Insulation resistance detection circuit, method and device

Abstract

The present invention discloses an insulation resistance detection circuit, method and device, aiming to solve the technical problem that the existing insulation resistance detection technology can only guarantee the measurement accuracy under stable working conditions. Its technical solution is: an insulation resistance detection circuit, including an operational amplifier, the output end of the operational amplifier is connected to an external circuit, the positive port is connected in series with a first resistor and a second resistor, the second resistor is connected in parallel with a second switch; the negative port is connected in series with a third resistor, a fourth resistor and a fourth switch, the fourth resistor is connected in parallel with the third switch, and the fourth switch can be grounded. An insulation resistance detection method, based on the above circuit, first receives charging information to obtain the actual input voltage value, and then calculates the system internal resistance based on it, and then calculates the insulation resistance. An insulation resistance detection device includes an insulation detection circuit, an acquisition module and a data processing module. The insulation detection circuit obtains electrical signals, and the acquisition module collects signals and transmits them to the data processing module to calculate the insulation resistance.

Description

Technical Field

[0001] The present invention relates to the field of circuit electronic technology, and specifically to an insulation resistance detection circuit, method and device. Background Art

[0002] As the global automotive industry accelerates its transformation to electrification, the electric vehicle market continues to expand. As the core power source, the high-voltage electrical system of electric vehicles is usually composed of many high-voltage components, such as power batteries, motor controllers, drive motors, etc., and complex line connections. Its operating voltage is often as high as hundreds of volts, and some models can even reach kilovolts.

[0003] In such a high-voltage environment, insulation performance becomes a key factor in the safe operation of electric vehicles. Once the insulation system fails, the insulation performance will be reduced, which may cause an electrical short circuit and make the metal shell of the vehicle electrified, which will directly endanger the lives of passengers and surrounding people and cause electric shock accidents. In addition, poor insulation performance may also cause damage to electrical equipment, affect the normal operation of the vehicle, increase maintenance costs, and even cause serious consequences such as fire.

[0004] The current mainstream insulation resistance calculation method is the balanced bridge measurement method, which requires measuring the insulation resistance value in a static process. The balanced bridge measurement method changes the circuit state through an electronic switch, thereby changing the voltage on the insulation resistance of the positive and negative electrodes of the battery, and then solves the insulation resistance by combining the circuit equations under two different switch states. However, this method has obvious limitations. It can only guarantee a certain insulation resistance measurement accuracy under stable working conditions. Under actual complex and changeable working conditions, such as vehicle acceleration, deceleration, bumps, or different ambient temperature and humidity conditions, the insulation accuracy error is large. This is mainly because various factors in actual working conditions, such as changes in battery charging and discharging states, the influence of parasitic parameters in the circuit, and changes in material properties caused by temperature and humidity, will cause the actual value of the insulation resistance to fluctuate, and traditional measurement methods are difficult to adapt to these changes in real time and accurately, and thus cannot always provide reliable insulation detection results.

[0005] Therefore, in the context of the continuous development of electric vehicle technology, there is an urgent need for a circuit and implementation method that can quickly and accurately detect insulation resistance to adapt to various complex working conditions, ensure that the high-voltage electrical system of electric vehicles always maintains good insulation performance throughout their entire service life, improve the safety and reliability of the vehicle, and provide strong guarantees for the large-scale popularization and safe application of electric vehicles. Summary of the invention

[0006] The object of the present invention is to provide an insulation resistance detection circuit, method and device to overcome the deficiency that the existing insulation resistance detection technology can only ensure the measurement accuracy under stable working conditions.

[0007] In order to achieve the above object, the present invention adopts the following technical solution: An insulation resistance detection circuit includes an operational amplifier, wherein an output end of the operational amplifier is connected to an external circuit; A first resistor R1 and a second resistor R2 are connected in series to the forward port of the operational amplifier, and a second switch S2 is connected in parallel to the second resistor R2; The negative port of the operational amplifier is connected in series with a third resistor R3, a fourth resistor R4 and a fourth switch S4. The fourth resistor R4 is connected in parallel with the third switch S3. The fourth switch S4 can be switched to a grounding state.

