Insulation impedance detection circuit, impedance detection method, converter and photovoltaic centrifuge

Abstract

The invention discloses an insulation impedance detection circuit, an impedance detection method, a converter and a photovoltaic centrifuge. The insulation impedance detection circuit includes: an impedance detection module connected between the positive and negative poles of a DC bus to be tested, the impedance detection module includes: a first resistance bridge and a second resistance bridge arranged in parallel, the first resistance bridge is connected to the positive pole of the DC bus to be tested through a sampling resistor R1, the second resistance bridge is connected to the negative pole of the DC bus to be tested through a sampling resistor R2, the sampling resistor R1 and the sampling resistor R2 are both configured with a voltage sampling chip, and the impedance detection module calculates the insulation impedance value of the DC bus to be tested according to the voltage values ​​of the two sampling resistors before and after the switch S is switched. The invention can realize the calculation of insulation impedance value, and has the advantages of low cost and high precision.

Description

Technical Field

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

[0002] Photovoltaic insulation impedance is an indicator for judging the electrical insulation performance of photovoltaic modules. Aging of power cables and other insulating materials or even insulation damage will greatly reduce the insulation strength, which will affect personnel safety and the normal operation of low-voltage electrical equipment. Testing photovoltaic insulation performance is of great significance to ensuring the normal operation of operation and maintenance personnel and electrical equipment.

[0003] The current mainstream insulation impedance detection method is the unbalanced resistance method, such as the invention patent with application number 201610067090.5, which directly collects the voltage values ​​of the positive and negative poles of the bus to the ground, combines the output value of the DC leakage current sensor, and calculates the branch grounding resistance value. Directly sampling the voltage values ​​of the positive and negative poles of the DC bus to the ground requires a voltage sensor. The more accurate the voltage sensor, the greater the cost, the lower the practicality, and it is difficult to be widely used.

[0004] Moreover, even if a sampling resistor is designed in the impedance detection circuit and the voltage of the sampling resistor is detected to convert the positive and negative poles of the DC bus to the ground, the impedance calculation formula will amplify the error of the sampling voltage by hundreds of times due to the very large unbalanced resistance value. At the same time, there is a certain error in the voltage sampling chip itself, and sampling correction is generally required through software. However, each impedance detection module may require a different correction value. The existing voltage sampling chip correction method is to manually set the correction value and correct the sampling chip individually, which has poor flexibility and is difficult to correct.

[0005] Therefore, how to design a low-cost insulation impedance detection circuit that can calculate the insulation impedance value is a technical problem that needs to be solved urgently in the industry. Summary of the invention

[0006] In order to solve the defects existing in the prior art, the present invention proposes an insulation impedance detection circuit, an impedance detection method, an inverter and a photovoltaic centrifuge. The insulation impedance detection circuit sets a sampling resistor between the positive and negative poles of the DC bus to be tested, and samples the voltage value of the sampling resistor through a voltage sampling chip to realize insulation impedance value calculation with low circuit cost.

[0007] The technical solution adopted by the present invention is to design an insulation impedance detection circuit, including: an impedance detection module connected between the positive and negative poles of the DC bus to be tested, the impedance detection module including: a first resistance bridge and a second resistance bridge arranged in parallel, the first resistance bridge is composed of a resistor R3 and a resistor R4 connected in series, the connecting line between the resistor R3 and the resistor R4 is grounded, the second resistance bridge is composed of the resistor R5, the resistor R6 and a switch S separated between the resistor R5 and the resistor R6, and the resistor R5 or the resistor R6 is grounded through the switch S.

[0008] Resistors R3 and R5 are connected to the positive electrode of the DC bus to be measured through sampling resistor R1, resistors R4 and R6 are connected to the negative electrode of the DC bus to be measured through sampling resistor R2, sampling resistors R1 and R2 are both equipped with voltage sampling chips, and the impedance detection module calculates the insulation impedance value of the DC bus to be measured according to the voltage values ​​of the two sampling resistors before and after the switch S is switched.

