An insulation detection failure diagnosis method

Abstract

The present invention discloses an insulation detection failure diagnosis method. In an unbalanced bridge circuit, the upper bridge arm switch K is controlled P , and the lower bridge arm switch K N are simultaneously closed. At the same time, the switch K between the upper and lower bridge arms and the vehicle body ground is controlled PE to be disconnected. The voltage values #imgabs0# and #imgabs1# of the sampling resistors R P1 and R N1 are respectively collected and calculated. The sampling resistor R P1 is the resistor at the positive pole of the upper half bridge arm, and the sampling resistor R N1 is the resistor at the negative pole of the lower half bridge arm. Then, the internal total voltage V BAT 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. Whether V BAT is 0 is used to judge the cause of the failure. The method of the present invention provides a diagnosis method for single failure and multiple failure faults in the case where the external input signal of the unbalanced bridge method fails and affects the normal insulation detection and judgment.

Description

Technical Field

[0001] The present invention belongs to the technical field of insulation resistance detection in a battery management system, and particularly relates to a method for diagnosing insulation detection failure. Background Art

[0002] In a battery management system (BMS), insulation resistance detection is a very important function, which can be used to evaluate the insulation performance of a battery system and help understand whether there are problems such as leakage, grounding faults or insulation aging in the device. 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 energy storage field, 1500V high-voltage systems have become the mainstream solutions in the energy storage market in recent years, and are also moving towards voltage levels above 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 in a high-voltage environment is a key factor to ensure the reliability and safety of the system. High-quality insulation can prevent leakage and short circuits, thus ensuring the safety of the battery. If the insulation performance of the system deteriorates, there may be potential leakage hazards, which may lead to problems with personal safety. In severe cases, it may even cause short circuits and fires in the battery module, resulting in irreparable losses. Therefore, it is necessary to specially consider and design the insulation detection function of the battery pack, real-time monitor the insulation status of the battery pack, 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 methods for the BMS to detect insulation resistance mainly include the balanced bridge method, the unbalanced bridge method, and the AC voltage injection method, etc. Among them, the unbalanced bridge method has the advantages of relatively simple circuit structure, high sampling accuracy, good electromagnetic compatibility (EMC) and stability, and has been widely used in the insulation detection schemes 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 shell, 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 by listing a system of equations according to Kirchhoff's current law.

[0004] In the BMS hardware architecture that uses the unbalanced bridge method to detect insulation resistance, the BMS internally samples the voltages of the positive and negative sampling resistors of the upper and lower bridge arms through two A / D sampling circuits respectively. The physical wiring connected to the BMS input port from the outside includes: ① the positive battery pack collection line (BAT+), ② the negative battery pack collection line (BAT-), and ③ the protective ground wire (PE, Protective-Earth). Since this method requires additional collection lines to be connected to the high-voltage collection part of the battery management system, in the complex electrical environment and operating conditions of the whole vehicle, there is a possibility of faults such as short circuits or disconnections of the above-mentioned collection wire harnesses, as well as poor contact due to loose connectors, which will affect the normal collection of the required signals and lead to the inability to obtain the expected results after the insulation detection function module is executed. 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 levels, without considering the faults that occur in the external input signals themselves, that is, the situation where the insulation detection fails due to the failure of one or more of the input signals BAT+, BAT-, and PE. Therefore, the existing insulation detection algorithms can only calculate the insulation resistance when all input signals are default normal, and cannot identify which one or which ones of the failure faults when the detection fails. This will lead to the inability to normally report alarm information and execute protection actions due to detection failure when an insulation fault actually occurs, bringing potential safety hazards. Summary of the Invention

[0005] In order to make up for the deficiencies of the existing technology, the purpose of the present invention is to provide an insulation detection failure diagnosis method to solve the situation where the detection fails but the specific failure fault cannot be identified when using the unbalanced bridge method to detect insulation resistance.