[0008] The fourth switch S4 is connected to the negative port of the operational amplifier in a default state, and the operational amplifier is in a proportional operation mode in this state; when the fourth switch S4 is grounded, the operational amplifier is in a follower mode in this state.

[0009] An insulation resistance detection method is based on an insulation resistance detection circuit, comprising: Receive charging information, including maximum charging voltage and charging current, and input voltage to obtain actual input voltage value; Calculate the system internal resistance based on the actual input voltage value; Calculate the insulation resistance based on the system internal resistance.

[0010] The steps are to calculate the system internal resistance according to the actual input voltage value, including: The fourth switch S4 is closed to detect the voltage of the upper arm, which is recorded as U1, and then the second switch S2 is closed to detect the voltage of the upper arm, which is recorded as U1'; the second switch S2 is opened to close the third switch S3 and the fourth switch S4, and the voltage of the upper arm is detected, which is recorded as U1''; The lower arm voltage U2 is calculated based on U and U1, the lower arm voltage U2' is calculated based on U and U1', and the lower arm voltage U2'' is calculated based on U and U1''; Compare the sizes of U2-U1 and U2''-U1'' to obtain the comparison result; If the comparison result is U2-U1>U2''-U1'', use U1 and U2 to calculate the system internal resistance; If the comparison result is U2''-U1''>U2-U1'', use U1'' and U2'' to calculate the system internal resistance.

[0011] Steps If the comparison result is U2-U1>U2''-U1'', use U1 and U2 to calculate the system internal resistance. The calculation formula is as follows:

[0012]

[0013] Wherein, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Ra is the internal resistance of the upper arm system, and Rb is the internal resistance of the lower arm system.

[0014] Steps If the comparison result is U2''-U1''>U2-U1, use U1'' and U2'' to calculate the system internal resistance. The calculation formula is as follows:

[0015]

[0016] Wherein, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Ra is the internal resistance of the upper arm system, and Rb is the internal resistance of the lower arm system.

[0017] Steps to calculate insulation resistance based on system internal resistance include: Disconnect all switches, connect the ground terminals of the charging terminal and the detection terminal, and detect the total voltage V to ground; The fourth switch S4 is closed to detect the voltage of the upper arm, which is recorded as V1. The second switch S2 is then closed to detect the voltage of the upper arm, which is recorded as V1'. The second switch S2 is opened to close the third switch S3 and the fourth switch S4 to detect the voltage of the upper arm, which is recorded as V1''. The lower arm voltage V2 is calculated based on V and V1, the lower arm voltage V2' is calculated based on V and V1', and the lower arm voltage V2'' is calculated based on V and V1''; If U1 and U2 are used to calculate the internal resistance of the system, then V1, V2, V1', and V2' are used to calculate the insulation resistance; If U1'' and U2'' are used to calculate the system internal resistance, V1, V2, V1'', and V2'' are used to calculate the insulation resistance.

[0018] If you use U1 and U2 to calculate the system internal resistance, use V1, V2, V1', and V2' to calculate the insulation resistance. The calculation formula is as follows:

[0019]

[0020]

[0021]

[0022]

[0023]

[0024] Wherein R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, and Ry is the insulation resistance of the lower arm.

[0025] If you use U1 and U2 to calculate the system internal resistance, use V1, V2, V1', and V2' to calculate the insulation resistance. The calculation formula is as follows:

[0026]

[0027]

[0028]

[0029]

[0030]

[0031] Wherein R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, and Ry is the insulation resistance of the lower arm.

