A battery system and a method for estimating SOC thereof

Abstract

The present invention relates to a battery system and a method for estimating the state of charge (SOC) thereof, belonging to the technical field of energy storage batteries. The present invention connects an adjustable resistor in series with each parallel battery branch in the battery system, and detects the internal resistance of each battery branch before and after battery charging and discharging. If the internal resistance difference between any two battery branches is too large, the adjustable resistors in the relevant battery branches are adjusted to make the internal resistance of each branch equal. This ensures that the charge and discharge currents of each battery branch remain consistent, and the amount of charge in each battery branch remains consistent. SOC estimation is performed based on the current charge and discharge currents, significantly improving the accuracy of SOC estimation for the battery system.

Description

Technical Field

[0001] The present invention relates to a battery system and a method for estimating the SOC thereof, and belongs to the technical field of energy storage batteries. Background Art

[0002] With the gradual promotion of electric vehicles, the service life of power batteries has become increasingly prominent. In the field of passenger buses, due to the large mass of the entire vehicle, a large current and power need to be matched. Multiple standard battery packs are often used, in series, parallel, or a combination of series and parallel. Standard battery packs need to be placed at different locations such as the top, bottom, and rear cabin of the vehicle, and connected in series and parallel using high-voltage wires. In the field of passenger buses, the form of first series connection and then parallel connection is often adopted, which ensures the platform voltage and can provide a large amount of power. Multiple battery packs in series form multiple branches, and the multiple branches are merged in the high-voltage distribution box. However, in multiple branches, due to the inconsistency of the internal resistance of each battery pack and the inconsistency of the length of the high-voltage wire connecting the battery pack, the internal resistance of the two branches will be inconsistent.

[0003] Coaches and public buses often need to be recharged during the day due to their long operating hours. Taking the example of charging from 40% to 100%, due to the inconsistent internal resistance of each branch, the charging current of the branch with smaller internal resistance is large, and the battery cells in its battery pack charge quickly, and will reach the charging cut-off voltage first. At this time, the entire battery system is judged to be fully charged. Due to the difference in internal resistance between branches, the branch with larger internal resistance is not actually fully charged. However, when estimating the power of the battery system, the inconsistent internal resistance has never been taken into account, resulting in inaccurate estimated SOC value. Summary of the Invention

[0004] The purpose of the present invention is to provide a battery system and a method for estimating the SOC thereof, so as to solve the problem of inaccurate SOC estimation in the current battery system due to inconsistent battery internal resistance.

[0005] In order to solve the above technical problems, the present invention provides a method for improving the estimation of the SOC of a battery system, which method comprises the following steps:

[0006] 1) An adjustable resistor is installed in series on each parallel battery branch of the battery system;

[0007] 2) Before charging or discharging the battery system, the internal resistance of each battery branch is detected. When the difference between the internal resistances of any two battery branches is greater than a set threshold, the adjustable resistor on the battery branch is adjusted so that the difference between the internal resistances of any two battery branches is less than the set threshold.

[0008] 3) When the difference in internal resistance between any two battery branches is less than a set threshold, the SOC is estimated based on the charge or discharge current.

[0009] The present invention installs an adjustable resistor in series on each parallel battery branch of the battery system, detects the internal resistance of each battery branch before and after battery charging and discharging, and if there is a large difference in the internal resistance of any two battery branches, adjusts the adjustable resistors on the relevant battery branches to make the internal resistance of each branch equal, thereby ensuring that the charging and discharging currents of each battery branch are consistent, and the power of each battery branch is consistent. SOC estimation is performed according to the charging and discharging currents at this time, which can greatly improve the SOC estimation accuracy of the battery system.

[0010] Furthermore, the internal resistance of each battery branch is measured by a battery management system.

[0011] Furthermore, in order to reduce energy consumption while ensuring SOC accuracy, when adjusting the adjustable resistor on the battery branch, it is necessary to ensure that the difference in internal resistance between any two battery branches is less than a set threshold, so that the resistance of the adjusted adjustable resistor is minimized.

[0012] Furthermore, to ensure minimum energy consumption, when adjusting the adjustable resistance on the battery branch, first make the adjustable resistance on the battery branch with larger internal resistance zero, and increase the adjustable resistance on the battery branch with smaller internal resistance.

