A method for updating equivalent resistance of a battery pack copper bar

Abstract

The application relates to the technical field of battery management systems, and provides a battery pack copper bar equivalent resistance updating method, which comprises the following steps: collecting the voltage of adjacent battery cells of a battery pack when the current is 0 for a certain time, and simultaneously calculating the voltage difference; collecting the voltage of adjacent battery cells of the battery pack under a certain current for a certain time, and simultaneously calculating the voltage difference; calculating the copper bar equivalent internal resistance according to the voltage difference and the sampling current; judging whether the difference between the obtained equivalent internal resistance and the copper bar equivalent internal resistance to be updated is less than a preset threshold value; if yes, updating the copper bar equivalent internal resistance; and if not, not operating. In the whole life cycle of the battery system, the algorithm periodically calculates and updates the copper bar equivalent resistance according to the working conditions, so that the influence of copper bar resistance value changes caused by aging and other factors is eliminated, the effectiveness and accuracy of the copper bar resistance value calculation are ensured, and the accuracy of the cross-copper-bar battery cell voltage sampling is ensured.

Description

Technical Field

[0001] This invention relates to the field of battery management system technology, and more specifically to a method for updating the equivalent resistance of copper busbars in a battery pack. Background Technology

[0002] As the demand for battery packs continues to increase, battery information collection, which is the foundation of battery pack management, includes sampling the voltage of each cell. In other words, accurate sampling of cell voltage is becoming increasingly important. Cells are connected by copper busbars. Ideally, the actual resistance of the battery pack is equal to the resistance of the cells, that is, there is no copper busbar resistance. However, in reality, copper busbars are not ideal wires and have resistance, which will cause voltage drop. During the entire life cycle of the battery pack, it is necessary to monitor the actual voltage of the cells. Among the monitoring of the actual voltage of the cells, the most difficult thing to obtain accurately is the resistance of the copper busbar. There are many factors that affect the change of copper busbar resistance: excessive battery pack discharge current, excessive battery pack discharge charge, excessively high or low ambient temperature, long-term non-use, and low usage frequency, etc.

[0003] Currently, the key to compensating for the actual voltage of the battery cell lies in obtaining the equivalent resistance of the copper busbar. CN110884389A disclosed a compensation method for cross-copper busbar voltage sampling in a power battery management system on March 17, 2020. This method only considers the influence of temperature, while other factors such as usage time, humidity, plating, the quality of the copper busbar itself, and manufacturing process and equipment that affect the change in copper busbar resistance are not taken into account. The factors considered are not comprehensive, and the calculated actual voltage of the battery cell is inaccurate. CN115441538A disclosed a method and system for optimizing battery voltage measurement accuracy based on BMS equalization circuit on December 6, 2022. This method considers the size of the connecting wires and establishes an equivalent model of the equalization circuit to calculate the equivalent resistance and the actual voltage. The problem is that it is only applicable to new battery packs. The equivalent resistance of the copper busbar is calculated in the early stage of the battery pack. However, as the battery pack is used, the equivalent resistance of the copper busbar will gradually change. The method provided by this patent cannot be updated in time after the resistance changes. At this time, using the initial equivalent resistance to calculate the voltage division of the copper busbar will produce a large error. Summary of the Invention

[0004] To address the problem that variations in the resistance of copper busbars in battery packs lead to inaccurate measurements of the actual cell voltage, this invention provides a method for updating the equivalent resistance of copper busbars in battery packs. This method can update the equivalent resistance of copper busbars, thereby improving the accuracy of cell voltage measurements.