[0032] An insulation resistance detection device, based on an insulation resistance detection circuit, comprises: Insulation detection circuit, used to obtain electrical signals; The acquisition module is used to collect the electrical signals obtained by the insulation detection circuit and output the values ​​to the data processing module; The data processing module is used to receive the electrical signal sent by the acquisition module and calculate the insulation resistance.

[0033] Compared with the prior art, the present invention has the following beneficial technical effects: The insulation resistance detection circuit of the present invention utilizes two topological designs of the operational amplifier, the follower and the proportional operation. The circuit structure is simplified by switching between the two modes through a fourth switch S4 that can switch the ground state. Compared with the traditional complex circuit design, unnecessary circuit connections and component redundancy are reduced, and the simplicity and stability of the circuit are improved. Due to the optimized design of the circuit, the use of electronic components in the pre-sampling part is reduced. This not only reduces the hardware cost, but also reduces the failure points that may be caused by too many components, and improves the reliability and maintainability of the entire circuit. The circuit can adapt to various complex working conditions. Under different environments, the circuit can work stably, providing a solid foundation for the subsequent accurate detection of insulation resistance. Compared with the circuits in the prior art that are easily affected under complex working conditions and have large precision errors, the circuit of the present invention has obvious advantages.

[0034] The insulation resistance detection method of the present invention can obtain multiple groups of voltage values ​​under different states by closing and opening switches in a specific order, and accurately calculate the system internal resistance based on these voltage values. The influence of the system internal resistance on the voltage under different circuit states is fully considered in the calculation process, and the voltage value combination most suitable for calculating the system internal resistance is selected by comparing the size of the voltage difference between the upper half arm and the lower half arm under different test resistance values, thereby improving the accuracy of the calculation. Compared with the traditional measurement method, the system internal resistance can be obtained more accurately, thereby realizing the accurate calculation of the insulation resistance, and the calculation accuracy is improved compared with the traditional method.

[0035] The insulation resistance detection device of the present invention integrates an insulation detection circuit, an acquisition module and a data processing module. The insulation resistance detection method can be run to detect the insulation resistance of the charging device. The insulation detection circuit is responsible for acquiring electrical signals, and the acquisition module collects and transmits these electrical signals to the data processing module, which performs the final insulation resistance calculation. This integrated design makes the device fully functional and compact in structure, and the various modules work together to improve the overall performance of the device. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 The figure is a schematic diagram of an insulation resistance detection circuit in an embodiment of the present invention.

[0037] Figure 2 Schematic diagram of an insulation resistance detection method in an embodiment of the present invention.

[0038] Figure 3 A schematic diagram of calculating the internal resistance of a system according to an actual input voltage value in a method for detecting insulation resistance in an embodiment of the present invention; Figure 4 A schematic diagram of calculating insulation resistance according to system internal resistance in an insulation resistance detection method in an embodiment of the present invention; Figure 5 This is a schematic diagram of an insulation resistance detection device in an embodiment of the present invention; Figure 6 The figure is a connection diagram of an insulation resistance detection circuit in an embodiment of the present invention.

[0039] In the figure, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, Ry is the insulation resistance of the lower arm, Ra is the internal resistance of the upper arm system, Rb is the internal resistance of the lower arm system, S1 is the first switch, S2 is the second switch, S3 is the third switch, and S4 is the fourth switch. DETAILED DESCRIPTION

[0040] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0041] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise" and the like indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the referred device or element must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0042] In the description of this application, it should be noted that, unless otherwise clearly specified and limited, the terms "installed", "provided with", "set / connected", "connected", etc. should be understood in a broad sense. For example, "connected" can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be a direct connection, or it can be indirectly connected through an intermediate medium, or it can be the internal communication of two components. For ordinary technicians in this field, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0043] In addition, the terms "first" and "second" are used for descriptive purposes only and should not be understood as indicating or implying relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include one or more of the features. In the description of the present invention, the meaning of "several" is two or more, unless otherwise clearly and specifically defined.

