Ground insulation impedance detection circuit and detection method

Abstract

The invention discloses a ground insulation resistance detection circuit and a detection method. The ground insulation resistance detection circuit comprises a resistor element, a plurality of relays and a sampling circuit, the positive electrode and / or the negative electrode of the photovoltaic equipment are / is grounded through the resistor element; the plurality of relays are respectively connected in parallel with part of resistors in the resistor element and are used for adjusting the equivalent resistance of the positive electrode and / or the negative electrode of the photovoltaic equipment to the ground; the sampling circuit is used for measuring the voltage of the positive electrode and / or the negative electrode of the photovoltaic equipment to the ground. Further, the resistor element comprises a plurality of resistors; at least one pair of resistors has the same resistance value, and the resistance value of at least one pair of resistors is integer multiples of the resistance value of the other resistor. According to the invention, the detection precision of the ground insulation impedance of the photovoltaic inverter can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of photovoltaic systems, and in particular to a ground insulation impedance detection circuit and a detection method. Background Art

[0002] In the photovoltaic inverter system, the photovoltaic inverter is affected by the external environment, causing the insulation impedance of the photovoltaic module input port to the ground to change, resulting in an increase in leakage current. When the residual leakage current is greater than, for example, 30mA, people who come into contact with the system will be at risk of electric shock. Therefore, in order to ensure the safe and reliable operation of the photovoltaic system and prevent electric shock, an insulation impedance detection circuit is required to detect the insulation impedance so as to promptly discover and eliminate safety hazards.

[0003] However, the conventional method for detecting the insulation impedance of photovoltaic inverters to the ground is usually to change the voltage of PV+ (positive pole) and PV- (negative pole) to the ground. A set of equations is established based on the voltage division state before and after the change, and the values ​​of the insulation impedance of PV+ and PV- to the ground are obtained by solving. However, when the impedance of PV+ to the ground is large, since the sampled voltage of PV- to the ground is small, simply changing the equivalent parallel impedance of PV- to the ground cannot cause much change in the voltage of PV+ and PV- to the ground. In addition, due to the influence of circuit noise, AD accuracy, and op amp offset current, the error of the voltage sampling value is large, resulting in a large difference between the calculated insulation impedance value and the actual value. Summary of the invention

[0004] The purpose of the present invention is to provide a ground insulation impedance detection circuit and detection method, which can improve the detection accuracy of the ground insulation impedance of a photovoltaic inverter.

[0005] In order to solve the above technical problems, the present invention provides a ground insulation impedance detection circuit, comprising: a resistor element, a plurality of relays and a sampling circuit;

[0006] The positive electrode and / or the negative electrode of the photovoltaic device is grounded via the resistance element;

[0007] The plurality of relays are respectively connected in parallel with some resistors in the resistance element to adjust the equivalent resistance of the positive electrode and / or the negative electrode of the photovoltaic device to the ground;

[0008] The sampling circuit is used to measure the voltage between the positive electrode and / or the negative electrode of the photovoltaic device and the ground.

[0009] Furthermore, the resistance element includes a plurality of resistors; at least one pair of the resistors has the same resistance value, and at least one pair of the resistors has a resistance value that is an integer multiple of a resistance value of another resistor.

[0010] Furthermore, the photovoltaic device includes a photovoltaic inverter.

[0011] Further, the resistor element includes: a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor and an eighth resistor;

[0012] The plurality of relays include: a first relay, a second relay, a third relay and a fourth relay;

[0013] The positive electrode of the photovoltaic device is grounded through the first resistor, the second resistor, the third resistor and the fourth resistor in sequence; the negative electrode of the photovoltaic device is grounded through the eighth resistor, the seventh resistor, the sixth resistor and the fifth resistor in sequence;

[0014] The first relay is connected in parallel with the second resistor;

[0015] The second relay is connected in parallel with the third resistor;

[0016] The third relay is connected in parallel with the sixth resistor;

[0017] The fourth relay is connected in parallel with the seventh resistor.

