An electric vehicle insulation fault positioning method based on parallel insulation resistance detection

Abstract

This application belongs to the field of insulation testing technology for new energy vehicles, specifically relating to a method for locating insulation faults in electric vehicles based on parallel insulation resistance detection. The method includes establishing a basic model of intermediate faults in the battery system, defining circuit parameters and fault locations; equating the intermediate fault resistance of the battery system in the basic model to the insulation resistance of the total positive and negative terminals to ground, obtaining a converted equivalent circuit for the insulation fault; calculating the total insulation resistance based on the equivalent relationship between the insulation resistance of the total positive terminal to ground and the insulation resistance of the total negative terminal to ground in the equivalent circuit, and determining the parallel resistance value of the insulation resistance of the total positive terminal to ground and the insulation resistance of the total negative terminal to ground; and calculating and locating the insulation fault location by measuring the total voltage of the battery system and the average voltage of the current battery pack, combined with the parallel resistance value. This application achieves accurate calculation of the total insulation resistance and precise location of the insulation fault.

Description

Technical Field

[0001] This invention belongs to the field of insulation testing technology for new energy vehicles, and specifically relates to a method for locating insulation faults in electric vehicles based on parallel insulation resistance detection. Background Technology

[0002] With the rapid development of new energy vehicles, the safety of electric vehicles has received increasing attention. Among these concerns, the insulation performance of the on-board high-voltage system is one of the key technologies for ensuring vehicle operational safety. According to the current national standard GB / T18384.1-2015 "Safety Requirements for Electric Vehicles," the whole-vehicle insulation resistance test involves measuring the insulation resistance between the positive and negative terminals of the on-board rechargeable energy storage system (REESS) and the vehicle body ground. The test results must meet the requirement that the insulation resistance error rate does not exceed 10% to ensure vehicle driving safety.

[0003] Current insulation testing methods typically measure the insulation resistance (Rp and Rn) between the battery system's positive and negative terminals and the vehicle's ground, using the minimum of these two values ​​as the overall vehicle insulation resistance. However, battery systems are usually composed of multiple battery cells connected in series and parallel. When an insulation fault occurs in the middle of the battery system, existing insulation resistance testing methods neglect the equivalent insulation resistance characteristics at this intermediate location, leading to deviations in the test results, with error rates reaching as high as 30% to 50%. This testing error causes the battery management system (BMS) to either miss or falsely report insulation faults, thus affecting maintenance efficiency and even jeopardizing vehicle driving safety.

[0004] Furthermore, existing insulation testing methods can only detect the total resistance of an insulation fault, but cannot accurately pinpoint the location of the fault. When the BMS reports an insulation fault, the driver or maintenance personnel must manually locate the fault point. This process is not only time-consuming and labor-intensive, but also misses the best rescue opportunity, leading to serious property damage.

[0005] Therefore, existing technologies have significant shortcomings in accurately detecting the insulation resistance of battery systems and locating fault points. There is an urgent need for a new insulation detection and fault location technology that can improve the accuracy of insulation detection and quickly and accurately locate insulation fault points. Summary of the Invention

[0006] This invention addresses the shortcomings of existing technologies by proposing a method for locating insulation faults in electric vehicles based on parallel insulation resistance detection. This method can improve the insulation detection accuracy of the battery management system (BMS) of electric vehicles and achieve rapid location of insulation fault points. Through an innovative insulation resistance detection method, this method optimizes the fault point location mechanism and solves the problems of large errors and poor fault location capabilities of existing detection methods without increasing hardware complexity.

[0007] This invention provides a method for locating insulation faults in electric vehicles based on parallel insulation resistance detection. The method includes:

[0008] Step 1: Establish a basic model of intermediate faults in the battery system, and define circuit parameters and fault locations;

[0009] Step 2: Equivalent the intermediate fault resistance of the battery system in the basic intermediate fault model to the insulation resistance of the total positive and negative terminals to ground, and obtain the converted insulation fault equivalent circuit.

[0010] Step 3: Based on the equivalent relationship between the total positive-to-ground insulation resistance and the total negative-to-ground insulation resistance in the equivalent circuit, calculate the total insulation resistance and determine the parallel resistance value of the total positive-to-ground insulation resistance and the total negative-to-ground insulation resistance.

