Battery pack internal resistance fault detection method, device, management unit and battery pack

Abstract

The present invention discloses a method, device, management unit and battery pack for detecting internal resistance faults of a battery pack. The internal resistance of the battery pack is calculated by combining the difference between the two charging state of charge values ​​with the largest difference with the charging time to obtain the equivalent internal resistance of the battery pack. The equivalent internal resistance of the battery pack has a dual meaning: on the one hand, if the equivalent internal resistance value is too small, there may be a risk of battery short circuit in the battery pack; on the other hand, if the equivalent internal resistance value is too small, the synchronization between the batteries in the battery pack is too poor, indicating that some batteries are seriously aged and there is a risk of failure.

Description

Technical Field

[0001] The invention relates to a battery management unit of a battery pack and battery pack fault analysis. Background Art

[0002] As the energy supply component of electric vehicles, battery packs are usually connected by several lithium-ion batteries. Lithium-ion batteries have safety risks such as fire and explosion due to their own characteristics. This safety is particularly important for cars. If such safety risks occur during the driving of the car, it directly threatens the life safety of the passengers. Therefore, battery pack fault detection is very important.

[0003] Battery pack fault detection is divided into real-time detection and risk assessment. Real-time detection of battery pack faults is usually achieved by detecting the temperature of each battery when the battery pack is working. Risk assessment is not real-time, and usually determines whether the battery has safety risks by testing the various performance of each battery one by one. On the one hand, such risk assessment usually requires special tools, and electric vehicles themselves cannot be equipped with such proprietary tools; on the other hand, electric vehicles themselves cannot measure the various performance of each battery in the battery pack one by one. Summary of the invention

[0004] Problem to be solved by the present invention: battery pack fault detection.

[0005] To solve the above problems, the solution adopted by the present invention is as follows:

[0006] According to the method for detecting internal resistance fault of a battery pack of the present invention, the method comprises the following steps:

[0007] Step S1 is used to: receive the battery voltage of each battery of the battery pack before and after charging, and obtain the charging time t;

[0008] Step S2 is used to: find out V1Max (Index1Max), V1Min (Index1Min), V2Max (Index2Max), and V2Min (Index2Min) according to the battery voltage of each battery before and after charging of the battery pack; wherein,

[0009] V1Max (Index1Max) indicates the maximum battery voltage before charging, and Index1Max indicates the identification of the battery;

[0010] V1Min (Index1Min) indicates the minimum battery voltage before charging, and Index1Min indicates the battery identification;

[0011] V2Max (Index2Max) indicates the maximum battery voltage after charging, and Index2Max indicates the identification of the battery;

[0012] V2Min (Index2Min) indicates the minimum battery voltage after charging, and Index2Min indicates the identification of the battery;

[0013] Step S3, for: if Index1Max and Index2Max are equal and Index1Min and Index2Min are equal, then calculate the internal resistance of the battery pack: R=Q×t÷SocOffset÷C÷C;

[0014] Among them, R is the internal resistance of the battery pack, Q is the total power of the battery pack, t is the charging time, C is the charge when the battery is fully charged, SocOffset = Soc2Max-Soc1Max-Soc2Min +Soc1Min;

[0015] Soc2Max, Soc1Max, Soc2Min and Soc1Min are the state of charge values ​​calculated by V2Max (Index2Max), V1Max (Index1Max), V2Min (Index2Min) and V1Min (Index1Min) according to the state of charge and voltage comparison table;

[0016] Step S4 is used to: if the internal resistance R of the battery pack is less than M, record the fault; wherein M is a preset threshold value.

[0017] Further, according to the method for detecting internal resistance fault of a battery pack of the present invention, step S1 comprises:

[0018] Step S11 is used to: receive the battery voltage of each battery before the battery pack starts charging;

[0019] Step S12 is used to: after the battery pack is charged, record the charging time t and receive the battery voltage of each battery;

[0020] The step S2 comprises:

[0021] Step S21 is used to: find out V1Max (Index1Max) and V1Min (Index1Min) according to the battery voltage of each battery received before charging the battery pack, and store V1Max (Index1Max) and V1Min (Index1Min);

[0022] Step S22 is used to find out V2Max (Index2Max) and V2Min (Index2Min) according to the battery voltage of each battery received after the battery pack is charged, and extract the stored V1Max (Index1Max) and V1Min (Index1Min).