[0044] Embodiment 1: In a specific embodiment of the present invention, an insulation resistance detection device is provided, such as Figure 5 As shown, it includes an insulation detection circuit for acquiring electrical signals; An acquisition module, used for collecting the electrical signals acquired by the insulation detection circuit and outputting the values ​​to a data processing module; The data processing module is used to receive the electrical signal sent by the acquisition module and calculate the insulation resistance.

[0045] The insulation resistance detection circuit in the insulation resistance detection device is as follows: Figure 1As shown, the circuit includes an operational amplifier, and an output terminal of the operational amplifier is connected to an external circuit; A first resistor R1 and a second resistor R2 are connected in series to the forward port of the operational amplifier, and a second switch S2 is connected in parallel to the second resistor R2; The negative port of the operational amplifier is connected in series with a third resistor R3, a fourth resistor R4 and a fourth switch S4. The fourth resistor R4 is connected in parallel with the third switch S3. The fourth switch S4 can be switched to a grounding state.

[0046] The insulation detection circuit uses two topological designs of the operational amplifier: follower and proportional operation. The fourth switch S4 is connected to the negative port of the operational amplifier in the default state, and the operational amplifier is in proportional operation mode in this state; when the fourth switch S4 is grounded, the operational amplifier is in follower mode in this state. Using one switch to be compatible with both circuit designs simplifies the circuit, and the front-stage sampling part can also reduce the use of electronic components.

[0047] When the insulation resistance detection device is connected to the charging vehicle, the connection between the insulation resistance detection circuit and the charging vehicle is as follows: Figure 6 As shown, the positive electrode of the detection circuit is connected to the positive electrode of the charging car, the negative electrode of the detection circuit is connected to the negative electrode of the charging car, and the detection circuit is connected to the ground terminal of the charging car through a first switch S1. The insulation resistance detection device as the detection end will perform insulation resistance detection on the charging car as the charging end before charging. The detection process is as follows Figure 2 As shown, including: Receive charging information, including maximum charging voltage and charging current, and input voltage to obtain actual input voltage value; Calculate the system internal resistance based on the actual input voltage value; Calculate the insulation resistance based on the system internal resistance.

[0048] First, receive charging information, including key parameters such as maximum charging voltage and charging current. This information provides basic data for subsequent calculations and detection.

[0049] Next, the actual input voltage value is obtained through the input voltage. This step ensures that the voltage data used in the detection process is accurate, laying the foundation for the subsequent accurate calculation of the system internal resistance and insulation resistance. Specifically, the input voltage can be monitored and collected in real time using devices such as voltage sensors, and the analog voltage signal can be converted into a digital signal and then transmitted to the data processing unit for further processing.

[0050] The process of calculating the system internal resistance based on the actual input voltage value is as follows Figure 3 As shown, including: Close the fourth switch S4 to detect the upper arm voltage, recorded as U1, then close the second switch S2 to detect the upper arm voltage, recorded as U1', open the second switch S2, close the third switch S3 and the fourth switch S4, detect the upper arm voltage, recorded as U1''; by adjusting the switch to obtain the upper arm voltage under different resistance networks, it is convenient to calculate the lower arm voltage and the system internal resistance through comparative analysis later.

[0051] The lower arm voltage U2 is calculated based on U1, the lower arm voltage U2' is calculated based on U1', and the lower arm voltage U2'' is calculated based on U1''. The calculation formula is as follows:

[0052]

[0053]

[0054] Where U is the actual input voltage value.

[0055] Compare the size of U2-U1 and U2''-U1'' to obtain the comparison result; this comparison step is to determine the voltage value combination used for the subsequent calculation of the system internal resistance. Because the impact of the system internal resistance on the voltage will be different under different circuit conditions, by comparing these two differences, the voltage value combination that is most suitable for calculating the system internal resistance can be selected to improve the accuracy of the calculation.