[0009] Preferably, the insulation impedance detection circuit also includes: a converter DC bus arranged in parallel with the DC bus to be tested, a positive correction resistor R7 and a switch S1 connected in series between the positive pole of the converter DC bus and the ground, and a negative correction resistor R8 and a switch S2 connected in series between the negative pole of the converter DC bus and the ground. The impedance detection module calculates the insulation impedance value of the converter DC bus according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, compares the insulation impedance value and the corresponding correction resistor, and corrects the voltage sampling chip according to the comparison result.

[0010] Preferably, when the difference between the insulation impedance value of the converter DC bus and the corresponding correction resistor exceeds a set impedance error value, the impedance detection module sends out an insulation impedance fault alarm signal.

[0011] Among them, when the switch S1 is turned on and the switch S2 is turned off, the impedance detection module calculates the positive electrode-to-ground impedance value of the converter DC bus according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, compares the positive electrode-to-ground impedance value with the positive electrode correction resistor, and calibrates the voltage sampling chip according to the comparison result; when the switch S1 is turned off and the switch S2 is turned on, the impedance detection module calculates the negative electrode-to-ground impedance value of the converter DC bus according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, compares the negative electrode-to-ground impedance value with the negative electrode correction resistor, and calibrates the voltage sampling chip according to the comparison result.

[0012] Preferably, the positive and negative poles of the converter DC bus are connected to the DC bus to be tested through circuit breaker S3 respectively; when the impedance detection module calculates the insulation impedance value of the converter DC bus, circuit breaker S3 is in a disconnected state, and the bus capacitor on the converter DC bus is discharged.

[0013] Preferably, the impedance detection module is provided with a positive interface connected to the sampling resistor R1 and a negative interface connected to the sampling resistor R2, the positive interface is connected to the positive pole of the converter DC bus through switch S4 and to the positive pole of the DC bus to be tested through switch S5, and the negative interface is connected to the negative pole of the converter DC bus through switch S6 and to the negative pole of the DC bus to be tested through switch S7.

[0014] Among them, when the impedance detection module calculates the insulation impedance value of the DC bus of the converter, switch S4 and switch S6 are turned on, and switch S5 and switch S7 are turned off; when the impedance detection module calculates the insulation impedance value of the DC bus to be tested, switch S4 and switch S6 are turned off, and switch S5 and switch S7 are turned on.

[0015] In a preferred embodiment, the resistance values ​​of the resistors R3 , R4 , R5 and R6 are the same.

[0016] The present invention also provides an impedance detection method for the above insulation impedance detection circuit, comprising the following steps:

[0017] Connect the impedance detection module between the positive and negative poles of the DC bus to be tested;

[0018] Switch the switch S so that one of the resistors R5 and R6 is grounded;

[0019] Detect the voltage values ​​of the sampling resistors R1 and R2, and calculate the positive voltage V of the DC bus to be tested based on the voltage values. 正对地1 and negative voltage to ground V 负对地1 ;

[0020] Switching the switch S so that the other of the resistor R5 and the resistor R6 is grounded;

[0021] Detect the voltage values ​​of the sampling resistors R1 and R2, and calculate the positive voltage V of the DC bus to be tested based on the voltage values. 正对地2 and negative voltage to ground V 负对地2 ;

[0022] According to V 正对地1 、V 负对地1 、V 正对地2 and V 负对地2 Calculate the insulation resistance value of the DC bus to be tested.

[0023] When V 正对地1 and V 负对地1 When the corresponding resistor R5 is grounded, V 正对地2 and V 负对地2 When the corresponding resistor R6 is grounded, the positive voltage V of the DC bus to be measured is calculated according to the voltage value. 正对地1 and negative voltage to ground V 负对地1 The calculation formula is Calculate the positive voltage V of the DC bus to be tested based on the voltage value 正对地2 and negative voltage to ground V 负对地2 The calculation formula is V R1 is the voltage value of the sampling resistor R1 when the resistor R5 is grounded, V R1 ’ is the voltage value of the sampling resistor R1 when the resistor R6 is grounded, V R2 is the voltage value of the sampling resistor R2 when the resistor R5 is grounded, V R2 ’ It is the voltage value of the sampling resistor R2 when the resistor R6 is grounded.

