Insulation detection circuit and system

Abstract

The invention relates to an insulation detection circuit and system. The insulation detection circuit comprises a voltage sampling module, a resistor switching module and a self-checking module. The voltage sampling module samples voltage values of the DC line anode and the DC line cathode. The resistance switching module changes the resistance value between the positive electrode of the direct-current line and the protective ground and the resistance value between the negative electrode of the direct-current line and the protective ground; the self-checking module is connected to the insulation detection circuit when module self-checking is carried out on the insulation detection circuit, and the resistance value between the positive electrode of the direct-current line and the protective ground and the resistance value between the negative electrode of the direct-current line and the protective ground are changed. According to the invention, timing self-inspection of the insulation detection circuit is supported, requirements for insulation detection and module self-inspection in American standard, European standard, national standard and Japanese standard can be met, the problem that real-time insulation detection cannot be carried out in the charging state and the non-charging state of the direct current charging pile in the prior art is solved, and the safety performance of the direct current charging pile is improved.

Description

Technical Field

[0001] The present application relates to the technical field of insulation detection, and in particular to an insulation detection circuit and system. Background Art

[0002] The output charging voltage of a DC charging pile is several hundred volts or even thousands of volts. If a DC charging pile device fails, resulting in an abnormally low insulation resistance between the high-voltage output line and the device casing, there is a safety risk of electric shock if a person touches the device casing. Therefore, before charging the car, the DC charging pile will detect whether the insulation resistance of the high-voltage line to the device casing (protective grounding, or PE) is within a safe range.

[0003] However, simply testing the insulation resistance before charging cannot avoid the safety risk of electric shock caused by equipment failure during the charging process. Currently, there is no solution that can perform real-time insulation testing on a DC charging pile in both the charging and non-charging states.

[0004] In addition, the insulation detection circuit in the related technology does not have a self-test function, and there is a risk that the insulation detection circuit itself will be damaged, resulting in inaccurate measurement results and failure to timely feedback the correct insulation detection status. In addition, the insulation detection circuit in the related technology is difficult to simultaneously meet the insulation detection requirements of European standards, American standards, Japanese standards and national standards. Summary of the invention

[0005] The insulation detection circuit and system provided in the present application at least solve the problem that the related technology cannot perform real-time insulation detection in the charging state and non-charging state of the DC charging pile.

[0006] An insulation detection circuit includes: a voltage sampling module 10, a resistance switching module 20 and a self-test module 30, wherein:

[0007] The voltage sampling module 10 is connected between the DC lines DC+, DC- and the protective ground PE, and is used to sample the voltage values ​​of the DC line positive pole DC+ and the DC line negative pole DC-;

[0008] The resistance switching module 20 is connected between the DC lines DC+, DC- and the protective grounding PE, and is used to change the resistance value between the DC line positive pole DC+ and the protective grounding PE and the resistance value between the DC line negative pole DC- and the protective grounding PE;

[0009] The self-test module 30 is connected between the DC lines DC+, DC- and the protective grounding PE. The self-test module 30 is used to connect to the insulation detection circuit when performing module self-test on the insulation detection circuit, and change the resistance value between the positive pole DC+ of the DC line and the protective grounding PE and the resistance value between the negative pole DC- of the DC line and the protective grounding PE.

[0010] An insulation detection system comprises a microcontroller MCU and the above insulation detection circuit.

[0011] The insulation detection circuit and system provided in the present application adopt a voltage sampling module to sample the voltage values ​​of the positive pole and the negative pole of the DC line; the resistance switching module changes the resistance value between the positive pole of the DC line and the protective grounding, as well as the resistance value between the negative pole of the DC line and the protective grounding; the self-test module is connected to the insulation detection circuit when performing module self-test on the insulation detection circuit, and the self-test module changes the resistance value between the positive pole of the DC line and the protective grounding, as well as the resistance value between the negative pole of the DC line and the protective grounding, solves the problem that the related technology cannot perform real-time insulation detection in the charging state and the non-charging state of the DC charging pile, and improves the safety performance of the DC charging pile. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] In order to more clearly illustrate the technical solutions in the present application or the prior art, the following briefly introduces the drawings required for use in the embodiments or the prior art descriptions. Obviously, the drawings described below are only some embodiments of the present application, and for those of ordinary skill in the art, other embodiments can be obtained based on these drawings without creative work.

