Insulation detection failure diagnosis method

Abstract

The invention discloses an insulation detection failure diagnosis method, which comprises the following steps of: in an unbalanced bridge circuit, controlling an upper bridge arm switch KP and a lower bridge arm switch KN to be switched on simultaneously, controlling a switch KPE between an upper bridge arm and a lower bridge arm and a vehicle body ground to be switched off simultaneously, respectively acquiring and calculating voltage values # imgabs0 # and # imgabs1 # of sampling resistors RP1 and RN1, the sampling resistor RN1 is a resistor of the negative electrode of the lower half bridge arm; the internal total voltage VBAT between the battery BAT + and the battery BAT-is calculated according to the obtained voltage values # imgabs2 # and # imgabs3 # and the voltage division ratio coefficient; and judging a fault reason according to whether the VBAT is 0 or not. According to the method, a single failure fault and multiple failure fault diagnosis method is provided for the situation that normal insulation detection judgment is affected after an external input signal of an unbalanced bridge method breaks down.

Description

Technical Field

[0001] The invention belongs to the technical field of insulation resistance detection in a battery management system, and in particular relates to an insulation detection failure diagnosis method. Background Art

[0002] In the battery management system (BMS), insulation resistance detection is a very important function that can be used to evaluate the insulation performance of the battery system and help understand whether the equipment has leakage, grounding faults or insulation aging. At present, the voltage level of electric vehicles has reached more than 800V, and the high-voltage platform supports higher charging power and faster charging speed; in the field of energy storage, the 1500V high-voltage system has become the mainstream solution in the energy storage market in recent years, and is also moving towards a voltage level of more than 2000V. With the development of energy storage systems and power battery systems towards high voltage, the importance of insulation performance has become more prominent. The insulation resistance under high-voltage environment is a key factor in ensuring the reliability and safety of the system. High-quality insulation can prevent leakage and short circuit, thereby ensuring the safety of the battery. If the insulation performance of the system decreases, there may be leakage hazards, which may lead to personal safety problems. In severe cases, it may even cause a short circuit in the battery module and cause a fire, resulting in irreparable losses. Therefore, it is necessary to specially consider and design the insulation detection function of the battery pack, monitor the insulation status of the battery pack in real time, and report alarm information and perform corresponding protection actions in a timely manner according to the monitoring results to ensure the safe and stable operation of the battery system.

[0003] At present, the main methods for BMS to detect insulation resistance include balanced bridge method, unbalanced bridge method and AC voltage injection method. Among them, the unbalanced bridge method has the advantages of relatively simple circuit structure, high sampling accuracy, electromagnetic compatibility (EMC) and good stability, and has been widely used in the insulation detection scheme of power and energy storage BMS. The basic principle of the unbalanced bridge method is to connect a series of resistors between the positive and negative poles of the battery and the grounded casing, and change the equivalent resistance of the two poles to the ground by alternately switching the switches on both sides, collect the unbalanced detection voltage values ​​on the positive and negative sampling resistors, and calculate the insulation resistance of the positive and negative poles according to Kirchhoff's current law.

[0004] In the BMS hardware architecture that uses the unbalanced bridge method to detect insulation resistance, the BMS uses two A / D sampling circuits to sample the voltage of the positive and negative sampling resistors of the upper and lower bridge arms respectively, and the physical wiring connected to the BMS input port from the outside includes: ① the positive acquisition line of the battery pack (BAT+), ② the negative acquisition line of the battery pack (BAT-), and ③ the protective grounding line (PE, Protective-Earth). Since this method requires additional acquisition lines to be connected to the high-voltage acquisition part of the battery management system, and under the complex electrical environment and operating conditions of the vehicle, there is a possibility that the above-mentioned acquisition harness will have a short circuit or disconnection, and the connector will be loose and have poor contact, which will affect the normal acquisition of the required signal, resulting in the insulation detection function module being unable to obtain the expected results after execution. That is, in the existing patented technologies, most of them focus on the improvement and optimization of the unbalanced bridge method at the software and algorithm implementation level, without considering the failure of the external input signal itself, that is, the failure of one or more of the input signals of BAT+, BAT-, and PE, resulting in the failure of insulation detection. Therefore, the existing insulation detection algorithm can only calculate the insulation resistance when all input signals are normal by default, but cannot identify which specific failure or failures occur when the detection fails. This will result in the inability to report alarm information and execute protection actions normally when an insulation fault actually occurs due to the detection failure, posing a safety hazard. Summary of the invention

[0005] In order to remedy the deficiencies of the prior art, the present invention aims to provide an insulation detection failure diagnosis method to solve the problem that detection failure occurs when the insulation resistance is detected by an unbalanced bridge method but the specific failure cannot be identified.