[0011] Step 4: Calculate and locate the insulation fault by measuring the total voltage of the battery system and the average voltage of the current battery pack, combined with the parallel resistance value.

[0012] Further, step 1 includes:

[0013] Step 1.1: Define the initial circuit, which includes the total voltage of the battery system, fault points distributed at different locations of the total voltage of the battery system, the insulation resistance of the upper and lower branches, the insulation resistance of the intermediate fault points, and a switch for controlling the state of the circuit.

[0014] Step 1.2: Based on the initial circuit defined in Step 1.1, determine the proportional location of the fault in the system;

[0015] Step 1.3: Based on the initial circuit defined in Step 1.1, determine the voltage distribution from the intermediate fault point to the total positive and total negative terminals of the battery system.

[0016] Further, in step 1.2, the relative position parameter of the insulation fault in the battery system is represented by Y, where the value of Y ranges from 0 to 1, specifically including:

[0017] When Y = 0, it indicates that the insulation fault occurred at the negative terminal of the battery system;

[0018] When Y=1, it indicates that the insulation fault occurs at the positive terminal of the battery system;

[0019] When 0 < Y < 1, it indicates that the insulation fault occurs at the midpoint between the total negative terminal and the total positive terminal of the battery system.

[0020] Further, step 2 includes:

[0021] Step 2.1: Construct an equivalent circuit for insulation faults. The equivalent circuit includes the total voltage of the battery system, the insulation resistance of the total positive electrode, the insulation resistance of the total negative electrode, the insulation resistance of the upper branch, the insulation resistance of the lower branch, and a switch for controlling the state of the control circuit.

[0022] Step 2.2: Based on the insulation fault equivalent circuit, determine the voltage of the upper and lower branches;

[0023] Step 2.3: Convert the fault resistor at the middle position into equivalent positive and negative insulation resistance.

[0024] Furthermore, in step 2.3, the equivalent insulation resistance R of the positive electrode to ground p Determined by the following formula:

[0025]

[0026] Equivalent insulation resistance R of negative electrode to ground n Determined by the following formula:

[0027]

[0028] In the formula: X represents the equivalent insulation resistance at the location of the insulation fault in the battery system; Y represents the relative position parameter of the insulation fault in the battery system; 1-Y represents the proportion of the voltage from the intermediate fault point to the total negative terminal of the battery system to the total voltage of the system.

[0029] Furthermore, step 3 includes:

[0030] Step 3.1: Determine the total insulation resistance using the parallel resistance formula based on the equivalent insulation resistance of the positive and negative sides;

[0031] Step 3.2: Treat the insulation resistance of the total positive and total negative terminals as a parallel relationship, and calculate the equivalent parallel resistance between the total positive and total negative terminals.

[0032] Further, in step 3.1, the total insulation resistance is determined by the following formula:

[0033]

[0034] In the formula: R p R represents the equivalent insulation resistance between the positive terminal and ground. n This represents the equivalent insulation resistance between the negative terminal and ground.

[0035] Furthermore, in step 3.2, the equivalent parallel resistance is determined by the following formula:

[0036]

[0037] In the formula: R pR represents the equivalent insulation resistance between the positive terminal and ground. n This represents the equivalent insulation resistance between the negative terminal and ground.

[0038] Furthermore, step 4 includes:

[0039] Step 4.1: Measure the battery system using an insulation monitoring device to obtain the fault leakage voltage, and obtain the average voltage of the current battery cell through the battery management system;

[0040] Step 4.2: Determine the location of the fault point in the battery system based on the ratio of the fault leakage voltage to the average voltage of the battery cell.

[0041] Furthermore, in step 4.2, the location of the insulation fault is determined by the following formula:

[0042]

[0043] The beneficial effects of this invention are:

[0044] First, the electric vehicle insulation fault location method based on parallel insulation resistance detection provided by this invention equates the intermediate fault resistance of the battery system to the insulation resistance of the total positive and negative terminals to ground. By combining the parallel resistance relationship and voltage measurement, it achieves accurate calculation of the total insulation resistance and precise location of the insulation fault. This method effectively solves the problems of large insulation resistance detection errors and difficulty in fault location in existing technologies, improving the accuracy and reliability of electric vehicle insulation fault detection and ensuring the safety and stability of the system.

