Off-line insulation resistance sampling circuit based on constant current converter system

Abstract

The present invention discloses an offline insulation resistance sampling circuit based on a constant current converter system, comprising an AD / DC module, a DC / DC module, a sampling circuit, a driving circuit, an MCU module, a communication module and an external resistor. The present invention can perform offline detection of the insulation resistance of a constant current power supply at any time, which not only improves the safety and reliability of the constant current power supply system, but also reduces the difficulty of detecting the insulation resistance of the constant current power supply system.

Description

Technical Field

[0001] The invention relates to the technical field of insulation resistance sampling circuits, and in particular to an off-line insulation resistance sampling circuit based on a constant current converter system. Background Art

[0002] The use of electronic products requires power lines to provide power. These power sources come from the mains, generators, batteries, etc., and then the various power sources with different voltages and currents are converted into stable and controllable voltages and currents through power converters, and provided to the products for use. Due to the dangers of different power sources, the power supply and electrical products need to be isolated, which poses a hidden danger to people and equipment. Summary of the invention

[0003] The purpose of the present invention is to provide an offline insulation resistance sampling circuit based on a constant current converter system in order to solve the above problems, including an AD / DC module, a DC / DC module, a sampling circuit, a drive circuit, an MCU module, a communication module and an external resistor;

[0004] The AD / DC module is used for inputting power supply voltage and voltage conversion; the AD / DC module is connected to the main power circuit through the DC / DC module; the input end of the sampling circuit is connected to the main power circuit and the output end of the AD / DC module; the output end of the sampling circuit is connected to the MCU module; the MCU module is connected to the main power circuit through the driving circuit; the MCU module is connected to the communication module; the communication module is used to connect to the host computer; the MUC module is connected to the DC / DC module through the driving circuit; the driving circuit is used for on-off control of the main power circuit and the DC / DC module; the sampling circuit is used to collect voltage samples of the main power circuit;

[0005] The main power circuit includes a first relay; the MCU module is connected to the first relay; a first end of a normally open contact of the first relay is connected to an input end of the main power circuit; a second end of a normally open contact of the first relay is connected to an output end of the main power circuit; and an external resistor is connected to the output end of the main power circuit;

[0006] The sampling circuit includes a 12V DC power supply, a boost power supply, a first resistor, a second resistor, a third resistor, at least one fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first voltage follower and differential amplifier circuit, a second voltage follower and differential amplifier circuit, a second relay, a third relay, a fourth relay and a triode; the boost power supply is connected to the first end of the first resistor and the first end of the second relay; the second end of the first resistor is connected to the first end of the normally open contact of the third relay and the first end of the normally open contact of the fourth relay; the second end of the normally open contact of the third relay is connected to the first output end of the main power circuit through the sixth resistor; the second output end of the main power circuit is connected to the second end of the normally open contact of the fourth relay through the seventh resistor; the second end of the second resistor is connected to the first resistor The first voltage follower and differential amplifier circuit is connected to the input end and the first end of the third resistor; the output end of the first voltage follower and differential amplifier circuit is connected to the MCU module; the second end of the third resistor is connected to the emitter of the transistor, the second end of the fifth resistor and is grounded; the collector of the transistor is connected to the second end of the fourth resistor; the first end of the fourth resistor is connected to the first end of the fifth resistor, the input end of the second voltage follower and differential amplifier circuit, and the normally open contact of the fifth relay; the second voltage follower and differential amplifier circuit is connected to the MCU module; the MCU module is connected to the first end of the second relay, the first end of the third relay, the first end of the fourth relay, and the first end of the fifth relay; the second end of the second relay, the second end of the third relay, the second end of the fourth relay, and the second end of the fifth relay are connected to a 12V DC power supply.

[0007] Specifically, the communication module is a CAN bus module.