[0006] The technical problem to be solved by the present invention can be achieved through the following technical solutions:

[0007] An insulation detection failure diagnosis method, the specific steps include:

[0008] S1. In the unbalanced bridge circuit, control the upper arm switch K P , lower arm switch K N Close at the same time and control the switch K between the upper and lower bridge arms and the vehicle body ground PE Disconnect, collect and calculate the sampling resistance R P1 and R N1 Voltage value and Sampling resistor R P1 is the resistance of the positive electrode of the upper half bridge arm, the sampling resistor R N1 is the resistance of the negative electrode of the lower half bridge arm;

[0009] S2. The voltage value obtained according to step S1 and Calculate the total internal pressure V between battery BAT+ and battery BAT- using the voltage divider ratio coefficient BAT ;

[0010] S3. Determine the total internal pressure value V calculated in step S2 BAT Is it 0? If V BAT = 0, it is preliminarily determined that a BAT+ or BAT- line break fault has occurred, and then further determined whether it is BAT+ or BAT- that is broken; if V BAT ≠0, then there is no disconnection fault between BAT+ and BAT-, and further determine whether there is a PE disconnection fault. PE disconnection refers to the disconnection of the high-voltage connection line between the vehicle body ground and the input connection point of the battery management system;

[0011] S4. If V BAT =0, the battery management system controls the switch K PE Close, collect and calculate the sampling resistance R again P1 And the sampling resistor R N1 Voltage value and according to and The value of determines the disconnection of BAT+ and BAT-;

[0012] S5. If V BAT ≠0, that is, under the premise that there is no BAT+ or BAT- line break fault, the battery management system controls the switch K PE Close, and keep the upper arm switch K P , lower arm switch K N Close, collect and calculate the sampling resistance R P1 And the sampling resistor R N1 The voltage value on the PE The calculated and Disconnect K in step S1 PE Calculated when and If the values ​​are equal, it is determined that a PE disconnection fault occurs.

[0013] Further, in the unbalanced bridge circuit, the input connection point from the positive electrode of the battery to the battery management system is recorded as point A, the input connection point from the vehicle body ground to the battery management system is recorded as point B, and the input connection point from the negative electrode of the battery to the battery management system is recorded as point C. BAT+ disconnection refers to the disconnection of the high-voltage connection line between the positive electrode of the battery and point A, BAT- disconnection refers to the disconnection of the high-voltage connection line between the negative electrode of the battery and point C, and PE disconnection refers to the disconnection of the high-voltage connection line between the PE of the vehicle body ground and point B;

[0014] The unbalanced bridge circuit includes an upper bridge arm and a lower bridge arm. The upper bridge arm includes bridge arm I and bridge arm III, and the lower bridge arm includes bridge arm II and bridge arm IV. Bridge arm I and bridge arm III are connected to the positive electrode of the battery and the reference ground, and bridge arm II and bridge arm IV are connected to the negative electrode of the battery. The resistor R P1 and resistor R P2 is the positive resistance of the upper bridge arm, and the resistance R N1 and resistor R N2 is the negative resistance of the lower bridge arm, where the resistance R P1 and resistor R N1 is the sampling resistor, resistor R P2 and resistor R N2 is the voltage divider resistor; K P is the upper arm switch, K N is the lower bridge arm switch, K PE It is the switch between the upper and lower bridge arms and the vehicle body ground, and the resistor R P Is the equivalent insulation resistance of the battery positive electrode to ground, resistance R N is the equivalent insulation resistance of the negative electrode of the battery to the ground, VBAT is the total voltage of the positive and negative electrodes of the battery, V P is the bridge arm I voltage, V N is the bridge arm II voltage, V P1 is the sampling resistor R P1 The voltage divider, V N1 is the sampling resistor R N1 The partial pressure.