[0018] Further, the resistance element includes: a first resistor, a second resistor, a third resistor, and a fourth resistor; the plurality of relays include: a first relay, a second relay, and a third relay;

[0019] The first resistor, the second resistor, the third resistor and the fourth resistor are connected in sequence between the positive and negative electrodes of the photovoltaic device; the positive electrode of the photovoltaic device is connected to one end of the first resistor; the negative electrode of the photovoltaic device is connected to one end of the fourth resistor;

[0020] One end of the first relay is connected between the other end of the first resistor and the second resistor, and the other end is grounded;

[0021] One end of the second relay is connected between one end of the third resistor away from the second resistor and the fourth resistor, and the other end is grounded;

[0022] One end of the third relay is connected between one end of the second resistor away from the first resistor and the third resistor, and the other end is grounded.

[0023] In addition, the present invention also proposes a method for detecting insulation impedance to ground, which uses the above-mentioned insulation impedance detection circuit to ground, and specifically includes the following steps:

[0024] Control the opening or closing of multiple relays;

[0025] The voltage between the positive electrode and the negative electrode of the photovoltaic device and the ground is measured by a sampling circuit to obtain a first voltage value between the positive electrode and the ground and a second voltage value between the negative electrode and the ground;

[0026] Determine the relative magnitude of the insulation resistance of the positive electrode and the negative electrode to ground according to the first voltage value and the second voltage value, and obtain the voltage values ​​of the positive electrode and the negative electrode to ground measured multiple times by controlling the opening or closing of the corresponding relay;

[0027] The insulation resistance values ​​of the positive electrode and the negative electrode of the photovoltaic device to the ground are calculated according to the first voltage value, the second voltage value and the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times.

[0028] Furthermore, the controlling of the opening or closing of the plurality of relays specifically includes:

[0029] The first relay and the third relay of the photovoltaic device are opened, and the second relay and the fourth relay are closed.

[0030] Further, judging the relative magnitude of the insulation resistance of the positive electrode and the negative electrode to the ground according to the first voltage value and the second voltage value, and obtaining the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times by controlling the opening or closing of the corresponding relay, specifically includes:

[0031] when or Determine the insulation resistance R of the positive electrode to ground X Less than or equal to the insulation resistance R of the negative pole to ground Y , controlling the third relay and the fourth relay to close, and the first relay and the second relay to open, and then sampling by the sampling circuit to obtain a third voltage value of the positive electrode to the ground and a fourth voltage value of the negative electrode to the ground;

[0032] According to the principle of series voltage division, the equations are as follows:

[0033]

[0034] Solve to get R X With R Y The values ​​are:

[0035]

[0036] Wherein n>3, V1 is the first voltage value of the positive pole to the ground, V2 is the second voltage value of the negative pole to the ground, V3 is the third voltage value of the positive pole to the ground, and V4 is the fourth voltage value of the negative pole to the ground; R1, R2, R3, R4, R5, R6, R7 and R8 are respectively the first resistor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the seventh resistor and the eighth resistor of the photovoltaic device, and R1=R4=R5=R8=R, R2=R3=R6=R7=NR, wherein N is a positive integer, and N>10.

[0037] Furthermore, when Determine the insulation resistance R of the positive electrode to ground X Greater than the insulation resistance R of the negative pole to ground Y , controlling the first relay and the second relay to close, and the third relay and the fourth relay to open, and then sampling by the sampling circuit to obtain a fifth voltage value of the positive electrode to the ground and a sixth voltage value of the negative electrode to the ground;

[0038] According to the principle of series voltage division, the equations are as follows:

[0039]

[0040] Solve to get R X With R Y The values ​​are:

[0041]

[0042] Wherein n>3, V5 and V6 are the fifth voltage value of the positive electrode to the ground and the sixth voltage value of the negative electrode to the ground respectively.

[0043] Furthermore, the controlling of the opening or closing of the plurality of relays specifically includes:

[0044] The first relay and the second relay of the photovoltaic device are opened, and the third relay is closed.

[0045] Further, judging the relative magnitude of the insulation resistance of the positive electrode and the negative electrode to the ground according to the first voltage value and the second voltage value, and obtaining the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times by controlling the opening or closing of the corresponding relay, specifically includes:

[0046] when or Determine the insulation resistance R of the positive electrode to ground X Less than or equal to the insulation resistance R of the negative pole to ground Y , controlling the second relay to close, the first relay and the third relay to open, and then sampling by the sampling circuit to obtain a third voltage value of the positive electrode to the ground and a fourth voltage value of the negative electrode to the ground;

[0047] According to the principle of series voltage division, the equations are as follows:

[0048]

[0049] Solve to get R X With R Y The values ​​are:

[0050]

[0051] Wherein n>3, V1 is the first voltage value of the positive pole to the ground, V2 is the second voltage value of the negative pole to the ground, V3 is the third voltage value of the positive pole to the ground, and V4 is the fourth voltage value of the negative pole to the ground; R1, R2, R3 and R4 are the first resistor, second resistor, third resistor and fourth resistor of the photovoltaic device respectively, R1=R4=R, R2=R3=NR, wherein N is a positive integer, and N>10.