[0056] If the comparison result is U2-U1>U2''-U1'', use U1 and U2 to calculate the system internal resistance. The calculation formula is as follows:

[0057]

[0058] Wherein, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Ra is the internal resistance of the upper arm system, and Rb is the internal resistance of the lower arm system.

[0059] If the comparison result is U2''-U1''>U2-U1'', use U1'' and U2'' to calculate the system internal resistance. The calculation formula is as follows:

[0060]

[0061] Wherein, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Ra is the internal resistance of the upper arm system, and Rb is the internal resistance of the lower arm system.

[0062] Calculate the insulation resistance value based on the system internal resistance. Figure 4As shown, including: All switches are opened, the first switch S1 is closed, the ground terminals of the charging terminal and the detection terminal are connected, and the total voltage V to the ground is detected; at this time, the circuit is in a special ground detection state, and the total voltage can be accurately measured.

[0063] The fourth switch S4 is closed to detect the voltage of the upper arm, which is recorded as V1. The second switch S2 is then closed to detect the voltage of the upper arm, which is recorded as V1'. The second switch S2 is opened to close the third switch S3 and the fourth switch S4 to detect the voltage of the upper arm, which is recorded as V1''. The lower arm voltage V2 is calculated based on V and V1, the lower arm voltage V2' is calculated based on V and V1', and the lower arm voltage V2'' is calculated based on V and V1''. The calculation formula is as follows:

[0064]

[0065]

[0066] If U1 and U2 are used to calculate the internal resistance of the system, that is, when U2-U1>U2''-U1'', V1, V2, V1', and V2' are used to calculate the insulation resistance. The calculation formula is as follows:

[0067]

[0068]

[0069]

[0070]

[0071]

[0072] Wherein R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, and Ry is the insulation resistance of the lower arm.

[0073] If U1'' and U2'' are used to calculate the internal resistance of the system, that is, when U2''-U1''>U2-U1, then V1, V2, V1'', and V2'' are used to calculate the insulation resistance. The calculation formula is as follows:

[0074]

[0075]

[0076]

[0077]

[0078]

[0079] Wherein R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, and Ry is the insulation resistance of the lower arm.

[0080] Embodiment 2: In a specific embodiment of the present invention, a charging pile capable of performing insulation resistance detection on a charging vehicle is provided, wherein the charging pile is configured with Figure 5 An insulation resistance detection device is shown. When a charging vehicle is connected to a charging pile, the vehicle will send a charging request message to the charging pile, which contains parameters such as the maximum charging voltage and charging current. After receiving this charging information, the charging pile will prepare for subsequent insulation detection and charging operations on the one hand, and store and transmit this information to the internal control unit on the other hand to prepare for subsequent calculations.

[0081] The insulation detection circuit in the charging pile starts working according to the detection method. First, close the fourth switch S4. At this time, the circuit is in a specific connection state. Through the action of the operational amplifier and related resistors, the upper arm voltage U1 is measured. Then, close the second switch S2, change the forward port resistor network structure, and measure the upper arm voltage U1'. Next, open the second switch S2 and close the third switch S3 and the fourth switch S4, change the circuit state again, and measure the upper arm voltage U1''.

[0082] Based on the measured U1, the lower arm voltage U2 is calculated using circuit knowledge such as the series voltage division principle; similarly, U2' is calculated based on U1', and U2'' is calculated based on U1'', and the sizes of U2-U1 and U2''-U1'' are compared.

[0083] If U2-U1>U2''-U1'', use U1 and U2 to calculate the system internal resistance Ra and Rb. The calculation formula is as follows:

[0084]

[0085] Wherein, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Ra is the internal resistance of the upper arm system, and Rb is the internal resistance of the lower arm system.

[0086] After the calculation of the system internal resistance is completed, all switches are disconnected, and the first switch S1 is closed to connect the charging end and the ground end of the detection end, and the total voltage V to the ground is detected by using a voltage sensor or other equipment.

