A method for detecting a short circuit in a battery pack

Abstract

The application provides a battery pack internal short circuit detection method, which avoids the complex modeling and SOC estimation process in the prior art, only needs to identify the battery DC internal resistance parameter, has low process complexity and small calculation amount, can provide good applicability for lithium iron phosphate batteries with a relatively flat OCV-SOC relationship curve, and greatly expands the application range. The method does not use temperature rise data in the internal short circuit detection process, thereby getting rid of the limitation of factors such as sensor specifications and arrangement positions on the detection accuracy, and can achieve good detection effect for various battery packs in a parallel connection and then series connection mode.

Description

Technical Field

[0001] This invention belongs to the field of battery pack fault diagnosis technology, specifically relating to a method for detecting internal short circuits in battery packs. Background Technology

[0002] With the widespread use of lithium-ion batteries in electric vehicles and energy storage, fires caused by battery thermal runaway occur frequently, seriously endangering battery safety. Among the many factors that induce lithium-ion batteries to develop into thermal runaway, internal short circuits are one of the more important and common situations. Therefore, timely and accurate detection of internal short circuit faults in batteries is essential. Existing lithium-ion battery internal short circuit detection technologies mainly detect abnormal electrical and thermal states caused by internal short circuits, and can be roughly divided into the following categories: 1) Threshold method: This method detects internal short circuits by judging whether the battery's voltage, temperature, voltage change rate, or temperature change rate exceeds a preset threshold. This type of method is currently only applicable to the detection of severe internal short circuits, and the detection effect is greatly limited by the placement of the temperature sensor; 2) Power consumption method: This method obtains the actual power consumption of the battery through the SOC estimation process and compares it with the actual power output to obtain the internal short circuit leakage situation and achieve detection. This type of method relies heavily on the accuracy of SOC estimation, and therefore is difficult to apply to lithium iron phosphate batteries with flat open-circuit voltage curves; 3) Remaining charge capacity method: This method judges the internal short circuit leakage situation by comparing the difference in remaining charge capacity between two adjacent charging processes. These methods require a complete charging process and have a long detection cycle, therefore they are only suitable for detecting minor internal short circuits; 4) Comparative analysis method: Internal short circuit detection is achieved by comparing and analyzing the consistency and correlation of voltage or other parameters among individual cells in a series battery pack. This method requires a large amount of parameters and data, resulting in high computational costs; 5) Sensor measurement method: For parallel battery packs, internal short circuit detection is achieved through a ring circuit topology and current sensors. This method requires changing the battery pack topology and adding additional sensors, significantly increasing the complexity and cost of the battery pack, greatly limiting its practicality. Summary of the Invention

[0003] In view of the above-mentioned technical problems existing in the field, the present invention provides a short circuit detection method for battery packs, specifically including the following steps:

[0004] S1. Real-time acquisition of terminal voltage and load current of each series-connected battery cell in the battery pack for charging or discharging conditions.

[0005] S2. Based on the collected terminal voltage and load current of each battery cell at the current time k, the average DC internal resistance of each battery cell and the battery pack is estimated respectively.

[0006] S3. Based on the estimated average DC internal resistance of the battery cell and battery pack at the current time k obtained in step S2, calculate the internal short-circuit current of each battery cell at the current time k, and filter and smooth the estimated internal short-circuit current.

[0007] S4. Use the result of S3 to determine whether the battery pack has an internal short circuit: if not, the battery pack is considered normal, and return to S2 to perform the detection at time k+1; if yes, the battery pack is considered to have an internal short circuit, and go to S5 to perform the detection at time k+1.

[0008] S5. Remove the battery cells that have experienced internal short circuits and recalculate the average terminal voltage of each battery cell in the battery pack. Combine the load current collected at time k+1 to estimate the average DC internal resistance of the non-short-circuited battery cells and the battery pack at time k+1.

[0009] S6. Perform the same process as S3 based on the result of step S5 to obtain the smoothed internal short-circuit current value of each battery cell at time k+1; calculate the estimated internal short-circuit resistance value based on the terminal voltage and internal short-circuit current estimate of the battery cell that has an internal short circuit at time k.

[0010] S7. Proceed to step S5 and continue execution, continuously outputting the estimated values ​​of the internal short-circuit current and internal short-circuit resistance of the battery cell that has experienced an internal short circuit.