[0052] Furthermore, when Determine the insulation resistance R of the positive electrode to ground X Greater than the insulation resistance R of the negative pole to ground Y , controlling the first relay to close, the third relay and the second relay to open, and then sampling by the sampling circuit to obtain a fifth voltage value of the positive electrode to the ground and a sixth voltage value of the negative electrode to the ground;

[0053] According to the principle of series voltage division, the equations are as follows:

[0054]

[0055] Solve to get R X With R Y The values ​​are:

[0056]

[0057] Wherein n>3, V5 and V6 are the fifth voltage value of the positive electrode to the ground and the sixth voltage value of the negative electrode to the ground respectively.

[0058] Through the above technical solution, the present invention has the following beneficial effects:

[0059] Through the setting of a resistor element, multiple relays and a sampling circuit; and the positive and / or negative poles of the photovoltaic device are grounded through the resistor element; multiple relays are respectively connected in parallel with some resistors in the resistor element to adjust the equivalent resistance of the positive and / or negative poles of the photovoltaic device to the ground; the sampling circuit is used to measure the voltage of the positive and / or negative poles of the photovoltaic device to the ground. The present invention improves the detection accuracy of the insulation impedance of the photovoltaic inverter to the ground by controlling the conduction and shutdown of the relay and utilizing the voltage division principle of the resistor. More accurate insulation impedance detection can more effectively prevent the risk of leakage, thereby improving the safety of the photovoltaic system. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 Schematic diagram of the circuit structure of a photovoltaic inverter in a ground insulation impedance detection circuit in one embodiment of the present invention;

[0061] Figure 2 This is a schematic diagram of a circuit structure when the second relay and the fourth relay of a photovoltaic inverter are closed, and the first relay and the third relay are disconnected in one embodiment of the present invention;

[0062] Figure 3 This is a schematic diagram of a circuit structure when the third relay and the fourth relay of a photovoltaic inverter are closed and the first relay and the second relay are disconnected in one embodiment of the present invention;

[0063] Figure 4 This is a schematic diagram of a circuit structure when the first relay and the second relay of a photovoltaic inverter are closed, and the third relay and the fourth relay are disconnected in one embodiment of the present invention;

[0064] Figure 5 It is a flow chart of a method for detecting the insulation impedance of a photovoltaic inverter to the ground in a method for detecting the insulation impedance to the ground in one embodiment of the present invention;

[0065] Figure 6 Schematic diagram of the circuit structure of a photovoltaic inverter in a ground insulation impedance detection circuit in another embodiment of the present invention;

[0066] Figure 7 A schematic diagram of a circuit structure when the third relay of a photovoltaic inverter is closed and the first relay and the second relay are disconnected in another embodiment of the present invention;

[0067] Figure 8 This is a schematic diagram of a circuit structure when the second relay of a photovoltaic inverter is closed and the first relay and the third relay are disconnected in another embodiment of the present invention;

[0068] Fig. 9 This is a schematic diagram of a circuit structure when the first relay of a photovoltaic inverter is closed and the second relay and the third relay are disconnected in another embodiment of the present invention;

[0069] Fig.10 It is a flow chart of a method for detecting the insulation impedance of a photovoltaic inverter to the ground in a method for detecting the insulation impedance to the ground in another embodiment of the present invention;

[0070] Fig.11 The figure is a flow chart of a method for detecting insulation impedance to ground in one embodiment of the present invention. DETAILED DESCRIPTION

[0071] A ground insulation impedance detection circuit and detection method of the present invention will be described in more detail below in conjunction with the accompanying drawings, wherein preferred embodiments of the present invention are shown. It should be understood that those skilled in the art can modify the present invention described herein while still achieving the beneficial effects of the present invention. Therefore, the following description should be understood as being widely known to those skilled in the art and not as a limitation of the present invention.

