Insulation detection circuit and insulation detection method for electrical system

Abstract

The invention discloses an insulation detection circuit. The insulation detection circuit comprises a first sampling resistor group comprising a plurality of first sampling resistors with different resistance values; one end of the third switch is connected with the other end of the first sampling resistor, and the other end is connected with an anode of a high-voltage power supply unit or a low-voltage power supply unit of the electrical system; comprising a plurality of second sampling resistors with different resistance values; one end of the fourth switch is connected with the other end of the second sampling resistor, and the other end is connected with the cathode of the high-voltage power supply unit or the low-voltage power supply unit; the first divider resistor is connected in series with the first sampling resistor; the second divider resistor is connected in series with the second sampling resistor; and the control unit is used for determining the accessed first sampling resistor and second sampling resistor and the first voltage and the second voltage at the two ends of the sampling resistor so as to determine the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit. The circuit can improve the insulation detection precision. The invention further discloses an insulation detection method.

Description

Technical Field

[0001] The invention relates to the technical field of insulation detection, and in particular to an insulation detection circuit and an insulation detection method for an electrical system. Background Art

[0002] With the development of the electric vehicle industry, the performance requirements of the battery management system (BMS) of the vehicle are getting higher and higher, among which the insulation detection function is the first to bear the brunt. The purpose of insulation detection is preventive maintenance. By regularly detecting the insulation condition, potential problems can be found before the insulation performance fails, so as to carry out necessary maintenance or replacement to avoid sudden failures. Insulation detection can also play a role in safety protection, ensuring that the insulation system can work reliably and reducing the risk of electrical accidents caused by insulation failure. Insulation detection also helps to timely understand the use of electrical equipment, carry out timely maintenance and better, which can extend the service life of electrical equipment and reduce costs. The most important performance of the insulation detection function is high precision, but high precision will bring higher cost pressure.

[0003] At present, the existing technology is to judge the insulation performance by detecting the insulation resistance. There are three main methods, namely the low-frequency signal injection method, the balanced resistance bridge method and the unbalanced resistance bridge method. In the low-frequency signal injection method, a signal generator is required, and the circuit components that constitute the signal generator are relatively complex, the cost is high, and the reliability is low. The balanced resistance bridge method uses multiple fixed resistors and multiple switches to form the main circuit of insulation detection. When the insulation resistance value is small, the detection accuracy is low. If the accuracy is to be improved when the insulation resistance value is small, the detection range will be reduced and the adaptability is low. The unbalanced resistance bridge method adds the number of fixed resistors and switches on the basis of the circuit used in the aforementioned balanced resistance bridge method. The insulation detection accuracy is not significantly improved, and the switches used must be high-voltage resistant photorelays, which significantly increases the cost.

[0004] It can be seen that the above existing solutions are difficult to balance the relationship between insulation detection accuracy and cost. Summary of the invention

[0005] The present invention provides an insulation detection circuit for an electrical system, which is used to solve the problem in the prior art that it is difficult to improve the insulation detection accuracy while controlling the cost.

[0006] In a first aspect, an embodiment of the present invention discloses an insulation detection circuit for an electrical system, the electrical system comprising a high voltage power supply unit and a low voltage power supply unit, the insulation detection circuit comprising:

[0007] A first sampling resistor group includes a plurality of first sampling resistors with different resistance values, and one end of each first sampling resistor is grounded;

[0008] a third switch, one end of the third switch being connectable to the other end of each first sampling resistor, and the other end of the third switch being connectable to the positive electrode of the high voltage power supply unit or the low voltage power supply unit;

[0009] A second sampling resistor group includes a plurality of second sampling resistors with different resistance values, and one end of each second sampling resistor is grounded;

[0010] a fourth switch, one end of the fourth switch being connectable to the other end of each second sampling resistor, and the other end of the fourth switch being connectable to the negative electrode of the high voltage power supply unit or the low voltage power supply unit;

[0011] a first voltage-dividing resistor, one end of which can be connected to the other end of the third switch, the other end of which is connected to the positive electrode of the high-voltage power supply unit or the low-voltage power supply unit, and the first voltage-dividing resistor is connected to the first sampling resistor to be connected;

[0012] A second voltage-dividing resistor, one end of which can be connected to the other end of the fourth switch, the other end of which is connected to the negative electrode of the high-voltage power supply unit or the low-voltage power supply unit, and the second voltage-dividing resistor is connected to the second sampling resistor to be connected;

[0013] The control unit is configured to determine the first sampling resistor and the second sampling resistor connected to the insulation detection circuit from the first sampling resistor group and the second sampling resistor group respectively by controlling the third switch and the fourth switch, and respectively determine the first voltage and the second voltage across the connected first sampling resistor and the second sampling resistor to determine the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit.

[0014] By adopting the above technical scheme, the insulation detection circuit of the present invention is provided with a first sampling resistor group and a second sampling resistor group, and a plurality of first sampling resistors are provided in the first sampling resistor group for switching, and a plurality of second sampling resistors are provided in the second sampling resistor group for switching, so that the size of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit can be changed. Since a first voltage-dividing resistor connected to the first sampling resistor and a second voltage-dividing resistor connected to the second sampling resistor are provided, a voltage-dividing effect is played, so that the size of the measured first voltage and the second voltage can be controlled, so that the voltage value of the measured first voltage and the voltage value of the second voltage can occupy the measurement range of the control unit as much as possible, so that the detection range can be improved, the accuracy of voltage detection can be improved, and then the accuracy of insulation detection can be improved. The third switch and the fourth switch used for switching the resistors do not need to adopt high-cost high-voltage resistant switches, so that the cost can be controlled and the cost is not too high.

[0015] According to another specific embodiment of the present invention, the control unit is further configured to determine the positive insulation resistance value and the negative insulation resistance value between the high-voltage power supply unit and the low-voltage power supply unit according to the first voltage and the second voltage across the connected first sampling resistor and the second sampling resistor, and determine the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit according to the positive insulation resistance value and the negative insulation resistance value.

[0016] According to another specific embodiment of the present invention, when it is determined that the insulation between the high-voltage power supply unit and the low-voltage power supply unit is abnormal, the first voltage-dividing resistor is connected in series with the connected first sampling resistor and then connected in parallel with the positive insulation resistor, and the second voltage-dividing resistor is connected in series with the connected second sampling resistor and then connected in parallel with the negative insulation resistor.

[0017] According to another specific embodiment of the present invention, it also includes:

[0018] a first switch, wherein one end of the first switch can be connected to the other end of the third switch, and the other end of the first switch is connected to one end of the first voltage-dividing resistor;

[0019] a second switch, one end of the second switch being connectable to the other end of the fourth switch, and the other end of the second switch being connectable to one end of the second voltage-dividing resistor;

[0020] Wherein, the first switch and the second switch are photorelays.

[0021] According to another specific embodiment of the present invention, the number of first sampling resistors in the first sampling resistor group is 2-4, and the sizes of the first sampling resistors are successively increased or decreased, the number of second sampling resistors in the second sampling resistor group is 2-4, and the sizes of the second sampling resistors are successively increased or decreased, and the number of first sampling resistors in the first sampling resistor group is the same as the number of second sampling resistors in the second sampling resistor group; and / or the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit are equal.