[0015] Furthermore, in step S1, when the battery management system controls the switch K PE After disconnection, the battery, bridge arm I-bridge arm II, bridge arm III-bridge arm IV form a parallel relationship, so the equivalent insulation resistance of bridge arm III and bridge arm IV is R P and R N It has no effect on bridge arm I and bridge arm II. Therefore, by applying the resistance voltage division law to the independent loop formed by bridge arm I, bridge arm II and the battery, the sampling resistance R can be calculated. P1 Voltage value on for:

[0016]

[0017] Similarly, the sampling resistor R N1 Voltage value on for:

[0018]

[0019] Further, for step S2, the upper bridge arm and the lower bridge arm of the unbalanced bridge circuit are symmetrical, that is, the positive sampling resistor and the negative sampling resistor have the same resistance value, the positive voltage divider resistor and the negative voltage divider resistor have the same resistance value, and the resistance value of the voltage divider resistor is much larger than the resistance value of the sampling resistor, that is, R P2 =R N2 >>R P1 =R N1 , assuming that the resistance ratio of the voltage divider resistor to the sampling resistor is k = R P2 / R P1 =R N2 / R N1 According to Ohm's law, the ratio of the bridge arm voltage to the sampling resistor voltage is V P / V P1 =V N / V N1 =k+1, the calculation formula for the total internal pressure is:

[0020]

[0021] Furthermore, in step S4, if the calculated It is determined that a BAT+ disconnection fault occurs at this time; that is, if BAT+ is disconnected, point A of bridge arm I is disconnected from the positive electrode BAT+ of the battery, and the total voltage of bridge arm I is 0, so the sampling resistor R P1 The voltage V P1 is also 0; at the same time, the battery and bridge arm III and the parallel branches of bridge arm II and bridge arm IV form a loop, and according to Ohm's law and the characteristics of series-parallel circuits, the total battery voltage V BAT , sampling resistor voltage value Sampling resistor R N1 , positive insulation resistance R P And the negative insulation resistance R N The following relationship exists:

[0022]

[0023] After simplification, we can get V N1 The values ​​are:

[0024]

[0025] That is When it is equal to the result of the above formula, it is determined that a BAT+ line break fault occurs at this time.

[0026] Furthermore, in step S4, if the calculated It is determined that a BAT- line break fault occurs at this time; that is, if BAT- is broken, the C point of bridge arm II and the negative electrode of the battery BAT- are disconnected, and the total voltage of bridge arm II is 0, so the sampling resistor R N1 The voltage V N1 is also 0; at the same time, the battery and bridge arm IV and the parallel branch of bridge arm I and bridge arm III form a loop, and according to Ohm's law and the characteristics of series-parallel circuits, the total battery voltage V BAT , sampling resistor voltage value Sampling resistor R P1 , positive insulation resistance R P And the negative insulation resistance R N The following relationship exists:

[0027]

[0028] After simplification, we can get V P1 The values ​​are:

[0029]

[0030] That is When it is equal to the result of the calculation of the above formula (7), it is determined that a BAT-line break fault has occurred.

[0031] Furthermore, in step S4, if Directly determine that a double fault of BAT+ and BAT- line disconnection has occurred.

[0032] Furthermore, in step S5, when the switch K PE , upper arm switch K P , lower arm switch K N When both are closed, the parallel connection of bridge arm Ⅰ and bridge arm Ⅲ and the parallel connection of bridge arm Ⅱ and bridge arm Ⅳ form a series relationship. First, calculate the parallel equivalent resistance of bridge arm Ⅰ and bridge arm Ⅲ and the parallel equivalent resistance of bridge arm Ⅱ and bridge arm Ⅳ. Then, calculate the voltage of the upper bridge arm and the lower bridge arm according to the voltage division law of the series circuit. Then, apply the voltage division law to bridge arm Ⅰ and bridge arm Ⅱ respectively to calculate the sampling resistance R P1 and R N1 Voltage on and The specific calculation formula is as follows:

[0033]

[0034] In the above formula, let R P =R N =∞, calculate and simplify to get:

[0035]

[0036] It can be seen that if and only if R P =R N =∞, and

[0037] Compared with the prior art, the present invention has the following advantages: the method of the present invention analyzes the possible failure problems that may occur when measuring insulation resistance using the unbalanced bridge method in a battery system, and provides a diagnosis method for single failure faults and multiple failure faults in response to the situation where a failure of the external input signal of the unbalanced bridge method affects the normal insulation detection judgment. It further analyzes the fault identification problem when a failure fault and an insulation fault exist at the same time, thereby improving the comprehensiveness and reliability of the insulation detection function in the battery management system. BRIEF DESCRIPTION OF THE DRAWINGS