[0023] According to the device for detecting internal resistance fault of a battery pack of the present invention, the device comprises the following modules:

[0024] Module M1 is used to: receive the battery voltage of each battery in the battery pack before and after charging, and obtain the charging time t;

[0025] Module M2 is used to find out V1Max (Index1Max), V1Min (Index1Min), V2Max (Index2Max), and V2Min (Index2Min) according to the battery voltage of each battery before and after charging of the battery pack; wherein,

[0026] V1Max (Index1Max) indicates the maximum battery voltage before charging, and Index1Max indicates the identification of the battery;

[0027] V1Min (Index1Min) indicates the minimum battery voltage before charging, and Index1Min indicates the identification of the battery;

[0028] V2Max (Index2Max) indicates the maximum battery voltage after charging, and Index2Max indicates the identification of the battery;

[0029] V2Min (Index2Min) indicates the minimum battery voltage after charging, and Index2Min indicates the identification of the battery;

[0030] Module M3, used for: if Index1Max and Index2Max are equal and Index1Min and Index2Min are equal, then calculate the internal resistance of the battery pack: R = Q × t ÷ SocOffset ÷ C ÷ C;

[0031] Among them, R is the internal resistance of the battery pack, Q is the total power of the battery pack, t is the charging time, C is the charge when the battery is fully charged, SocOffset = Soc2Max-Soc1Max-Soc2Min +Soc1Min;

[0032] Soc2Max, Soc1Max, Soc2Min and Soc1Min are the state of charge values ​​calculated by V2Max (Index2Max), V1Max (Index1Max), V2Min (Index2Min) and V1Min (Index1Min) according to the state of charge and voltage comparison table;

[0033] Module M4 is used to record a fault if the internal resistance R of the battery pack is less than M; wherein M is a preset threshold.

[0034] Further, according to the device for detecting internal resistance fault of a battery pack of the present invention, the module M1 comprises:

[0035] Module M11, used for: receiving the battery voltage of each battery before the battery pack starts charging;

[0036] Module M12, used to: after the battery pack is charged, record the charging time t and receive the battery voltage of each battery;

[0037] The module M2 comprises:

[0038] The module M21 is used to: find out V1Max (Index1Max) and V1Min (Index1Min) according to the battery voltage of each battery received before charging the battery pack, and store V1Max (Index1Max) and V1Min (Index1Min);

[0039] The module M22 is used to find out V2Max (Index2Max) and V2Min (Index2Min) according to the battery voltage of each battery received after the battery pack is fully charged, and extract the stored V1Max (Index1Max) and V1Min (Index1Min).

[0040] A management unit according to the present invention comprises a processor, a memory and a collection terminal; the processor is connected to the memory and the collection terminal; the memory stores a program instruction set; the processing can implement the following steps through the program instruction set stored in the memory:

[0041] Step S11, before the battery pack starts charging, receiving the battery voltage of each battery through the acquisition terminal;

[0042] Step S21, finding V1Max (Index1Max) and V1Min (Index1Min) according to the battery voltage of each battery received before charging the battery pack, and storing V1Max (Index1Max) and V1Min (Index1Min) in the memory;

[0043] V1Max (Index1Max) indicates the maximum battery voltage before charging, and Index1Max indicates the identification of the battery;

[0044] V1Min (Index1Min) indicates the minimum battery voltage before charging, and Index1Min indicates the identification of the battery;

[0045] Step S12, after the battery pack is charged, the charging time t is recorded, and the battery voltage of each battery is received through the acquisition terminal;

[0046] Step S22, finding V2Max (Index2Max) and V2Min (Index2Min) according to the battery voltage of each battery received after the battery pack is charged, and extracting the stored V1Max (Index1Max) and V1Min (Index1Min) from the memory;

[0047] V2Max (Index2Max) indicates the maximum battery voltage after charging, and Index2Max indicates the identification of the battery;

[0048] V2Min (Index2Min) indicates the minimum battery voltage after charging, and Index2Min indicates the identification of the battery;

[0049] Step S3: If Index1Max and Index2Max are equal and Index1Min and Index2Min are equal, then calculate the internal resistance of the battery pack: R=Q×t÷SocOffset÷C÷C;

[0050] Among them, R is the internal resistance of the battery pack, Q is the total power of the battery pack, t is the charging time, C is the charge when the battery is fully charged, SocOffset = Soc2Max-Soc1Max-Soc2Min +Soc1Min;

[0051] Soc2Max, Soc1Max, Soc2Min and Soc1Min are the state of charge values ​​calculated by V2Max (Index2Max), V1Max (Index1Max), V2Min (Index2Min) and V1Min (Index1Min) according to the state of charge and voltage comparison table;

[0052] Step S4: if the internal resistance R of the battery pack is less than M, a fault is recorded; wherein M is a preset threshold value.