[0022] According to another specific embodiment of the present invention, the control unit is further configured to, when the first voltage and the second voltage are not within the first preset voltage range, adjust the resistance values ​​of the first sampling resistor and the second sampling resistor from small to large until the first voltage and the second voltage are within the first preset voltage range, wherein the maximum value of the voltage measurable by the control unit is Vh, and the first preset voltage range is 0.3Vh≤V≤Vh;

[0023] And / or, when the first voltage and the second voltage are not within the second preset voltage range, the resistance values ​​of the first sampling resistor and the second sampling resistor are adjusted from large to small until the first voltage and the second voltage are within the second preset voltage range, wherein the maximum value of the voltage measurable by the control unit is Vh, and the second preset voltage range is 0≤V≤0.98Vh.

[0024] According to another specific embodiment of the present invention, it also includes:

[0025] a first diode, wherein an anode of the first diode is connected to the other end of the third switch, and a cathode of the first diode is connected to a positive electrode of the high voltage power supply unit or the low voltage power supply unit;

[0026] A second diode, wherein a cathode of the second diode is connected to the other end of the fourth switch, and an anode of the second diode is connected to a power supply ground of the high voltage power supply unit or the low voltage power supply unit.

[0027] According to another specific embodiment of the present invention, it also includes:

[0028] A reference power supply, coming from a high voltage power supply unit or a low voltage power supply unit, is used to supply power to the control unit;

[0029] A pull-up resistor, one end of the pull-up resistor is connected to the reference power supply, and the other end of the pull-up resistor is connected to the other end of the fourth switch.

[0030] According to another specific embodiment of the present invention, the high-voltage power supply unit is a battery pack for powering the electric motor of the electric vehicle, and / or the low-voltage power supply unit is a battery for powering other electrical devices in the electric vehicle.

[0031] In a second aspect, an embodiment of the present invention discloses an insulation detection method, wherein the insulation detection circuit for an electrical system described in any of the foregoing embodiments is used to perform insulation detection, wherein the electrical system includes a high voltage power supply unit and a low voltage power supply unit, and the insulation detection method includes:

[0032] Controlling the third switch and the fourth switch to respectively determine the first sampling resistor and the second sampling resistor connected to the insulation detection circuit from the first sampling resistor group and the second sampling resistor group; wherein the first sampling resistor group includes a plurality of first sampling resistors with different resistance values, the second sampling resistor group includes a plurality of second sampling resistors with different resistance values, the first sampling resistor is connected in series with the first voltage-dividing resistor, and the second sampling resistor is connected in series with the second voltage-dividing resistor;

[0033] Determine a first voltage across the first sampling resistor and a second voltage across the second sampling resistor;

[0034] Determine the positive electrode insulation resistance of the high voltage power supply unit or the low voltage power supply unit according to the first voltage, and determine the negative electrode insulation resistance of the high voltage power supply unit or the low voltage power supply unit according to the second voltage;

[0035] Determine whether the positive electrode insulation resistance and the negative electrode insulation resistance are both within a preset insulation resistance range;

[0036] If the positive electrode insulation resistance and / or the negative electrode insulation resistance is not within the preset insulation resistance range, it is determined that there is an insulation abnormality between the high voltage power supply unit and the low voltage power supply unit;

[0037] If the positive electrode insulation resistance and the negative electrode insulation resistance are both within the preset insulation resistance range, it is determined that there is no insulation abnormality between the high voltage power supply unit and the low voltage power supply unit.

[0038] By adopting the above technical scheme, the insulation detection method of the present invention adopts an insulation detection circuit, and by setting a first sampling resistor group and a second sampling resistor group, a plurality of first sampling resistors are set in the first sampling resistor group for switching, and a plurality of second sampling resistors are set in the second sampling resistor group for switching, so that the size of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit can be changed. Since a first voltage-dividing resistor is connected to the first sampling resistor and a second voltage-dividing resistor is connected to the second sampling resistor, a voltage-dividing effect is played, so that the size of the measured first voltage and the second voltage can be controlled, so that the voltage value of the measured first voltage and the voltage value of the second voltage can occupy the measurement range of the control unit as much as possible, thereby improving the detection range, and also improving the accuracy of insulation detection, and the third switch and the fourth switch used for switching the resistors do not need to adopt high-cost high-voltage resistant switches, so that the cost can be controlled and the cost is not too high. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 A schematic diagram of a circuit structure for insulation detection using a low-frequency signal injection method in the prior art is shown;

[0040] Figure 2 A schematic diagram of the circuit structure of insulation detection using a balanced resistance bridge method in the prior art is shown;

[0041] Figure 3 A schematic diagram of a circuit structure for insulation detection using an unbalanced resistance bridge method in the prior art is shown;

[0042] Figure 4 A schematic diagram showing the structure of an insulation detection circuit in an embodiment of the present invention is shown;

[0043] Figure 5 The following is a schematic diagram showing the process of the insulation detection method in the embodiment of the present invention. Figure 1 ;

[0044] Figure 6 The following is a schematic diagram showing the process of the insulation detection method in the embodiment of the present invention. Figure 2 ;

[0045] Figure 7 The following is a schematic diagram showing the process of the insulation detection method in the embodiment of the present invention. Figure 3 . DETAILED DESCRIPTION

[0046] The following specific embodiments illustrate the implementation of the present invention, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. Although the description of the present invention will be introduced in conjunction with the preferred embodiment, this does not mean that the features of this invention are limited to this implementation. On the contrary, the purpose of introducing the invention in conjunction with the implementation is to cover other options or modifications that may extend based on the claims of the present invention. In order to provide a deep understanding of the present invention, the following description will include many specific details. The present invention can also be implemented without using these details. In addition, in order to avoid confusion or blurring the focus of the present invention, some specific details will be omitted in the description. It should be noted that the embodiments of the present invention and the features in the embodiments can be combined with each other without conflict.

[0047] It should be noted that in this specification, similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, it does not need to be further defined and explained in the subsequent drawings.

[0048] The terms “first”, “second”, etc. are only used for distinguishing descriptions and should not be understood as indicating or implying relative importance.

[0049] In the description of this embodiment, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "connected", and "connected" should be understood in a broad sense, for example, it 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 embodiment can be understood according to specific circumstances.

[0050] In order to make the objectives, technical solutions and advantages of the present invention more clear, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0051] The inventors carefully studied the existing methods for insulation detection, namely, the low-frequency signal injection method, the balanced resistance bridge method and the unbalanced resistance bridge method, and found that it is difficult to balance the relationship between the accuracy and cost of insulation detection in the existing technologies.

[0052] refer to Figure 1 In the low-frequency signal injection method, the sampling resistor R, the capacitor C and Gen constitute the main circuit for insulation detection by the low-frequency signal injection method, and Gen represents the signal generator. Although the detection accuracy of the low-frequency signal injection method is high, the circuit components constituting the signal generator are relatively complex, so the cost is high and the reliability is low. For all circuit systems, as long as the circuit structure is complex, the reliability will be reduced.