[0013] Figure 1 It is a structural block diagram of the insulation detection circuit of an embodiment of the present application.

[0014] Figure 2 It is a structural schematic diagram of the insulation detection circuit of an embodiment of the present application.

[0015] Figure 3 It is an equivalent circuit diagram of the DC line to protective grounding in an embodiment of the present application.

[0016] Figure 4 It is a flow chart of insulation detection and self-test of the insulation detection circuit of the embodiment of the present application.

[0017] Figure 5 It is a structural block diagram of the insulation detection system of an embodiment of the present application.

[0018] Figure 6 It is a schematic diagram of an example of an insulation detection system according to an embodiment of the present application. DETAILED DESCRIPTION

[0019] The present application will be described in more detail below with reference to the accompanying drawings. Although certain embodiments of the present application are shown in the accompanying drawings, it should be understood that the present application can be implemented in various forms and should not be construed as being limited to the embodiments described herein, which are instead provided for a more thorough and complete understanding of the present application. It should be understood that the drawings and embodiments of the present application are only for exemplary purposes and are not intended to limit the scope of protection of the present application.

[0020] In order to achieve real-time insulation detection of a DC line to protective grounding, the present application provides an insulation detection circuit. Figure 1 is a structural block diagram of the insulation detection circuit of the embodiment of the present application. Figure 1 As shown, the insulation detection circuit includes: a voltage sampling module 10 , a resistance switching module 20 and a self-test module 30 .

[0021] The voltage sampling module 10 is connected between the DC line and the protective grounding, and is used to sample the voltage values ​​of the positive pole and the negative pole of the DC line. The resistance switching module 20 is connected between the DC line and the protective grounding, and is used to change the resistance value between the positive pole of the DC line and the protective grounding, and the resistance value between the negative pole of the DC line and the protective grounding; the self-test module 30 is connected between the DC line and the protective grounding, and is used to connect to the insulation detection circuit when performing module self-test on the insulation detection circuit, and change the resistance value between the positive pole of the DC line and the protective grounding, and the resistance value between the negative pole of the DC line and the protective grounding.

[0022] Figure 2 Schematic diagram of the structure of the insulation detection circuit of the embodiment of the present application. Figure 2 As shown, the voltage sampling module 10 connected between the positive pole DC+ of the DC line and the protective ground PE includes a resistor R11, a resistor R12, a voltage follower A11 and an isolation amplifier A12. The resistor R11 and the resistor R12 are connected in series between the positive pole DC+ of the DC line and the protective ground PE in sequence. The input end of the voltage follower A11 is connected to the node of the resistor R11 and the resistor R12, the output end of the voltage follower A11 is connected to the input end of the isolation amplifier A12, and the output end of the isolation amplifier A12 is connected to the microcontroller MCU. The voltage follower A11 ensures high impedance of the voltage input, and reduces the collected voltage value of DC+ to PE to a certain ratio (for example, 1 / 501) and then passes it to the isolation amplifier. The isolation amplifier A12 realizes high and low voltage isolation between the input and output and amplification of a certain ratio (for example, 1.5 times), and passes the obtained analog voltage to the microcontroller MCU, which is converted into the actual voltage value of DC+ to PE by the microcontroller MCU.