[0053] A battery pack according to the present invention comprises a battery array formed by a plurality of batteries, a collection circuit arranged on the battery array and the above-mentioned management unit; the collection circuit is capable of at least collecting the battery voltage of each battery; the processor of the management unit is connected to the collection circuit via the collection terminal.

[0054] The technical effects of the present invention are as follows: The present invention provides a method for judging whether a battery pack is faulty through the equivalent internal resistance of the battery pack. The calculated equivalent internal resistance of the battery pack has dual meanings: on the one hand, if the equivalent internal resistance is too small, there may be a risk of battery short circuit in the battery pack; on the other hand, if the equivalent internal resistance is too small, the synchronization between the batteries in the battery pack is too poor, indicating that some batteries are severely aged and there is a risk of failure. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 It is a schematic structural diagram of a battery pack embodiment of the present invention.

[0056] Figure 2 It is a structural diagram of an embodiment of a management unit of the present invention.

[0057] In the above figures, 100 is a housing, 200 is a battery array, 300 is a management unit, 400 is an acquisition circuit, 900 is an output connector, 301 is a processor, 302 is a memory, and 303 is an acquisition terminal. DETAILED DESCRIPTION

[0058] The present invention is further described in detail below with reference to the accompanying drawings.

[0059] Figure 1 An example of a battery pack for an electric vehicle is provided. The battery pack includes a housing 100 and a battery array 200 disposed in the housing 100, a management unit 300, a collection circuit 400, and an output connector 900 disposed on the housing 100. The battery array 200 is composed of a plurality of arranged batteries. In this embodiment, the battery array 200 is composed of four battery modules. Each battery module includes a plurality of batteries. The batteries of the battery array 200 are connected and output through the output connector 900. The collection circuit 400 is disposed on the battery array 200, and can at least collect the battery voltage of each battery. In this embodiment, in addition to being able to collect the battery voltage of each battery, the collection circuit 400 can also collect the temperature of each battery. The management unit 300 is a battery management system familiar to those skilled in the art, which is implemented by a circuit board, with reference to Figure 2 , at least includes a processor 301, a memory 302 and an acquisition terminal 303 arranged on a circuit board. The processor 301 is connected to the memory 302 and the acquisition terminal 303, and is connected to the acquisition circuit 400 through the acquisition terminal 303. The memory 302 is used to store program instruction sets and data. The processor 301 manages each battery in the battery pack by executing the program instruction set stored in the memory 302, such as implementing the charging and discharging management of the battery pack. The program instruction set here is a computer program instruction set. In this embodiment, the processor 301 implements a method for detecting internal resistance faults of a battery pack by executing a program instruction set. In this embodiment, the method for detecting internal resistance faults of a battery pack includes the following steps:

[0060] Step S11, receiving the battery voltage of each battery before the battery pack starts charging;

[0061] Step S21, finding V1Max (Index1Max) and V1Min (Index1Min) according to the battery voltage of each battery received before charging the battery pack, and storing V1Max (Index1Max) and V1Min (Index1Min) in the memory;

[0062] Step S12, after the battery pack is charged, the charging time t is recorded, and the battery voltage of each battery is received;

[0063] Step S22, finding V2Max (Index2Max) and V2Min (Index2Min) according to the battery voltage of each battery received after the battery pack is charged, and extracting the stored V1Max (Index1Max) and V1Min (Index1Min) from the memory;

[0064] Step S3: If Index1Max and Index2Max are equal and Index1Min and Index2Min are equal, then calculate the internal resistance of the battery pack: R=Q×t÷SocOffset÷C÷C;

[0065] Step S4: if the internal resistance R of the battery pack is less than M, a fault is recorded; wherein M is a preset threshold value.

[0066] In step S21, V1Max (Index1Max) indicates the maximum battery voltage before charging, and Index1Max indicates the identification of the battery; V1Min (Index1Min) indicates the minimum battery voltage before charging, and Index1Min indicates the identification of the battery. More specifically, step S21 finds the battery with the maximum battery voltage and the battery with the minimum battery voltage before charging. The battery with the maximum battery voltage is identified as Index1Max, and the corresponding voltage is V1Max (Index1Max); the battery with the minimum battery voltage is identified as Index1Min, and the corresponding voltage is V1Min (Index1Min).