[0053] refer to Figure 2 In the balanced resistance bridge method, Rp is the positive insulation resistance of the electric vehicle, and Rn is the negative insulation resistance of the electric vehicle. By detecting the voltage across Rp and Rn, the resistance values ​​of Rp and Rn can be converted to determine the insulation performance. Among them, Rp and Rn are not components that make up the circuit structure, but are only insulation resistances to be measured. The standard of the balanced resistance bridge method can refer to the national standard GBT 18384.1-2015. Figure 2 In the figure, Pack is the battery (i.e., battery pack) of the electric vehicle, and resistors R1, R2, R3, R4, switch S1, and switch S2 constitute the main circuit of insulation detection. Among them, R3 is much smaller than R1, R4 is much smaller than R2, R1 is equal to R2, and R3 is equal to R4. R1 and R2 act as voltage dividers, R3 and R4 are sampling resistors, and the control unit collects the voltage across R3 and R4. Since the maximum voltage of the control unit is usually limited to no more than 5V, larger resistors R3 and R4 are required for voltage division to avoid damage to the control unit. The voltage across R3 can be converted to the voltage across Rp, and then the resistance value of Rp can be converted. Similarly, the voltage across R4 can be converted to the voltage across Rn, and then the resistance value of Rn can be converted. The balanced resistance bridge method detects insulation resistance based on resistance voltage division. When the voltage on R3 or R4 measured by the control unit is small, since the ADC range measured by the control unit (i.e., the range of analog signals that can be converted, i.e., the maximum and minimum analog voltage values ​​that can be measured) is fixed, the smaller the proportion of the measured voltage in the range, the greater the error. Therefore, although the balanced resistance bridge method has a simple circuit structure and low cost, the insulation detection accuracy is low when the actual insulation resistance is small. In order to ensure the measurement range and measurement accuracy, when determining the resistance value of the voltage divider resistor (i.e., R1 and R2), it is necessary to make the maximum total pressure (i.e., the total pressure value of the actual electric vehicle battery pack) divided by the value (i.e., the voltage value measured at both ends of R3 and R4) as full as possible of the entire control unit ADC range. However, the total pressure value of the actual electric vehicle battery pack will change during use. The smaller the actual total pressure value is than the maximum total pressure value, the greater the error of the measurement result. Therefore, in order to improve the accuracy, the range of total pressure variation should be as small as possible. Therefore, if the insulation detection accuracy is to be improved, the voltage detection range will be reduced, so the adaptability is low and it is difficult to ensure that high insulation detection accuracy can be maintained under different insulation resistances.

[0054] In the unbalanced resistance bridge method, Figure 3As shown, Rp and Rn are the positive and negative insulation resistances of the electric vehicle, respectively. By detecting the voltage across Rp and Rn, the resistance values ​​of Rp and Rn can be converted to determine the insulation performance. Pack is the battery (i.e., battery pack) of the electric vehicle. Resistors R1, R2, R3, R4, R5, R6, switches S1, S2, S3, and S4 constitute the main circuit for insulation detection. The above 6 resistors and 4 switches are standard for insulation detection using the unbalanced resistance bridge method and cannot be omitted. Among them, R1 is equal to R2, R3 is equal to R4, and R5 is equal to R6. This setting is convenient for simplifying calculations, and the entire circuit has strong pressure resistance and is relatively stable. During the detection process, when the actual resistance values ​​of Rp and Rn are close, there is a problem of inaccurate measurement. By adjusting whether S3 and S4 are closed, an unbalanced bridge can be formed, so that the voltage difference between Rp and Rn becomes larger, and then the voltage difference that can be measured on R3 and R4 is large. Widening the gap is more conducive to improving the accuracy of measurement. Specifically, when the unbalanced resistor of the unbalanced resistance bridge is connected to the circuit, the transformation ratio of the total voltage divider is reduced, and the entire ADC range of the control unit is used as much as possible, thereby improving the high-voltage detection accuracy, and then improving the resistance detection accuracy, which means improving the insulation detection accuracy. The circuit of the unbalanced resistance bridge method is optimized on the basis of the circuit of the balanced resistance bridge, and the high-precision resistance detection range is expanded, but switches S3 and S4 are added to the positive and negative bridge arms. Since S3 and S4 will also withstand the voltage of the total voltage level of the battery pack, switches S3 and S4 need to be able to withstand high voltage. In addition, S3 and S4 need to have programmable functions. At present, only photorelays in the industry have the advantages of simple control circuit, small leakage current, small size and high reliability. Therefore, S3 and S4 need to be high-voltage photorelays with the same specifications as the switching switches S1 and S2 to avoid damage. The cost of such photorelays is very high, and the cost has increased significantly.

[0055] The inventor hopes to improve the existing technology so that the insulation detection can be further improved in accuracy while the cost is not too high.

[0056] First, refer to Figure 4 , an embodiment of the present invention discloses an insulation detection circuit for an electrical system. The electrical system includes a high voltage power supply unit and a low voltage power supply unit. For example, in Figure 4 In the figure, the high-voltage power supply unit can be a high-voltage battery pack of an electric vehicle (such as an electric car) to supply power to the electric motor of the electric vehicle. The low-voltage power supply unit (not shown in the figure) can be a battery to supply power to other electrical devices (such as a control unit) in the electric vehicle.

[0057] The insulation detection circuit includes a first sampling resistor group, a second sampling resistor group, a third switch S3 and a fourth switch S4. The first sampling resistor group includes a plurality of first sampling resistors with different resistance values, one end of each first sampling resistor is grounded (i.e. Figure 4 ). For example, the first sampling resistor group may be Figure 4 The third switch S3 is composed of resistors R3, R5, R7 and R9 with different resistance values. One end of the third switch S3 can be connected to the other end of each first sampling resistor, and the other end of the third switch S3 is connected to the positive electrode of the high voltage power supply unit or the low voltage power supply unit. The third switch S3 can be used to switch the first sampling resistor connected to the insulation detection circuit in the first sampling resistor group. Specifically, Figure 4 In the illustrated embodiment, the third switch S3 can switch the resistor connected to the insulation detection circuit among R3, R5, R7 and R9. The second sampling resistor group includes a plurality of second sampling resistors with different resistance values, and one end of each second sampling resistor is grounded (i.e. Figure 4 ). For example, the second sampling resistor group may be Figure 4 The fourth switch S4 is composed of resistors R4, R6, R8 and R10 with different resistance values. One end of the fourth switch S4 can be connected to the other end of each second sampling resistor, and the other end of the fourth switch S4 is connected to the negative electrode of the high voltage power supply unit or the low voltage power supply unit. Figure 4 In the illustrated embodiment, the fourth switch S4 can switch the resistors among R4 , R6 , R8 and R10 connected to the insulation detection circuit.

[0058] The insulation detection circuit also includes a first voltage-dividing resistor R1 and a second voltage-dividing resistor R2. One end of the first voltage-dividing resistor R1 can be connected to the other end of the third switch S3, the other end of the first voltage-dividing resistor R1 is connected to the positive electrode of the high-voltage power supply unit or the low-voltage power supply unit, and the first voltage-dividing resistor R1 is connected to the first sampling resistor to be connected. One end of the second voltage-dividing resistor R2 can be connected to the other end of the fourth switch S4, the other end of the second voltage-dividing resistor R2 is connected to the negative electrode of the high-voltage power supply unit or the low-voltage power supply unit, and the second voltage-dividing resistor R2 is connected to the second sampling resistor to be connected.