[0013] The present invention also provides a battery system comprising at least two parallel battery branches, each battery branch comprising a plurality of battery packs connected in series, each battery branch being connected in series with an adjustable resistor, and detecting the internal resistance of each battery branch before charging or discharging the battery system. When the difference in internal resistance between any two battery branches is greater than a set threshold, the adjustable resistor on the battery branch is adjusted so that the difference in internal resistance between any two battery branches is less than the set threshold.

[0014] The present invention installs an adjustable resistor in series on each parallel battery branch of the battery system, detects the internal resistance of each battery branch before and after battery charging and discharging, and if there is a large difference in the internal resistance of any two battery branches, adjusts the adjustable resistors on the relevant battery branches to make the internal resistance of each branch equal, thereby ensuring that the charging and discharging currents of each battery branch are consistent, and the power of each battery branch is consistent. SOC estimation is performed according to the charging and discharging currents at this time, which can greatly improve the SOC estimation accuracy of the battery system.

[0015] Furthermore, the battery system further comprises a battery management system, wherein the battery management unit is connected to each battery branch and is used to detect the internal resistance of each battery branch and adjust the adjustable resistor according to the detected internal resistance.

[0016] Furthermore, in order to reduce energy consumption while ensuring SOC accuracy, when adjusting the adjustable resistor on the battery branch, it is necessary to ensure that the difference in internal resistance between any two battery branches is less than a set threshold, so that the resistance of the adjusted adjustable resistor is minimized.

[0017] Furthermore, the adjustable resistor is arranged in a high-voltage distribution box. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the principle of a 3-series and 2-parallel battery system in the prior art;

[0019] Figure 2 It is a schematic diagram of the principle of the battery system of the prior art;

[0020] Figure 3 Schematic diagram of the battery system of the present invention. DETAILED DESCRIPTION

[0021] The specific embodiments of the present invention will be further described below with reference to the accompanying drawings.

[0022] Examples of battery systems

[0023] The battery system of this embodiment is as follows Figure 1 As shown, it includes two parallel battery branches, each battery branch includes three battery packs connected in series. For a battery system installed in an electric vehicle or hybrid vehicle, the positive and negative poles of each battery branch are connected to a high-voltage distribution box, and are connected together through the high-voltage distribution box. The high-voltage distribution box is provided with a charging interface and a discharging interface. The battery system is charged and discharged through the charging interface and the discharging interface on the high-voltage distribution box. Figure 2 During the actual installation of the battery system, due to factors such as the consistency of bolt torque and wiring harness length, there will inevitably be differences in internal resistance between the battery branches in the battery system. This will cause different currents to flow through each battery branch, leading to inaccurate SOC (capacity) estimation results.

[0024] To this end, the present invention proposes a new battery system, such as Figure 3 As shown, it includes parallel battery branches, and each battery branch includes several battery packs connected in series. The number of battery branches and the number of battery packs on the branches can be configured according to the actual needs of the battery system. In order to avoid inconsistent internal resistance on each battery branch, the present invention connects an adjustable resistor in series on each battery branch, and the positive pole of each battery branch is connected together in the high-voltage distribution box, and the negative pole of each battery branch is connected together in the high-voltage distribution box, wherein the adjustable resistors in series on each battery branch are also arranged in the high-voltage distribution box.

[0025] In addition, to facilitate the detection of internal resistance and the adjustment and control of the adjustable resistor, the battery system of the present invention also includes a battery management system (BMS). The battery management system is arranged in a control box and is connected to each battery branch. The battery management system can detect the internal resistance of each branch and can control the adjustable resistor on the corresponding battery branch according to the difference in internal resistance of each branch, so that the internal resistance of each battery branch is not much different. The specific control process is as follows:

[0026] Before charging and discharging the battery system, the BMS sends a signal to measure the internal resistance of each battery branch (the resistance of the adjustable resistor on each branch is 0 at this time), determine the size of the internal resistance of each battery branch, and determine whether the difference between the internal resistances of any two battery branches is greater than the set threshold. If so, it indicates that there is an internal resistance inconsistency problem on the battery branches. At this time, the adjustable resistor on the branch with smaller battery internal resistance is adjusted to increase the internal resistance of the branch, so that the difference between the internal resistances of the two battery paths is no greater than the set threshold. According to the same control method, the internal resistance of any two battery paths is no greater than the set threshold. The size of the set threshold can be determined according to actual conditions.