[0045] Secondly, in the preferred implementation, the present invention, through steps 1.1 to 1.3, can systematically define and analyze the initial circuit state of the battery system and accurately locate the proportional location and voltage distribution of the fault. This method helps to clarify the voltage relationship between the fault point and the positive and negative electrodes of the battery system, thereby providing accurate data support for insulation resistance detection. By accurately analyzing the circuit structure and voltage distribution, it effectively solves the problem of inaccurate fault location and voltage detection in the prior art, reduces measurement errors, and improves the accuracy and reliability of insulation resistance detection. It is particularly suitable for diagnosing insulation faults at intermediate nodes of the battery system.

[0046] Third, in the preferred implementation, step 1.2 of the present invention introduces a parameter Y (0≤Y≤1) to represent the relative position of the insulation fault in the battery system, which can accurately reflect the distribution of the fault point between the total negative electrode and the total positive electrode: when Y=0, the fault is located at the total negative electrode; when Y=1, the fault is located at the total positive electrode; and when 0<Y<1, the fault is located in the middle position between the two. This parameterized description effectively solves the problem that traditional methods cannot accurately locate the insulation fault.

[0047] Fourth, in the preferred implementation, the present invention, through the implementation of step 2, converts the complex battery system fault resistance into equivalent positive and negative electrode insulation resistance based on the insulation fault equivalent circuit, and accurately calculates the equivalent insulation resistance values ​​of the positive and negative electrodes by combining the voltage ratio parameter. This method can accurately locate the fault location, simplify the calculation process of insulation resistance detection, and effectively reduce detection errors;

[0048] Fifth, in a preferred implementation, this invention, through step 3, treats the equivalent insulation resistances of the positive and negative electrode sides as a parallel relationship, calculates the total insulation resistance using the parallel resistance formula, and further optimizes the calculation process of the equivalent parallel resistance. This method can accurately decompose and simplify the insulation resistance of complex battery systems into a calculable form, effectively improving the accuracy and efficiency of insulation resistance detection. Furthermore, through the mathematical formula R... 总 The calculations ensured the accurate assessment of the location and resistance value of insulation faults;

[0049] Sixth, in the preferred implementation, the present invention, through the implementation of step 4, uses an insulation monitoring device to measure the battery system, obtain the fault leakage voltage, and calculates the ratio with the average voltage of the battery cells, which can accurately locate the location of the fault. This method improves the accuracy of fault diagnosis, helps to quickly identify insulation fault points in the battery system, thereby shortening the fault investigation time and improving detection efficiency. Attached Figure Description

[0050] Figure 1 This is a flowchart of the electric vehicle insulation fault location method based on parallel insulation resistance detection according to the present invention;

[0051] Figure 2 This is a schematic diagram illustrating the equivalent circuit of the battery system midpoint insulation fault and the equivalent circuit of the battery system total positive and total negative insulation fault in an embodiment of the present invention, which are combined for equivalent conversion.

[0052] Figure 3 This is a real-vehicle test scenario diagram of an embodiment of the present invention;

[0053] Figure 4 This is a schematic diagram illustrating the principle of artificially triggered insulation faults according to an embodiment of the present invention;

[0054] Figure 5 This is a graph showing the insulation resistance of the total positive and total negative terminals in an embodiment of the present invention. Detailed Implementation

[0055] To enable those skilled in the art to better understand the technical solutions of this application, the following will provide a more detailed description of this application in conjunction with the accompanying drawings and embodiments.

[0056] In the description of this application, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance; the term "multiple" refers to two or more unless otherwise expressly defined. The terms "install," "connect," "link," and "fix" should be interpreted broadly. For example, "connect" can mean a fixed connection, a detachable connection, or an integral connection; "link" can mean a direct connection or an indirect connection through an intermediate medium. Those skilled in the art can understand the specific meaning of the above terms in this application based on the specific circumstances.

[0057] In the description of this application, it should be understood that the terms "upper", "lower", "left", "right", "front", "rear", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or unit referred to must have a specific orientation or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.

[0058] In the description of this specification, the terms "one embodiment / mode," "some embodiments / modes," "specific embodiment / mode," etc., refer to a specific feature, structure, material, or characteristic described in connection with that embodiment / mode or example, which is included in at least one embodiment / mode or example of this application. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment / mode or example. Furthermore, the specific features, structures, materials, or characteristics described may be combined in any suitable manner in one or more embodiments / modes or examples.