[0008] The offline insulation resistance sampling method based on the offline insulation resistance sampling circuit based on the constant current converter system comprises the steps of:

[0009] Input high-level insulation resistance detection signal to the MCU module;

[0010] The MCU module outputs a level signal to the first relay to control the on and off of the main power circuit. The MCU module controls the output of the boost power supply to provide a reference voltage for the sampling circuit.

[0011] The voltage signal is output to the MCU module through voltage following and differential amplification to calculate the actual voltage value of the boost power supply;

[0012] The MCU module controls the normally open contacts of the fourth relay and the fifth relay to close, and the boost power supply output passes through the first resistor, the fourth relay, the fifth relay, the fifth resistor, the third resistor, and the second resistor to return to the negative end of the boost power supply to form a loop, and a voltage signal Vs is generated at the fifth resistor, and this voltage signal Vs is input to the MCU module;

[0013] The voltage signal is output to the MCU module through voltage following and differential amplification to calculate the size of the external resistance.

[0014] Specifically, the process of calculating the external resistance includes:

[0015] Assume that the external resistor is Rz; the output voltage of the DC / DC module is V0, and the second voltage follower and differential amplifier circuit includes a first voltage follower, an eighth resistor R8, a first capacitor, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a first operational amplifier and a thirteenth resistor; the first end of the fourth resistor is connected to the second end of the eighth resistor through the first voltage follower; the first end of the eighth resistor is connected to the first end of the first capacitor and the second end of the ninth resistor; the first end of the ninth resistor is connected to the first end of the tenth resistor and the same-direction input end of the first operational amplifier; the second end of the tenth resistor and the second end of the eleventh resistor are grounded; the first end of the eleventh resistor is connected to the second end of the twelfth resistor and the reverse input end of the first operational amplifier; the first end of the twelfth resistor is connected to the output end of the first operational amplifier and the second end of the thirteenth resistor; the first end of the thirteenth resistor is connected to the MCU module.

[0016] Divide Rz into 6 segments: Rz>100Mohm, 100Mohm>Rz>10Mohm, 10Mohm>Rz>1Mohm, 1Mohm>Rz>100kohm, 100kohm>Rz>10kohm, 10kohm>Rz;

[0017] If the measured Vs voltage is less than 0.3V, then Rz is greater than 100Mohm;

[0018] If 3V>Vs>0.3V is measured, Rz=V / Vs*(Rf / Re)*R5-Rf-R5;

[0019] If Vs>3V is measured, then Rz<10Mohm;

[0020] MCU controls the transistor to conduct, making R4 and R5 connected in parallel, obtaining resistance Rm=1 / (1 / R4+1 / R5), generating voltage Vs1. If the voltage Vs1 measured by MCU is less than 0.3V, then Rz is greater than 10Mohm;

[0021] If the MCU measures 3V>Vs>0.3V, through Vs=V0*Rm / (Rf+Rm+Rz)*(Rf / Re), it is calculated that Rz=V0 / Vs*(Rf / Re)*Rm-Rf-Rm;

[0022] If MCU measures Vs>3V, then Rz<1Mohm;

[0023] By testing the value of Vs and changing the B and A pins of the MCU, the resistance values ​​of 1Mohm>Rz>100kohm, 100kohm>Rz>10kohm, and 10kohm>Rz are measured. After the test, turn off the RLY2 relay;

[0024] MCU controls the third relay to close, so as to test the insulation resistance value between the positive end of the main circuit and the ground;

[0025] Close the third relay to obtain the minimum value of the external resistance Rz, then use the LED to display the end of the insulation resistance range, and send the insulation resistance value to the host computer via CAN;

[0026] Close the fifth relay connected to the ground wire, the second relay, and the first relay contact in sequence, turn off the power supply, and restore the main power.