[0024] Preferably, the positive voltage V of the DC bus to be tested is calculated according to the voltage value 正对地1 and negative voltage to ground V 负对地1 Afterwards, determine whether |V 正对地1 +V 负对地1 -V DC |≥V 设定 , V DC is the bus voltage of the DC bus to be tested, V 设定 To set the voltage error value;

[0025] If so, compare V 正对地1 and V 负对地1 The size of V 正对地1 >V 负对地1 When V 正对地1 =V 正对地1 、V 负对地1 =V DC -V 正对地1 , when V 正对地1 ≤V 负对地1 When V 负对地1 =V 负对地1 、V 正对地1 =V DC -V 负对地1 ;

[0026] If not, store V 正对地1 =V 正对地1 、V 负对地1 =V 负对地1 .

[0027] Preferably, the positive voltage V of the DC bus to be tested is calculated according to the voltage value 正对地2 and negative voltage to ground V 负对地2 Afterwards, determine whether |V 正对地2 +V 负对地2 -V DC |≥V 设定 , V DC is the bus voltage of the DC bus to be tested, V 设定To set the voltage error value;

[0028] If so, compare V 正对地2 and V 负对地2 The size of V 正对地2 >V 负对地2 When V 正对地2 =V 正对地2 、V 负对地2 =V DC -V 正对地2 , when V 正对地2 ≤V 负对地2 When V 负对地2 =V 负对地2 、V 正对地2 =V DC -V 负对地2 ;

[0029] If not, store V 正对地2 =V 正对地2 、V 负对地2 =V 负对地2 .

[0030] Preferably, when V 正对地1 and V 负对地1 The corresponding resistor R5 is grounded, V 正对地2 and V 负对地2 When the corresponding resistor R6 is grounded, according to V 正对地1 、V 负对地1 、V 正对地2 and V 负对地2 The calculation formula for calculating the insulation impedance value of the DC bus to be tested is: Rx is the impedance value of the positive electrode to the ground, and Ry is the impedance value of the negative electrode to the ground.

[0031] Preferably, the impedance detection method further comprises: first calibrating the voltage sampling chip, and then connecting the impedance detection module between the positive and negative poles of the DC bus to be tested after the calibration is completed.

[0032] The present invention also proposes a current transformer using the insulation impedance detection circuit.

[0033] The present invention also provides a photovoltaic centrifuge having the above-mentioned converter, wherein the above-mentioned DC bus to be tested is a DC bus of a photovoltaic module.

[0034] Compared with the prior art, the present invention has the following technical effects:

[0035] 1. Design a sampling resistor between the positive and negative poles of the DC bus to be tested. Each sampling resistor is equipped with a lower-cost voltage sampling chip. The collected voltage value is used to convert the positive and negative poles of the bus to the ground. The circuit cost is low and the practicality is high.

[0036] 2. The impedance detection module is externally designed with a correction circuit, which corrects the sampling accuracy of the voltage sampling chip, improves the calculation accuracy of the insulation impedance value, and reduces the error of the impedance calculation value;

[0037] 3. The correction circuit is applicable to different impedance detection modules. The impedance detection module can perform self-correction before calculating the insulation impedance value of the DC bus to be measured. After the correction is completed, the voltage value of the sampling resistor is collected. It is highly flexible and suitable for popularization. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] The present invention is described in detail below with reference to the embodiments and accompanying drawings, wherein:

[0039] Figure 1 It is a connection diagram of the impedance detection module in the present invention;

[0040] Figure 2 It is a connection diagram of the insulation impedance detection circuit in the present invention;