[0059] As per the instruction manual Figure 1 This invention proposes a method for locating insulation faults in electric vehicles based on parallel insulation resistance detection, comprising:

[0060] Step 1: Establish a basic model of intermediate faults in the battery system, and define circuit parameters and fault locations.

[0061] The purpose of Step 1 is to establish a basic model of intermediate faults in the battery system, define fault parameters and fault locations, clarify the location of the fault and the relationships between various circuit parameters, and analyze the impact of the fault on the system voltage distribution and insulation resistance. This provides a theoretical basis for subsequently converting the intermediate fault resistance into the equivalent insulation resistance of the system's total positive and negative terminals.

[0062] Step 1 includes:

[0063] Step 1.1: Define the initial circuit, which includes the total voltage of the battery system, fault points distributed at different locations of the total voltage of the battery system, the insulation resistance of the upper and lower branches, the insulation resistance of the intermediate fault points, and switches used to control the state of the circuit.

[0064] Step 1.2: Based on the initial circuit defined in Step 1.1, determine the proportional location of the fault in the system.

[0065] Step 1.3: Based on the initial circuit defined in Step 1.1, determine the voltage distribution from the intermediate fault point to the total positive and negative terminals of the battery system.

[0066] As per the instruction manual Figure 2 , Figure 2 This demonstrates how to perform a combined equivalent transformation between the equivalent circuit of a battery system midpoint insulation fault and the equivalent circuit of a battery system total positive and total negative insulation fault. Figure 2 (a) shows the original circuit model of the intermediate fault point, including the influence of the intermediate fault resistance X and its location Y on the overall voltage distribution. K1 and K2 represent switches used to control the circuit closure of the upper branch (positive side) and the lower branch (negative side), respectively. U1 and U2 represent the voltages of the upper and lower branches, respectively. R1 and R2 represent the insulation resistances of the upper and lower branches, respectively. X represents the equivalent insulation resistance at the location of the insulation fault in the battery system.

[0067] Y represents the relative position parameter of the insulation fault in the battery system, ranging from 0 ≤ Y ≤ 1. When Y = 0, the fault occurs at the negative terminal of the battery system (near the lowest voltage point); when Y = 1, the fault occurs at the positive terminal of the battery system (near the highest voltage point); and when 0 < Y < 1, the fault occurs at the midpoint between the negative and positive terminals of the battery system. s This represents the total voltage of the battery system. (1-Y)U s This indicates the voltage distribution from a midpoint fault to the negative terminal. YU s This indicates the voltage distribution from the midpoint fault to the positive terminal.

[0068] Based on the basic model of intermediate faults in a battery system, by closing only switch K1, the voltage relationship of the upper branch of the basic model can be obtained:

[0069]

[0070] Based on the basic model of intermediate faults in a battery system, by closing only switch K2, the voltage relationship of the lower branch of the basic model can be obtained:

[0071]

[0072] Step 2: Equivalent the intermediate fault resistance of the battery system in the basic intermediate fault model to the insulation resistance of the total positive and negative terminals to ground, and obtain the converted insulation fault equivalent circuit.

[0073] The purpose of step 2 is to transform the circuit model of the intermediate fault in the battery system from step 1 into the equivalent insulation resistance X at the fault point through mathematical methods and equivalent transformations, thereby converting it into the equivalent insulation resistance R between the total positive and negative terminals of the battery system and ground. p and R n This simplifies the circuit structure and facilitates subsequent calculations and fault analysis.

[0074] Step 2 includes:

[0075] Step 2.1: Construct an equivalent circuit for insulation faults. The equivalent circuit includes the total voltage of the battery system, the insulation resistance of the total positive terminal, the insulation resistance of the total negative terminal, the insulation resistance of the upper branch, the insulation resistance of the lower branch, and the switch controlling the state of the control circuit.

[0076] As per the instruction manual Figure 2 , Figure 2 (b) is the equivalent conversion circuit of (a), which converts the effect of the intermediate fault into the insulation resistance R of the total positive and total negative terminals. p and R n , where R p R represents the insulation resistance between the battery system's positive terminal and the vehicle's ground. n This represents the insulation resistance between the battery system's main negative terminal and the vehicle's ground. The insulation resistances R1 and R2 of the upper and lower branches remain constant. The total voltage of the battery system is U. s .