[0011] Furthermore, step S2 specifically includes performing the following steps:

[0012] 1) Calculate the average terminal voltage U based on the voltage of all series-connected battery cells. t,m :

[0013]

[0014] In the formula, n is the total number of battery cells connected in series in the battery pack, U t,i The terminal voltage of the i-th battery cell connected in series; the average terminal voltage U t,i With load current I load Together they reflect the average electrical performance and serve as a stability reference;

[0015] 2) Using the average terminal voltage and load current calculated in step 1) as input, output the estimated value of the average DC internal resistance of each battery cell and battery pack using an estimation model based on, but not limited to, Kalman filtering, recursive least squares, or pulse DC internal resistance calculation.

[0016] Furthermore, step S3 specifically includes the following steps:

[0017] 1) Calculate the internal short-circuit current I of each battery cell at time k using the following formula. sc,j :

[0018]

[0019] In the formula, R 0,m R is the estimated average DC internal resistance of the battery pack at time k. 0,i Let be the estimated DC internal resistance of the i-th battery cell at time k;

[0020] 2) Apply sliding window filtering to the estimated internal short-circuit current. Specific filtering methods include, but are not limited to, mean filtering or median filtering.

[0021] Further, step S4 determines whether an internal short circuit has occurred in the battery pack, specifically based on the internal short circuit detection range requirement set by the internal short circuit current detection threshold I. th The value is compared with the smoothed internal short-circuit current estimate. If the internal short-circuit current estimate exceeds the detection threshold, an internal short circuit is determined to have occurred. At the same time, the estimated DC internal resistance R of the battery cell with the internal short circuit is recorded. 0,sc .

[0022] Furthermore, after removing the battery cells that have experienced internal short circuits in step S5, the average terminal voltage of each battery cell in the battery pack is recalculated based on the following formula:

[0023]

[0024] In the formula, This is the terminal voltage of the battery cell where an internal short circuit occurs.

[0025] The battery pack internal short-circuit detection method provided by this invention avoids the complex modeling and SOC estimation processes of existing technologies. It only requires identification of the battery's DC internal resistance parameter, resulting in low process complexity and minimal computational load. Even for lithium iron phosphate batteries with relatively flat OCV-SOC curves, it offers good applicability, greatly expanding its application range. This method does not use temperature rise data during internal short-circuit detection, thus eliminating limitations on detection accuracy caused by sensor specifications and placement. It achieves good detection results for various battery packs using a parallel-then-series connection method. Attached Figure Description

[0026] Figure 1 This is a flowchart illustrating the overall process of the method provided by the present invention.

[0027] Figure 2 This is a schematic diagram of the battery pack result and the corresponding Rint equivalent circuit model in one embodiment of the present invention;

[0028] Figure 3 (a) is the dynamic discharge condition selected in one embodiment of the present invention;

[0029] Figure 3(b) is the voltage curve of each battery cell when a 1Ω internal short circuit occurs in the series-connected battery cell 2 of the battery pack according to an embodiment of the present invention.

[0030] Figure 4 This is a schematic diagram of the Rint equivalent circuit model for smoothing filtering and obtaining the average model in this invention.

[0031] Figure 5 (a) Estimation results of internal short-circuit current for a battery cell that has not experienced an internal short circuit in one embodiment of the present invention;

[0032] Figure 5 (b) Estimation of the internal short-circuit current of battery cell 2 experiencing an internal short circuit in one embodiment of the present invention;

[0033] Figure 5 (c) Estimation of the internal short-circuit resistance of battery cell 2 that has an internal short circuit in one embodiment of the present invention. Detailed Implementation

[0034] The technical solution of the present invention will now be clearly and completely described with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] The battery pack short circuit detection method provided by this invention, such as... Figure 1 As shown, the specific steps include:

[0036] S1. Real-time acquisition of terminal voltage and load current of each series-connected battery cell in the battery pack for charging or discharging conditions.

[0037] S2. Based on the collected terminal voltage and load current of each battery cell at the current time k, the average DC internal resistance of each battery cell and the battery pack is estimated respectively.

[0038] S3. Based on the estimated average DC internal resistance of the battery cell and battery pack at the current time k obtained in step S2, calculate the internal short-circuit current of each battery cell at the current time k, and filter and smooth the estimated internal short-circuit current.

[0039] S4. Use the result of S3 to determine whether the battery pack has an internal short circuit: if not, the battery pack is considered normal, and return to S2 to perform the detection at time k+1; if yes, the battery pack is considered to have an internal short circuit, and go to S5 to perform the detection at time k+1.