[0041] Figure 3 It is a schematic diagram of the process of the detection method of the present invention. DETAILED DESCRIPTION

[0042] like Figure 1 As shown, the insulation impedance detection circuit proposed in the present invention can be but is not limited to being used in a converter. The insulation impedance detection circuit includes an impedance detection module, which detects and calculates the insulation impedance value of a DC bus to be measured. The impedance detection module can be connected to the DC bus to be measured as an independent module. In a preferred embodiment, the insulation impedance detection circuit also includes a correction circuit arranged outside the impedance detection module. The impedance detection module is connected to the DC bus to be measured or the DC bus of the converter through the correction circuit. The resistance values ​​of all resistors in the insulation impedance detection circuit are known.

[0043] like Figure 2 As shown, specifically, the impedance detection module is connected between the positive and negative poles of the DC bus to be tested, and the impedance detection module includes: a first resistance bridge and a second resistance bridge arranged in parallel, the first resistance bridge is composed of a resistor R3 and a resistor R4 connected in series, the connection line between the resistor R3 and the resistor R4 is grounded, and the second resistance bridge is composed of a resistor R5, a resistor R6 and a switch S separated between the resistor R5 and the resistor R6, and the resistor R5 or the resistor R6 is grounded through the switch S. In order to facilitate the calculation of the insulation impedance value, in a preferred embodiment, the resistance values ​​of the resistors R3, R4, R5 and R6 are the same.

[0044] The resistor R3 and the resistor R5 are both connected to the positive electrode of the DC bus to be measured through the sampling resistor R1, and the resistor R4 and the resistor R6 are both connected to the negative electrode of the DC bus to be measured through the sampling resistor R2. The sampling resistor R1 and the sampling resistor R2 are both configured with a voltage sampling chip. The first voltage sampling chip collects the voltage across the sampling resistor R1, and the second voltage sampling chip collects the voltage across the sampling resistor R2. The voltage sampling chip can use an optocoupler isolation chip, which has low cost and controllable accuracy. The impedance detection module calculates the insulation impedance value of the DC bus to be measured according to the voltage values ​​of the two sampling resistors before and after the switch S is switched. The insulation impedance value includes the positive electrode to ground impedance and the negative electrode to ground impedance. The calculation method is described in detail later.

[0045] The correction circuit outside the impedance detection module includes: a converter DC bus arranged in parallel with the DC bus to be tested, a positive correction resistor R7 and a switch S1 connected in series between the positive pole of the converter DC bus and the ground, and a negative correction resistor R8 and a switch S2 connected in series between the negative pole of the converter DC bus and the ground.

[0046] The positive and negative poles of the converter DC bus are connected to the DC bus to be tested through the circuit breaker S3 respectively. Before calibrating the voltage sampling chip, the capacitor on the converter DC bus is charged first. After charging is completed, the circuit breaker S3 is placed in the disconnected state, and the bus capacitor on the converter DC bus is discharged. During the calibration process, the impedance detection module calculates the insulation impedance value of the converter DC bus according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, compares the insulation impedance value and the corresponding calibration resistor, and calibrates the voltage sampling chip according to the comparison result. The calibration here refers to calibrating the AD value of the voltage sampling chip, that is, reducing the sampling error of the voltage sampling chip.

[0047] The impedance detection module is provided with a positive interface connected to the sampling resistor R1 and a negative interface connected to the sampling resistor R2. The positive interface is connected to the positive pole of the converter DC bus through switch S4 and to the positive pole of the DC bus to be measured through switch S5. The negative interface is connected to the negative pole of the converter DC bus through switch S6 and to the negative pole of the DC bus to be measured through switch S7. The working state of the correction circuit is as follows.