[0059] The insulation detection circuit also includes a control unit. The control unit is configured to determine the first sampling resistor and the second sampling resistor connected to the insulation detection circuit from the first sampling resistor group and the second sampling resistor group respectively by controlling the third switch S3 and the fourth switch S4. The control unit is also configured to respectively determine the first voltage and the second voltage across the connected first sampling resistor and the second sampling resistor to determine the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit. Specifically, the control unit can detect the first voltage across the first sampling resistor, and the control unit can also detect the second voltage across the second sampling resistor, and the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit can be determined based on the first voltage and the second voltage. Figure 4 In the embodiment, MON_Vp corresponds to the analog-to-digital conversion port of the positive pole of the control unit, and can collect the voltage value of the first voltage; MON_Vn corresponds to the analog-to-digital conversion port of the negative pole of the control unit, and can collect the voltage value of the second voltage.

[0060] In the present invention, by setting a first sampling resistor group and a second sampling resistor group in the insulation detection circuit, setting a plurality of first sampling resistors in the first sampling resistor group for switching, and setting a plurality of second sampling resistors in the second sampling resistor group for switching, the size of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit can be changed. Since a first voltage-dividing resistor connected to the first sampling resistor and a second voltage-dividing resistor connected to the second sampling resistor are also set to play a voltage-dividing role, the size of the measured first voltage and the second voltage can be controlled, so that the voltage value of the measured first voltage and the voltage value of the second voltage can occupy the range measured by the control unit as much as possible (that is, the range of the analog-to-digital converter ADC of the control unit), so that the detection range can be improved, the accuracy of voltage detection can be improved, and the accuracy of insulation detection can be improved. In addition, since the first voltage-dividing resistor R1 and the second voltage-dividing resistor R2 can play a voltage-dividing role, the first voltage across the first sampling resistor and the second voltage across the second sampling resistor can be controlled not to be too high, and can be low voltages, and then the third switch S3 connected to the first sampling resistor and the fourth switch S4 connected to the second sampling resistor can be low-voltage switching switches, and there is no need to use extremely costly high-voltage resistant switches, thereby controlling costs and preventing costs from being too high.

[0061] In the above embodiment, the control unit is also configured to determine the positive insulation resistance value and the negative insulation resistance value between the high-voltage power supply unit and the low-voltage power supply unit according to the first voltage and the second voltage across the connected first sampling resistor and the second sampling resistor, and determine the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit according to the positive insulation resistance value and the negative insulation resistance value.

[0062] Specifically, the resistance value of the positive electrode insulation resistance Rp can be converted according to the first voltage, and the resistance value of the negative electrode insulation resistance Rn can be converted according to the second voltage, and then the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit can be determined according to the positive electrode insulation resistance Rp and the negative electrode insulation resistance Rn. The conversion can be performed by measuring only the first voltage and the second voltage without measuring the current.

[0063] Among them, the specific formulas for calculating the resistance value of the positive electrode insulation resistance Rp according to the first voltage and the resistance value of the negative electrode insulation resistance Rn according to the second voltage are as follows, where Formula 1 is the calculation formula for the resistance value of the positive electrode insulation resistance Rp, and Formula 2 is the calculation formula for the resistance value of the negative electrode insulation resistance Rn:

[0064]

[0065] Among them, Rp is the positive electrode insulation resistance, Rn is the negative electrode insulation resistance, Upack is the total voltage of the high-voltage power supply unit (when the high-voltage power supply unit is a battery pack, Upack is the total voltage of the battery pack), V1_ADC is the first voltage, V2_ADC is the second voltage, R1 is the first voltage-dividing resistor, R3 is the resistance value of the first sampling resistor connected to the insulation detection circuit, R2 is the second voltage-dividing resistor, and R4 is the resistance value of the second sampling resistor connected to the insulation detection circuit.

[0066] Among them, the positive insulation resistance Rp and the negative insulation resistance Rn are the insulation resistances generated when an insulation fault occurs in the high voltage power supply unit or the low voltage power supply unit, and are not actual circuit components. Figure 4 , Rp and Rn are connected by a dotted line. Figure 4 It is used to indicate that under normal circumstances (for example, when there is no abnormality in the insulation performance), Rp and Rn can be ignored. When an insulation problem occurs, it means that Rp and Rn connect the high-voltage power supply unit to the low-voltage power supply unit.

[0067] Further, in the case of determining that the insulation between the high-voltage power supply unit and the low-voltage power supply unit is abnormal, the first voltage-dividing resistor R1 is connected in series with the connected first sampling resistor and then connected in parallel with the positive electrode insulation resistor Rp, and the second voltage-dividing resistor R2 is connected in series with the connected second sampling resistor and then connected in parallel with the negative electrode insulation resistor Rn. Since the combination formed by the first voltage-dividing resistor R1 and the first sampling resistor is in parallel with the positive electrode insulation resistor Rp, when the first voltage-dividing resistor R1 exists, by changing the size of the first sampling resistor connected to the insulation detection circuit, the first voltage correspondingly collected on the first sampling resistor can be changed. Correspondingly, since the combination formed by the second voltage-dividing resistor R2 and the second sampling resistor is in parallel with the negative electrode insulation resistor Rn, when the second voltage-dividing resistor R2 exists, by changing the size of the second sampling resistor connected to the insulation detection circuit, the second voltage correspondingly collected on the second sampling resistor can be changed. By controlling the size of the voltage values ​​measured by the first voltage and the second voltage, the measured voltage value can be made to occupy the range measured by the control unit as much as possible, thereby improving the detection range, improving the accuracy of voltage detection, and thus improving the accuracy of insulation detection.

[0068] The present invention further improves the balanced resistance bridge method of the prior art, and changes the magnitude of the measurable first voltage and the second voltage by increasing the optional resistance value of the first sampling resistor and the optional resistance value of the second sampling resistor. When the positive electrode insulation resistance Rp and the negative electrode insulation resistance Rn are actually small, the magnitude of the measured first voltage and the second voltage can be changed, so that the measured voltage value can still occupy the entire measurement range of the control unit as much as possible, thereby improving the voltage detection accuracy, and then improving the insulation detection accuracy. The full range insulation detection accuracy is high, the adaptability to different insulation conditions is high, and the adaptability to different high-voltage power supply units and low-voltage power supply units is high. The circuit elements used are low in cost, simple in circuit elements, and simple in circuit structure. The added third switch and fourth switch do not need to use high-cost switches with high requirements for high voltage resistance, thereby achieving no significant increase in cost. Compared with the prior art, the above technical solution of the present invention has low cost and high reliability, and the accuracy of insulation detection can be very high, which is easy to popularize.

