circuit; The sampling circuit includes a first impedance adjustment sub-circuit and a second impedance adjustment sub-circuit; The first impedance adjustment sub-circuit is connected between the positive output terminal of any PV branch and ground to increase the impedance between the positive output terminal and ground. The first impedance adjustment sub-circuit includes a first resistor and a first switch. One end of the first resistor is connected to the positive output terminal of any PV branch, and the other end of the first resistor is connected to one end of the first switch. The other end of the first switch is grounded. The impedance between the positive output terminal of the PV branch and ground is adjusted by closing or opening the first switch. The second impedance adjustment sub-circuit is connected between the negative output terminal of any PV branch and ground to increase the impedance between the negative output terminal and ground. The second impedance adjustment sub-circuit includes a second resistor and a second switch. One end of the second resistor is grounded, and the other end of the second resistor is connected to one end of the second switch. The other end of the second switch is connected to the negative output terminal of any PV branch. The impedance between the negative output terminal of the PV branch and ground is adjusted by closing or opening the second switch. The control logic circuit is used to, when adjusting the impedance of the output terminal of any PV branch to ground, acquire the first voltage of the negative output terminal of the PV branch to ground when the first switch is closed and the second switch is open, the second voltage of the negative output terminal of the PV branch to ground when the first switch is open and the second switch is closed, and the output voltage of the PV branch, calculate the insulation impedance of the PV branch based on the first voltage, the second voltage and the output voltage, and determine whether the insulation impedance of any PV branch is abnormal based on a preset threshold. The insulation impedance of the PV branch is calculated based on the first voltage, the second voltage, and the output voltage using the following formula: in, This indicates the insulation resistance of the PV branch. This represents the equivalent resistance of the positive output terminal of the PV branch to ground. This represents the equivalent resistance of the negative output terminal of the PV branch to ground; an intermediate variable. , The output voltage of the PV branch is determined based on the first voltage and the second voltage.

2. The branch insulation impedance detection circuit according to claim 1, characterized in that, It also includes: a first voltage equalization sub-circuit and a second voltage equalization sub-circuit; The first voltage equalization sub-circuit is connected between the positive output terminal of any PV branch and ground, and the second voltage equalization sub-circuit is connected between the negative output terminal of any PV branch and ground. The first voltage equalization sub-circuit and the second voltage equalization sub-circuit are used to equalize the voltage of the positive output terminal and the negative output terminal relative to ground.

3. The branch insulation impedance detection circuit according to claim 2, characterized in that, The first voltage equalization sub-circuit includes at least one resistor, and the second voltage equalization sub-circuit includes at least one resistor; The at least one resistor in the first voltage equalization sub-circuit is connected between the positive output terminal of any PV branch and ground, and the at least one resistor in the second voltage equalization sub-circuit is connected between the negative output terminal of any PV branch and ground.

4. The branch insulation impedance detection circuit according to claim 3, characterized in that, The first voltage equalization sub-circuit includes a third resistor and a fourth resistor. One end of the third resistor is connected to the positive output terminal of any PV branch, the other end of the third resistor is connected to one end of the fourth resistor, and the other end of the fourth resistor is grounded. The second voltage equalization sub-circuit includes a fifth resistor and a sixth resistor. One end of the fifth resistor is grounded, and the other end of the fifth resistor is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to the negative output terminal of any PV branch.

5. The branch insulation impedance detection circuit according to claim 2, characterized in that, The first voltage equalization sub-circuit includes a third resistor and a fourth resistor. One end of the third resistor is connected to the positive output terminal of any PV branch, the other end of the third resistor is connected to one end of the fourth resistor, and the other end of the fourth resistor is grounded. The second voltage equalization sub-circuit includes a fifth resistor and a sixth resistor. One end of the fifth resistor is grounded, and the other end of the fifth resistor is connected to one end of the sixth resistor. The other end of the sixth resistor is connected to the negative output terminal of any PV branch. The first impedance adjustment sub-circuit includes a first resistor and a first switch; wherein, one end of the first resistor is connected to the positive output terminal of any PV branch, the other end of the first resistor is connected to one end of the first switch, and the other end of the first switch is connected between the third resistor and the fourth resistor. The second impedance adjustment sub-circuit includes a second resistor and a second switch; wherein, one end of the second resistor is grounded, the other end of the second resistor is connected to one end of the second switch, and the other end of the second switch is connected between the fifth resistor and the sixth resistor.

6. The branch insulation impedance detection circuit according to claim 4 or 5, characterized in that, The third resistor has the same resistance value as the fifth resistor, and the fourth resistor has the same resistance value as the sixth resistor.

7. A method for detecting the insulation impedance of a branch circuit, characterized in that, Based on the branch insulation impedance detection circuit according to any one of claims 1 to 6, the branch insulation impedance detection method includes: If it is determined that the insulation impedance of the string inverter to ground is abnormal, each rotary switch of the string inverter is closed in turn, and the insulation impedance of the string inverter to ground is determined again. If it is determined again that the insulation impedance of the string inverter to ground is abnormal, the sampling circuit is connected to the output terminal of the PV branch corresponding to the currently closed rotary switch, and the impedance of the output terminal of the PV branch to ground is adjusted to obtain the corresponding sampling voltage of the output terminal to ground. The insulation impedance of the PV branch is determined based on different sampling voltages and the output voltage of the PV branch. Determine whether the insulation impedance of the PV branch is abnormal based on a preset threshold. When the branch insulation impedance detection circuit includes the sampling circuit of claim 6, determining the insulation impedance of the PV branch based on different sampling voltages and the output voltage of the PV branch includes: The first voltage of the negative output terminal of the PV branch to ground when the first switch is closed and the second switch is open, the second voltage of the negative output terminal of the PV branch to ground when the first switch is open and the second switch is closed, and the output voltage of the PV branch are obtained. The insulation impedance of the PV branch is calculated based on the first voltage, the second voltage and the output voltage. The insulation impedance of the PV branch is calculated based on the first voltage, the second voltage, and the output voltage using the following formula: in, This indicates the insulation resistance of the PV branch. This represents the equivalent resistance of the positive output terminal of the PV branch to ground. This represents the equivalent resistance of the negative output terminal of the PV branch to ground; an intermediate variable. , The output voltage of the PV branch is determined based on the first voltage and the second voltage.

8. The branch insulation impedance detection method according to claim 7, characterized in that, The step of determining whether the insulation impedance of the PV branch is abnormal based on a preset threshold includes: If the insulation impedance of the PV branch does not reach the preset threshold, it is determined that the insulation impedance of the PV branch is abnormal.

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