Battery Pack Equalization Control Using Adaptive SOC-OCV Curves
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Solution Overview
Problem
The inconsistency in self-discharging rates and initial State of Charge (SOC) among cells in a battery pack leads to reduced available capacity, as existing methods for equalization, such as determining SOC differences using Open Circuit Voltage (OCV), are inaccurate due to hysteresis effects, resulting in imprecise equalizing information.
Innovation Solution
The method involves selecting either the charging or discharging SOC-OCV curve based on voltage intervals to determine the target SOC-OCV curve, calculating SOC differences, and then determining the equalizing time for each cell based on these differences and nominal capacity, thereby accounting for hysteresis effects.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If SOC difference is determined using OCV and SOC-OCV curve, then equalization control can be implemented, but measurement precision deteriorates due to hysteresis effect causing inaccurate SOC difference estimation
Solution Approach 1:
The patent applies dynamics by making the SOC-OCV curve selection adaptive based on the operating state. The system dynamically switches between charging SOC-OCV curve and discharging SOC-OCV curve according to whether the battery is in charging or discharging mode, thereby adapting to the hysteresis effect which differs between charging and discharging processes. This dynamic curve selection resolves the contradiction by ensuring accurate SOC difference measurement for the current operating state.
Solution Approach 2:
The patent changes the parameter of SOC-OCV curve selection based on the operating state. By determining whether the battery is charging or discharging and selecting the corresponding curve (charging SOC-OCV or discharging SOC-OCV), the system adjusts the measurement parameter to match the current state, thereby eliminating the error caused by hysteresis effect and improving SOC difference estimation accuracy.
2Productivity
If equalization is performed to increase available capacity, then battery pack performance improves, but device complexity increases due to need for precise equalization determination
Solution Approach 1:
The patent segments the SOC-OCV relationship into two distinct curves: charging SOC-OCV curve and discharging SOC-OCV curve. By dividing the single SOC-OCV relationship into state-specific segments, the system can select the appropriate curve for the current operating state, thereby simplifying the determination process while maintaining high accuracy for equalization control.
Solution Approach 2:
The patent performs preliminary action by pre-establishing both charging and discharging SOC-OCV curves before actual operation. The system determines the operating state in advance and selects the corresponding pre-prepared curve, avoiding complex real-time calculations and simplifying the equalization determination process while ensuring accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach allows for precise acquisition of equalizing information and accurate calculation of equalizing time for cells with hysteresis effects, enhancing the overall performance and capacity utilization of the battery pack.
Implementation Method 1
due to a hysteresis effect of some of the cells, which refers to an inconsistency between a charging OCV and a discharging OCV of a cell
Data Source
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AI summary
The present application discloses a method, apparatus, device and medium for equalization control of battery packs. The method may include: acquiring a voltage of each of a plurality of cells of the battery pack; on the condition that one or more voltages of the voltages of the plurality of cells are within a preset voltage interval, selecting a target State of Charge (SOC)-Open Circuit Voltage (OCV) curve from a charging SOC-OCV curve and a discharging SOC-OCV curve stored for the battery pack based on the voltages within the preset voltage interval; acquiring a target SOC of each cell based on the target SOC-OCV curve and the voltage of each cell; calculating, for each cell, a SOC difference between the target SOC of the cell and a reference SOC; calculating an equalizing time for each cell based on the SOC difference of each cell; the preset voltage interval is determined based on a hysteresis interval. According to embodiments of the present application, the equalizing information can be precisely obtained for cells with a hysteresis effect.