[0005] To solve the above-mentioned technical problems, the present invention adopts the following technical solution:

[0006] A method for updating the equivalent resistance of a battery pack copper busbar includes the following steps:

[0007] Step X1: Stop the battery pack from discharging and continue for a preset time t1, then collect the voltage U between the positive terminal of cell i and the negative terminal of the battery pack. i The voltage U between the positive terminal of adjacent cell i-1 and the negative terminal of the battery pack i-1 Calculate the voltage difference ΔU i =U i -U i-1 , where i∈[1,n], and n is the number of battery cells;

[0008] Step X2: Maintain the battery pack at a preset current I1 for discharge. After a preset duration t2, collect the voltage V between the positive terminal of battery cell i and the negative terminal of the battery pack. i The voltage V between the positive terminal of adjacent cell i-1 and the negative terminal of the battery pack i-1 Calculate the voltage difference ΔV i =V i -V i-1 ;

[0009] Step X3: Calculate the equivalent resistance R of the copper busbar. i =|ΔU i -ΔV i | / I1;

[0010] Step X4: Read the equivalent resistance R of the copper busbar to be updated. 0i Calculate R 0i With R i The difference R = |R i -R 0i |;

[0011] Step X5: If the difference R is greater than the preset update threshold, then the equivalent resistance R of the copper busbar to be updated will be... 0i Updated to QUOTE If the difference R is not greater than the preset update threshold, no operation will be performed.

[0012] Preferably, before performing step X4, steps X1 to X3 are repeated multiple times to obtain multiple copper busbar equivalent resistances R. ij , j∈[1,m], where m is the number of repetitions, calculate the difference ΔR=R max -R min R max and R min The equivalent resistance R of multiple copper busbars are respectively ij If the difference between the maximum and minimum values ​​is greater than the preset threshold, then steps X1 to X3 are repeated m times, and the difference ΔR is calculated again until the difference ΔR is less than or equal to the preset threshold. Then, the equivalent resistance R of multiple copper busbars is calculated. ij The average value is used as the equivalent resistance R of the copper busbar. iThe preset examination threshold is greater than the preset update threshold.

[0013] Preferably, the number of times m from step X1 to step X3 is repeated is 10.

[0014] Preferably, the update method further includes a trigger update step, which is performed during battery pack operation discharge, and the trigger update step includes:

[0015] Monitor the charge amount of the battery pack during operation discharge. When the charge amount of the battery pack during operation discharge exceeds the preset charge threshold, wait for the battery pack to finish discharging before triggering the execution of steps X1 to X5.

[0016] Preferably, the update method further includes a current-triggered update step, which is performed during battery pack operation and discharge, and includes:

[0017] Monitor the working discharge current of the battery pack. If the working discharge current is greater than the preset current threshold, wait for the working discharge of the battery pack to end, and then trigger the execution of steps X1 to X5. Otherwise, if the working discharge current is not greater than the preset current threshold, no operation is performed.

[0018] Preferably, steps X1 to X5 are triggered periodically according to a preset triggering cycle.

[0019] Preferably, the preset duration t1 is greater than or equal to one hour.

[0020] Preferably, the preset duration t2 is less than or equal to 5 minutes.

[0021] Preferably, the preset current I1 ∈ [0.2C, 0.5C], where C is the battery discharge rate.

[0022] Preferably, the preset current I1 is 0.5C.

[0023] The beneficial technical effects of this invention include:

[0024] 1. Taking a single cell in the battery pack as the smallest unit, match the corresponding equivalent resistance of the copper busbar. Throughout the entire life cycle of the battery pack, update the corresponding equivalent resistance of the copper busbar multiple times. Consider the different copper busbar resistance values ​​between different cells in the battery pack to make the calculation of the equivalent resistance of the copper busbar more accurate, thereby making the calculation of the actual resistance of the cell more accurate.

[0025] 2. It is not necessary to build a model of copper busbar resistance changes in advance, nor is it necessary to consider the influence of factors such as temperature on the equivalent resistance of copper busbars separately. Instead, the equivalent resistance of copper busbars is directly calculated based on the sampled cell current and cell voltage difference. After judgment, it is decided whether to update the equivalent resistance of copper busbars in the battery pack. The calculation is simpler, has a wide range of applications, is more efficient, and ensures the normal operation of the battery pack.