[0027] The beneficial effect of the present invention is that the present invention can perform offline detection of the insulation resistance of the constant current power supply at any time, which not only improves the safety and reliability of the auxiliary constant current power supply system, but also reduces the difficulty of detecting the insulation resistance of the auxiliary constant current power supply system. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 is a system block diagram of the present invention;

[0029] Figure 2 It is a circuit schematic diagram of the present invention;

[0030] Figure 3 is a circuit diagram of a specific embodiment of the present invention;

[0031] Figure 4 It is the operation logic diagram of the present invention.

[0032] In the figure: RLY1-first relay; RLY1A, RLY1B-first relay contacts; RLY2-second relay; RLY3-fourth relay; RLY4 fourth relay; RLY5-fifth relay; C1, C2-capacitors; Q1, Q2, Q3-transistors; R1~R17-resistors; Rz-external resistor; V1-first operational amplifier; V2-second operational amplifier; V3-third operational amplifier; V4-fourth operational amplifier; CN1, CN2-connectors. DETAILED DESCRIPTION

[0033] The present invention will be further described below in conjunction with the accompanying drawings:

[0034] As attached Figure 1 As shown, the present invention is an offline insulation resistance sampling circuit based on a constant current converter system, including an AD / DC module, a DC / DC module, a sampling circuit, a drive circuit, an MCU module, a communication module and an external resistor;

[0035] The AD / DC module is used for inputting power supply voltage and voltage conversion; the AD / DC module is connected to the main power circuit through the DC / DC module; the input end of the sampling circuit is connected to the main power circuit and the output end of the AD / DC module; the output end of the sampling circuit is connected to the MCU module; the MCU module is connected to the main power circuit through the driving circuit; the MCU module is connected to the communication module; the communication module is used to connect to the host computer; the MUC module is connected to the DC / DC module through the driving circuit; the driving circuit is used for on-off control of the main power circuit and the DC / DC module; the sampling circuit is used to collect voltage samples of the main power circuit;

[0036] The main power circuit includes a first relay; the MCU module is connected to the first relay; a first end of a normally open contact of the first relay is connected to an input end of the main power circuit; a second end of a normally open contact of the first relay is connected to an output end of the main power circuit; and an external resistor is connected to the output end of the main power circuit;

[0037] The sampling circuit includes a 12V DC power supply, a boost power supply, a first resistor, a second resistor, a third resistor, at least one fourth resistor, a fifth resistor, a sixth resistor, a seventh resistor, a first voltage follower and differential amplifier circuit, a second voltage follower and differential amplifier circuit, a second relay, a third relay, a fourth relay and a triode; the boost power supply is connected to the first end of the first resistor and the first end of the second relay; the second end of the first resistor is connected to the first end of the normally open contact of the third relay and the first end of the normally open contact of the fourth relay; the second end of the normally open contact of the third relay is connected to the first output end of the main power circuit through the sixth resistor; the second output end of the main power circuit is connected to the second end of the normally open contact of the fourth relay through the seventh resistor; the second end of the second resistor is connected to the first resistor The first voltage follower and differential amplifier circuit is connected to the input end and the first end of the third resistor; the output end of the first voltage follower and differential amplifier circuit is connected to the MCU module; the second end of the third resistor is connected to the emitter of the transistor, the second end of the fifth resistor and is grounded; the collector of the transistor is connected to the second end of the fourth resistor; the first end of the fourth resistor is connected to the first end of the fifth resistor, the input end of the second voltage follower and differential amplifier circuit, and the normally open contact of the fifth relay; the second voltage follower and differential amplifier circuit is connected to the MCU module; the MCU module is connected to the first end of the second relay, the first end of the third relay, the first end of the fourth relay, and the first end of the fifth relay; the second end of the second relay, the second end of the third relay, the second end of the fourth relay, and the second end of the fifth relay are connected to a 12V DC power supply.