[0023] The voltage sampling module 10 connected between the negative pole DC- of the DC line and the protective ground PE includes a resistor R21, a resistor R22, an inverting proportional amplifier A21 and an isolation amplifier A22, wherein the resistor R21 and the resistor R22 are sequentially connected in series between the negative pole DC- of the DC line and the protective ground PE, the input end of the inverting proportional amplifier A21 is connected to the node of the resistor R21 and the resistor R22, the output end of the inverting proportional amplifier A21 is connected to the input end of the isolation amplifier A22, and the output end of the isolation amplifier A22 is connected to the microcontroller MCU. In this embodiment, a negative phase power supply is not used, and the isolation amplifier does not support negative phase voltage input. Therefore, an inverting proportional amplifier A21 is used to realize voltage detection and obtain the positive phase voltage input of the isolation amplifier. The inverting proportional amplifier A21 inverts the voltage of DC- to PE and reduces it to a certain proportion (e.g., 1 / 500) and then transmits it to the isolation amplifier. The isolation amplifier A22 realizes high and low voltage isolation between input and output and amplification at a certain ratio (for example, 1.5 times), and transmits the obtained analog voltage to the microcontroller MCU, which converts it into the actual voltage value of DC- to PE.

[0024] The resistor switching module 20 includes a resistor R13, a resistor R14 and an isolating switch U11, wherein the resistor R13 and the resistor R14 are connected in series between the DC line DC+ and the protective ground PE in sequence, the output end Sa of the isolating switch U11 is connected in parallel with the resistor R14, and the input end of the isolating switch U11 is connected to the microcontroller MCU. Based on the above resistor switching module 20, the isolating switch U11 is controlled by the microcontroller MCU to switch, and the resistance value of the resistor connected in series with the DC line DC+ and the protective ground is changed twice, and the voltage values ​​of two DC+ to PE are obtained.

[0025] The resistor switching module 20 includes a resistor R23, a resistor R24 ​​and an isolating switch U21, wherein the resistor R23 and the resistor R24 ​​are connected in series between the DC line DC- and the protective ground PE in sequence, the output end Sb of the isolating switch U21 is connected in parallel with the resistor R24, and the input end of the isolating switch U21 is connected to the microcontroller MCU. Based on the above resistor switching module 20, the isolating switch U21 is controlled by the microcontroller MCU to switch, and the resistance value of the resistor connected in series with the DC line DC- and the protective ground is changed twice, and the voltage value of two DC- to PE is obtained.

[0026] The self-test module 30 includes a resistor R SYX and isolating switch K1, resistor R STX The output terminal S2 of the isolating switch K1 is connected in series between the DC line positive pole DC+ and the protective ground PE, and the input terminal of the isolating switch K1 is connected to the microcontroller MCU. The self-test module 30 also includes a resistor R STY , resistor RSTY The output end S2 of the isolating switch K1 is connected in series between the negative pole DC- of the DC line and the protective ground PE.

[0027] When performing insulation resistance detection, the self-test module 30 is not connected to the circuit, that is, the output end S2 of the isolation switch K2 is disconnected.

[0028] Figure 2 The switch S1 in the circuit is used to connect the insulation detection circuit to the circuit. The switch S1 can be a relay. When S1 is closed and S2 is open, the insulation detection starts. After obtaining the two voltage values ​​of DC+ to PE and the two voltage values ​​of DC- to PE, the microcontroller MCU can calculate the insulation resistance value of DC+ or DC- to PE according to the set program based on the circuit principle.

[0029] Figure 3 is an equivalent circuit diagram of the DC line to protective grounding in an embodiment of the present application, Figure 3 R x Represents the insulation resistance of DC+ to PE, R y Represents the insulation resistance of DC- to PE. To simplify the calculation, the resistance values ​​of resistors R11 and R21 are equal, the resistance values ​​of resistors R12 and R22 are equal, the resistance values ​​of resistors R13 and R23 are equal, and the resistance values ​​of resistors R14 and R24 are equal. When Sa is closed and the insulation resistance is infinite, the resistance value of DC+ to PE is A = (R11 + R12) || R13; when Sb is closed and the insulation resistance is infinite, the resistance value of DC- to PE is also equal to A; when Sa is disconnected and the insulation resistance is infinite, the resistance value of DC+ to PE is B = (R11 + R12) || (R13 + R14); when Sb is disconnected and the insulation resistance is infinite, the resistance value of DC- to PE is also equal to B.