[0072] The present invention is described in more detail in the following paragraphs by way of example with reference to the accompanying drawings. The advantages and features of the present invention will become more apparent from the following description. It should be noted that the accompanying drawings are in very simplified form and are not in exact proportions, and are only used to facilitate and clearly assist in explaining the purpose of the embodiments of the present invention.

[0073] like Figure 1-10 As shown, an embodiment of the present invention provides a ground insulation impedance detection circuit, including a resistor element, multiple relays and a sampling circuit.

[0074] Specifically, the positive electrode and / or negative electrode of the photovoltaic device is grounded through the resistor element; a plurality of the relays are respectively connected in parallel with some of the resistors in the resistor element to adjust the equivalent resistance of the positive electrode and / or negative electrode of the photovoltaic device to the ground; the sampling circuit is used to measure the voltage of the positive electrode and / or negative electrode of the photovoltaic device to the ground. Different combination states of the relays allow the sampling circuit to measure the voltage of the positive electrode and / or negative electrode of the photovoltaic device to the ground under different resistance configurations, which helps to obtain more accurate voltage data.

[0075] In this embodiment, the resistor element includes a plurality of resistors; at least one pair of the resistors has the same resistance value, and at least one pair of the resistors has a resistance value that is an integer multiple of a resistance value of another resistor.

[0076] In a specific example, the photovoltaic device includes a photovoltaic inverter.

[0077] For example, taking the photovoltaic inverter as an example, continue to refer to Figure 1-Figure 4 As shown, in one embodiment, the resistor element includes: a first resistor R1, a second resistor R2, a third resistor R3, a fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7 and an eighth resistor R8.

[0078] Specifically, the multiple relays include: a first relay S1, a second relay S2, a third relay S3, and a fourth relay S4; the positive pole PV+ of the photovoltaic inverter (i.e., the photovoltaic device) is grounded through the first resistor R1, the second resistor R2, the third resistor R3, and the fourth resistor R4 in sequence; the negative pole PV- of the photovoltaic inverter is grounded through the eighth resistor R8, the seventh resistor R7, the sixth resistor R6, and the fifth resistor R5 in sequence; the first relay S1 is connected in parallel with the second resistor R2; the second relay S2 is connected in parallel with the third resistor R3; the third relay S3 is connected in parallel with the sixth resistor R6; the fourth relay S4 is connected in parallel with the seventh resistor R7. By controlling the on and off of the relay, the resistance network in the circuit can be changed to obtain different voltage values ​​to the ground. The insulation impedance to the ground can be calculated more accurately by the voltage value. The parallel and series configurations of the relays provide a variety of circuit states, so that the detection circuit can be flexibly adjusted according to actual needs to adapt to different detection conditions.

[0079] Among them, the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 are connected in series in sequence, and the end of the first resistor R1 away from the second resistor R2 is connected to the positive electrode PV+ of the photovoltaic inverter; the end of the fourth resistor R4 away from the third resistor R3 is grounded. The eighth resistor R8, the seventh resistor R7, the sixth resistor R6 and the fifth resistor R5 are connected in series in sequence, and the end of the eighth resistor R8 away from the seventh resistor R7 is connected to the positive electrode PV- of the photovoltaic inverter; the end of the fifth resistor R5 away from the sixth resistor R6 is grounded.

[0080] In another embodiment, continue to refer to Figure 6-Figure 9 As shown, the resistance element includes: a first resistor R1, a second resistor R2, a third resistor R3, and a fourth resistor R4; the plurality of relays include: a first relay S1, a second relay S2, and a third relay S3.

[0081] Specifically, the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 are connected in sequence between the positive and negative poles of the photovoltaic inverter; the positive pole PV+ of the photovoltaic inverter is connected to one end of the first resistor R1; the negative pole PV- of the photovoltaic inverter is connected to one end of the fourth resistor R4; one end of the first relay S1 is connected between the other end of the first resistor R1 and the second resistor R2, and the other end is grounded; one end of the second relay S2 is connected between the end of the third resistor R3 away from the second resistor R2 and the fourth resistor R4, and the other end is grounded; one end of the third relay S3 is connected between the end of the second resistor R2 away from the first resistor R1 and the third resistor R3, and the other end is grounded. By controlling the conduction and shutdown of the relay, the resistance network in the circuit can be changed to obtain different voltage values ​​to the ground. The insulation impedance to the ground can be calculated more accurately through the voltage value. The parallel and series configurations of the relay provide a variety of circuit states, so that the detection circuit can be flexibly adjusted according to actual needs to adapt to different detection conditions.