[0077] Step 2.2: Determine the voltage of the upper and lower branches based on the equivalent circuit of the insulation fault.

[0078] By closing only switch K1, the voltage relationship of the upper branch in the equivalent circuit of the insulation fault is obtained:

[0079]

[0080] By closing only switch K2, the voltage relationship of the lower branch of the equivalent circuit for the insulation fault is obtained:

[0081]

[0082] Step 2.3: Convert the fault resistor at the middle position into equivalent positive and negative insulation resistance.

[0083] By simplifying formulas (1)-(4), the equivalent insulation resistance R of the positive electrode to ground is... p Determined by the following formula:

[0084]

[0085] Equivalent insulation resistance R of negative electrode to ground n Determined by the following formula:

[0086]

[0087] In equations (5) and (6), X represents the equivalent insulation resistance at the location of the insulation fault in the battery system; Y represents the relative position parameter of the insulation fault in the battery system; and 1-Y represents the voltage from the intermediate fault point to the total negative terminal of the battery system as a percentage of the total system voltage U. s The proportion (i.e., positional relationship).

[0088] Step 3: Based on the equivalent relationship between the total positive-to-ground insulation resistance and the total negative-to-ground insulation resistance in the equivalent circuit, calculate the total insulation resistance and determine the parallel resistance values ​​of the total positive-to-ground insulation resistance and the total negative-to-ground insulation resistance.

[0089] The purpose of step 3 is to determine the total insulation resistance of the battery system by using the equivalent insulation resistance relationship between the total positive and total negative terminals and ground, and to express it as the parallel value of the two insulation resistances. This provides a mathematical model and calculation basis for the accurate evaluation of the insulation performance of the battery system.

[0090] Step 3 includes:

[0091] Step 3.1: Calculate the equivalent insulation resistance R between the positive and negative terminals. p and R n The total insulation resistance X is determined using the parallel resistance formula:

[0092]

[0093] It should be noted that the total insulation resistance X represents the actual resistance at the fault point.

[0094] Step 3.2: Connect the insulation resistance R between the positive and negative terminals. p and R n Treating them as a parallel connection, calculate the equivalent parallel resistance R between the total positive and total negative terminals. 总 .

[0095]

[0096] Step 4: Calculate and locate the insulation fault by measuring the total voltage of the battery system and the average voltage of the current battery pack, combined with the parallel resistance value.

[0097] The purpose of step 4 is to accurately calculate the location Y of the insulation fault point by measuring the total voltage of the battery system, the fault leakage voltage, and the average voltage of the battery cells. This step provides a practical means to quickly locate the fault point and improve fault repair efficiency.

[0098] Step 4 includes:

[0099] Step 4.1: Measure the battery system using an insulation monitoring device to obtain the fault leakage voltage, and obtain the average voltage of the current battery cell through the battery management system (BMS).

[0100] Step 4.2: Determine the location of the fault point in the battery system based on the ratio of the fault leakage voltage to the average voltage of the battery cells.

[0101] The location of the insulation fault is calculated using the following formula:

[0102]

[0103] Example

[0104] By comparing the insulation resistance detection methods of the prior art with the insulation resistance detection methods of the present invention, the beneficial effects of the present invention are explained.

[0105] The existing insulation testing method is as follows: insulation resistance should be measured at the most suitable stage and at an appropriate frequency to obtain the minimum insulation resistance value. If the insulation circuit is not integrated into the REESS (Rechargeable Energy Storage System for electric and hybrid vehicles, referring to a battery pack or energy storage device for storing electrical energy), the insulation resistance is measured directly by opening the key switch; if the insulation circuit is integrated into the REESS, the insulation resistance of the switch-off circuit is measured. When measuring the insulation resistance of the REESS, the resistance between the two terminals and the electrical platform is measured:

[0106] The higher value is defined as U1 and the lower value as U2. The two insulation resistances are defined as R1 and R2 respectively, where R2 = Ri (i.e. the smaller value of the insulation resistance). Therefore, R2 is finally determined as the insulation resistance Ri of REESS.