[0030] When Sa is closed and Sb is open, the voltage value U between DC+ and DC- to PE can be measured. x1 , U y1 :

[0031]

[0032] When Sa is disconnected and Sb is closed, the voltage value U between DC+ and DC- to PE can be measured. x2 , U y2 :

[0033]

[0034] Expand the above two equations:

[0035]

[0036] Arranging the above two equations, we can get:

[0037]

[0038] Further expansion:

[0039]

[0040] Subtracting the two equations, we get:

[0041]

[0042] Can be obtained:

[0043]

[0044] Transform the above two equations:

[0045]

[0046] Subtracting the two equations, we get:

[0047]

[0048] Can be obtained:

[0049]

[0050] It should be noted that the above calculation process uses known or public circuit principles.

[0051] In this embodiment, the MCU determines whether the insulation detection fails by the detected insulation resistance value and takes corresponding measures. For example, when the MCU detects that the insulation resistance value R is less than 100Ω / V, it is an insulation fault, and charging needs to be stopped immediately and reported to the platform; when the MCU detects that the insulation resistance value is 100Ω / V≤R<500Ω / V, it is an insulation abnormality, after completing the current charging, stop subsequent charging and report to the platform; when the MCU detects that the insulation resistance value R is greater than or equal to 500Ω / V, the insulation is normal.

[0052] The self-test module 30 performs a self-test of the insulation detection circuit according to the instructions of the microcontroller MCU or at a fixed time to detect whether the insulation resistance detection function of the insulation detection circuit and the connection with the PE are normal. The self-test module 30 integrates a resistor R with a known resistance value. STx and R STY , for example, 500kΩ. If self-test is performed at a fixed time, after the insulation detection circuit is powered on, close S1, open S2, and measure the insulation resistance R of DC+ and DC- to PE for the first time x and R yThen the self-test module 30 starts the first self-test of the insulation detection circuit. After the self-test passes, the timer starts working. Before reaching 1h, S2 is disconnected, and the insulation detection circuit continues to detect the insulation resistance of the high-voltage line to PE; when the timer reaches the set value (for example, 1 hour), the self-test module 30 is triggered to self-test the insulation detection circuit, and S2 is closed.

[0053] The insulation resistances are known to be R x and R y When Sa is closed, the resistance value of DC+ to PE is C = (R11 + R12) ∥ R13 ∥ R x ; When Sb is closed, the resistance value of DC- to PE is E = (R21 + R22) ∥ R23 ∥ R y ; When Sa is disconnected, the resistance value of DC+ to PE is D = (R11 + R12) ∥ (R13 + R14) ∥ R x ; When Sb is disconnected, the resistance value of DC- to PE is F = (R21 + R22) ∥ (R23 + R24) ∥ R y .

[0054] When Sa is closed and Sb is open, the voltage value U between DC+ and DC- to PE can be measured. STx1 , U STy1 :

[0055]

[0056] When Sa is disconnected and Sb is closed, the voltage value U between DC+ and DC- to PE can be measured. STx2 , U STy2 :

[0057]

[0058] Expand the above two equations:

[0059]

[0060] Arranging the above two equations, we can get:

[0061]

[0062] Further expansion:

[0063]

[0064] Multiply the two equations by the coefficient to eliminate R STY , the transformation can be obtained:

[0065]

[0066] Subtracting the two equations, we get:

[0067]

[0068] Can be obtained:

[0069]

[0070] Transform the above two equations to eliminate R STX We can get:

[0071]

[0072] Subtracting the two equations, we get:

[0073]

[0074] Can be obtained:

[0075]

[0076] Figure 4 is a self-test flow chart of the insulation detection circuit of the embodiment of the present application, such as Figure 4 As shown in the figure, the self-test process of the insulation detection circuit includes the following steps:

[0077] Whenever the timer reaches 1h or a self-test instruction is received, the self-test of the insulation detection circuit begins. First, the insulation resistance values ​​of DC+ and DC- to PE are recorded; then the switch S2 is closed to connect the self-test module to the circuit loop; the switch Sa is closed, the switch Sb is opened, and the voltage values ​​of DC+ and DC- to PE are measured; the switch Sa is opened, the switch Sb is closed, and the voltage values ​​of DC+ and DC- to PE are measured; then the insulation resistance values ​​of DC+ and DC- to PE, as well as the voltage values ​​of DC+ and DC- to PE measured twice, are substituted into the above R STX and R STY , calculate R STX and R STY To ensure reliability, R is measured and calculated multiple times (3 times in this embodiment). STX and R STY , calculate the arithmetic mean u and standard deviation σ of the three measured values, and then check whether the three measured values ​​are within the range of [u-3σ,u+3σ]. If there is a data that exceeds the range, it will be eliminated; for the measured values ​​that do not exceed the range, calculate the arithmetic mean u as the final measured R STX and R STY The MCU will calculate the resistance value of R based on the final measured value. STX and R STY Is the resistance value within R STX and R STY The actual resistance value of R is used to judge whether the insulation detection circuit is abnormal. STXand R STY The actual resistance value is 500kΩ, and the measurement error is 10%. If the resistor R STX and R STY The resistance value is within [450kΩ, 550kΩ], indicating that the insulation detection circuit is working properly. Disconnect switch S2, resume insulation resistance detection, and reset the timer to count again for 1h. STX and R STY The resistance value is not within [450kΩ, 550kΩ], indicating that the insulation detection circuit is malfunctioning. At this time, disconnect S1, the insulation detection circuit stops working, and informs the main control board that the insulation detection circuit is abnormal and cannot continue to detect the insulation resistance.

[0078] In some embodiments, the isolating switches U11 and U21 are optical couplers, and the isolating switch K1 is a relay. The use of optical couplers and relays ensures the electrical isolation performance of the insulation detection circuit and prevents the microcontroller MCU from being directly connected to the high-voltage line.

[0079] In some embodiments, the current flowing through the resistor R11 and the resistor R12 (or the resistor R21 and the resistor R22) is not greater than 1 mA; the voltage of the DC line to the protective ground is greater than or equal to 100 volts and less than or equal to 1000 volts. For example, the resistance of the resistor R11 and the resistor R12 connected in series is 6 megohms, and when the voltage of the positive and negative poles of the DC line is 1000 volts, it can also be ensured that the current flowing through the resistor R11 and the resistor R12 is not greater than 1 mA.

[0080] In some embodiments, the current flowing through the resistor R13 and the resistor R14 (or the resistor R23 and the resistor R24) is not greater than 4 mA; the voltage of the DC line to the protective ground is greater than or equal to 100 volts and less than or equal to 1000 volts. For example, the resistance value of the resistor R13 is 800 kiloohms, and the resistance value of the resistor R14 is 200 kiloohms. When the positive and negative voltages of the DC line are 1000 volts, it can also be ensured that the current flowing through the resistor R13 and the resistor R14 is not greater than 4 mA.

[0081] In some embodiments, the current flowing through the resistor R STX or resistor R STY The current is not greater than 2 mA; the voltage of the DC line to the protective ground is greater than or equal to 100 volts and less than or equal to 1000 volts. For example, the resistor R STX and R STY The resistance value is 500 kilo-ohms. When the positive and negative voltages of the branch lines are 1000 volts, it can also ensure that the current flowing through the resistor R STX or resistor | STYThe current is no more than 2 mA. Generally speaking, a leakage current less than 30 mA can avoid the risk of electric shock to personnel. The embodiment of the present application controls the above current within 4 mA, achieving leakage current safety protection at the level of medical electrical equipment and improving the safety of the product.