[0048] When the voltage sampling chip is calibrated, switch S4 and switch S6 are turned on, switch S5 and switch S7 are turned off, then switch S1 is turned on, switch S2 is turned off, the positive correction resistor is connected in series between the positive pole and the ground of the converter DC bus, the resistance value of the positive correction resistor is the actual positive pole to ground impedance value of the converter DC bus, switch S in the impedance detection module is switched, resistor R5 and resistor R6 are grounded respectively, the impedance detection module calculates the positive pole to ground impedance value of the converter DC bus according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, compares the positive pole to ground impedance value with the positive correction resistor, that is, compares the calculated positive pole to ground impedance value with the actual positive pole to ground impedance value, and calibrates the voltage sampling chip according to the comparison result. Then, when switch S1 is disconnected and switch S2 is connected, the negative electrode correction resistor is connected in series between the converter DC bus and the negative electrode and the ground. The resistance value of the negative electrode correction resistor is the actual negative electrode-to-ground impedance value of the converter DC bus. Switch switch S in the impedance detection module to ground resistors R5 and R6 respectively. The impedance detection module calculates the negative electrode-to-ground impedance value of the converter DC bus according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, and compares the negative electrode-to-ground impedance value with the negative electrode correction resistor, that is, compares the calculated negative electrode-to-ground impedance value with the actual negative electrode-to-ground impedance value, and calibrates the voltage sampling chip again according to the comparison result. It should be noted that the order of the two corrections can be swapped, and the present invention does not limit this.

[0049] When the impedance detection module calculates the insulation impedance value of the DC bus to be measured, switches S4 and S6 are disconnected, switches S5 and S7 are connected, switches S1 and S2 are also disconnected, and switch S in the impedance detection module is switched to ground resistors R5 and R6 respectively. The impedance detection module calculates the insulation impedance value of the DC bus to be measured based on the voltage values ​​of the two sampling resistors before and after the switch S is switched.

[0050] like Figure 3 As shown, the present invention also provides an impedance detection method of the above insulation impedance detection circuit, comprising the following steps:

[0051] The impedance detection module is connected between the positive and negative electrodes of the DC bus to be tested, that is, the switch S4 and the switch S6 are disconnected, the switch S5 and the switch S7 are connected, the switch S1 and the switch S2 are disconnected, the sampling resistor R1 is connected to the positive electrode of the DC bus to be tested, and the sampling resistor R2 is connected to the negative electrode of the DC bus to be tested;

[0052] Switch S so that one of the resistors R5 and R6 is grounded. Figure 2 When the middle switch S is closed to the upper side, the resistor R5 is grounded; when the switch S is closed to the lower side, the resistor R6 is grounded;

[0053] Detect the voltage values ​​of the sampling resistors R1 and R2, and calculate the positive voltage V of the DC bus to be tested based on the voltage values. 正对地1 and negative voltage to ground V负对地1 ;

[0054] Switching the switch S so that the other of the resistor R5 and the resistor R6 is grounded;

[0055] Detect the voltage values ​​of the sampling resistors R1 and R2, and calculate the positive voltage V of the DC bus to be tested based on the voltage values. 正对地2 and negative voltage to ground V 负对地2 ;

[0056] According to V 正对地1 、V 负对地1 、V 正对地2 and V 负对地2 Calculate the insulation resistance value of the DC bus to be tested.

[0057] In the following text, V 正对地1 and V 负对地1 When the corresponding resistor R5 is grounded, V 正对地2 and V 负对地2 Taking the grounding of the corresponding resistor R6 as an example, the specific calculation method in the detection method is explained.

[0058] Calculate the positive voltage V of the DC bus to be tested based on the voltage value 正对地1 and negative voltage to ground V 负对地1 The calculation formula is Calculate the positive voltage V of the DC bus to be tested based on the voltage value 正对地2 and negative voltage to ground V 负对地2 The calculation formula is V R1 is the voltage value of the sampling resistor R1 when the resistor R5 is grounded, V R1 ’ is the voltage value of the sampling resistor R1 when the resistor R6 is grounded, V R2 is the voltage value of the sampling resistor R2 when the resistor R5 is grounded, V R2 ’ It is the voltage value of the sampling resistor R2 when the resistor R6 is grounded.