[0038] Figure 1 This is a schematic diagram of the insulation detection failure diagnosis circuit of the present invention;

[0039] Figure 2 This is a flow chart of the insulation detection failure diagnosis method of the present invention;

[0040] Figure 3 This is the principle diagram of the insulation detection failure diagnosis circuit of the present invention (BAT+broken line);

[0041] Figure 4 This is the schematic diagram of the insulation detection failure diagnosis circuit of the present invention (BAT-broken wire);

[0042] Figure 5 This is a schematic diagram of the insulation detection failure diagnosis circuit of the present invention (PE line break). DETAILED DESCRIPTION

[0043] In order to enable those skilled in the art to more clearly understand the technical solution of the present application, an insulation detection failure diagnosis method of the present invention is further described below in conjunction with the accompanying drawings.

[0044] like Figure 1 As shown, in the unbalanced bridge circuit involved in the present application, the input connection point from the positive electrode of the battery to the battery management system is recorded as point A, the input connection point from the vehicle body ground to the battery management system is recorded as point B, and the input connection point from the negative electrode of the battery to the battery management system is recorded as point C. BAT+ disconnection refers to the disconnection of the high-voltage connection line between the positive electrode of the battery and point A, BAT- disconnection refers to the disconnection of the high-voltage connection line between the negative electrode of the battery and point C, and PE disconnection refers to the disconnection of the high-voltage connection line between the PE of the vehicle body ground and point B.

[0045] The unbalanced bridge circuit includes an upper bridge arm and a lower bridge arm. The upper bridge arm and the lower bridge arm are symmetrical. The upper bridge arm includes bridge arm I and bridge arm III, and the lower bridge arm includes bridge arm II and bridge arm IV. Bridge arm I and bridge arm III are connected to the positive electrode of the battery and the reference ground, and bridge arm II and bridge arm IV are connected to the negative electrode of the battery. The resistor R P1 and resistor R P2 is the positive resistance of the upper bridge arm, and the resistance R N1 and resistor R N2 is the negative resistance of the lower bridge arm, where the resistance R P1 and resistor R N1 is the sampling resistor, resistor R P2 and resistor R N2 is the voltage divider resistor; K P is the upper arm switch, K N is the lower bridge arm switch, K PE It is the switch between the upper and lower bridge arms and the vehicle body ground, and the resistor R P Is the equivalent insulation resistance of the battery positive electrode to ground, resistance R N is the equivalent insulation resistance of the negative electrode of the battery to the ground, VBAT is the total voltage of the positive and negative electrodes of the battery, V P is the bridge arm I voltage, V N is the bridge arm II voltage, V P1 is the sampling resistor R P1 The voltage divider, V N1 is the sampling resistor R N1 The partial pressure.

[0046] like Figure 2 As shown, a method for diagnosing insulation detection failure includes the following steps:

[0047] (I) In an unbalanced bridge circuit, the battery management system controls the upper bridge arm switch K P , lower arm switch K N Close at the same time and control the switch K between the upper and lower bridge arms and the vehicle body ground PE Disconnect, collect and calculate the sampling resistance R P1 And the sampling resistor R N1 Voltage value and Sampling resistor R P1 is the resistance of the positive electrode of the upper half bridge arm, the sampling resistor R N1 is the resistance of the negative pole of the lower half bridge arm. Voltage value and Collect and calculate the sampling resistance R for the first time P1 And the sampling resistor R N1 Voltage value.

[0048] Specifically, when the battery management system controls the switch K PE After disconnection, Figure 1It can be seen that at this time, the battery, bridge arm I-bridge arm II, bridge arm III-bridge arm IV form a parallel relationship, so the equivalent insulation resistance of bridge arm III and bridge arm IV is R P and R N It has no effect on bridge arm I and bridge arm II. Therefore, by applying the resistance voltage division law to the independent loop formed by bridge arm I, bridge arm II and the battery, the sampling resistance R can be calculated. P1 Voltage value on for:

[0049]

[0050] Similarly, the sampling resistor R N1 Voltage value on for:

[0051]

[0052] (ii) Voltage value obtained according to step S1 and Calculate the total internal pressure V between battery BAT+ and battery BAT- using the voltage divider ratio coefficient BAT .