[0082] The present application also provides an insulation detection system, Figure 5 is a structural block diagram of the insulation detection system of the embodiment of the present application, such as Figure 5 As shown, the system includes a microcontroller 100 and the above-mentioned insulation detection circuit 200. A calculation device is provided in the microcontroller 100 for calculating the insulation resistance R according to the above-mentioned formula. x , R y The resistance value or resistor R STX , R STY resistance value.

[0083] In some embodiments, the insulation detection system further includes: a communication module using a ground isolation chip, the communication module is connected to the microcontroller 100, and is used to communicate with the charging control board of the DC line. The communication module may include at least one RS485 communication module working as a slave device, and at least one CAN communication module, which is used to receive commands from the charging pile control board and transmit the insulation resistance detection results to the control board in real time. The communication chips in the communication module all use ground isolation chips.

[0084] In some of the embodiments, the microcontroller 100 includes a timer for counting the disconnection duration of the output terminal S2 of the isolation switch K1 .

[0085] The above-mentioned insulation detection system can detect the insulation resistance in real time, and complete the inspection within 10 seconds after the insulation resistance fails and report it to the main control board of the charging pile through the communication module, so that the main control board can cut off the power in time to ensure the safety of personnel.

[0086] Figure 6 is a schematic diagram of an example of an insulation detection system according to an embodiment of the present application. Figure 6 Two insulation detection circuits connected to the DC line input terminal and the DC line output terminal respectively, a microcontroller and a communication module are shown.

[0087] The above embodiments provided in this application can adapt to the insulation detection standards of many countries in China, the United States, Japan and Europe. The above embodiments not only meet the requirements of the national standard GB / T 18487.1-2023 that "the insulation resistance value is detected once before charging, and the resistance value is lower than 100Ω / V, indicating an abnormality, and an alarm is required within 10s", but also meet the requirements of the European standard IEC 61851-23-2020 that "real-time detection of insulation resistance during charging, an alarm is required if the insulation resistance value is lower than 500Ω / V, and charging needs to be stopped immediately if it is lower than 100Ω / V, and all operations are completed within 10s", meet the requirements of the American standard UL 2231-2-2020 that "a module self-check is completed every 1 hour during the charging process to confirm that the module itself is normal", and meet the requirements of the American standard and Japanese standard CHAdemo that "real-time detection of insulation resistance value during charging, a resistance value lower than 100Ω / V indicates an abnormality, and an alarm must be issued within 10s", which improves safety while also enhancing the competitiveness of high-voltage DC charging pile products.

[0088] The term "embodiment" in this specification refers to specific features, structures or characteristics described in conjunction with the embodiment that can be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily mean the same embodiment, nor does it mean that it is mutually exclusive with other embodiments and is independent or optional. The various embodiments in this specification are described in a related manner, and the same or similar parts between the various embodiments refer to each other. In particular, for the device, equipment, and system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts refer to the partial description of the method embodiment.

[0089] The above-described embodiments only express several implementation methods of the present application, and the descriptions thereof are relatively specific and detailed, but they cannot be understood as limiting the scope of protection. It should be pointed out that, for a person of ordinary skill in the art, several modifications and improvements can be made without departing from the concept of the present application, and these all belong to the scope of protection of the present application. Therefore, the scope of protection of the present application shall be subject to the attached claims.