[0006] The technical problems to be solved by the present invention can be realized 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 bridge arm switch K P and the lower bridge arm switch K N to be closed simultaneously, and at the same time control the switch K PE between the upper and lower bridge arms and the vehicle body ground to be disconnected, and respectively collect and calculate the voltage values P1 and N1 of the sampling resistors R and The sampling resistor R P1 is the resistor of the positive pole of the upper half bridge arm, and the sampling resistor R N1 is the resistor of the negative pole of the lower half bridge arm;

[0009] S2. According to the voltage values and Calculate the total internal voltage V between battery BAT+ and battery BAT- and the voltage division ratio coefficient BAT ;

[0010] S3. Determine whether the total internal voltage value V calculated in step S2 BAT is 0. If V BAT = 0, it is preliminarily determined that there is a disconnection fault in BAT+ or BAT-. Then, further determine whether it is BAT+ or BAT- that is disconnected. If V BAT ≠ 0, there is no disconnection fault in BAT+ and BAT-. 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 of the whole vehicle and the input connection point from the vehicle body ground of the whole vehicle to the battery management system;

[0011] S4. If V BAT = 0, the battery management system controls the switch K PE to close, and collect and calculate the voltage values of the sampling resistors R P1 and sampling resistor R N1 again, and and According to and values, determine the disconnection conditions of BAT+ and BAT-;

[0012] S5. If V BAT ≠ 0, that is, on the premise that there is no disconnection fault in BAT+ or BAT-, the battery management system controls the switch K PE to close, and at the same time continue to keep the upper-bridge-arm switch K P , lower-bridge-arm switch K N closed, collect and calculate the voltage values on the sampling resistors R P1 and sampling resistor R N1 . If the calculated PE and and after closing K PE are equal to the calculated and values when K

[0013] is disconnected in step S1, it is determined that a PE disconnection fault has occurred. Further, in the unbalanced bridge circuit, the input connection point from the battery positive electrode to the battery management system is denoted as point A, the input connection point from the vehicle body ground of the whole vehicle to the battery management system is denoted as point B, and the input connection point from the battery negative electrode to the battery management system is denoted as point C. BAT+ disconnection refers to the disconnection of the high-voltage connection line between the battery positive electrode and point A, BAT- disconnection refers to the disconnection of the high-voltage connection line between the battery negative electrode and point C, and PE disconnection refers to the disconnection of the high-voltage connection line between the vehicle body ground PE and point B;

[0014] The unbalanced bridge circuit includes an upper bridge arm and a lower bridge arm. The upper bridge arm includes arm Ⅰ and arm Ⅲ, and the lower bridge arm includes arm Ⅱ and arm Ⅳ. Arm Ⅰ and arm Ⅲ are the ends connecting the positive pole of the battery and the reference ground, and arm Ⅱ and arm Ⅳ are the ends connecting the negative pole of the battery. Resistor R P1 and resistor R P2 are the positive pole resistors of the upper bridge arm. Resistor R N1 and resistor R N2 are the negative pole resistors of the lower bridge arm. Among them, resistor R P1 and resistor R N1 are sampling resistors, and resistor R P2 and resistor R N2 are voltage-dividing resistors; K P is the upper bridge arm switch, K N is the lower bridge arm switch, K PE is the switch between the upper and lower bridge arms and the vehicle body ground. Resistor R P is the equivalent insulation resistance of the battery positive pole to the ground, and resistor R N is the equivalent insulation resistance of the battery negative pole to the ground. VBAT is the total voltage of the battery positive and negative poles, V P is the voltage of arm Ⅰ, V N is the voltage of arm Ⅱ, V P1 is the voltage division of the sampling resistor R P1 , and V N1 is the voltage division of the sampling resistor R N1 .

[0015] Furthermore, in the step S1, when the battery management system controls the switch K PE to be disconnected, the battery, arm Ⅰ - arm Ⅱ, and arm Ⅲ - arm Ⅳ form a parallel relationship. Therefore, the equivalent insulation resistors R P and R N of arm Ⅲ and arm Ⅳ have no impact on arm Ⅰ and arm Ⅱ. Therefore, applying the resistance voltage division law to the independent loop formed by arm Ⅰ, arm Ⅱ, and the battery, the voltage value P1 on the sampling resistor R can be calculated as:

[0016]

[0017] Similarly, the voltage value N1 on the sampling resistor R is:

[0018]

[0019] Further, for the step S2, the upper bridge arm and the lower bridge arm of the unbalanced bridge circuit are symmetric, that is, the resistance values of the positive sampling resistor and the negative sampling resistor are the same, the resistance values of the positive voltage-dividing resistor and the negative voltage-dividing resistor are the same, and the resistance value of the voltage-dividing resistor is much larger than the resistance value of the sampling resistor, that is, R P2 = R N2 >> R P1 = R N1 , let the resistance ratio of the voltage-dividing resistor to the sampling resistor be k = R P2 / R P1 = R N2 / R N1 , according to Ohm's law, the ratio of the bridge arm voltage to the voltage division of the sampling resistor is V P / V P1 = V N / V N1 = k + 1, and the calculation formula for the total internal voltage can be obtained as:

[0020]

[0021] Further, in the step S4, if it is calculated that then it is determined that a BAT+ disconnection fault occurs at this time; that is, if BAT+ is disconnected, at this time, point A of arm Ⅰ is disconnected from the battery positive pole BAT+, and the total voltage of arm Ⅰ is 0. Therefore, the voltage V P1 across the sampling resistor R P1 is also 0; at the same time, the battery and the parallel branch of arm Ⅲ and the parallel branch of arm Ⅱ and arm Ⅳ form a loop, and according to Ohm's law and the characteristics of series-parallel circuits, the total battery voltage V BAT , the sampling resistor voltage value the sampling resistor R N1 , the positive insulation resistor R P and the negative insulation resistor R N have the following relationship:

[0022]

[0023] After simplification, the value of V N1 can be obtained as:

[0024]

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

[0026] Further, in the step S4, if it is calculated that It is determined that a BAT-disconnection fault occurs at this time; that is, if BAT is disconnected, at this time, point C of arm II is disconnected from the negative pole BAT of the battery, and the total voltage of arm II is 0. Therefore, the voltage V N1 across the sampling resistor R N1 is also 0; at the same time, the battery and the parallel branch of arm IV and the parallel branch of arms I and III form a loop, and according to Ohm's law and the characteristics of series-parallel circuits, the total battery voltage V BAT , the voltage value of the sampling resistor the sampling resistor R P1 , the positive insulation resistor R P and the negative insulation resistor R N have the following relationship:

[0027]

[0028] After simplification, the value of V P1 can be obtained as:

[0029]

[0030] That is, when is equal to the calculation result of the above formula (7), it is determined that a BAT-disconnection fault occurs at this time.

[0031] Furthermore, in step S4, if it is directly determined that a double fault of BAT+ and BAT- disconnection occurs.

[0032] Furthermore, in step S5, when the switch K PE , the upper-bridge-arm switch K P , and the lower-bridge-arm switch K N are all closed, the parallel connection of arms I and III and the parallel connection of arms II and IV form a series relationship. First, calculate the parallel equivalent resistance of arms I and III and the parallel equivalent resistance of arms II and IV, and then calculate the voltages 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 arms I and II respectively to calculate the voltages V P1 and V N1 across the sampling resistors R and The specific calculation formula is as follows:

[0033]

[0034] In the above formula, let R P = R N = ∞, and after calculation and simplification, it can be obtained:

[0035]

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

[0037] Compared with the prior art, the present invention has the following advantages: By analyzing the possible failure problems that may occur when using the unbalanced bridge method to measure the insulation resistance in the battery system, and aiming at the situation where the normal insulation detection and judgment are affected after a fault occurs in the external input signal of the unbalanced bridge method, the diagnosis methods for single failure faults and multiple failure faults are given, and further, the fault identification problem when failure faults and insulation faults exist simultaneously is analyzed, improving the comprehensiveness and reliability of the insulation detection function in the battery management system. Description of the Drawings

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

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

[0040] Figure 3 is the schematic circuit diagram of the insulation detection failure diagnosis of the present invention (BAT+ disconnection);

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

[0042] Figure 5 is the schematic circuit diagram of the insulation detection failure diagnosis of the present invention (PE disconnection). Detailed Embodiments

[0043] To enable those skilled in the art to more clearly understand the technical solutions of the present application, the following further describes an insulation detection failure diagnosis method of the present invention with reference to the accompanying drawings.