[0107] As per the instruction manual Figure 3-4 Using existing insulation testing methods, when the insulation fault point of the battery system occurs at the midpoint between the non-total positive and non-total negative, an experiment was conducted on a commercial vehicle from a well-known automaker with a battery system consisting of four battery boxes connected in series. Different resistances were artificially short-circuited between the positive terminal of battery box No. 2 and the vehicle body to artificially trigger an insulation fault. Through on-site vehicle testing, it was found that the insulation resistance value detected by the existing insulation testing method was not equal to the actual insulation resistance value, i.e., R_total ≠ Min(Rp, Rn), and there was an error of 30% to 50% between the detected value and the actual value.

[0108] Short-circuit different resistance values to trigger the BMS to report an insulation fault. Through the short-circuit test in the actual scenario, the insulation resistance detection results of the insulation detection method of the prior art are obtained, as shown in Table 1:

[0109] Table 1

[0110]

[0111] As can be seen from Table 1, the error rate in the table is between 30.6% and 50%, indicating that there is a large deviation between the insulation resistance value measured by the insulation detection method of the prior art and the actually set short-circuit resistance value.

[0112] Further, according to formulas (5) and (6), the insulation resistance R Figure 5 of the total positive pole and the total negative pole shown in the attached drawings of the specification is generated p and R n curves. The existing insulation detection method uses the "take the minimum value" principle to measure the insulation resistance R p and R n , but there are obvious errors in actual applications. The specific situation is as follows:

[0113] When Y = 0, R p = X, R n = ∞, and the insulation resistance is correctly measured as X with an error of zero.

[0114] When Y = 1, R p = ∞, R n = X, and the insulation resistance is still correctly measured as X with an error of zero.

[0115] However, when 0 < Y < 1, taking the smaller value according to the existing insulation detection method, the insulation resistance is not equal to the actual value X, and the error is larger when approaching Y = 0.5.

[0116] When Y = 0.5, R p = 2X, R n = 2X, the measured value of the insulation resistance is 2X, and the error reaches X, that is, 100% of the actual value.

[0117] Therefore, according to the existing insulation detection method (that is, the insulation resistance takes the smaller value of the two), although the insulation resistance of the total positive and total negative of the battery can be accurately tested, it is not applicable to the insulation resistance detection of the midpoint of the battery system.

[0118] According to the same test environment, using the insulation resistance detection of this application, the equivalent circuit of the insulation fault at the midpoint of the battery system and the equivalent circuit of the insulation fault of the total positive and total negative of the battery system are联立等效转换 (the text here seems to be incorrect, it might be "jointly equivalent transformed"), and the insulation resistance detection results obtained are shown in Table 2:

[0119] Table 2

[0120]

[0121] As can be seen from Table 2, the insulation resistance testing method of this application yields measured values ​​that are closer to the actual short-circuit resistance values. There is a slight negative error, with an error rate between -3.0% and -8.8%. Compared with existing insulation resistance testing methods, the error is significantly reduced and the testing accuracy is higher.

[0122] This invention equates the intermediate fault resistance of the battery system to the insulation resistance of the positive and negative electrodes to ground. By combining the parallel resistance relationship and voltage ratio parameter, a fault location parameter Y is introduced to accurately describe the fault distribution. Furthermore, the ratio of the leakage voltage to the average voltage of the battery cell is obtained using an insulation monitoring device, thereby achieving precise fault location and accurate calculation of the total insulation resistance. This effectively solves the problems of large detection errors and inaccurate fault location in the prior art, and improves the accuracy, efficiency, and reliability of insulation fault diagnosis in electric vehicle battery systems.

[0123] The above descriptions are merely embodiments of the present invention, and common knowledge regarding specific structures and characteristics of the solutions is not described in detail here. It will be apparent to those skilled in the art that the present invention is not limited to the details of the above exemplary embodiments, and that the present invention can be implemented in other specific forms without departing from the spirit or essential characteristics of the invention. Therefore, the embodiments should be considered exemplary and non-limiting in all respects, and the scope of the present invention is defined by the appended claims rather than the foregoing description. Therefore, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention. No reference numerals in the claims should be construed as limiting the scope of the claims.