[0082] In addition, combined Figure 5 , Fig.10 and Fig.11 As shown, this embodiment also proposes a method for detecting insulation impedance to ground, using the above-mentioned insulation impedance detection circuit to ground, and specifically comprising the following steps:

[0083] S1, control the opening or closing of multiple relays;

[0084] S2, measuring the voltage between the positive electrode and the negative electrode of the photovoltaic device and the ground through a sampling circuit to obtain a first voltage value between the positive electrode and the ground and a second voltage value between the negative electrode and the ground;

[0085] S3. Determine the relative magnitude of the insulation resistance of the positive electrode and the negative electrode to the ground according to the first voltage value and the second voltage value, and obtain the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times by controlling the opening or closing of the corresponding relay;

[0086] S4. Calculate the insulation resistance value of the positive electrode and the negative electrode of the photovoltaic device to the ground according to the first voltage value, the second voltage value and the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times.

[0087] Continuing to take the photovoltaic inverter as an example, in one embodiment, continue to refer to Figure 1-Figure 5 As shown, the control of opening or closing of the plurality of relays specifically includes: opening the first relay S1 and the third relay S3 of the photovoltaic inverter, and closing the second relay S2 and the fourth relay S4.

[0088] In this embodiment, the voltage between the positive pole and the negative pole of the photovoltaic device and the ground is measured by a sampling circuit to obtain a first voltage value of the positive pole to the ground and a second voltage value of the negative pole to the ground, specifically including: sampling the voltage between the positive pole PV+ and the negative pole PV- of the photovoltaic inverter and the ground by the sampling circuit to obtain the first voltage value V1 and the second voltage value V2.

[0089] In a specific example, judging the relative size of the insulation resistance of the positive electrode and the negative electrode to the ground according to the first voltage value and the second voltage value, and obtaining the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times by controlling the opening or closing of the corresponding relay, specifically includes: when Determine the insulation resistance R of the positive electrode PV+ to ground X Smaller than (or much smaller than) the negative PV-to-ground insulation resistance R Y , control the third relay S3 and the fourth relay S4 to close, the first relay S1 and the second relay S2 to open, and then sample the third voltage value V3 of the positive electrode PV+ to the ground and the fourth voltage value V4 of the negative electrode PV- to the ground through the sampling circuit; according to the principle of series voltage division, the equation group is obtained as follows:

[0090]

[0091] Solve to get R X With R Y The values ​​are:

[0092]

[0093] Wherein n>3, V1 is the first voltage value of the positive pole PV+ to the ground, V2 is the second voltage value of the negative pole PV- to the ground, V3 is the third voltage value of the positive pole to the ground, and V4 is the fourth voltage value of the negative pole to the ground; R1, R2, R3, R4, R5, R6, R7 and R8 are respectively the first resistor R1, the second resistor R2, the third resistor R3, the fourth resistor R4, the fifth resistor R5, the sixth resistor R6, the seventh resistor R7 and the eighth resistor R8 of the photovoltaic inverter, and R1=R4=R5=R8=R, R2=R3=R6=R7=NR, wherein N is a positive integer, and N>10.

[0094] In another specific example, when Determine the insulation resistance R of the positive electrode PV+ to ground X Equal to (or approximately equal to) the negative PV-to-ground insulation resistance R Y, control the third relay S3 and the fourth relay S4 to be closed, the first relay S1 and the second relay S2 to be opened, and then sample the third voltage value V3 of the positive electrode PV+ to the ground and the fourth voltage value V4 of the negative electrode PV- to the ground through the sampling circuit; according to the principle of series voltage division, the equation group is obtained as follows:

[0095]

[0096] Solve to get R X With R Y The values ​​are:

[0097]

[0098] In another embodiment, when Determine the insulation resistance R of the positive electrode PV+ to ground X Greater than (or much greater than) the negative PV-to-ground insulation resistance R Y , control the first relay S1 and the second relay S2 to close, the third relay S3 and the fourth relay S4 to open, and then sample the fifth voltage value V5 of the positive electrode PV+ to the ground and the sixth voltage value V6 of the negative electrode PV- to the ground through the sampling circuit; according to the principle of series voltage division, the equation group is obtained as follows:

[0099]

[0100] Solve to get R X With R Y The values ​​are:

[0101]

[0102] Wherein n>3, V5 and V6 are the fifth voltage value of the positive pole PV+ to the ground and the sixth voltage value of the negative pole PV- to the ground respectively.