[0067] In step S22, V2Max (Index2Max) indicates the maximum battery voltage after charging, and Index2Max indicates the identification of the battery; V2Min (Index2Min) indicates the minimum battery voltage after charging, and Index2Min indicates the identification of the battery. More specifically, step S22 finds the battery with the maximum battery voltage and the battery with the minimum battery voltage after charging. The battery with the maximum battery voltage is identified as Index2Max, and the corresponding voltage is V2Max (Index2Max); the battery with the minimum battery voltage is identified as Index2Min, and the corresponding voltage is V2Min (Index2Min).

[0068] In step S21 and step S22, the battery identification corresponds to the position of the battery in the battery array, and is usually represented by an integer serial number.

[0069] In step S11 and step 12, the battery voltage of each battery is received through the acquisition terminal 303 and the acquisition circuit 400. Step S11 and step 12 constitute the aforementioned step S1, that is, receiving the battery voltage of each battery before and after charging of the battery pack, and obtaining the charging time t.

[0070] Step S21 and step S22 constitute the aforementioned step S2, that is, according to the battery voltage of each battery before and after charging of the battery pack, V1Max (Index1Max), V1Min (Index1Min), V2Max (Index2Max), and V2Min (Index2Min) are found.

[0071] In the calculation formula of the battery pack internal resistance in step S3, R is the battery pack internal resistance, Q is the total power of the battery pack, t is the charging time, C is the charge when the battery is fully charged, and SocOffset = Soc2Max-Soc1Max-Soc2Min +Soc1Min. Soc2Max, Soc1Max, Soc2Min and Soc1Min are the state of charge values ​​calculated by V2Max (Index2Max), V1Max (Index1Max), V2Min (Index2Min) and V1Min (Index1Min) according to the state of charge and voltage comparison table. The state of charge value ranges from 0 to 1.

[0072] Step S3: The calculation formula of the battery pack internal resistance is as follows:

[0073] For the sake of convenience, the battery marked as IndexMin is called the first battery, and the battery marked as IndexMax is called the second battery. Here, IndexMin=Index1Min=Index2Min, IndexMax=Index1Max=Index2Max.

[0074] The state of charge of the first battery is charged from Soc1Min to Soc2Min, and the required charge amount is C×(Soc2Min-Soc1Min). According to the charging time t, the required effective average current is Imin= C×(Soc2Min-Soc1Min)÷t.

[0075] Similarly, the state of charge of the second battery is charged from Soc1Max to Soc2Max, and the effective average current required is Imax= C×(Soc2Max-Soc1Max)÷t.

[0076] Obviously, Imax and Imin are not the same, and considering the battery status, the working state of the second battery is better than that of the first battery, so correspondingly, Imax is usually greater than Imin. In the actual charging process, since all the batteries in the battery pack are connected in series, the actual current passing through the first battery and the second battery is the same. However, the effective average current of the two batteries here is different, so this situation can be regarded as an equivalent resistor connected in parallel to the first battery, and the current passing through the equivalent resistor is I=Imax-Imin= C×(Soc2Max-Soc1Max)÷t-C×(Soc2Min-Soc1Min)÷t, that is, I=C×SocOffset÷t. Among them, SocOffset=Soc2Max-Soc1Max-Soc2Min +Soc1Min.

[0077] On the other hand, the state of charge of the first battery is charged from Soc1Min to Soc2Min, and the electric energy charged into the battery is SoeMin=Q0×(Soc2Min-Soc1Min). The state of charge of the second battery is charged from Soc1Max to Soc2Max, and the electric energy charged into the battery is SoeMax=Q0×(Soc2Max-Soc1Max). Among them, Q0 is the remaining power when a single battery is fully charged. Obviously, SoeMax and SoeMin are not the same. The difference in the electric energy charged into the two batteries can be regarded as the heat consumed by the equivalent resistor connected in parallel with the aforementioned first battery, that is, SoeMax-SoeMin=I×I×R0×t. Among them, R0 is the resistance value of the resistance passing through the equivalent resistor. Substituting the aforementioned current I=C×SocOffset÷t passing through the equivalent resistor, we can get R0=(SoeMax-SoeMin)÷(I×I×t)=Q0×t÷SocOffset÷C÷C.

[0078] If Q0 in the above equivalent internal resistance calculation formula is substituted with the total battery pack power Q, the equivalent internal resistance of the entire battery pack can be obtained as R = Q×t÷SocOffset÷C÷C. It should be emphasized that C here refers to the data of a single battery, and Q refers to the data of the entire battery pack.