[0038] The second voltage follower and differential amplifier circuit includes a first voltage follower, an eighth resistor R8, a first capacitor, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a first operational amplifier and a thirteenth resistor; the first end of the fourth resistor is connected to the second end of the eighth resistor through the first voltage follower; the first end of the eighth resistor is connected to the first end of the first capacitor and the second end of the ninth resistor; the first end of the ninth resistor is connected to the first end of the tenth resistor and the same-direction input end of the first operational amplifier; the second end of the tenth resistor and the second end of the eleventh resistor are grounded; the first end of the eleventh resistor is connected to the second end of the twelfth resistor and the reverse input end of the first operational amplifier; the first end of the twelfth resistor is connected to the output end of the first operational amplifier and the second end of the thirteenth resistor; the first end of the thirteenth resistor is connected to the MCU module.

[0039] Specifically, as attached Figure 3 As shown, the working principle of the offline insulation resistance sampling circuit is:

[0040] When the system needs insulation resistance detection, a high level will be given to U4 through CN1. When the MCU detects a low level, the MCU starts insulation resistance detection. In addition, it can also be given to the MCU through CAN communication to let the MCU give a signal to start insulation resistance detection.

[0041] At this time, the MCU gives a high level to the first relay RLY1, disconnecting the contacts of the first relay in the main power circuit;

[0042] MCU outputs a high level, so that the 500VDC / DC module outputs 500Vdc voltage, and then MCU gives a high level to RLY-VS, so that relay RLY2 is turned on, and 500V voltage passes through resistor R2. Resistor R2 can be replaced by multiple resistors in series. The voltage formed on resistor R3 is followed by V1 voltage and then differentially amplified, and then transmitted to VS-500V of MCU. Let R14=R16=Ra, R15=R17=Rb, R2=Rc, the actual voltage value of 500V power module is V500, the voltage detected by MCU pin is VS-500V=Vx, through Vx=V500*R3 / (Rc+R3)*(Rb / Ra), we can get V500=Vx*Ra*(Rc+R3) / (Rb*R3), then the actual voltage value of 500V power module is tested;

[0043] At this time, the MCU sends a high-level signal to the RLY-PE port to close the RLY5 relay. At this time, the insulation detection circuit is connected to the ground. The operating logic is as shown in the attached figure. Figure 4 shown.

[0044] MCU then gives a high level signal to RLY-OUT- (the control input terminal of RLY4 relay) to close RLY4 relay. At this time, the voltage of V500 is connected to the main line through relay RLY4 and R7, and then to the ground through the external line resistance, and then to CN1, RLY5 and R5 resistor to return to the negative end of the DC / DC module, forming a loop and generating a voltage on the R5 resistor. This voltage is followed by the voltage of the V3 operational amplifier and differentially amplified to obtain a voltage Vs, which is transmitted to MCU. Here, R9=R11=Re, R10=R12=Rf, R7=Rf, and the external insulation resistance is Rz; due to the wide range of Rz resistance, Rz is divided into 6 segments: Rz>100Mohm, 100Mohm>Rz>10Mohm, 10Mohm>Rz>1Mohm, 1Mohm>Rz>100kohm, 100kohm>Rz>10kohm, 10kohm>Rz;

[0045] (1) If the Vs voltage measured by the MCU is less than 0.3V, then Rz is greater than 100Mohm;

[0046] (2) If the MCU measures 3V>Vs>0.3V, through Vs=V500*R33 / (Rf+R5+Rz)*(Rf / Re), the MCU can calculate Rz=R500 / Vs*(Rf / Re)*R5-Rf-R5;

[0047] (3) If the MCU measures Vs>3V, then Rz<10Mohm;

[0048] (4) Then, the MCU gives a high level to the C pin, turning on the transistor Q3, connecting R5 and R4 in parallel, and obtaining a resistance Rm = 1 / (1 / R4 + 1 / R5), generating a new voltage Vs. If the Vs voltage measured by the MCU is less than 0.3V, then Rz is greater than 10Mohm;