[0059] Furthermore, since the voltage sampling chip is nonlinear and has a large error when the sampling voltage is low, in order to increase V 正对地1 and V 负对地1 The accuracy of the DC bus voltage V to ground is calculated based on the voltage value. 正对地1 and negative voltage to ground V 负对地1 After that, since the correct relationship should be V 正对地1 +V 负对地1 =V DC , so by judging whether |V 正对地1 +V 负对地1 -V DC |≥V 设定, we can determine whether the calculated voltage to ground is accurate, V DC is the bus voltage of the DC bus to be measured, which can be obtained by direct acquisition, V 设定 To set the voltage error value, it can be set by manual input according to actual conditions;

[0060] If so, compare V 正对地1 and V 负对地1 The size of V 正对地1 >V 负对地1 When V 正对地1 =V 正对地1 、V 负对地1 =V DC -V 正对地1 , when V 正对地1 ≤V 负对地1 When V 负对地1 =V 负对地1 、V 正对地1 =V DC -V 负对地1 ;

[0061] If not, store V 正对地1 =V 正对地1 、V 负对地1 =V 负对地1 .

[0062] Similarly, in order to increase V 正对地2 and V 负对地2 The accuracy of the DC bus voltage V to ground is calculated based on the voltage value. 正对地2 and negative voltage to ground V 负对地2 After that, since the correct relationship should be V 正对地2 +V 负对地2 =V DC , so by judging whether |V 正对地2 +V 负对地2 -V DC |≥V 设定 , it can be determined whether the calculated voltage to ground is accurate;

[0063] If so, compare V 正对地2 and V 负对地2 The size of V 正对地2 >V 负对地2 When V 正对地2 =V 正对地2 、V 负对地2 =V DC -V 正对地2 , when V 正对地2 ≤V 负对地2 When V 负对地2 =V 负对地2 、V 正对地2 =VDC -V 负对地2 ;

[0064] If not, store V 正对地2 =V 正对地2 、V 负对地2 =V 负对地2 .

[0065] Finally, according to V 正对地1 、V 负对地1 、V 正对地2 and V 负对地2 The calculation formula for calculating the insulation impedance value of the DC bus to be tested is: Rx is the impedance value of the positive electrode to the ground, and Ry is the impedance value of the negative electrode to the ground.

[0066] It should be noted that during the calibration process, the DC bus to be tested is disconnected from the impedance detection module, and the converter DC bus is connected to the impedance detection module as the DC bus to be tested. The subsequent switching of the switch S and the calculation process of the insulation impedance value are exactly the same as above.

[0067] Preferably, the impedance detection method also includes: first calibrating the voltage sampling chip, and then connecting the impedance detection module between the positive and negative poles of the DC bus to be tested after the calibration is completed. The calibration process has been described in detail above and will not be repeated here. Furthermore, during the calibration process, after closing switches S4 and S6 and opening switches S5 and S7, the impedance detection board first detects and calculates the insulation impedance value of the converter DC bus, and only judges the converter insulation impedance performance without considering the accuracy of the calculated impedance value. If the difference between the insulation impedance value and the corresponding correction resistance exceeds the set impedance error value, an insulation impedance fault alarm signal is issued and the calibration process stops. Among them, the set impedance error value can be set by manual input according to actual conditions.

[0068] The present invention also proposes a photovoltaic centrifuge with the above converter, the DC bus to be tested is the DC bus of the photovoltaic module, and the insulation impedance value of the photovoltaic module is detected and calculated by the impedance detection module.

[0069] 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 in the protection scope of the present invention.