[0044] As Figure 1 shown, in the unbalanced bridge circuit involved in the present application, the input connection point from the battery positive electrode to the battery management system is denoted as point A, the input connection point from the vehicle body ground to the battery management system is denoted as point B, and the input connection point from the battery negative electrode to the battery management system is denoted as point C. BAT+ disconnection refers to the disconnection of the high-voltage connection line between the battery positive electrode and point A, BAT- disconnection refers to the disconnection of the high-voltage connection line between the battery negative electrode and point C, and PE disconnection refers to the disconnection of the high-voltage connection line between the vehicle body ground PE 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 arm Ⅰ and arm Ⅲ, and the lower bridge arm includes arm Ⅱ and arm Ⅳ. Arm Ⅰ and arm Ⅲ are the ends connected to the positive pole of the battery and the reference ground, and arm Ⅱ and arm Ⅳ are the ends connected to the negative pole of the battery. Resistor R P1 and resistor R P2 are the positive pole resistors of the upper bridge arm. Resistor R N1 and resistor R N2 are the negative pole resistors of the lower bridge arm. Among them, resistor R P1 and resistor R N1 are sampling resistors, and resistor R P2 and resistor R N2 are voltage-dividing resistors; K P is the upper bridge arm switch, K N is the lower bridge arm switch, K PE is the switch between the upper and lower bridge arms and the vehicle body ground. Resistor R P is the equivalent insulation resistance of the battery positive pole to the ground, and resistor R N is the equivalent insulation resistance of the battery negative pole to the ground. VBAT is the total voltage of the battery positive and negative poles, V P is the voltage of arm Ⅰ, V N is the voltage of arm Ⅱ, V P1 is the voltage division of the sampling resistor R P1 , and V N1 is the voltage division of the sampling resistor R N1 .

[0046] As Figure 2 shown, an insulation detection failure diagnosis method includes the following steps:

[0047] (1) In the unbalanced bridge circuit, the battery management system controls the upper bridge arm switch K P , the lower bridge arm switch K N to close simultaneously, and at the same time controls the switch K PE between the upper and lower bridge arms and the vehicle body ground to disconnect. Respectively collect and calculate the voltage values of the sampling resistor R P1 and the sampling resistor R N1 and The sampling resistor R P1 is the resistor of the positive pole of the upper half bridge arm, and the sampling resistor R N1 is the resistor of the negative pole of the lower half bridge arm. The voltage values and are respectively the voltage values of the first collection and calculation of the sampling resistor R P1 and the sampling resistor R N1 .

[0048] Specifically, after the battery management system controls the switch K PE to disconnect, from Figure 1 ​It can be seen that at this time, the battery, arm I - arm II, and arm III - arm IV are in a parallel relationship. Therefore, the equivalent insulation resistances R P and R N of arm III and arm IV have no impact on arm I and arm II. Therefore, by applying the resistance voltage division law to the independent loop formed by arm I, arm II, and the battery, the voltage value P1 across the sampling resistor R can be calculated as follows:

[0049]

[0050] Similarly, the voltage value N1 across the sampling resistor R is:

[0051]

[0052] (2) According to the voltage values and obtained in step S1 and the voltage division ratio coefficient, calculate the internal total voltage V BAT between battery BAT+ and battery BAT-.

[0053] In an unbalanced bridge circuit, the upper and lower half - bridge arms are symmetric, that is, the resistance values of the positive - electrode sampling resistor and the negative - electrode sampling resistor are the same, the resistance values of the positive - electrode voltage - dividing resistor and the negative - electrode voltage - dividing resistor are the same, and the resistance value of the voltage - dividing resistor is much larger than the resistance value of the sampling resistor, that is, R P2 = R N2 >> R P1 = R N1 Let the resistance ratio of the voltage - dividing resistor to the sampling resistor be k = R P2 / R P1 = R N2 / R N1 According to Ohm's law, the ratio of the bridge - arm voltage to the voltage division of the sampling resistor is V P / V P1 = V N / V N1 = k + 1. The calculation formula for the internal total voltage can be obtained as follows:

[0054]

[0055] (3) Determine whether the internal total voltage value V BAT calculated in step S2 is 0. If V BAT = 0, it is initially determined that a BAT+ disconnection or BAT - disconnection fault has occurred, and then further determine whether it is BAT+ or BAT - that has a disconnection; if V BAT ≠0, there is no BAT+ and BAT - disconnection fault, and further determine whether there is a PE disconnection fault.

[0056] If V BAT = 0, then V P1 = V N1 = 0. Therefore, leg I, leg II, and the battery do not form a loop, indicating that leg I and the positive terminal BAT+ of the battery are in an open state; or leg II and the negative terminal BAT- of the battery are in an open state. Thus, it can be preliminarily determined that a BAT+ disconnection or BAT- disconnection fault has occurred.

[0057] (4) If V BAT = 0, the battery management system controls the switch K PE to close, and collects and calculates the voltage values of the sampling resistors R P1 and R N1 again. and According to and to judge the disconnection situation of BAT+ and BAT-. The voltage values and are the voltage values of the sampling resistors R P1 and R N1 collected and calculated for the second time, respectively.