[0026] Other features and advantages of the present invention will be disclosed in detail in the following detailed description and accompanying drawings. Attached Figure Description

[0027] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the battery pack cell connections;

[0029] Figure 2 A flowchart for updating the equivalent resistance of the copper busbar in a battery pack;

[0030] Among them: 1. Current sensor, 2. Voltage sensor, 3. Battery cell. Detailed Implementation

[0031] The following specific embodiments illustrate the implementation of the present invention. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be noted that, unless otherwise specified, the following embodiments and features described therein can be combined with each other.

[0032] This invention provides a method for updating the equivalent resistance of copper busbars in a battery pack, specifically including:

[0033] Combination Figure 1 The battery pack includes several battery cells connected in series, where n is the number of battery cells. The battery cells are connected by copper busbars, and the equivalent resistance of the copper busbar to be updated is denoted as R. oi , i∈[1,n].

[0034] The battery management system (BMS) of the battery pack includes at least a current sensor, a voltage sensor, a memory, and a controller. The voltage sensor is connected to the battery cell in parallel, and a sampling line is used to sample the cell voltage. Each sampling line has n switches controlling the connection of a single battery cell, and these switches are controlled by the controller. The current sensor is connected to the battery cell in series. The memory stores the equivalent resistance of the copper busbar to be updated, including the initial equivalent resistance and the updated equivalent resistance.

[0035] like Figure 2 As shown, the equivalent resistance R of the copper busbar 02 The update method steps are as follows:

[0036] Step X1: Stop the battery pack from discharging. At this time, no external load is connected. The discharge is stopped for a preset duration t1, which is one hour. Close switch S2 and open the other switches. Determine if the duration is one hour. If it is less than one hour, no sampling is performed; if it is not less than one hour, sampling is performed. Sample the voltage U2 of battery cell 2, where U2 is the voltage of cell 2 relative to the negative terminal of the battery pack. Close switch S1 and open the other switches. Collect the voltage U1 of adjacent cell 1 relative to the negative terminal of the battery pack. Calculate the voltage difference ΔU2: ΔU2 = U2 - U1.

[0037] Step X2: Maintain the battery pack at a preset current I1 during discharge. The external load is denoted as RL. After a preset discharge duration t2, the preset current I1 = 0.5C, where C is the battery discharge rate. The preset duration t2 is five minutes. Close switch S2 and open the other switches. Determine if the duration is five minutes. If less than five minutes, no sampling is performed; if not less than five minutes, sampling is performed. Maintain the current at I1 and measure the voltage V2 of battery cell 2 relative to the negative terminal of the battery pack. Close switch S1 and open the other switches to measure the voltage V1 of adjacent battery cell 1 relative to the negative terminal of the battery pack. Calculate the voltage difference ΔV2: ΔV2 = V2 - V1.

[0038] Step X3, calculate

[0039]

[0040] R2 is the equivalent resistance of the copper busbar, which includes the contact resistance between the copper busbar and the battery cell and the ohmic internal resistance of the copper busbar.

[0041] Step X4: Read the equivalent resistance R of the copper busbar to be updated from the memory. 02 The memory is FLASH, and R is calculated. 02 The difference between R and R2 is R = |R2 - R 02 |

[0042] Step X5: Determine the equivalent internal resistance R of the copper busbar to be updated. 02 The value of R2 is related to the equivalent internal resistance R of the copper busbar to be replaced. 02 If the difference R between R2 and R2 is greater than the preset update threshold, then the equivalent internal resistance R of the copper busbar to be updated is... 02 The value is updated to R2. If the difference R is not greater than the preset update threshold, no operation is performed. The preset update threshold is set to the copper busbar resistance change value that the user needs to consider.

[0043] Before executing step X4, repeat steps X1 to X3 a total of m times to obtain multiple copper busbar equivalent resistances R. 2j , j∈[1,10], calculate the difference ΔR=R max -R min R max and R min The equivalent resistance R of multiple copper busbars are respectively 2j The maximum and minimum values ​​are calculated. If the difference ΔR is greater than the preset threshold, steps X1 to X3 are repeated 10 times, and the difference ΔR is calculated again until the difference ΔR is less than or equal to the preset threshold. Then, the equivalent resistance R of multiple copper busbars is calculated. 2j The average value is used as the equivalent resistance R2 of the copper busbar. The preset inspection threshold is greater than the preset update threshold. The purpose of repeated measurements is to eliminate errors. The purpose of setting the preset inspection threshold is to remove the equivalent resistance value that is too large or too small when the measurement is wrong.