Claims

1. Insulation impedance detection circuit, characterized in that, include: An impedance detection module connected between the positive and negative poles of the DC bus to be tested, a converter DC bus arranged in parallel with the DC bus to be tested, a positive correction resistor R7 and a switch S1 connected in series between the positive pole of the converter DC bus and ground, and a negative correction resistor R8 and a switch S2 connected in series between the negative pole of the converter DC bus and ground; The impedance detection module includes: a first resistance bridge and a second resistance bridge arranged in parallel, the first resistance bridge is composed of a resistor R3 and a resistor R4 connected in series, the connection line between the resistor R3 and the resistor R4 is grounded, the second resistance bridge is composed of a resistor R5, a resistor R6 and a switch S separated between the resistor R5 and the resistor R6, and the resistor R5 or the resistor R6 is grounded through the switch S; The resistor R3 and the resistor R5 are both connected to the positive electrode of the DC bus to be measured through the sampling resistor R1, and the resistor R4 and the resistor R6 are both connected to the negative electrode of the DC bus to be measured through the sampling resistor R2. The sampling resistor R1 and the sampling resistor R2 are both configured with a voltage sampling chip. The impedance detection module calculates the insulation impedance value of the DC bus of the converter according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, compares the insulation impedance value with the corresponding correction resistor, and corrects the voltage sampling chip according to the comparison result; The impedance detection module calculates the insulation impedance value of the DC bus to be tested according to the voltage values ​​of the two sampling resistors before and after the switch S is switched.

2. The insulation impedance detection circuit according to claim 1, characterized in that: When the difference between the insulation impedance value of the converter DC bus and the corresponding correction resistor exceeds a set impedance error value, the impedance detection module sends out an insulation impedance fault alarm signal.

3. The insulation impedance detection circuit according to claim 1, characterized in that: When the switch S1 is turned on and the switch S2 is turned off, the impedance detection module calculates the positive electrode-to-ground impedance value of the converter DC bus according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, compares the positive electrode-to-ground impedance value with the positive electrode correction resistor R7, and calibrates the voltage sampling chip according to the comparison result; When the switch S1 is disconnected and the switch S2 is connected, the impedance detection module calculates the negative electrode-to-ground impedance value of the converter DC bus according to the voltage values ​​of the two sampling resistors before and after the switch S is switched, compares the negative electrode-to-ground impedance value with the negative electrode correction resistor R8, and calibrates the voltage sampling chip according to the comparison result.

4. The insulation impedance detection circuit according to claim 1, characterized in that: The positive and negative poles of the converter DC bus are connected to the DC bus to be tested via circuit breaker S3 respectively; When the impedance detection module calculates the insulation impedance value of the converter DC bus, the circuit breaker S3 is in an open state, and the bus capacitor on the converter DC bus is discharged.

5. The insulation impedance detection circuit according to claim 1, characterized in that: The impedance detection module is provided with a positive interface connected to the sampling resistor R1 and a negative interface connected to the sampling resistor R2, the positive interface is connected to the positive electrode of the converter DC bus through a switch S4 and to the positive electrode of the DC bus to be measured through a switch S5, and the negative interface is connected to the negative electrode of the converter DC bus through a switch S6 and to the negative electrode of the DC bus to be measured through a switch S7; When the impedance detection module calculates the insulation impedance value of the DC bus of the converter, the switch S4 and the switch S6 are turned on, and the switch S5 and the switch S7 are turned off; When the impedance detection module calculates the insulation impedance value of the DC bus to be measured, the switch S4 and the switch S6 are disconnected, and the switch S5 and the switch S7 are connected.

6. The insulation impedance detection circuit according to any one of claims 1 to 5, characterized in that: The resistance values ​​of the resistors R3 , R4 , R5 and R6 are the same.

7. An impedance detection method for an insulation impedance detection circuit, wherein the impedance detection circuit adopts the impedance detection circuit according to any one of claims 1 to 6, characterized in that: The detection method comprises the following steps: Connecting the impedance detection module between the positive and negative electrodes of the DC bus to be tested; Switching the switch S so that one of the resistor R5 and the resistor R6 is grounded; Detect the voltage values ​​of the sampling resistor R1 and the sampling resistor R2, and calculate the positive voltage V of the DC bus to be tested based on the voltage values. 正对地1 and negative voltage to ground V 负对地1 ; Switching the switch S so that the other of the resistor R5 and the resistor R6 is grounded; Detect the voltage values ​​of the sampling resistor R1 and the sampling resistor R2, and calculate the positive voltage V of the DC bus to be tested based on the voltage values. 正对地2 and negative voltage to ground V 负对地2 ; According to the V 正对地1 、V 负对地1 、V 正对地2 and V 负对地2 Calculate the insulation impedance value of the DC bus to be tested.