[0053] In the unbalanced bridge circuit, the upper and lower bridge arms are symmetrical, that is, the positive sampling resistor and the negative sampling resistor have the same resistance value, the positive voltage divider resistor and the negative voltage divider resistor have the same resistance value, and the voltage divider resistor is much larger than the sampling resistor, that is, R P2 =R N2 >>R P1 =R N1 , assuming that the resistance ratio of the voltage divider resistor to the sampling resistor is k = R P2 / R P1 =R N2 / R N1 According to Ohm's law, the ratio of the bridge arm voltage to the sampling resistor voltage is V P / V P1 =V N / V N1 =k+1. The calculation formula for the total internal pressure is:

[0054]

[0055] (III) Determine the total internal pressure value V calculated in step S2 BAT Is it 0? If V BAT = 0, it is preliminarily determined that a BAT+ or BAT- line break fault has occurred, and then further determined whether it is BAT+ or BAT- that is broken; if V BAT ≠0, then there is no disconnection fault between BAT+ and BAT-, and further determine whether there is a PE disconnection fault.

[0056] If V BAT =0, then V P1 =V N1 =0, so the bridge arm I, bridge arm II and the battery do not form a circuit, which means that the bridge arm I and the positive electrode BAT+ of the battery are disconnected; or the bridge arm II and the negative electrode BAT- of the battery are disconnected. Therefore, it can be preliminarily determined that a BAT+ disconnection or BAT- disconnection fault has occurred.

[0057] (IV) If V BAT =0, the battery management system controls the switch K PE Close, collect and calculate the sampling resistance R again P1 And the sampling resistor R N1 Voltage value and according to and The value of determines the disconnection of BAT+ and BAT-. and The second acquisition and calculation of the sampling resistance R P1 And the sampling resistor R N1 Voltage value.

[0058] (1) If we calculate It is determined that a BAT+ disconnection fault occurs at this time.

[0059] like Figure 3 As shown in the figure, in the unbalanced bridge circuit, if BAT+ is disconnected, point A of bridge arm I is disconnected from the positive electrode BAT+ of the battery, and the total voltage of bridge arm I is 0. Therefore, the sampling resistor R P1 The voltage V P1 is also 0; at the same time, the battery and bridge arm III and the parallel branches of bridge arm II and bridge arm IV form a loop, and according to Ohm's law and the characteristics of series-parallel circuits, the total battery voltage V BAT , sampling resistor voltage value Sampling resistor R N1 , positive insulation resistance R P And the negative insulation resistance R N The following relationship exists:

[0060]

[0061] After simplification, we can get V N1 The values ​​are:

[0062]

[0063] That is When it is equal to the result of the above formula (5), it is determined that a BAT+line break fault occurs.

[0064] (2) If the calculation is It is determined that a BAT-line break fault occurs at this time.

[0065] like Figure 4 As shown in the figure, in the unbalanced bridge circuit, if BAT- is disconnected, the point C of bridge arm II and the negative electrode of the battery BAT- are disconnected, and the total voltage of bridge arm II is 0, so the sampling resistor R N1 The voltage V N1 is also 0; at the same time, the battery and bridge arm IV and the parallel branch of bridge arm I and bridge arm III form a loop, and according to Ohm's law and the characteristics of series-parallel circuits, the total battery voltage V BAT , sampling resistor voltage value Sampling resistor R P1 , positive insulation resistance R P And the negative insulation resistance R N The following relationship exists:

[0066]

[0067] After simplification, we can get V P1 The values ​​are:

[0068]

[0069] That is When it is equal to the result of the calculation of the above formula (7), it is determined that a BAT-line break fault has occurred.

[0070] (3) If As a special case where two line break fault conditions are met at the same time, it is directly determined that a double line break fault of BAT+ and BAT- occurs.

[0071] (V) If V BAT ≠0, that is, under the premise that there is no BAT+ or BAT- line break fault, the battery management system controls the switch K PE Close, and keep the upper arm switch K P , lower arm switch K N Close, collect and calculate the sampling resistance R P1 And the sampling resistor R N1 The voltage value on the PE The calculated and Disconnect K in step S1 PE Calculated when and If the values ​​are equal, it is determined that a PE disconnection fault occurs.