[0103] By judging according to the above conditions The interval in which the corresponding relay is located is controlled to open and close, and the positive pole PV+ and negative pole PV- to ground voltages are obtained for the second time. The two-variable linear equation group is combined with the positive pole PV+ and negative pole PV- to ground voltages obtained for the first time to solve the insulation impedance of the photovoltaic inverter to ground.

[0104] In another embodiment, continue to refer to Figure 6-Figure 10 As shown, the control of opening or closing of multiple relays specifically includes: opening the first relay S1 and the second relay S2 of the photovoltaic inverter, and closing the third relay S3.

[0105] In this embodiment, the voltage between the positive pole and the negative pole of the photovoltaic device and the ground is measured by a sampling circuit to obtain a first voltage value of the positive pole to the ground and a second voltage value of the negative pole to the ground, specifically including: sampling the voltage between the positive pole PV+ and the negative pole PV- of the photovoltaic inverter and the ground by the sampling circuit to obtain the first voltage value V1 and the second voltage value V2.

[0106] In a specific example, judging the relative size of the insulation resistance of the positive electrode and the negative electrode to the ground according to the first voltage value and the second voltage value, and obtaining the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times by controlling the opening or closing of the corresponding relay, specifically includes: when Determine the insulation resistance R of the positive electrode PV+ to ground X Smaller than (or much smaller than) the negative PV-to-ground insulation resistance R Y , control the second relay S2 to close, the first relay S1 and the third relay S3 to open, and then sample the third voltage value V3 of the positive electrode PV+ to the ground and the fourth voltage value V4 of the negative electrode PV- to the ground through the sampling circuit; according to the principle of series voltage division, the equation group is obtained as follows:

[0107]

[0108] Solve to get R X With R Y The values ​​are:

[0109]

[0110]

[0111] Wherein n>3, V1 is the first voltage value of the positive pole PV+ to the ground, V2 is the second voltage value of the negative pole PV- to the ground, V3 is the third voltage value of the positive pole to the ground, and V4 is the fourth voltage value of the negative pole to the ground; R1, R2, R3 and R4 are respectively the first resistor R1, the second resistor R2, the third resistor R3 and the fourth resistor R4 of the photovoltaic inverter, R1=R4=R, R2=R3=NR, wherein N is a positive integer, and N>10.

[0112] In another specific example, when Determine the insulation resistance R of the positive electrode PV+ to ground X Equal to (or approximately equal to) the negative PV-to-ground insulation resistance R Y , control the second relay S2 to close, the first relay S1 and the third relay S3 to open, and then sample the third voltage value V3 of the positive electrode PV+ to the ground and the fourth voltage value V4 of the negative electrode PV- to the ground through the sampling circuit; according to the principle of series voltage division, the equation group is obtained as follows:

[0113]

[0114] Solve to get R X With R Y The values ​​are:

[0115]

[0116] In another specific example, when Determine the insulation resistance R of the positive electrode PV+ to ground X Greater than (or much greater than) the negative PV-to-ground insulation resistance R Y , control the first relay S1 to close, the third relay S3 and the second relay S2 to open, and then sample the fifth voltage value V5 of the positive electrode PV+ to the ground and the sixth voltage value V6 of the negative electrode PV- to the ground through the sampling circuit; according to the principle of series voltage division, the equation group is obtained as follows:

[0117]

[0118] Solve to get R X With R Y The values ​​are:

[0119]

[0120] Wherein n>3, V5 and V6 are the fifth voltage value of the positive pole PV+ to the ground and the sixth voltage value of the negative pole PV- to the ground respectively.

[0121] By judging according to the above conditions The interval in which the corresponding relay is located is controlled to open and close, and the positive pole PV+ and negative pole PV- to ground voltages are obtained for the second time. The two-variable linear equation group is combined with the positive pole PV+ and negative pole PV- to ground voltages obtained for the first time to solve the insulation impedance of the photovoltaic inverter to ground.