[0069] Furthermore, in each of the above embodiments, the insulation detection circuit further includes a first switch S1 and a second switch S2. One end of the first switch S1 can be connected to the other end of the third switch S3, and the other end of the first switch S1 is connected to one end of the first voltage-dividing resistor R1. One end of the second switch S2 can be connected to the other end of the fourth switch S4, and the other end of the second switch S2 can be connected to one end of the second voltage-dividing resistor R2. The first switch S1 and the second switch S2 are photorelays. Reference Figure 4When the insulation detection circuit performs insulation detection, the first switch S1 and the second switch S2 are closed. The first switch S1 and the second switch S2 are selection switches responsible for accessing high voltage (can open or close the conduction path of the circuit). Using photorelays as the first switch S1 and the second switch S2 can ensure the switch's ability to withstand high voltage and improve reliability.

[0070] In the above embodiments, the number of first sampling resistors in the first sampling resistor group is 2-4, and the size of the first sampling resistors increases or decreases successively. The number of second sampling resistors in the second sampling resistor group is 2-4, and the size of the second sampling resistors increases or decreases successively, and the number of first sampling resistors in the first sampling resistor group is the same as the number of second sampling resistors in the second sampling resistor group.

[0071] Among them, the first sampling resistors in the first sampling resistor group are all fixed resistors, and the second sampling resistors in the second sampling resistor group are also fixed resistors. Variable resistors have low reliability and poor precision, and it is difficult to accurately adjust the resistance value. By setting multiple fixed resistors as the first sampling resistor group and the second sampling resistor group, it is convenient to accurately switch the resistance value of the insulation detection circuit, which helps to improve the detection accuracy.

[0072] The number of first sampling resistors in the first sampling resistor group and the number of second sampling resistors in the second sampling resistor group can be selected according to actual needs. Usually, two first sampling resistors with different resistance values ​​are set in the first sampling resistor group, and two second sampling resistors with different resistance values ​​are set in the second sampling resistor group to meet the detection requirements. The resistance value of the first sampling resistor in the first sampling resistor group corresponds to the resistance value of the second sampling resistor in the second sampling resistor group.

[0073] The resistance of the first sampling resistor increases successively. Correspondingly, the resistance of the second sampling resistor also increases successively. Among them, the magnitude of the resistance increasing successively can be designed according to actual needs, and can be jointly determined by the total voltage variation range of the high-voltage power supply unit (such as the battery pack) and the resistance range of the insulation resistance (including the positive insulation resistance and the negative insulation resistance). It is only necessary to make the first voltage and the second voltage at both ends of the first sampling resistor and the second sampling resistor collected by the control unit to occupy the maximum range of the voltage measured by the control unit. Similarly, in other embodiments, the resistance of the first sampling resistor can decrease successively, and accordingly, the resistance of the second sampling resistor also decreases successively.

[0074] Further, in the above embodiments, on the condition that the first voltage and the second voltage are within the voltage range measured by the control unit (i.e., the range of the analog-to-digital converter ADC of the control unit), the resistance values of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit can also be made equal, which helps to simplify the calculation of the positive insulation resistance Rp and the negative insulation resistance Rn.

[0075] The control unit is further configured to, when the first voltage and the second voltage are not within the first preset voltage range, increase the resistance values of the first sampling resistor and the second sampling resistor from small to large until the first voltage and the second voltage are within the first preset voltage range.

[0076] One of the end point values of the first preset voltage range can be set to a smaller voltage threshold. The smaller voltage threshold here can also be jointly determined by the total voltage change range of the high-voltage power supply unit (such as a battery pack) and the resistance value range of the insulation resistance (including the positive insulation resistance and the negative insulation resistance), and can be designed according to actual requirements. In this embodiment, the maximum voltage that the control unit can measure is Vh, the smaller voltage threshold is 0.3Vh, and the first preset voltage range can be 0.3Vh ≤ V ≤ Vh.

[0077] In other words, when the first voltage and the second voltage are lower than the above smaller voltage threshold 0.3Vh, it indicates that the resistance values of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit are smaller at this time. At this time, the control unit switches the third switch S3 and the fourth switch S4 to make the resistance values of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit larger. Refer to Figure 4 , taking the first sampling resistor group including 4 first sampling resistors (R3, R5, R7, R9) with different resistance values, the second sampling resistor group including 4 second sampling resistors (R4, R6, R8, R10) with different resistance values, and the first preset voltage range of 0.3Vh ≤ V ≤ Vh as an example. Assume that the resistance value size relationship of the first sampling resistor and the second sampling resistor in the insulation detection circuit is as follows: R3 = R4 < R5 = R6 < R7 = R8 < R9 = R10. The initially connected resistors to the insulation detection circuit are R3 and R4. When it is detected that at least one of the first voltage across R3 and the second voltage across R4 is less than 0.3Vh, the switches S3 and S4 are switched so that R5 and R6 are connected to the insulation detection circuit. At this time, the circuit voltage division ratio increases, and R5 and R6 can obtain a higher voltage, so that the control unit can obtain a larger voltage signal. After connecting R5 and R6, if at least one of the first voltage and the second voltage sampled by the control unit is still less than 0.3Vh at this time, the switches S3 and S4 are continuously switched so that R7 and R8 are connected to the circuit until the first voltage and the second voltage sampled by the control unit are greater than or equal to 0.3Vh.

[0078] By adopting the above-mentioned resistance adjustment method, the utilization rate of the range (i.e., the range of detecting the first voltage and the second voltage) of the analog-to-digital conversion function of the control unit (the first voltage and the second voltage initially collected are analog quantities, and the control unit needs to convert the analog quantities into digital quantities) can be improved, and the amplitude of the collected effective voltage signal is increased, while the noise amplitude is not affected, and the noise amplitude is not increased. Therefore, the signal-to-noise ratio of the entire insulation detection system can be improved (the signal-to-noise ratio is the ratio of the effective voltage signal amplitude to the noise amplitude), the voltage collection accuracy can be improved, and thus the accuracy of insulation detection can also be improved.

[0079] In another embodiment, the control unit is further configured to, when the first voltage and the second voltage are not within the second preset voltage range, adjust the resistance values ​​of the first sampling resistor and the second sampling resistor from large to small until the first voltage and the second voltage are within the second preset voltage range.

[0080] One of the endpoint values ​​of the second preset voltage range can be set to a larger voltage threshold (for example, a voltage threshold that is about to exceed the maximum range of the voltage measured by the control unit, and the range is, for example, an analog quantity acquisition range). The larger voltage threshold here can also be determined by the total voltage variation range of the high-voltage power supply unit (such as a battery pack) and the resistance range of the insulation resistance (including the positive insulation resistance and the negative insulation resistance), and can be designed according to actual needs. In this embodiment, the maximum value of the voltage that can be measured by the control unit is Vh, the larger voltage threshold is 0.98Vh, and the second preset voltage range can be 0≤V≤0.98Vh.