8. The impedance detection method according to claim 7, characterized in that: When V 正对地1 and V 负对地1 When the corresponding resistor R5 is grounded, V 正对地2 and V 负对地2 When the corresponding resistor R6 is grounded, Calculate the positive voltage V of the DC bus to be tested according to the voltage value 正对地1 and negative voltage to ground V 负对地1 The calculation formula is Calculate the positive voltage V of the DC bus to be tested according to the voltage value 正对地2 and negative voltage to ground V 负对地2 The calculation formula is V R1 is the voltage value of the sampling resistor R1 when the resistor R5 is grounded, V R1 ’ is the voltage value of the sampling resistor R1 when the resistor R6 is grounded, V R2 is the voltage value of the sampling resistor R2 when the resistor R5 is grounded, V R2 ’ It is the voltage value of the sampling resistor R2 when the resistor R6 is grounded.

9. The impedance detection method according to claim 7, characterized in that: The positive voltage V of the DC bus to be tested is calculated according to the voltage value 正对地1 and negative voltage to ground V 负对地1 Afterwards, determine whether |V 正对地1 +V 负对地1 -V DC |≥V 设定 , V DC is the bus voltage of the DC bus to be tested, V 设定 To set the voltage error value; If so, compare V 正对地1 and V 负对地1 The size of V 正对地1 >V 负对地1 When V 正对地1 =V 正对地1 、V 负对地1 =V DC -V 正对地1 , when V 正对地1 ≤V 负对地1 When V 负对地1 =V 负对地1 、V 正对地1 =V DC -V 负对地1 ; If not, store V 正对地1 =V 正对地1 、V 负对地1 =V 负对地1 .

10. The impedance detection method according to claim 7, characterized in that: The positive voltage V of the DC bus to be tested is calculated according to the voltage value 正对地2 and negative voltage to ground V 负对地2 Afterwards, determine whether |V 正对地2 +V 负对地2 -V DC |≥V 设定 , V DC is the bus voltage of the DC bus to be tested, V 设定 To set the voltage error value; If so, compare V 正对地2 and V 负对地2 The size of V 正对地2 >V 负对地2 When V 正对地2 =V 正对地2 、V 负对地2 =V DC -V 正对地2 , when V 正对地2 ≤V 负对地2 When V 负对地2 =V 负对地2 、V 正对地2 =V DC -V 负对地2 ; If not, store V 正对地2 =V 正对地2 、V 负对地2 =V 负对地2 .

11. The impedance detection method according to claim 7, characterized in that: When V 正对地1 and V 负对地1 The corresponding resistor R5 is grounded, V 正对地2 and V 负对地2 When the corresponding resistor R6 is grounded, according to the V 正对地1 、V 负对地1 、V 正对地2 and V 负对地2 The calculation formula for calculating the insulation impedance value of the DC bus to be tested is: Rx is the impedance value of the positive electrode to the ground, and Ry is the impedance value of the negative electrode to the ground.

12. The impedance detection method according to claim 7, characterized in that: The impedance detection method further includes: first calibrating the voltage sampling chip, and then connecting the impedance detection module between the positive and negative poles of the DC bus to be tested after the calibration is completed.

13. A converter, characterized in that The converter adopts the insulation impedance detection circuit according to any one of claims 1 to 6.

14. A photovoltaic centrifuge, characterized in that: The photovoltaic centrifuge has the converter according to claim 13, and the DC bus to be tested is a DC bus of a photovoltaic module.

Images