[0087] Close the fourth switch S4 again and measure the upper arm voltage V1; close the second switch S2 and measure the upper arm voltage V1'; open the second switch S2, close the third switch S3 and the fourth switch S4, and measure the upper arm voltage V1''. Calculate the lower arm voltage V2 based on V1, calculate V2' based on V1', and calculate V2'' based on V1''. Use V1, V2, V1', and V2' to calculate the insulation resistance. The calculation formula is as follows:

[0088]

[0089]

[0090]

[0091]

[0092]

[0093] Wherein R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, and Ry is the insulation resistance of the lower arm.

[0094] If U2''-U1''>U2-U1'', use U1'' and U2'' to calculate the system internal resistance. The calculation formula is as follows:

[0095]

[0096] Wherein, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Ra is the internal resistance of the upper arm system, and Rb is the internal resistance of the lower arm system.

[0097] Close the fourth switch S4 again and measure the upper arm voltage V1; close the second switch S2 and measure the upper arm voltage V1'; open the second switch S2 and close the third switch S3 and the fourth switch S4 to measure the upper arm voltage V1''. Calculate the lower arm voltage V2 based on V1, calculate V2' based on V1', and calculate V2'' based on V1''. Using V1, V2, V1'', and V2'', the calculation formula is as follows:

[0098]

[0099]

[0100]

[0101]

[0102]

[0103] Wherein R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, and Ry is the insulation resistance of the lower arm.

[0104] After the data processing module calculates the insulation resistance Rx and Ry, it compares them with the preset standard insulation resistance. If both Rx and Ry are greater than the standard insulation resistance, it means that the insulation performance of the charging vehicle is good, and the charging pile can start normal charging operation and output the appropriate charging voltage and current to the vehicle.

[0105] If the calculated insulation resistance is less than the standard insulation resistance, the charging pile stops charging and sends an insulation fault alarm message to the vehicle. At the same time, a fault prompt is displayed on the charging pile display screen to inform the user that there is a problem with the vehicle insulation and that maintenance is required. In addition, the charging pile can also upload fault information to the background management system, so that maintenance personnel can understand the situation in a timely manner and handle it.

[0106] Through the above embodiments, the insulation resistance detection circuit, method and device of the present invention can effectively overcome the problem of insufficient accuracy of the existing insulation resistance detection technology under complex working conditions, realize rapid and accurate detection of insulation resistance, and improve the safety and reliability of the high-voltage electrical system of electric vehicles. During the charging process of electric vehicles, the insulation resistance can be detected in a timely and accurate manner to ensure charging safety and reduce safety accidents caused by insulation problems, providing a strong guarantee for the large-scale popularization and safe application of electric vehicles. At the same time, this technology also has broad application prospects in other fields involving insulation detection of high-voltage electrical systems.

[0107] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. The above embodiments and descriptions are only preferred examples of the present invention and are not intended to limit the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, which fall within the scope of the present invention. The scope of protection of the present invention is defined by the attached claims and their equivalents.

Claims

1. An insulation resistance detection circuit, characterized in that: An operational amplifier is included, wherein an output terminal of the operational amplifier is connected to an external circuit; The operational amplifier forward port is connected in series with a first resistor R1 and a second resistor R2, and the second resistor R2 is connected in parallel with a second switch S2; The negative port of the operational amplifier is connected in series with a third resistor R3, a fourth resistor R4 and a fourth switch S4. The fourth resistor R4 is connected in parallel with the third switch S3. The fourth switch S4 can be switched to a grounding state.

2. An insulation resistance detection circuit, characterized in that: The fourth switch S4 is connected to the negative port of the operational amplifier in a default state, and the operational amplifier is in a proportional operation mode in this state; when the fourth switch S4 is grounded, the operational amplifier is in a follower mode in this state.