[0044] The timing for updating the equivalent resistance of the copper busbar includes both user-initiated updates and automatic battery pack triggering. This not only meets the personalized customization needs of different users but also covers the changes in the equivalent resistance of the copper busbar under normal circumstances.

[0045] Users can actively configure the system to periodically execute steps X1 to X5 throughout the battery pack's entire lifespan. This period can be half a month, one month, or three months, and can be set differently based on usage frequency to meet monitoring requirements. Different user groups have different usage frequency needs for the battery pack. If frequently used, the cycle can be once a day; if infrequently used, once a month; if idle, once a quarter. When reactivated, the cycle can be changed back to once a day. Self-discharge of the battery pack is always present. Even when the battery is in a state of no charging and no use for extended periods, electrochemical reactions will still occur within the battery, causing changes in the equivalent resistance of the copper busbar, thus affecting the calculation of the actual cell voltage.

[0046] The update method further includes a trigger update step, under which the battery pack actively updates the equivalent resistance of the copper busbars when a trigger condition is met. The trigger update step is executed during battery pack operation and discharge, and includes:

[0047] At any given time, monitor the current and corresponding duration of the battery pack's working discharge, i.e. the amount of charge discharged by the battery pack. When the amount of charge discharged by the battery pack exceeds a preset charge threshold, wait for the battery pack to finish discharging before triggering steps X1 to X5. The battery pack's working discharge state includes the battery pack's working current being 0 and the working current not being 0.

[0048] The update method further includes a current-triggered update step, under which the battery pack actively updates the equivalent resistance of the copper busbars when the trigger condition is met. The current-triggered update step is executed during battery pack operation and discharge, and includes:

[0049] At any given time, monitor the current of the battery pack during operation. If the current during operation is greater than a preset current threshold and continues for any duration, wait for the battery pack to finish discharging before triggering steps X1 to X5. Conversely, if the current during operation is not greater than the preset current threshold, no operation is performed. The preset current threshold is the maximum allowable discharge current of the battery pack. When the battery discharge current is too large, it may cause a change in the equivalent resistance of the copper busbar. The battery pack will automatically trigger an update to prevent inaccurate voltage calculation due to resistance changes.

[0050] The storage device can be an SD card or other storage unit.

[0051] This invention provides an application of a method for updating the equivalent resistance of copper busbars in a battery pack, used to calculate the actual voltage of a single cell in the battery pack, specifically including:

[0052] Step S1, at any time T, make the battery pack sampling current I. T When switch S2 is closed and the other switches are open, sample the voltage U2 of cell 2 relative to the negative terminal of the battery pack. When switch S1 is closed and the other switches are open, sample the voltage U1 of cell 1 relative to the negative terminal of the battery pack. Calculate the voltage difference and record it as ΔU2, where ΔU2 = U2 - U1.

[0053] Step S2, read the equivalent resistance R of the copper busbar in the memory. 02 .

[0054] Step S3, based on the read copper busbar equivalent resistance R of cell 2 02 The voltage difference between cell 2 and cell 1 and the sampling current I T The actual voltage U2' of cell 2 relative to the negative terminal of cell 1 is calculated using the following formula:

[0055] U2'=ΔU2-I T *R 02 .

[0056] Throughout the entire battery pack lifecycle, the equivalent resistance of the copper busbar is continuously calculated and updated through user-initiated operations or automatic updates triggered by the battery pack. This eliminates the impact of changes in copper busbar resistance caused by factors such as aging and temperature rise, ensuring the effectiveness and accuracy of the copper busbar equivalent resistance calculation, thereby guaranteeing the accuracy of the actual voltage sampling of the battery cells.