[0027] There are many ways to measure internal resistance. For example, the internal resistance of the battery branch can be determined by measuring the open-circuit voltage and instantaneous short-circuit current of the battery branch. Alternatively, the internal resistance can be calculated based on the current changes by adjusting the adjustable resistor on the battery branch. To minimize the energy consumption problems caused by the use of adjustable resistors, the present invention also ensures that the resistance of the adjusted adjustable resistor is minimized while ensuring consistent internal resistance. Specifically, the adjustable resistor on the battery branch with larger internal resistance can be first controlled to zero, and then the resistance of the adjustable resistor on the battery branch with smaller internal resistance can be increased to minimize overall energy consumption.

[0028] Example of estimation method

[0029] The estimation method of the present invention is based on the existing battery system, and an adjustable resistor is installed in series on each parallel battery branch of the battery system; before the battery system is charged or discharged, the internal resistance of each battery branch is detected, and when the difference between the internal resistance of any two battery branches is greater than a set threshold, the adjustable resistor on the battery branch is adjusted so that the difference between the internal resistance of any two battery branches is less than the set threshold; when the difference between the internal resistance of any two battery branches is less than the set threshold, the SOC is estimated based on the charging or discharging current. The specific implementation means have been described in detail in the battery system embodiment and will not be repeated here.

[0030] The present invention installs an adjustable resistor in series on each parallel battery branch of the battery system, detects the internal resistance of each battery branch before and after battery charging and discharging, and if there is a large difference in the internal resistance of any two battery branches, adjusts the adjustable resistors on the relevant battery branches to make the internal resistance of each branch equal, thereby ensuring that the charging and discharging currents of each battery branch are consistent, and the power of each battery branch is consistent. SOC estimation is performed according to the charging and discharging currents at this time, which can greatly improve the SOC estimation accuracy of the battery system.

Claims

1. A method for estimating the SOC of a battery system, characterized in that: The estimation method includes the following steps: 1) Install an adjustable resistor in series on each parallel battery branch of the battery system; 2) Before charging or discharging the battery system, the internal resistance of each battery branch is detected. When the difference between the internal resistances of any two battery branches is greater than a set threshold, the adjustable resistor on the battery branch is adjusted so that the difference between the internal resistances of any two battery branches is less than the set threshold. The set threshold is used to measure the consistency of the battery branches. When the difference between the internal resistances of any two battery branches is greater than the set threshold, it indicates that the two battery branches have inconsistent internal resistances. 3) When the difference in internal resistance between any two battery branches is less than a set threshold, the SOC is estimated based on the charge or discharge current.

2. The method for estimating the SOC of a battery system according to claim 1, wherein: The internal resistance of each battery branch is measured by a battery management system.

3. The method for estimating the SOC of a battery system according to claim 1 or 2, characterized in that: When adjusting the adjustable resistor on the battery branch, it is necessary to ensure that the difference in internal resistance between any two battery branches is less than a set threshold value, so that the resistance value of the adjusted adjustable resistor is minimized.

4. The method for estimating the SOC of a battery system according to claim 3, wherein: When adjusting the adjustable resistance on the battery branch, first make the adjustable resistance on the battery branch with larger internal resistance zero, and then increase the adjustable resistance on the battery branch with smaller internal resistance.

5. A battery system comprising at least two parallel battery branches, each battery branch comprising a plurality of battery packs connected in series, characterized in that: An adjustable resistor is connected in series on each battery branch. Before the battery system is charged or discharged, the internal resistance of each battery branch is detected. When the difference between the internal resistances of any two battery branches is greater than a set threshold, the adjustable resistor on the battery branch is adjusted so that the difference between the internal resistances of any two battery branches is less than the set threshold. The set threshold is used to measure the consistency of the battery branches. When the difference between the internal resistances of any two battery branches is greater than the set threshold, it indicates that the two battery branches have inconsistent internal resistances. When the difference between the internal resistances of any two battery branches is less than the set threshold, the SOC is estimated based on the charging or discharging current.

6. The battery system according to claim 5, characterized in that The battery system further comprises a battery management system, which is connected to each battery branch and is used to detect the internal resistance of each battery branch and adjust the adjustable resistor according to the detected internal resistance.

7. The battery system according to claim 5 or 6, characterized in that: When adjusting the adjustable resistor on the battery branch, it is necessary to ensure that the difference in internal resistance between any two battery branches is less than a set threshold value, so that the resistance value of the adjusted adjustable resistor is minimized.

8. The battery system according to claim 5, characterized in that The adjustable resistor is arranged in the high-voltage distribution box.

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