[0049] (5) If the MCU measures 3V>Vs>0.3V, through Vs=V500*Rm / (Rf+Rm+Rz)*(Rf / Re), the MCU can calculate Rz=R500 / Vs*(Rf / Re)*Rm-Rf-Rm;

[0050] (6) If the MCU measures Vs>3V, then Rz<1Mohm;

[0051] (7) In the same way, by testing the value of Vs and changing the B and A pins of the MCU, the resistance values ​​of 1Mohm>Rz>100kohm, 100kohm>Rz>10kohm, and 10kohm>Rz are measured. After the test is completed, turn off the RLY2 relay;

[0052] Same as step 5, MCU gives RLY-OUT+ a high level signal to close the RLY1 relay to test the insulation resistance value of the positive end of the main circuit to the ground.

[0053] After testing steps 5 and 6, close the RLY3 relay to obtain the minimum value of Rz, then use the LED to display the end of the insulation resistance range, and send the insulation resistance value to the host computer via CAN.

[0054] After the test is completed, turn off the RLY5 relay and RLY2 relay connected to the ground wire in turn, turn off the 500V power supply, and restore the relays RLY1A and RLY1B of the main power circuit.

[0055] The present invention can perform offline detection of the insulation resistance of the constant current power supply at any time, which not only improves the safety and reliability of the auxiliary constant current power supply system, but also reduces the difficulty of detecting the insulation resistance of the auxiliary constant current power supply system.

[0056] The technical solution of the present invention is not limited to the above-mentioned specific embodiments. All technical variations made according to the technical solution of the present invention fall within the protection scope of the present invention.