[0081] In other words, when the first voltage and the second voltage are higher than the larger voltage threshold 0.98Vh, it means that the resistance of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit is too large. At this time, the control unit switches the third switch S3 and the fourth switch S4 to reduce the resistance of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit. Figure 4, taking the example that the first sampling resistor group includes 4 first sampling resistors (R3, R5, R7, R9) with different resistance values, the second sampling resistor group includes 4 second sampling resistors (R4, R6, R8, R10) with different resistance values, and the second preset voltage range is 0 ≤ V ≤ 0.98Vh. Similarly, assume the resistance value relationship between the first sampling resistor and the second sampling resistor in the insulation detection circuit is as follows: R3 = R4 < R5 = R6 < R7 = R8 < R9 = R10. The initially connected resistors to the insulation detection circuit are R9 and R10. When it is detected that at least one of the first voltage across R9 and the second voltage across R10 is greater than 0.98Vh, switches S3 and S4 are switched to connect R7 and R8 to the insulation detection circuit. At this time, the circuit voltage division ratio decreases, and R7 and R8 can obtain lower voltages, so that the control unit can obtain smaller voltage signals. After connecting R7 and R8, if at least one of the first voltage and the second voltage collected by the control unit at this time is still greater than 0.98Vh, switches S3 and S4 are continuously switched to connect R5 and R6 to the circuit until the first voltage and the second voltage collected by the control unit are less than or equal to 0.98Vh.

[0082] Adopting the above resistance adjustment method can also improve the range utilization rate of the analog-to-digital conversion function of the control unit (the initially collected first voltage and second voltage are analog quantities, and the control unit needs to convert the analog quantities into digital quantities), that is, the range for detecting the first voltage and the second voltage. The amplitude of the collected effective voltage signal is increased, and thus the signal-to-noise ratio of the entire insulation detection system can be improved, the voltage acquisition accuracy can be improved, and the accuracy of insulation detection can also be improved.

[0083] By combining the above adjustment method of adjusting the sampling resistor value from small to large and the adjustment method of adjusting the sampling resistor value from large to small, it is also helpful to improve the adaptability of the insulation detection circuit to different high-voltage power supply units. High-voltage power supply units with different high voltages can all use the above insulation detection circuit for insulation detection, and the adaptation range of the above insulation detection circuit is wide.

[0084] For the above two sampling resistor value adjustment methods (that is, the adjustment method of adjusting the sampling resistor value from small to large and the adjustment method of adjusting the sampling resistor value from large to small), when actually performing insulation detection, one of the methods can be selected to adjust the sizes of the first sampling resistor and the second sampling resistor connected. Selecting one of them can already improve the accuracy of insulation detection, or both methods can be detected once to further ensure the accuracy and precision of insulation detection.

[0085] In the above embodiments, continue to refer to Figure 4The insulation detection circuit further includes a first diode D1 and a second diode D2. The anode of the first diode D1 is connected to the other end of the third switch S3, and the cathode of the first diode D1 is connected to the positive electrode of the high voltage power supply unit or the low voltage power supply unit. The cathode of the second diode D2 is connected to the other end of the fourth switch S4, and the anode of the second diode D2 is connected to the power supply ground of the high voltage power supply unit or the low voltage power supply unit.

[0086] The first diode D1 and the second diode D2 are responsible for clamping the overvoltage of the analog-to-digital conversion input port of the control unit (i.e., MON_Vp and MON_Vn, which can collect voltage). Clamping is a measure to limit the potential of a specific point to a specified potential. If the first sampling resistor or the second sampling resistor connected to the circuit is switched incorrectly during actual use, the first voltage and the second voltage may be too large, which may in turn cause the voltage of the input MON_Vp or MON_Vn to be too large, exceeding the maximum withstand voltage range of the control unit and damaging the control unit. By using the first diode D1 and the second diode D2 for clamping, even if the first sampling resistor or the second sampling resistor connected to the circuit is switched incorrectly, it can still be ensured that the voltage of the input ports MON_Vp and MON_Vn of the control unit does not exceed the maximum withstand voltage range of the control unit, thereby protecting the analog-to-digital conversion input ports MON_Vp and MON_Vn of the control unit.

[0087] Exemplarily, the voltage resistance range of the input port of the control unit is, for example, -0.3V to VCC+0.3V, and the voltage drop of the first diode D1 and the second diode D2 can be selected to be less than 0.3V. When the first diode D1 and the second diode D2 are used for clamping, for MON_Vp, the voltage value of the input MON_Vp will be limited to a range less than VCC (battery pack positive voltage) plus a forward voltage drop of the first diode D1, that is, the voltage value of the input MON_Vp will be limited to a range greater than -0.3V and less than VCC+0.3V, and will not exceed the maximum voltage resistance range of the input port of the control unit.

[0088] For MON_Vn, the voltage value of the input MON_Vn will be limited to be less than the forward voltage drop of the negative second diode D2, that is, the voltage value of the input MON_Vp will be limited to a range greater than -0.3V and will not exceed the maximum withstand voltage range of the input port of the control unit.

[0089] Furthermore, in each of the above embodiments, the insulation detection circuit also includes a reference power supply Vref, and the reference power supply Vref comes from a high-voltage power supply unit or a low-voltage power supply unit, and is used to power the control unit. The insulation detection circuit also includes a power supply VCC. Among them, the high-voltage power supply unit can be a battery pack, which is used to power the electric motor of the electric vehicle. The low-voltage power supply unit can be a battery, which is used to power other electrical devices in the electric vehicle, for example, it can power the control unit. The voltage of the battery pack can usually reach hundreds of volts, and the battery pack is a high-voltage power supply device; the voltage of the battery can usually be around 12V, and the battery is a low-voltage power supply device. The control unit can be a single-chip microcomputer. Exemplarily, the electric vehicle also has a power chip, reference Figure 4 The power supply VCC can be stepped down by a battery (i.e., a low-voltage power supply unit) that supplies power to the control unit through a power chip. The power supply VCC can specifically be used to supply power to the digital circuit part of the control unit. The reference power supply Vref can also be stepped down by a battery (i.e., a low-voltage power supply unit) that supplies power to the control unit through a power chip. The reference power supply Vref can specifically be used to supply power to the analog circuit part of the control unit. The reference power supply Vref and the power supply VCC are independent of each other and do not affect each other. The voltage values ​​of the two are the same. The control unit has both digital circuits and analog circuits, and can convert analog quantities (i.e., analog signals) and digital quantities (i.e., digital signals) to each other to achieve voltage acquisition.

[0090] The insulation detection circuit also includes a pull-up resistor R11, one end of the pull-up resistor R11 is connected to a reference power supply Vref, and the other end of the pull-up resistor R11 is connected to the other end of the fourth switch S4. The pull-up resistor R11 can shift the negative voltage of MON_Vn into a positive voltage through the voltage superposition theorem in the circuit principle. Wherein, both the negative voltage and the positive voltage are analog quantities, the negative voltage refers to the voltage relative to the ground (i.e., GND) of the control unit as a negative value, and the positive voltage refers to the voltage relative to the ground (i.e., GND) of the control unit as a positive value. Since the control unit can only detect positive voltage and cannot detect negative voltage, it is necessary to set a pull-up resistor R11 to shift the negative voltage of MON_Vn into a positive voltage, thereby realizing voltage detection.