[0079] It should be pointed out that the internal resistance of the battery pack calculated in step S3 is not the actual internal resistance of the battery pack, but an equivalent resistance, which is only used for fault detection analysis. According to the formula: R = Q × t ÷ SocOffset ÷ C ÷ C. The larger the SocOffset, the smaller the R value, and the smaller the SocOffset, the larger the R value. On the other hand, according to the calculation formula of SocOffset: SocOffset = Soc2Max-Soc1Max-Soc2Min +Soc1Min, it means that SocOffset is the difference between the two most different charging state of charge values ​​in the battery pack, which represents the synchronization between the batteries in the battery pack. The higher the synchronization between the batteries in the battery pack, the smaller the SocOffset, and the larger the R value; the worse the synchronization between the batteries in the battery pack, the larger the SocOffset, and the smaller the R value. Therefore, if the R value is too small, it means that the synchronization between the batteries in the battery pack is too poor. Even if there is no risk of short circuit, it means that some batteries are seriously aged and there is a risk of failure. Therefore, it can also be regarded as a fault. Therefore, the calculated internal resistance of the battery pack of the present invention has a dual warning significance.

[0080] In step S4, the battery pack internal resistance R is less than M, which means that if the battery pack internal resistance is too small, there may be a risk of internal short circuit of the battery. In this embodiment, if three faults are recorded, the faults are reported to the vehicle management system.

[0081] In addition, it should be noted that step S1 of this embodiment involves the battery pack charging process. The processor 301 manages the battery pack charging process by executing the program instruction set. How the processor 301 manages the battery pack charging process is not within the scope of the present invention and need not be elaborated in this specification.

Claims

1. A method for detecting internal resistance fault of a battery pack, characterized in that: The method comprises the following steps: Step S1 is used to: receive the battery voltage of each battery of the battery pack before and after charging, and obtain the charging time t; Step S2 is used to: find out V1Max (Index1Max), V1Min (Index1Min), V2Max (Index2Max), and V2Min (Index2Min) according to the battery voltage of each battery before and after charging of the battery pack; wherein, V1Max (Index1Max) indicates the maximum battery voltage before charging, and Index1Max indicates the identification of the battery; V1Min (Index1Min) indicates the minimum battery voltage before charging, and Index1Min indicates the identification of the battery; V2Max (Index2Max) indicates the maximum battery voltage after charging, and Index2Max indicates the identification of the battery; V2Min (Index2Min) indicates the minimum battery voltage after charging, and Index2Min indicates the identification of the battery; Step S3, for: if Index1Max and Index2Max are equal and Index1Min and Index2Min are equal, then calculate the internal resistance of the battery pack: R=Q×t÷SocOffset÷C÷C; Among them, R is the internal resistance of the battery pack, Q is the total power of the battery pack, t is the charging time, C is the charge when the battery is fully charged, SocOffset = Soc2Max-Soc1Max-Soc2Min +Soc1Min; Soc2Max, Soc1Max, Soc2Min and Soc1Min are the state of charge values ​​calculated by V2Max (Index2Max), V1Max (Index1Max), V2Min (Index2Min) and V1Min (Index1Min) according to the state of charge and voltage comparison table; Step S4 is used to: if the internal resistance R of the battery pack is less than M, record the fault; wherein M is a preset threshold value.

2. The method for detecting internal resistance fault of a battery pack according to claim 1, characterized in that: The step S1 comprises: Step S11 is used to: receive the battery voltage of each battery before the battery pack starts charging; Step S12 is used to: after the battery pack is charged, record the charging time t and receive the battery voltage of each battery; The step S2 comprises: Step S21 is used to: find out V1Max (Index1Max) and V1Min (Index1Min) according to the battery voltage of each battery received before charging the battery pack, and store V1Max (Index1Max) and V1Min (Index1Min); Step S22 is used to find out V2Max (Index2Max) and V2Min (Index2Min) according to the battery voltage of each battery received after the battery pack is charged, and extract the stored V1Max (Index1Max) and V1Min (Index1Min).