Claims

1. An insulation detection circuit, characterized in that include: A voltage sampling module (10), a resistance switching module (20) and a self-test module (30), wherein: The voltage sampling module (10) is connected between a DC line (DC+, DC-) and a protective ground (PE), and the voltage sampling module (10) is used to sample the voltage values ​​of the positive pole (DC+) of the DC line and the negative pole (DC-) of the DC line; The resistance switching module (20) is connected between the DC line (DC+, DC-) and the protective ground (PE), and the resistance switching module (20) is used to change the resistance value between the positive pole (DC+) of the DC line and the protective ground (PE) and the resistance value between the negative pole (DC-) of the DC line and the protective ground (PE); The self-test module (30) is connected between a DC line (DC+, DC-) and a protective ground (PE), and is used to connect to the insulation detection circuit when performing module self-test on the insulation detection circuit, thereby changing the resistance value between the DC line positive pole (DC+) and the protective ground (PE) and the resistance value between the DC line negative pole (DC-) and the protective ground (PE).

2. The insulation detection circuit according to claim 1, characterized in that: The voltage sampling module (10) comprises a first resistor (R11, R21), a second resistor (R12, R22), a voltage detection unit (A11, A21) and an isolation amplifier (A12, A22); the first resistor (R11, R21) and the second resistor (R12, R22) are sequentially connected in series between a DC line (DC+, DC-) and a protective ground (PE); an input end of the voltage detection unit (A11, A21) is connected to a node of the first resistor (R11, R21) and the second resistor (R12, R22); an output end of the voltage detection unit (A11, A21) is connected to an input end of the isolation amplifier (A12, A22); and an output end of the isolation amplifier (A12, A22) is connected to a microcontroller (MCU).

3. The insulation detection circuit according to claim 1, characterized in that: The resistor switching module (20) comprises a third resistor (R13, R23), a fourth resistor (R14, R24) and a first isolating switch (U11, U21); the third resistor (R13, R23) and the fourth resistor (R14, R24) are sequentially connected in series between a DC line (DC+, DC-) and a protective ground (PE); the output end of the first isolating switch (U11, U21) is connected in parallel with the fourth resistor (R14, R24); and the input end of the first isolating switch (U11, U21) is connected to a microcontroller (MCU).

4. The insulation detection circuit according to claim 1, characterized in that: The self-test module (30) includes a fifth resistor (R STX , R STY ) and the second isolation switch (K1), the fifth resistor (R STX , R STY ) and the output end of the second isolating switch (K1) are connected in series between the DC line (DC+, DC-) and the protective ground (PE) in sequence, and the input end of the second isolating switch (K1) is connected to a microcontroller (MCU).

5. The insulation detection circuit according to claim 3 or 4, characterized in that: The first isolating switch (U11, U21) is an optical coupler; the second isolating switch (K1) is a relay.

6. The insulation detection circuit according to claim 2, characterized in that: The current flowing through the first resistor (R11, R21) and the second resistor (R12, R22) is not greater than 1 mA; the voltage of the DC line (DC+, DC-) to the protective ground (PE) is greater than or equal to 100 volts and less than or equal to 1000 volts.

7. The insulation detection circuit according to claim 3, characterized in that: The current flowing through the third resistor (R13, R23) and the fourth resistor (R14, R24) is no more than 4 mA; the voltage of the DC line (DC+, DC-) to the protective ground (PE) is greater than or equal to 100 volts and less than or equal to 1000 volts.

8. The insulation detection circuit according to claim 4, characterized in that: flows through the fifth resistor (R STX , R STY ) is no more than 2 mA; the voltage of the DC line (DC+, DC-) to the protective ground (PE) is greater than or equal to 100 volts and less than or equal to 1000 volts.

9. An insulation detection system, characterized in that The invention comprises a microcontroller (MCU) and the insulation detection circuit according to any one of claims 1 to 8.

10. The insulation detection system according to claim 9, characterized in that: The insulation detection system further comprises: a communication module using a ground isolation chip, the communication module being connected to the microcontroller (MCU) and being used to communicate with a charging control board of the DC line (DC+, DC-); The microcontroller (MCU) comprises a timer for counting the disconnection duration of the output end of the second isolating switch (K1).

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