[0091] Second, reference Figure 5 The embodiment of the present invention discloses an insulation detection method, which uses the insulation detection circuit for an electrical system described in any one of the embodiments of the first aspect to perform insulation detection, and the electrical system includes a high-voltage power supply unit and a low-voltage power supply unit. The insulation detection method includes the following steps:

[0092] S1: Control the third switch and the fourth switch to respectively determine the first sampling resistor and the second sampling resistor connected to the insulation detection circuit from the first sampling resistor group and the second sampling resistor group.

[0093] The first sampling resistor group includes a plurality of first sampling resistors with different resistance values, and the second sampling resistor group includes a plurality of second sampling resistors with different resistance values. The first sampling resistor is connected in series with the first voltage-dividing resistor, and the second sampling resistor is connected in series with the second voltage-dividing resistor. The third switch can switch the first sampling resistor connected to the insulation detection circuit in the first sampling resistor group, and the fourth switch can switch the second sampling resistor connected to the insulation detection circuit in the second sampling resistor group.

[0094] S2: Determine a first voltage across the first sampling resistor and a second voltage across the second sampling resistor.

[0095] S3: determining a positive electrode insulation resistance of the high voltage power supply unit or the low voltage power supply unit according to the first voltage, and determining a negative electrode insulation resistance of the high voltage power supply unit or the low voltage power supply unit according to the second voltage.

[0096] Among them, the positive electrode insulation resistance and the negative electrode insulation resistance can reflect the insulation condition between the high voltage power supply unit and the low voltage power supply unit.

[0097] S4: Determine whether the positive electrode insulation resistance and the negative electrode insulation resistance are both within a preset insulation resistance range.

[0098] If not, that is, the positive electrode insulation resistance and / or the negative electrode insulation resistance is not within the preset insulation resistance range, it is determined at S41 that there is an insulation abnormality between the high voltage power supply unit and the low voltage power supply unit.

[0099] If so, that is, both the positive electrode insulation resistance and the negative electrode insulation resistance are within the preset insulation resistance range, it is determined in S42 that there is no insulation abnormality between the high voltage power supply unit and the low voltage power supply unit.

[0100] That is, if the positive electrode insulation resistance is not within the preset insulation resistance range, it means that there is an insulation abnormality between the high-voltage power supply unit and the low-voltage power supply unit. Alternatively, if the negative electrode insulation resistance is not within the preset insulation resistance range, it means that there is an insulation abnormality between the high-voltage power supply unit and the low-voltage power supply unit. Alternatively, if both the positive electrode insulation resistance and the negative electrode insulation resistance are not within the preset insulation resistance range, it means that there is an insulation abnormality between the high-voltage power supply unit and the low-voltage power supply unit. Only when both the positive electrode insulation resistance and the negative electrode insulation resistance are within the preset insulation resistance range can it be said that there is no insulation abnormality between the high-voltage power supply unit and the low-voltage power supply unit.

[0101] By adopting the above technical scheme, the insulation detection method of the present invention adopts an insulation detection circuit, and by setting a first sampling resistor group and a second sampling resistor group, a plurality of first sampling resistors are set in the first sampling resistor group for switching, and a plurality of second sampling resistors are set in the second sampling resistor group for switching, so that the size of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit can be changed. Since a first voltage-dividing resistor is connected to the first sampling resistor and a second voltage-dividing resistor is connected to the second sampling resistor, a voltage-dividing effect is played, so that the size of the measured first voltage and the second voltage can be controlled, so that the voltage value of the measured first voltage and the voltage value of the second voltage can occupy the measurement range of the control unit as much as possible, thereby improving the detection range, and also improving the accuracy of insulation detection, and the third switch and the fourth switch used for switching the resistors do not need to adopt high-cost high-voltage resistant switches, so that the cost can be controlled and the cost is not too high.

[0102] Exemplarily, the preset insulation resistance range may be, for example, an insulation resistance greater than 500Ω, and may be determined more specifically with reference to the national standard GBT 18384.1-2015.

[0103] Further, in the above embodiment, reference Figure 6 , step S2 specifically includes the following steps:

[0104] S21: Obtain a first sampling voltage of a first sampling resistor and a second sampling voltage of a second sampling resistor.

[0105] The first sampled voltage may be a voltage on a first sampling resistor directly detected and collected by the control unit, and the second sampled voltage may be a voltage on a second sampling resistor directly detected and collected by the control unit.

[0106] S22: Determine whether the first sampling voltage and the second sampling voltage are both within a first preset voltage range.

[0107] If the first sampling voltage and the second sampling voltage are both within the first preset voltage range, executing S221: determining that the first sampling voltage is the first voltage, and determining that the second sampling voltage is the second voltage.

[0108] At this time, it indicates that the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit are reasonable, the voltages across the first sampling resistor and the second sampling resistor can occupy the entire range of the control unit as much as possible, and the measured first voltage and second voltage are accurate.

[0109] If the first sampling voltage and / or the second sampling voltage is not within the first preset voltage range, execute S222: switch the third switch and the fourth switch to increase the resistance of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit, and reacquire the first sampling voltage and the second sampling voltage until the first sampling voltage and the second sampling voltage are within the first preset voltage range.

[0110] Among them, if any one of the first sampling voltage and the second sampling voltage is not within the first preset voltage range, it means that the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit are unreasonable. That is, when the first sampling voltage is not within the first preset voltage range, it is necessary to adjust the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit; when the second sampling voltage is not within the first preset voltage range, it is also necessary to adjust the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit; when both the first sampling voltage and the second sampling voltage are not within the first preset voltage range, it is even more necessary to adjust the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit.

[0111] The maximum value of the voltage that can be measured by the control unit is Vh, and the first preset voltage range is 0.3Vh≤V≤Vh.

[0112] Further, in another embodiment, referring to Figure 7 , the above step S2 may further specifically include the following steps:

[0113] S021: Obtain a first sampling voltage of a first sampling resistor and a second sampling voltage of a second sampling resistor.

[0114] S022: Determine whether the first sampling voltage and the second sampling voltage are both within a second preset voltage range.

[0115] If the first sampling voltage and the second sampling voltage are both within the second preset voltage range, executing S0221: determining that the first sampling voltage is the first voltage, and determining that the second sampling voltage is the second voltage.

[0116] At this time, it indicates that the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit are reasonable, the voltages across the first sampling resistor and the second sampling resistor can occupy the entire range of the control unit as much as possible, and the measured first voltage and second voltage are accurate.

[0117] If the first sampling voltage and / or the second sampling voltage is not within the second preset voltage range, execute S0222: switch the third switch and the fourth switch to reduce the resistance of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit, and reacquire the first sampling voltage and the second sampling voltage until the first sampling voltage and the second sampling voltage are within the second preset voltage range.

[0118] Among them, if any one of the first sampling voltage and the second sampling voltage is not within the second preset voltage range, it means that the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit are unreasonable. That is, when the first sampling voltage is not within the second preset voltage range, it is necessary to adjust the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit; when the second sampling voltage is not within the second preset voltage range, it is also necessary to adjust the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit; when both the first sampling voltage and the second sampling voltage are not within the second preset voltage range, it is even more necessary to adjust the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit.

[0119] The maximum value of the voltage that can be measured by the control unit is Vh, and the second preset voltage range is 0≤V≤0.98Vh.