[0072] like Figure 5 As shown, when switch KPE , K P and K N When all are closed, the parallel connection of bridge arm Ⅰ and bridge arm Ⅲ and the parallel connection of bridge arm Ⅱ and bridge arm Ⅳ form a series relationship. First, calculate the parallel equivalent resistance of bridge arm Ⅰ and bridge arm Ⅲ and the parallel equivalent resistance of bridge arm Ⅱ and bridge arm Ⅳ, and then calculate the voltage of the upper and lower bridge arms according to the voltage division law of the series circuit, and then apply the voltage division law to bridge arm Ⅰ and bridge arm Ⅱ respectively to calculate the voltage on the sampling resistors RP1 and RN1 and The specific calculation formula is shown in (8)(9):

[0073]

[0074] In particular, under ideal conditions, the insulation equivalent resistance R P and R N is infinite, in the above formulas (8) and (9), let R P =R N =∞, calculate and simplify to get:

[0075]

[0076]

[0077] It can be seen that if and only if R P =R N =∞, the simplified results of formula (8) (9) are (10) (11), which are the same as formula (1) (2), that is, and In the practical application of the present invention, the insulation resistance R between the positive and negative electrodes of the battery and the vehicle body ground is P and R N The resistance value cannot be infinite, so it can be considered that the calculation results of formula (8) (9) and formula (1) (2) are not actually equal. Therefore, when PE is connected to point B normally, the control switch K PE Before and after closing, the sampling resistor R P1 and R N1 If PE is disconnected, the actual PE and point B will remain disconnected. PE Before and after closing and opening, the sampling resistor R P1 and R N1 The voltage value on the MOSFET will not change.

[0078] Close switch K PE Then the result calculated by formula (8) and (9) is consistent with the disconnection K PEThe results calculated according to formula (1) and (2) are then compared. If the voltages of the corresponding sampling resistors are the same, it indicates that a PE disconnection fault has occurred.

[0079] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for diagnosing insulation failure, characterized in that: The specific steps include: S1. In the unbalanced bridge circuit, control the upper arm switch K P , lower arm switch K N Close at the same time and control the switch K between the upper and lower bridge arms and the vehicle body ground PE Disconnect, collect and calculate the sampling resistance R P1 and R N1 Voltage value and Sampling resistor R P1 is the resistance of the positive electrode of the upper half bridge arm, the sampling resistor R N1 is the resistance of the negative electrode of the lower half bridge arm; S2. The voltage value obtained according to step S1 and Calculate the total internal pressure V between battery BAT+ and battery BAT- using the voltage divider ratio coefficient BAT ; S3. Determine the total internal pressure value V calculated in step S2 BAT Is it 0? If V BAT = 0, it is preliminarily determined that a BAT+ or BAT- line break fault has occurred, and then further determined whether it is BAT+ or BAT- that is broken; if V BAT ≠0, then there is no disconnection fault between BAT+ and BAT-, and further determine whether there is a PE disconnection fault. PE disconnection refers to the disconnection of the high-voltage connection line between the vehicle body ground and the input connection point of the battery management system; S4. If V BAT =0, the battery management system controls the switch K PE Close, collect and calculate the sampling resistance R again P1 And the sampling resistor R N1 Voltage value and according to and The value of determines the disconnection of BAT+ and BAT-; S5. If V BAT ≠0, that is, under the premise that there is no BAT+ or BAT- line break fault, the battery management system controls the switch K PE Close, and keep the upper arm switch K P , lower arm switch K N Close, collect and calculate the sampling resistance R P1 And the sampling resistor R N1 The voltage value on the PE The calculated and Disconnect K in step S1 PE Calculated when and If the values ​​are equal, it is determined that a PE disconnection fault occurs.

2. The insulation detection failure diagnosis method according to claim 1, characterized in that: In the unbalanced bridge circuit, the input connection point from the positive electrode of the battery to the battery management system is marked as point A, the input connection point from the vehicle body ground to the battery management system is marked as point B, and the input connection point from the negative electrode of the battery to the battery management system is marked as point C; the unbalanced bridge circuit includes an upper bridge arm and a lower bridge arm, the upper bridge arm includes bridge arm I and bridge arm III, the lower bridge arm includes bridge arm II and bridge arm IV, bridge arm I and bridge arm III are one end connecting the positive electrode of the battery and the reference ground, bridge arm II and bridge arm IV are one end connecting the negative electrode of the battery, and the resistor R P1 and resistor R P2 is the positive resistance of the upper bridge arm, and the resistance R N1 and resistor R N2 is the negative resistance of the lower bridge arm, where the resistance R P1 and resistor R N1 is the sampling resistor, resistor R P2 and resistor R N2 is the voltage divider resistor; K P is the upper arm switch, K N is the lower bridge arm switch, K PE It is the switch between the upper and lower bridge arms and the vehicle body ground, and the resistor R P Is the equivalent insulation resistance of the battery positive electrode to ground, resistance R N is the equivalent insulation resistance of the negative electrode of the battery to the ground, VBAT is the total voltage of the positive and negative electrodes of the battery, V P is the bridge arm I voltage, V N is the bridge arm II voltage, V P1 is the sampling resistor R P1 The voltage divider, V N1 is the sampling resistor R N1 The partial pressure.