[0058] (1) If it is calculated that then it is determined that a BAT+ disconnection fault has occurred at this time.

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

[0060]

[0061] After simplification, the value of V N1 can be obtained as:

[0062]

[0063] That is, when is equal to the calculation result of the above formula (5), it is determined that a BAT+ disconnection fault has occurred at this time.

[0064] (2) If the calculation gives then it is determined that a BAT - disconnection fault occurs at this time.

[0065] As Figure 4 shown, in the unbalanced bridge circuit, if BAT - is disconnected, at this time, point C of arm Ⅱ is disconnected from the negative pole of the battery BAT -, and the total voltage of arm Ⅱ is 0. Therefore, the voltage V N1 across the sampling resistor R N1 is also 0; at the same time, the battery and the parallel branch of arm Ⅳ and the parallel branch of arm Ⅰ and arm Ⅲ form a loop, and according to Ohm's law and the characteristics of series - parallel circuits, the total battery voltage V BAT , the voltage value of the sampling resistor the sampling resistor R P1 , the positive - pole insulation resistor R P and the negative - pole insulation resistor R N have the following relationship:

[0066]

[0067] After simplification, the value of V P1 is:

[0068]

[0069] That is, when is equal to the calculation result of the above formula (7), it is determined that a BAT - disconnection fault occurs at this time.

[0070] (3) If As a special case that simultaneously satisfies the conditions of two disconnection faults, it is directly determined that a double - fault of BAT + and BAT - disconnection occurs.

[0071] (5) If V BAT ≠0, that is, under the premise that there is no BAT + or BAT - disconnection fault, the battery management system controls the switch K PE to close, and at the same time, continues to keep the upper - arm switch K P , the lower - arm switch K N closed, collects and calculates the voltage values across the sampling resistor R P1 and the sampling resistor R N1 . If the PE calculated after closing K and are equal to the PE calculated when K is disconnected in step S1 and values, then it is determined that a PE disconnection fault occurs.

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

[0073]

[0074] In particular, in the ideal case, the insulation equivalent resistances R P and R N are infinite. In the above formulas (8) and (9), let R P = R N = ∞, and calculate and simplify to obtain:

[0075]

[0076]

[0077] It can be seen that when and only when R P = R N = ∞, the simplified results of formulas (8) and (9) are (10) and (11), which are the same as formulas (1) and (2), that is and However, due to the fact that in the actual application of the present invention, the insulation resistances R P and R N between the positive and negative electrodes of the battery and the vehicle body ground cannot be infinite, it can be considered that the calculation results of formulas (8) and (9) and formulas (1) and (2) are actually not equal. Therefore, when the connection between PE and point B is normal, before and after the control switch K PE is turned off and on, the voltage values on the sampling resistors R P1 and R N1 will change. If the PE is disconnected, the actual PE and point B will always be in a disconnected state. Then, before and after the battery management system controls K PE to be closed and opened, the voltage values on the sampling resistors R P1 and R N1 will not change.

[0078] Compare the results calculated according to formulas (8) and (9) after closing the switch K PE with those after disconnecting K PECompare the results calculated according to formulas (1) and (2). 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 foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements for some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions 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 division ratio coefficient k BAT , the upper arm and lower arm of the unbalanced bridge circuit are symmetrical, the positive sampling resistor and the negative sampling resistor have the same resistance, the positive voltage divider resistor and the negative voltage divider resistor have the same resistance, and the voltage divider resistor is much larger than the sampling resistor, that is, R P2 =R N2 >>R P1 =R N1 , let the resistance ratio of the voltage divider resistor and the sampling resistor be the voltage divider ratio coefficient 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: 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; 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 ground, V BAT 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.

2. The insulation detection failure diagnosis method according to claim 1, 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, and the sampling resistance R can be calculated. P1 Voltage value on for: Similarly, the sampling resistor R N1 Voltage value on for:

3. The insulation detection failure diagnosis method according to claim 1, 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 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.

4. The insulation detection failure diagnosis method according to claim 1, 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 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.

5. The insulation detection failure diagnosis method according to claim 1, characterized in that: In step S4, if Directly determine that a double fault of BAT+ and BAT- line disconnection has occurred.

6. The insulation detection failure diagnosis method according to claim 1, 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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