[0122] In this embodiment, a photovoltaic inverter is taken as an example, and specific parameter values ​​are substituted to calculate the insulation resistance to ground, for example, N=11, R1=R4=R5=R8=1MΩ, R2=R3=R6=R7=N×R1=11MΩ, VBUS=500V, n=5, The specific calculation results are shown in Table 1.

[0123] Table 1. Calculation of insulation resistance value of photovoltaic inverter to ground

[0124]

[0125]

[0126] In summary, the ground insulation impedance detection circuit and detection method proposed by the present invention have the following advantages:

[0127] Through the setting of a resistor element, multiple relays and a sampling circuit; and the positive and / or negative poles of the photovoltaic device are grounded through the resistor element; multiple relays are respectively connected in parallel with some resistors in the resistor element to adjust the equivalent resistance of the positive and / or negative poles of the photovoltaic device to the ground; the sampling circuit is used to measure the voltage of the positive and / or negative poles of the photovoltaic device to the ground. The present invention improves the detection accuracy of the insulation impedance of the photovoltaic inverter to the ground by controlling the conduction and shutdown of the relay and utilizing the voltage division principle of the resistor. More accurate insulation impedance detection can more effectively prevent the risk of leakage, thereby improving the safety of the photovoltaic system.

[0128] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention is also intended to include these modifications and variations.

Claims

1. A ground insulation impedance detection circuit, characterized in that: include: Resistor elements, multiple relays, and sampling circuits; The positive electrode and / or the negative electrode of the photovoltaic device is grounded via the resistance element; The plurality of relays are respectively connected in parallel with some resistors in the resistance element to adjust the equivalent resistance of the positive electrode and / or the negative electrode of the photovoltaic device to the ground; The sampling circuit is used to measure the voltage between the positive electrode and / or the negative electrode of the photovoltaic device and the ground.

2. The ground insulation impedance detection circuit according to claim 1, characterized in that: The resistor element includes a plurality of resistors; at least one pair of the resistors has the same resistance value, and at least one pair of the resistors has a resistance value that is an integer multiple of a resistance value of another resistor.

3. The ground insulation impedance detection circuit according to claim 1, characterized in that: The photovoltaic device includes a photovoltaic inverter.

4. The ground insulation impedance detection circuit according to claim 1, characterized in that: The resistor element includes: a first resistor, a second resistor, a third resistor, a fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor and an eighth resistor; The plurality of relays include: a first relay, a second relay, a third relay and a fourth relay; The positive electrode of the photovoltaic device is grounded through the first resistor, the second resistor, the third resistor and the fourth resistor in sequence; the negative electrode of the device is grounded through the eighth resistor, the seventh resistor, the sixth resistor and the fifth resistor in sequence; The first relay is connected in parallel with the second resistor; The second relay is connected in parallel with the third resistor; The third relay is connected in parallel with the sixth resistor; The fourth relay is connected in parallel with the seventh resistor.

5. The ground insulation impedance detection circuit according to claim 1, characterized in that: The resistance element includes: a first resistor, a second resistor, a third resistor, and a fourth resistor; the plurality of relays include: a first relay, a second relay, and a third relay; The first resistor, the second resistor, the third resistor and the fourth resistor are connected in sequence between the positive and negative electrodes of the photovoltaic device; the positive electrode of the photovoltaic device is connected to one end of the first resistor; the negative electrode of the device is connected to one end of the fourth resistor; One end of the first relay is connected between the other end of the first resistor and the second resistor, and the other end is grounded; One end of the second relay is connected between one end of the third resistor away from the second resistor and the fourth resistor, and the other end is grounded; One end of the third relay is connected between one end of the second resistor away from the first resistor and the third resistor, and the other end is grounded.

6. A method for detecting insulation impedance to ground, using the insulation impedance detection circuit to ground as described in any one of claims 1 to 5, characterized in that: The details include: Control the opening or closing of multiple relays; The voltage between the positive electrode and the negative electrode of the photovoltaic device and the ground is measured by a sampling circuit to obtain a first voltage value between the positive electrode and the ground and a second voltage value between the negative electrode and the ground; Determine the relative magnitude of the insulation resistance of the positive electrode and the negative electrode to ground according to the first voltage value and the second voltage value, and obtain the voltage values ​​of the positive electrode and the negative electrode to ground measured multiple times by controlling the opening or closing of the corresponding relay; The insulation resistance values ​​of the positive electrode and the negative electrode of the photovoltaic device to the ground are calculated according to the first voltage value, the second voltage value and the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times.