[0040] S5. Remove the battery cells that have experienced internal short circuits and recalculate the average terminal voltage of each battery cell in the battery pack. Combine the load current collected at time k+1 to estimate the average DC internal resistance of the non-short-circuited battery cells and the battery pack at time k+1.

[0041] S6. Perform the same process as S3 based on the result of step S5 to obtain the smoothed internal short-circuit current value of each battery cell at time k+1; calculate the estimated internal short-circuit resistance value based on the terminal voltage and internal short-circuit current estimate of the battery cell that has an internal short circuit at time k.

[0042] S7. Proceed to step S5 and continue execution, continuously outputting the estimated values ​​of the internal short-circuit current and internal short-circuit resistance of the battery cell that has experienced an internal short circuit.

[0043] In a preferred embodiment of the present invention, a lithium iron phosphate battery pack with 1 parallel and 4 series connections is used as the target for internal short-circuit detection to perform the method of the present invention. Figure 2 The diagram illustrates the battery pack's assembly configuration and the corresponding Rint equivalent circuit model. Resistors of varying resistance values ​​are connected in parallel across the positive and negative terminals of battery cell 2 to simulate different degrees of internal short-circuit faults. This battery pack utilizes... Figure 3 (a) The battery is discharged under the Dynamic Stress Test (DST) shown in Figure (a), and the terminal voltage and load current of each battery cell are collected in real time. When a simulated 1Ω internal short circuit occurs in battery cell 2, the terminal voltage response of each battery cell is as follows: Figure 3 As shown in (b).

[0044] In this preferred embodiment of the present invention, step S2 specifically includes performing the following steps:

[0045] 1) Calculate the average terminal voltage U based on the voltage of all battery cells. t,m :

[0046]

[0047] In the formula, n is the total number of battery cells connected in series in the battery pack, U t,i The terminal voltage of the i-th battery cell connected in series; the average terminal voltage U t,i With load current I load Together they reflect the average electrical performance and serve as a stability reference;

[0048] 2) Utilize the estimation model based on Kalman filtering to output estimated values ​​of the average DC internal resistance of each battery cell and battery pack, including:

[0049] 2.1) Based on the Rint equivalent circuit model of each battery cell, the discretized state-space equations are established:

[0050]

[0051] In the formula, the subscripts k and k+1 represent the corresponding time points, U ocv,k R represents the open-circuit voltage of the battery cell at time k. 0,k This represents the average DC internal resistance of the battery cell at time k;

[0052] 2.2) Estimate the DC internal resistance R using the Kalman filter method. 0,k :

[0053] State prediction:

[0054] Status Update:

[0055] In the formula, A = [1 0; 0 1], H = [1 - I load,k All of these are coefficient matrices of the state-space equations; The parameter vector to be identified, K k P is the Kalman filter gain; k The initial covariance matrix is ​​set as P0 = [1,0; 0,1], the process noise matrix is ​​Q = [1e-9,0; 0,1e-9], where 1e-9 represents 1 x 10 to the power of -9, and the measurement noise matrix is ​​R = 0.05.

[0056] In this preferred embodiment, step S3 specifically includes the following steps:

[0057] 1) Calculate the internal short-circuit current I of each battery cell at time k using the following formula. sc,j :

[0058]

[0059] In the formula, R 0,m R is the estimated average DC internal resistance of the battery pack at time k. 0,i Let be the estimated DC internal resistance of the i-th battery cell at time k;

[0060] 2) Apply sliding window filtering to the estimated internal short-circuit current, specifically choosing mean filtering or median filtering.

[0061] In step S4, the internal short-circuit current detection threshold I is specifically set. th =2A, thus setting the detectable internal short-circuit fault range to an internal short-circuit resistance of less than 1.325Ω. In this embodiment, the smoothed internal short-circuit current estimate is compared with a threshold. If the current exceeds the threshold at battery cell 2, an internal short circuit is determined to have occurred. Simultaneously, the estimated DC internal resistance R of the battery cell with the internal short circuit is recorded. 0,sc,2 Then proceed to S5 to perform the check at time k+1.

[0062] In this preferred embodiment, the following process is performed in step S5:

[0063] 1) After removing battery cell 2 that experienced an internal short circuit, recalculate the average terminal voltage of each battery cell in the battery pack based on the following formula:

[0064]

[0065] 2) The average DC internal resistance of each battery cell is estimated again using the aforementioned Kalman filtering method.