Claims

1. An offline insulation resistance sampling circuit based on a constant current converter system, characterized in that: Including AD / DC module, DC / DC module, sampling circuit, drive circuit, MCU module, communication module and external resistor; The AD / DC module is used for inputting power supply voltage and voltage conversion; the AD / DC module is connected to the main power circuit through the DC / DC module; the input end of the sampling circuit is connected to the main power circuit and the output end of the AD / DC module; the output end of the sampling circuit is connected to the MCU module; the MCU module is connected to the main power circuit through the drive circuit; the MCU module is connected to the communication module; the communication module is used to connect to the host computer; the MCU module is connected to the DC / DC module through the drive circuit; the drive circuit is used for on-off control of the main power circuit and the DC / DC module; the sampling circuit is used to collect the voltage of the main power circuit; The main power circuit includes a first relay; the MCU module is connected to the first relay; the first relay includes a first relay RLY1A and a first relay RLY1B, a first terminal of a normally open contact of the first relay RLY1A is connected to a first input terminal of the main power circuit, and a first terminal of a normally open contact of the first relay RLY1B is connected to a second input terminal of the main power circuit; a second terminal of a normally open contact of the first relay RLY1A is connected to a first output terminal of the main power circuit, and a second terminal of a normally open contact of the first relay RLY1B is connected to a second output terminal of the main power circuit; and an output terminal of the main power circuit is connected to an external resistor; The sampling circuit includes a 12V DC power supply, a boost power supply, a first resistor R1, a second resistor R2, a third resistor R3, at least one fourth resistor R4, a fifth resistor R5, a sixth resistor R6, a seventh resistor R7, a first voltage follower and differential amplifier circuit, a second voltage follower and differential amplifier circuit, a second relay RLY2, a third relay RLY3, a fourth relay RLY4, a fifth relay RLY5 and transistors Q1, Q2, Q3; the boost power supply is connected to the first end of the first resistor R1 and the first end of the normally open contact of the second relay RLY2; the second end of the normally open contact of the third relay is connected to the first output end of the main power circuit through the sixth resistor; the second output end of the main power circuit is connected to the second end of the normally open contact of the fourth relay through the seventh resistor; the second end of the first resistor R1 is connected to the first end of the normally open contact of the third relay RLY3 and the first end of the normally open contact of the fourth relay RLY4; The first end of the second resistor R2 is connected to the second end of the normally open contact of the second relay RLY2, and the second end of the second resistor R2 is connected to the input end of the first voltage follower and differential amplifier circuit and the first end of the third resistor R3; the output end of the first voltage follower and differential amplifier circuit is connected to the MCU module; the second end of the third resistor R3 is respectively connected to the emitter of the transistors Q1, Q2, and Q3 and the second end of the fifth resistor R5, and the second end of the third resistor R3 is also grounded; the collectors of the transistors Q1, Q2, and Q3 are respectively connected to the second ends of the three fourth resistors R4; the bases of the transistors Q1, Q2, and Q3 are respectively connected to the MCU module; the first ends of the three fourth resistors R4 are all connected to the first end of the fifth resistor R5, the input end of the second voltage follower and differential amplifier circuit and the first end of the normally open contact of the fifth relay RLY5; the output end of the second voltage follower and differential amplifier circuit is connected to the MCU module; the MCU module is connected to the first coil end of the second relay RLY2, the first coil end of the third relay RLY3, the first coil end of the fourth relay RLY4 and the first coil end of the fifth relay RLY5; the second coil end of the second relay RLY2, the second coil end of the third relay RLY3, the second coil end of the fourth relay RLY4 and the second coil end of the fifth relay RLY5 are connected to a 12V DC power supply; The first voltage follower and differential amplifier circuit includes a first operational amplifier V1, a second operational amplifier V2, a third resistor R3, a thirteenth resistor R13, a fourteenth resistor R14, a fifteenth resistor R15, a sixteenth resistor R16, a seventeenth resistor R17, and a second capacitor C2. The same-direction input terminal of the first operational amplifier V1 is connected to the second end of the second resistor R2 and the first end of the third resistor R3. The output terminal of the first operational amplifier V1 is connected to the first end of the thirteenth resistor R13. The second end of the thirteenth resistor R13 is connected to the first end of the fourteenth resistor R14 and the first end of the second capacitor. The second end of the fourteenth resistor R14 is connected to the first end of the fifteenth resistor R15 and the same-direction input terminal of the second operational amplifier V2. The second end of the second capacitor is connected to the second end of the fifteenth resistor R15 and the first end of the sixteenth resistor R16, and is grounded. The second end of the sixteenth resistor R16 is connected to the first end of the seventeenth resistor R17 and the reverse input terminal of the second operational amplifier V2. The output terminal of the second operational amplifier V2 is connected to the MCU module. The second voltage follower and differential amplifier circuit includes a third operational amplifier V3, an eighth resistor R8, a first capacitor, a ninth resistor R9, a tenth resistor R10, an eleventh resistor R11, a twelfth resistor R12, a fourth operational amplifier V4 and a thirteenth resistor R13; the first end of the fourth resistor R4 is connected to the second end of the eighth resistor R8 through the third operational amplifier V3; the first end of the eighth resistor R8 is connected to the first end of the first capacitor and the second end of the ninth resistor R9; the first end of the ninth resistor R9 is connected to the first end of the tenth resistor R10 and the same-direction input end of the fourth operational amplifier V4; the second end of the first capacitor, the second end of the tenth resistor R10, and the second end of the eleventh resistor R11 are connected and grounded; the first end of the eleventh resistor R11 is connected to the second end of the twelfth resistor R12 and the reverse input end of the fourth operational amplifier V4; the first end of the twelfth resistor R12 is connected to the output end of the fourth operational amplifier V4 and the second end of the thirteenth resistor R13; the first end of the thirteenth resistor R13 is connected to the MCU module.

2. The offline insulation resistance sampling circuit based on the constant current converter system according to claim 1, characterized in that: The communication module is a CAN bus module.