[0120] Although the present invention has been illustrated and described with reference to certain preferred embodiments of the present invention, it should be understood by those skilled in the art that the above is a further detailed description of the present invention in conjunction with specific embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. Those skilled in the art may make various changes in form and details, including making several simple deductions or substitutions, without departing from the spirit and scope of the present invention.

Claims

1. An insulation detection circuit for an electrical system, the electrical system comprising a high voltage power supply unit and a low voltage power supply unit, characterized in that: include: A first sampling resistor group includes a plurality of first sampling resistors with different resistance values, and one end of each of the first sampling resistors is grounded; a third switch, wherein one end of the third switch can be connected to the other end of each of the first sampling resistors, and the other end of the third switch is connected to the positive electrode of the high voltage power supply unit or the low voltage power supply unit; A second sampling resistor group includes a plurality of second sampling resistors with different resistance values, and one end of each of the second sampling resistors is grounded; a fourth switch, wherein one end of the fourth switch can be connected to the other end of each of the second sampling resistors, and the other end of the fourth switch is connected to the negative electrode of the high voltage power supply unit or the low voltage power supply unit; a first voltage-dividing resistor, one end of which can be connected to the other end of the third switch, the other end of which is connected to the positive electrode of the high-voltage power supply unit or the low-voltage power supply unit, and the first voltage-dividing resistor is connected to a first sampling resistor to be connected; a second voltage-dividing resistor, one end of which can be connected to the other end of the fourth switch, the other end of which is connected to the negative electrode of the high-voltage power supply unit or the low-voltage power supply unit, and the second voltage-dividing resistor is connected to a second sampling resistor to be connected; The control unit is configured to determine the first sampling resistor and the second sampling resistor connected to the insulation detection circuit from the first sampling resistor group and the second sampling resistor group respectively by controlling the third switch and the fourth switch, and respectively determine the first voltage and the second voltage across the first sampling resistor and the second sampling resistor connected to determine the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit.

2. The insulation detection circuit for an electrical system according to claim 1, characterized in that: The control unit is further configured to determine the resistance value of the positive insulation resistance and the negative insulation resistance between the high-voltage power supply unit and the low-voltage power supply unit according to the first voltage and the second voltage across the first sampling resistor and the second sampling resistor connected, and determine the insulation condition between the high-voltage power supply unit and the low-voltage power supply unit according to the resistance value of the positive insulation resistance and the negative insulation resistance.

3. The insulation detection circuit for an electrical system according to claim 2, characterized in that: When it is determined that the insulation between the high-voltage power supply unit and the low-voltage power supply unit is abnormal, the first voltage-dividing resistor is connected in series with the connected first sampling resistor and then connected in parallel with the positive insulation resistor, and the second voltage-dividing resistor is connected in series with the connected second sampling resistor and then connected in parallel with the negative insulation resistor.

4. The insulation detection circuit for an electrical system according to claim 1, characterized in that: Also includes: a first switch, wherein one end of the first switch can be connected to the other end of the third switch, and the other end of the first switch is connected to one end of the first voltage-dividing resistor; a second switch, wherein one end of the second switch can be connected to the other end of the fourth switch, and the other end of the second switch can be connected to one end of the second voltage-dividing resistor; Wherein, the first switch and the second switch are photorelays.

5. The insulation detection circuit for an electrical system according to claim 1, characterized in that: The number of the first sampling resistors in the first sampling resistor group is 2-4, and the sizes of the first sampling resistors are gradually increased or decreased; the number of the second sampling resistors in the second sampling resistor group is 2-4, and the sizes of the second sampling resistors are gradually increased or decreased; and the number of the first sampling resistors in the first sampling resistor group is the same as the number of the second sampling resistors in the second sampling resistor group; And / or, the resistance values ​​of the first sampling resistor and the second sampling resistor connected to the insulation detection circuit are equal.

6. The insulation detection circuit for an electrical system according to claim 1, characterized in that: The control unit is further configured to, when the first voltage and the second voltage are not within a first preset voltage range, adjust the resistance values ​​of the first sampling resistor and the second sampling resistor from small to large until the first voltage and the second voltage are within the first preset voltage range, wherein the maximum value of the voltage measurable by the control unit is Vh, and the first preset voltage range is 0.3Vh≤V≤Vh; And / or, when the first voltage and the second voltage are not within the second preset voltage range, the resistance values ​​of the first sampling resistor and the second sampling resistor are adjusted from large to small until the first voltage and the second voltage are within the second preset voltage range, wherein the maximum value of the voltage measurable by the control unit is Vh, and the second preset voltage range is 0≤V≤0.98Vh.

7. The insulation detection circuit for an electrical system according to claim 1, characterized in that: Also includes: a first diode, wherein an anode of the first diode is connected to the other end of the third switch, and a cathode of the first diode is connected to a positive electrode of the high voltage power supply unit or the low voltage power supply unit; A second diode, wherein a cathode of the second diode is connected to the other end of the fourth switch, and an anode of the second diode is connected to a power supply ground of the high voltage power supply unit or the low voltage power supply unit.

8. The insulation detection circuit for an electrical system according to claim 1, characterized in that: Also includes: A reference power supply, coming from the high voltage power supply unit or the low voltage power supply unit, for supplying power to the control unit; A pull-up resistor, one end of which is connected to the reference power supply, and the other end of which is connected to the other end of the fourth switch.

9. The insulation detection circuit for an electrical system according to any one of claims 1 to 7, characterized in that: The high-voltage power supply unit is a battery pack for supplying power to the electric motor of the electric vehicle, and / or the low-voltage power supply unit is a storage battery for supplying power to other electrical devices in the electric vehicle.

10. An insulation detection method, characterized in that: An insulation detection circuit for an electrical system according to any one of claims 1 to 7 is used to perform insulation detection, the electrical system comprising a high voltage power supply unit and a low voltage power supply unit, and the insulation detection method comprises: Controlling the third switch and the fourth switch to determine the first sampling resistor and the second sampling resistor connected to the insulation detection circuit from the first sampling resistor group and the second sampling resistor group, respectively; wherein the first sampling resistor group includes a plurality of the first sampling resistors with different resistance values, the second sampling resistor group includes a plurality of the second sampling resistors with different resistance values, the first sampling resistor is connected in series with the first voltage-dividing resistor, and the second sampling resistor is connected in series with the second voltage-dividing resistor; Determine a first voltage across the first sampling resistor and a second voltage across the second sampling resistor; Determine the positive electrode insulation resistance of the high voltage power supply unit or the low voltage power supply unit according to the first voltage, and determine the negative electrode insulation resistance of the high voltage power supply unit or the low voltage power supply unit according to the second voltage; Determining whether the positive electrode insulation resistance and the negative electrode insulation resistance are both within a preset insulation resistance range; If the positive electrode insulation resistance and / or the negative electrode insulation resistance is not within the preset insulation resistance range, it is determined that there is an insulation abnormality between the high voltage power supply unit and the low voltage power supply unit; If the positive electrode insulation resistance and the negative electrode insulation resistance are both within the preset insulation resistance range, it is determined that there is no insulation abnormality between the high voltage power supply unit and the low voltage power supply unit.

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