[0066] In step S6, for each battery cell that has not experienced an internal short circuit, the smoothed internal short circuit current estimate is obtained using the estimated average DC internal resistance; for battery cell 2 that has experienced an internal short circuit, the estimated internal short circuit current is obtained based on the terminal voltage and internal short circuit current estimate of the battery cell that experienced an internal short circuit at time k, using the formula: Calculate its internal short-circuit resistance.

[0067] Step S7 continuously provides estimated values ​​for the internal short-circuit current and internal short-circuit resistance of the internal short-circuit battery cell, such as... Figure 5 (a) and Figure 5 (b) shows the estimated short-circuit current of each battery cell in the battery pack according to an embodiment of the present invention. Battery cell 2 triggers an internal short circuit at 904s, and the internal short-circuit fault is diagnosed in 120s. Figure 5 (c) shows the estimated internal short-circuit resistance of battery cell 2 180s after triggering the internal short circuit. After 600s of triggering the 1Ω internal short circuit, the maximum voltage difference between the battery cells in the battery pack is still only 10mV, which is within the normal allowable range of a conventional BMS and cannot be detected directly by the terminal voltage.

[0068] It should be understood that the sequence number of each step in the embodiments of the present invention does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of the present invention.

[0069] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for detecting short circuits within a battery pack, characterized in that: Specifically, the following steps are included: S1. Real-time acquisition of terminal voltage and load current of each series-connected battery cell in the battery pack for charging or discharging conditions. S2. Based on the collected terminal voltage and load current of each battery cell at the current time k, the average DC internal resistance of each battery cell and the battery pack is estimated respectively. S3. Based on the estimated average DC internal resistance of the battery cell and battery pack at time k obtained in step S2, calculate the internal short-circuit current of each battery cell at time k, and filter and smooth the estimated internal short-circuit current; specifically including the following steps: S3.1 Calculate the internal short-circuit current I of each battery cell at time k using the following formula. sc,j : In the formula, U t,m U is the average terminal voltage. t,i Let I be the terminal voltage of the i-th battery cell connected in series. load R is the load current. 0,m R is the estimated average DC internal resistance of the battery pack at time k. 0,i Let be the estimated DC internal resistance of the i-th battery cell at time k; S3.2 performs sliding window filtering on the estimated internal short-circuit current; S4. Use the result of S3 to determine whether the battery pack has an internal short circuit: if not, the battery pack is considered normal, and return to S2 to perform the detection at time k+1; if yes, the battery pack is considered to have an internal short circuit, and go to S5 to perform the detection at time k+1. S5. Remove the battery cells that have experienced internal short circuits and recalculate the average terminal voltage of each battery cell in the battery pack. Combine the load current collected at time k+1 to estimate the average DC internal resistance of the non-short-circuited battery cells and the battery pack at time k+1. S6. Perform the same process as S3 based on the result of step S5 to obtain the smoothed internal short-circuit current value of each battery cell at time k+1; calculate the estimated internal short-circuit resistance value based on the terminal voltage and internal short-circuit current estimate of the battery cell that has an internal short circuit at time k. S7. Proceed to step S5 and continue execution, continuously outputting the estimated values ​​of the internal short-circuit current and internal short-circuit resistance of the battery cell that has experienced an internal short circuit.

2. The method as described in claim 1, characterized in that: Step S2 specifically includes performing the following steps: S2.1 Calculate the average terminal voltage U based on the voltage of all series-connected battery cells. t,m : In the formula, n is the total number of battery cells connected in series in the battery pack, U t,i The terminal voltage of the i-th battery cell connected in series; the average terminal voltage U t,i With load current I load Together they reflect the average electrical performance and serve as a stability reference; S2.2 Using the average terminal voltage and load current calculated in step S2.1 as input, the estimated value of the average DC internal resistance of each battery cell and battery pack is output using a suitable estimation model.

3. The method as described in claim 1, characterized in that: Step S4 determines whether an internal short circuit has occurred in the battery pack, specifically based on the internal short circuit detection range requirements set by the internal short circuit current detection threshold I. th The value is compared with the smoothed internal short-circuit current estimate. If the internal short-circuit current estimate exceeds the detection threshold, an internal short circuit is determined to have occurred. At the same time, the estimated DC internal resistance R of the battery cell with the internal short circuit is recorded. 0,sc .

4. The method as described in claim 2, characterized in that: After removing the battery cells with internal short circuits in step S5, the average terminal voltage of each battery cell in the battery pack is recalculated based on the following formula: In the formula, This is the terminal voltage of the battery cell where an internal short circuit occurs.

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