3. The offline insulation resistance sampling method based on the offline insulation resistance sampling circuit based on the constant current converter system according to claim 1, characterized in that: Includes steps: Input high-level insulation resistance detection signal to the MCU module; At this time, the MCU gives a high level to the first relay RLY1, disconnecting the contact of the first relay RLY1 in the main power circuit; The MCU module outputs a high level, allowing the 500V boost power supply to output a 500Vdc voltage. Then the MCU gives a high level to the RLY-VS pin, turning on the second relay RLY2. The 500V voltage passes through the second resistor R2. The voltage formed on the third resistor R3 is amplified by the voltage follower and differential amplifier of the first operational amplifier V1, and then transmitted to the VS-500V pin of the MCU. Let R14=R16=Ra, R15=R17=Rb, R2=Rc, the actual output voltage value of the 500V boost power supply module is V500, and the voltage detected by the VS-500V pin of the MCU is Vx. Through Vx=V500*R3 / (Rc+R3)*(Rb / Ra), V500=Vx*Ra*(Rc+R3) / (Rb*R3) is obtained, and the actual output voltage value of the 500V boost power supply is tested; At this time, the MCU module gives a high-level signal to the RLY-PE port to close the fifth relay RLY5. At this time, the insulation detection circuit is connected to the ground; The MCU module then gives a high-level signal to RLY-OUT-, closing the fourth relay RLY4. At this time, the voltage of V500 is connected to the main line through the fourth relay RLY4 and the seventh resistor R7, and then to the ground through the external line resistor, and then to the CN1 connector, the fifth relay RLY5 and the fifth resistor R5 to return to the negative end of the boost power supply, forming a loop, and generating a voltage on the fifth resistor R5. This voltage is followed by the third operational amplifier V3 voltage and differentially amplified to obtain a voltage signal Vs, which is transmitted to the MCU. Here, R9=R11=Re, R10=R12=Rf, R7=Rf, and the external insulation resistance is Rz; Rz is divided into 6 segments: Rz>100Mohm, 100Mohm>Rz>10Mohm, 10Mohm>Rz>1Mohm, 1Mohm>Rz>100kohm, 100kohm>Rz>10kohm, 10kohm>Rz; (1) If the Vs voltage measured by the MCU module is less than 0.3V, then Rz is greater than 100Mohm; (2) If the MCU module measures 3V>Vs>0.3V, through Vs=V500*R5 / (Rf+R5+Rz)*(Rf / Re), the MCU calculates Rz=V500 / Vs*(Rf / Re)*R5-Rf-R5; (3) If the MCU module measures Vs>3V, then Rz<10Mohm; (4) Then, the MCU module gives a high level to the C pin, turning on the transistor Q3, connecting the fourth resistor R4 and the fifth resistor R5 in parallel, and obtaining a resistance Rm=1 / (1 / R4+1 / R5), generating a new voltage Vs. If the Vs voltage measured by the MCU is less than 0.3V, then Rz is greater than 10Mohm; (5) If the MCU module measures 3V>Vs>0.3V, Vs=V500*Rm / (Rf+Rm+Rz)*(Rf / Re), Rz=V500 / Vs*(Rf / Re)*Rm-Rf-Rm is calculated; (6) If the MCU module measures Vs>3V, then Rz<1Mohm; (7) By testing the value of Vs and changing the B pin and A pin of the MCU module, the resistance values ​​of 1Mohm>Rz>100kohm, 100kohm>Rz>10kohm, and 10kohm>Rz are measured; after the test is completed, the second relay RLY2 is closed; Same as step (5), the MCU module gives a high level signal to the RLY-OUT+ pin to close the third relay RLY3, so as to test the insulation resistance value of the positive end of the main circuit to the ground; After testing steps (5) and (6), the third relay RLY3 is closed to obtain the minimum value of the external resistance Rz, and then the insulation resistance range is displayed by LED, and the insulation resistance value is sent to the host computer via CAN; After the test is completed, turn off the RLY5 relay and RLY2 relay connected to the ground wire in turn, turn off the 500V power supply, and restore the first relays RLY1A and RLY1B of the main power circuit.

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