[0057] The applicant of this invention has provided a detailed description of the embodiments of the invention in conjunction with the accompanying drawings. However, those skilled in the art should understand that the above embodiments are merely preferred embodiments of the invention. The detailed description is only intended to help readers better understand the spirit of the invention and is not intended to limit the scope of protection of the invention. On the contrary, any improvements or modifications made based on the inventive spirit of the invention should fall within the scope of protection of the invention.

Claims

1. A method for updating the equivalent resistance of a battery pack copper busbar, characterized in that, Includes the following steps: Step X1: Stop the battery pack from discharging and continue for a preset time t1, then collect the voltage U between the positive terminal of cell i and the negative terminal of the battery pack. i The voltage U between the positive terminal of adjacent cell i-1 and the negative terminal of the battery pack i-1 Calculate the voltage difference ΔU i =U i -U i-1 , where i∈[1,n], and n is the number of battery cells; Step X2: Maintain the battery pack at a preset current I1 for discharge. After a preset duration t2, collect the voltage V between the positive terminal of battery cell i and the negative terminal of the battery pack. i The voltage V between the positive terminal of adjacent cell i-1 and the negative terminal of the battery pack i-1 Calculate the voltage difference ΔV i =V i -V i-1 ; Step X3: Calculate the equivalent resistance R of the copper busbar. i =|ΔU i -ΔV i | / I1; Step X4: Read the equivalent resistance R of the copper busbar to be updated. 0i Calculate R 0i With R i The difference R = |R i -R 0i |; Step X5: If the difference R is greater than the preset update threshold, then the equivalent resistance R of the copper busbar to be updated will be... 0i Updated to R i If the difference R is not greater than the preset update threshold, no operation is performed; Before executing step X4, steps X1 to X3 are repeated multiple times to obtain multiple copper bus equivalent resistances R. ij , j∈[1,m], where m is the number of repetitions, calculate the difference ΔR=R max -R min R max and R min The equivalent resistance R of multiple copper busbars are respectively ij If the difference between the maximum and minimum values ​​is greater than the preset threshold, then steps X1 to X3 are repeated m times, and the difference ΔR is calculated again until the difference ΔR is less than or equal to the preset threshold. Then, the equivalent resistance R of multiple copper busbars is calculated. ij The average value is used as the equivalent resistance R of the copper busbar. i The preset examination threshold is greater than the preset update threshold; The update method further includes a current-triggered update step, which is performed during battery pack operation and discharge. The current-triggered update step includes: Monitor the working discharge current of the battery pack. If the working discharge current is greater than the preset current threshold, wait for the working discharge of the battery pack to end, and then trigger the execution of steps X1 to X5. Otherwise, if the working discharge current is not greater than the preset current threshold, no operation is performed.

2. The method for updating the equivalent resistance of a battery pack copper busbar according to claim 1, characterized in that, The number of times m from step X1 to step X3 is repeated is 10.

3. A method for updating the equivalent resistance of a battery pack copper busbar according to any one of claims 1 to 2, characterized in that, The update method further includes a trigger update step, which is executed during battery pack operation and discharge. The trigger update step includes: Monitor the charge amount of the battery pack during operation discharge. When the charge amount of the battery pack during operation discharge exceeds the preset charge threshold, wait for the battery pack to finish discharging before triggering the execution of steps X1 to X5.

4. A method for updating the equivalent resistance of a battery pack copper busbar according to any one of claims 1 to 2, characterized in that, According to the preset trigger cycle, steps X1 to X5 are periodically triggered.

5. A method for updating the equivalent resistance of a battery pack copper busbar according to any one of claims 1 to 2, characterized in that, The preset duration t1 is greater than or equal to one hour.

6. A method for updating the equivalent resistance of a battery pack copper busbar according to any one of claims 1 to 2, characterized in that, The preset duration t2 is less than or equal to 5 minutes.

7. A method for updating the equivalent resistance of a battery pack copper busbar according to any one of claims 1 to 2, characterized in that, The preset current I1∈[0.2C,0.5C], where C is the battery discharge rate.

8. The method for updating the equivalent resistance of a battery pack copper busbar according to claim 7, characterized in that, The preset current I1 is 0.5C.

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