Claims

1. A method for locating insulation faults in electric vehicles based on parallel insulation resistance detection, characterized in that, The methods include: Step 1: Establish a basic model of intermediate faults in the battery system, and define circuit parameters and fault locations; In step 1, the relative position parameter of the insulation fault in the battery system is represented by Y, and the value range of Y is 0≤Y≤1. Specifically, when Y=0, it means that the insulation fault occurs at the total negative terminal of the battery system; when Y=1, it means that the insulation fault occurs at the total positive terminal of the battery system; when 0<Y<1, it means that the insulation fault occurs at the intermediate position between the total negative terminal and the total positive terminal of the battery system. Step 2: Equivalent the intermediate fault resistance of the battery system in the basic intermediate fault model to the insulation resistance of the total positive and negative terminals to ground, and obtain the converted insulation fault equivalent circuit. In step 2, the equivalent insulation resistance R between the positive electrode and ground p Determined by the following formula: Equivalent insulation resistance R of negative electrode to ground n Determined by the following formula: In the formula: X represents the equivalent insulation resistance at the location of the insulation fault in the battery system; Y represents the relative position parameter of the insulation fault in the battery system; 1-Y represents the proportion of the voltage from the intermediate fault point to the total negative terminal of the battery system to the total voltage of the system. Step 3: Based on the equivalent relationship between the total positive-to-ground insulation resistance and the total negative-to-ground insulation resistance in the equivalent circuit, calculate the total insulation resistance and determine the parallel resistance value of the total positive-to-ground insulation resistance and the total negative-to-ground insulation resistance. Step 4: Calculate and locate the insulation fault by measuring the total voltage of the battery system and the average voltage of the current battery pack, combined with the parallel resistance value; In step 4, the location of the insulation fault is determined by the following formula:

2. The method for locating insulation faults in electric vehicles based on parallel insulation resistance detection according to claim 1, characterized in that, Step 1 includes: Step 1.1: Define the initial circuit, which includes the total voltage of the battery system, fault points distributed at different locations of the total voltage of the battery system, the insulation resistance of the upper and lower branches, the insulation resistance of the intermediate fault points, and a switch for controlling the state of the circuit. Step 1.2: Based on the initial circuit defined in Step 1.1, determine the proportional location of the fault in the system; Step 1.3: Based on the initial circuit defined in Step 1.1, determine the voltage distribution from the intermediate fault point to the total positive and total negative terminals of the battery system.

3. The method for locating insulation faults in electric vehicles based on parallel insulation resistance detection according to claim 1, characterized in that, Step 2 includes: Step 2.1: Construct an equivalent circuit for insulation faults. The equivalent circuit includes the total voltage of the battery system, the insulation resistance of the total positive electrode, the insulation resistance of the total negative electrode, the insulation resistance of the upper branch, the insulation resistance of the lower branch, and a switch for controlling the state of the control circuit. Step 2.2: Based on the insulation fault equivalent circuit, determine the voltage of the upper and lower branches; Step 2.3: Convert the fault resistor at the middle position into equivalent positive and negative insulation resistance.

4. The method for locating insulation faults in electric vehicles based on parallel insulation resistance detection according to claim 3, characterized in that, Step 3 includes: Step 3.1: Determine the total insulation resistance using the parallel resistance formula based on the equivalent insulation resistance of the positive and negative sides; Step 3.2: Treat the insulation resistance of the total positive and total negative terminals as a parallel relationship, and calculate the equivalent parallel resistance between the total positive and total negative terminals.

5. The method for locating insulation faults in electric vehicles based on parallel insulation resistance detection according to claim 4, characterized in that, In step 3.1, the total insulation resistance is determined by the following formula: In the formula: R p R represents the equivalent insulation resistance between the positive terminal and ground. n This represents the equivalent insulation resistance between the negative terminal and ground.

6. The method for locating insulation faults in electric vehicles based on parallel insulation resistance detection according to claim 5, characterized in that, In step 3.2, the equivalent parallel resistance is determined by the following formula: In the formula: R p R represents the equivalent insulation resistance between the positive terminal and ground. n This represents the equivalent insulation resistance between the negative terminal and ground.

7. The method for locating insulation faults in electric vehicles based on parallel insulation resistance detection according to claim 4, characterized in that, Step 4 includes: Step 4.1: Measure the battery system using an insulation monitoring device to obtain the fault leakage voltage, and obtain the average voltage of the current battery cell through the battery management system; Step 4.2: Determine the location of the fault point in the battery system based on the ratio of the fault leakage voltage to the average voltage of the battery cell.

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