3. The insulation detection failure diagnosis method according to claim 2, characterized in that: In step S1, when the battery management system controls the switch K PE After disconnection, the resistance voltage division law is applied to the independent loop formed by bridge arm I, bridge arm II and the battery to calculate the sampling resistance R P1 Voltage value on for: Similarly, the sampling resistor R N1 The voltage value V (1 N ) 1 is:

4. The insulation detection failure diagnosis method according to claim 2, characterized in that: For step S2, the upper bridge arm and the lower bridge arm of the unbalanced bridge circuit are symmetrical, the positive sampling resistor and the negative sampling resistor have the same resistance value, the positive voltage divider resistor and the negative voltage divider resistor have the same resistance value, and the resistance value of the voltage divider resistor is much larger than the resistance value of the sampling resistor, that is, R P2 =R N2 >>R P1 =R N1 , assuming that the resistance ratio of the voltage divider resistor to the sampling resistor is k = R P2 / R P1 =R N2 / R N1 According to Ohm's law, the ratio of the bridge arm voltage to the sampling resistor voltage is V P / V P1 =V N / V N1 =k+1, the calculation formula for the total internal pressure is:

5. The insulation detection failure diagnosis method according to claim 2, characterized in that: In step S4, if the calculated It is determined that a BAT+ disconnection fault occurs at this time; that is, if BAT+ is disconnected, point A of bridge arm I is disconnected from the positive electrode BAT+ of the battery, and the total voltage of bridge arm I is 0, so the sampling resistor R P1 The voltage V P1 is also 0; at the same time, the battery and bridge arm III and the parallel branches of bridge arm II and bridge arm IV form a loop, and according to Ohm's law and the characteristics of series-parallel circuits, the total battery voltage V BAT , sampling resistor voltage value Sampling resistor R N1 , positive insulation resistance R P And the negative insulation resistance R N The following relationship exists: After simplification, we can get V N1 The values ​​are: That is When it is equal to the result of the above formula, it is determined that a BAT+ line break fault occurs at this time.

6. The insulation detection failure diagnosis method according to claim 2, characterized in that: In step S4, if the calculated It is determined that a BAT- line break fault occurs at this time; that is, if BAT- is broken, the C point of bridge arm II and the negative electrode of the battery BAT- are disconnected, and the total voltage of bridge arm II is 0, so the sampling resistor R N1 The voltage V N1 is also 0; at the same time, the battery and bridge arm IV and the parallel branches of bridge arm I and bridge arm III form a loop, and according to Ohm's law and the characteristics of series-parallel circuits, the total battery voltage V BAT , sampling resistor voltage value Sampling resistor R P1 , positive insulation resistance R P And the negative insulation resistance R N The following relationship exists: After simplification, we can get V P1 The values ​​are: That is When it is equal to the result of the calculation of the above formula (7), it is determined that a BAT-line break fault has occurred.

7. The insulation detection failure diagnosis method according to claim 4, characterized in that: In step S4, if Directly determine that a double fault of BAT+ and BAT- line disconnection has occurred.

8. The insulation detection failure diagnosis method according to claim 2, characterized in that: In step S5, when switch K PE , upper arm switch K P , lower arm switch K N When both are closed, the parallel connection of bridge arm Ⅰ and bridge arm Ⅲ and the parallel connection of bridge arm Ⅱ and bridge arm Ⅳ form a series relationship. First, calculate the parallel equivalent resistance of bridge arm Ⅰ and bridge arm Ⅲ and the parallel equivalent resistance of bridge arm Ⅱ and bridge arm Ⅳ. Then, calculate the voltage of the upper bridge arm and the lower bridge arm according to the voltage division law of the series circuit. Then, apply the voltage division law to bridge arm Ⅰ and bridge arm Ⅱ respectively to calculate the sampling resistance R P1 and R N1 Voltage on and The specific calculation formula is as follows: In the above formula, let R P =R N =∞, calculate and simplify to get: It can be seen that if and only if R P =R N =∞, and

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