7. The method for detecting insulation impedance to ground according to claim 6, characterized in that: The controlling of opening or closing of the plurality of relays specifically comprises: The first relay and the third relay of the photovoltaic device are opened, and the second relay and the fourth relay are closed.

8. The method for detecting insulation impedance to ground according to claim 7, characterized in that: The step of determining the relative magnitude of the insulation resistance of the positive electrode and the negative electrode to the ground according to the first voltage value and the second voltage value, and obtaining the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times by controlling the opening or closing of the corresponding relay, specifically includes: when Determine the insulation resistance R of the positive electrode to ground X is less than or equal to the insulation resistance RY of the negative electrode to the ground, controlling the third relay and the fourth relay to close, and the first relay and the second relay to open, and then sampling by the sampling circuit to obtain a third voltage value of the positive electrode to the ground and a fourth voltage value of the negative electrode to the ground; According to the principle of series voltage division, the equations are as follows: Solve to get R X With R Y The values ​​are: Wherein n>3, V1 is the first voltage value of the positive pole to the ground, V2 is the second voltage value of the negative pole to the ground, V3 is the third voltage value of the positive pole to the ground, and V4 is the fourth voltage value of the negative pole to the ground; R1, R2, R3, R4, R5, R6, R7 and R8 are respectively the first resistor, the second resistor, the third resistor, the fourth resistor, the fifth resistor, the sixth resistor, the seventh resistor and the eighth resistor of the photovoltaic device, and R1=R4=R5=R8=R, R2=R3=R6=R7=NR, wherein N is a positive integer, and N>10.

9. The method for detecting insulation impedance to ground according to claim 8, characterized in that: when Determine the insulation resistance R of the positive electrode to ground X Greater than the insulation resistance R of the negative pole to ground Y , controlling the first relay and the second relay to close, and the third relay and the fourth relay to open, and then sampling by the sampling circuit to obtain a fifth voltage value of the positive electrode to the ground and a sixth voltage value of the negative electrode to the ground; According to the principle of series voltage division, the equations are as follows: Solve to get R X With R Y The values ​​are: Wherein n>3, V5 and V6 are the fifth voltage value of the positive electrode to the ground and the sixth voltage value of the negative electrode to the ground respectively.

10. The method for detecting insulation impedance to ground according to claim 6, characterized in that: The controlling of opening or closing of the plurality of relays specifically comprises: The first relay and the second relay of the photovoltaic device are opened, and the third relay is closed.

11. The method for detecting insulation impedance to ground according to claim 10, characterized in that: The step of determining the relative magnitude of the insulation resistance of the positive electrode and the negative electrode to the ground according to the first voltage value and the second voltage value, and obtaining the voltage values ​​of the positive electrode and the negative electrode to the ground measured multiple times by controlling the opening or closing of the corresponding relay, specifically includes: when Determine the insulation resistance R of the positive electrode to ground X Less than or equal to the insulation resistance R of the negative pole to ground Y , controlling the second relay to close, the first relay and the third relay to open, and then sampling by the sampling circuit to obtain a third voltage value of the positive electrode to the ground and a fourth voltage value of the negative electrode to the ground; According to the principle of series voltage division, the equations are as follows: Solve to get R X With R Y The values ​​are: Wherein n>3, V1 is the first voltage value of the positive pole to the ground, V2 is the second voltage value of the negative pole to the ground, V3 is the third voltage value of the positive pole to the ground, and V4 is the fourth voltage value of the negative pole to the ground; R1, R2, R3 and R4 are the first resistor, second resistor, third resistor and fourth resistor of the photovoltaic device respectively, R1=R4=R, R2=R3=NR, wherein N is a positive integer, and N>10.

12. The method for detecting insulation impedance to ground according to claim 11, characterized in that: when Determine the insulation resistance R of the positive electrode to ground X Greater than the insulation resistance R of the negative pole to ground Y , controlling the first relay to close, the third relay and the second relay to open, and then sampling by the sampling circuit to obtain a fifth voltage value of the positive electrode to the ground and a sixth voltage value of the negative electrode to the ground; According to the principle of series voltage division, the equations are as follows: Solve to get R X With R Y The values ​​are: Wherein n>3, V5 and V6 are the fifth voltage value of the positive electrode to the ground and the sixth voltage value of the negative electrode to the ground respectively.

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