3. A device for detecting internal resistance fault of a battery pack, characterized in that: The device includes the following modules: Module M1 is used to: receive the battery voltage of each battery in the battery pack before and after charging, and obtain the charging time t; Module M2 is used to find out V1Max (Index1Max), V1Min (Index1Min), V2Max (Index2Max), and V2Min (Index2Min) according to the battery voltage of each battery before and after charging of the battery pack; wherein, V1Max (Index1Max) indicates the maximum battery voltage before charging, and Index1Max indicates the identification of the battery; V1Min (Index1Min) indicates the minimum battery voltage before charging, and Index1Min indicates the identification of the battery; V2Max (Index2Max) indicates the maximum battery voltage after charging, and Index2Max indicates the identification of the battery; V2Min (Index2Min) indicates the minimum battery voltage after charging, and Index2Min indicates the identification of the battery; Module M3, used for: if Index1Max and Index2Max are equal and Index1Min and Index2Min are equal, then calculate the internal resistance of the battery pack: R = Q × t ÷ SocOffset ÷ C ÷ C; Among them, R is the internal resistance of the battery pack, Q is the total power of the battery pack, t is the charging time, C is the charge when the battery is fully charged, SocOffset = Soc2Max-Soc1Max-Soc2Min +Soc1Min; Soc2Max, Soc1Max, Soc2Min and Soc1Min are the state of charge values ​​calculated by V2Max (Index2Max), V1Max (Index1Max), V2Min (Index2Min) and V1Min (Index1Min) according to the state of charge and voltage comparison table; Module M4 is used to record a fault if the internal resistance R of the battery pack is less than M; wherein M is a preset threshold.

4. The device for detecting internal resistance fault of a battery pack as claimed in claim 3, characterized in that: The module M1 comprises: Module M11, used for: receiving the battery voltage of each battery before the battery pack starts charging; Module M12, used to: after the battery pack is charged, record the charging time t and receive the battery voltage of each battery; The module M2 comprises: The module M21 is used to: find out V1Max (Index1Max) and V1Min (Index1Min) according to the battery voltage of each battery received before charging the battery pack, and store V1Max (Index1Max) and V1Min (Index1Min); The module M22 is used to find out V2Max (Index2Max) and V2Min (Index2Min) according to the battery voltage of each battery received after the battery pack is fully charged, and extract the stored V1Max (Index1Max) and V1Min (Index1Min).

5. A management unit, characterized in that: The system comprises a processor, a memory and a collection terminal; the processor is connected to the memory and the collection terminal; the memory stores a program instruction set; the processor can implement the following steps by executing the program instruction set stored in the memory: Step S11, before the battery pack starts charging, receiving the battery voltage of each battery through the acquisition terminal; Step S21, finding V1Max (Index1Max) and V1Min (Index1Min) according to the battery voltage of each battery received before charging the battery pack, and storing V1Max (Index1Max) and V1Min (Index1Min) in the memory; V1Max (Index1Max) indicates the maximum battery voltage before charging, and Index1Max indicates the identification of the battery; V1Min (Index1Min) indicates the minimum battery voltage before charging, and Index1Min indicates the identification of the battery; Step S12, after the battery pack is charged, the charging time t is recorded, and the battery voltage of each battery is received through the acquisition terminal; Step S22, finding V2Max (Index2Max) and V2Min (Index2Min) according to the battery voltage of each battery received after the battery pack is charged, and extracting the stored V1Max (Index1Max) and V1Min (Index1Min) from the memory; V2Max (Index2Max) indicates the maximum battery voltage after charging, and Index2Max indicates the identification of the battery; V2Min (Index2Min) indicates the minimum battery voltage after charging, and Index2Min indicates the identification of the battery; Step S3: If Index1Max and Index2Max are equal and Index1Min and Index2Min are equal, then calculate the internal resistance of the battery pack: R=Q×t÷SocOffset÷C÷C; Among them, R is the internal resistance of the battery pack, Q is the total power of the battery pack, t is the charging time, C is the charge when the battery is fully charged, SocOffset = Soc2Max-Soc1Max-Soc2Min +Soc1Min; Soc2Max, Soc1Max, Soc2Min and Soc1Min are the state of charge values ​​calculated by V2Max (Index2Max), V1Max (Index1Max), V2Min (Index2Min) and V1Min (Index1Min) according to the state of charge and voltage comparison table; Step S4: if the internal resistance R of the battery pack is less than M, a fault is recorded; wherein M is a preset threshold value.

6. A battery pack, characterized in that: It comprises a battery array formed by a plurality of batteries, a collection circuit arranged on the battery array and a management unit as claimed in claim 5; the collection circuit can at least collect the battery voltage of each battery; the processor of the management unit is connected to the collection circuit through the collection terminal.

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