3. An insulation resistance detection method, based on the insulation resistance detection circuit according to claim 1, characterized in that: include: Receive charging information, including maximum charging voltage and charging current, and input voltage to obtain actual input voltage value; Calculate the system internal resistance based on the actual input voltage value; Calculate the insulation resistance based on the system internal resistance.

4. The insulation resistance detection method according to claim 3, characterized in that: The steps of calculating the system internal resistance according to the actual input voltage value include: The fourth switch S4 is closed to detect the voltage of the upper arm, which is recorded as U1, and then the second switch S2 is closed to detect the voltage of the upper arm, which is recorded as U1'; the second switch S2 is opened to close the third switch S3 and the fourth switch S4, and the voltage of the upper arm is detected, which is recorded as U1''; The lower arm voltage U2 is calculated based on U and U1, the lower arm voltage U2' is calculated based on U and U1', and the lower arm voltage U2'' is calculated based on U and U1''; Compare the sizes of U2-U1 and U2''-U1'' to obtain the comparison result; If the comparison result is U2-U1>U2''-U1'', use U1 and U2 to calculate the system internal resistance; If the comparison result is U2''-U1''>U2-U1'', use U1'' and U2'' to calculate the system internal resistance.

5. The insulation resistance detection method according to claim 4, characterized in that: If the comparison result of the above steps is U2-U1>U2''-U1'', then use U1 and U2 to calculate the system internal resistance, and the calculation formula is as follows: Wherein, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Ra is the internal resistance of the upper arm system, and Rb is the internal resistance of the lower arm system.

6. The insulation resistance detection method according to claim 4, characterized in that: If the comparison result of the above step is U2''-U1''>U2-U1, then use U1'' and U2'' to calculate the system internal resistance, and the calculation formula is as follows: Wherein, R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Ra is the internal resistance of the upper arm system, and Rb is the internal resistance of the lower arm system.

7. The insulation resistance detection method according to claim 4, characterized in that: The step of calculating the insulation resistance value according to the internal resistance of the system includes: Disconnect all switches, connect the ground terminals of the charging terminal and the detection terminal, and detect the total voltage V to ground; The fourth switch S4 is closed to detect the voltage of the upper arm, which is recorded as V1. The second switch S2 is then closed to detect the voltage of the upper arm, which is recorded as V1'. The second switch S2 is opened to close the third switch S3 and the fourth switch S4 to detect the voltage of the upper arm, which is recorded as V1''. The lower arm voltage V2 is calculated based on V and V1, the lower arm voltage V2' is calculated based on V and V1', and the lower arm voltage V2'' is calculated based on V and V1''; If U1 and U2 are used to calculate the internal resistance of the system, then V1, V2, V1', and V2' are used to calculate the insulation resistance; If U1'' and U2'' are used to calculate the system internal resistance, V1, V2, V1'', and V2'' are used to calculate the insulation resistance.

8. The insulation resistance detection method according to claim 7, characterized in that: If U1 and U2 are used to calculate the system internal resistance in the above steps, the insulation resistance is calculated using V1, V2, V1', and V2'. The calculation formula is as follows: Wherein R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, and Ry is the insulation resistance of the lower arm.

9. The insulation resistance detection method according to claim 7, characterized in that: If U1 and U2 are used to calculate the system internal resistance in the above steps, the insulation resistance is calculated using V1, V2, V1', and V2'. The calculation formula is as follows: Wherein R1 is the first resistor, R2 is the second resistor, R3 is the third resistor, R4 is the fourth resistor, Rx is the insulation resistance of the upper arm, and Ry is the insulation resistance of the lower arm.

10. An insulation resistance detection device, based on the insulation resistance detection circuit according to claim 1, characterized in that: include: Insulation detection circuit, used to obtain electrical signals; An acquisition module, used for collecting the electrical signals acquired by the insulation detection circuit and outputting the values ​​to a data processing module; The data processing module is used to receive the electrical signal sent by the acquisition module and calculate the insulation resistance.

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