Battery Cell Equalization Using OCV and Closed-Circuit Voltage
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Solution Overview
Problem
Existing battery systems struggle to equalize the capacities of battery cells when their voltages do not pass through specific measurement points, thereby compromising the estimation accuracy of the internal state of the cells.
Innovation Solution
A battery system that includes an adjusting unit and a control device to determine the suitability of two control methods (using open circuit voltage or closed circuit voltage) for equalization based on predetermined conditions, ensuring that the appropriate method is used to secure an opportunity for equalization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If a single control method (SOC-OCV characteristics) is used for equalization, then the equalization process is simple to implement, but the opportunity for equalization cannot be secured when voltages do not pass through measurement points
Solution Approach 1:
The system dynamically switches between two control methods (first control method using voltage change rate and second control method using SOC-OCV characteristics) based on real-time battery state detection. This dynamic adaptation ensures that the appropriate equalization method is selected according to current operating conditions, securing equalization opportunities while maintaining operational simplicity through automated method selection.
Solution Approach 2:
The system changes the control parameter from a fixed SOC-OCV characteristic-based approach to a flexible parameter selection that includes both voltage change rate (dV/dt) and SOC-OCV characteristics. By monitoring battery state parameters and switching between different control parameters, the system ensures equalization opportunities are captured regardless of voltage trajectory.
2Measurement precision
If the first control method (open circuit voltage) is used, then the equalization accuracy is high, but the opportunity for equalization is reduced when power is being output
Solution Approach 1:
The system dynamically selects between open circuit voltage-based control (first method) and closed circuit voltage-based control (second method) based on whether power is being output. When power output is zero or below threshold, the high-accuracy open circuit voltage method is used. When power is being output, the system switches to the closed circuit voltage method, ensuring equalization opportunities are maintained across all operating conditions while preserving accuracy when possible.
Solution Approach 2:
The control parameter changes from open circuit voltage (high accuracy but limited applicability) to closed circuit voltage (lower accuracy but broader applicability) based on operating conditions. This parameter adaptation allows the system to maintain equalization capability during power output while achieving high accuracy during idle or charging states.
3Reliability
If the second control method (closed circuit voltage) is preferentially used, then the opportunity for equalization is secured, but the equalization accuracy may be compromised
Solution Approach 1:
The system dynamically adjusts the preference between control methods based on real-time conditions. Rather than statically preferring one method, the system switches to the second control method (closed circuit voltage) only when necessary to secure equalization opportunities during power output, while reverting to the first control method (open circuit voltage) when conditions allow for higher accuracy. This dynamic balancing resolves the contradiction between opportunity and accuracy.
Solution Approach 2:
The system changes the voltage measurement parameter from open circuit voltage to closed circuit voltage based on operating conditions. By monitoring power output status and switching measurement parameters accordingly, the system ensures equalization opportunities are captured during power output while maintaining high accuracy measurements during idle or charging states where open circuit voltage is available.
Data Source
AI summary
The battery system is a system for equalizing the capacity of each cell included in a battery in which a plurality of cells having a plateau region in a charge-discharge curve are connected in series, and includes an equalization unit for adjusting the capacity of each cell, and an ECU for controlling the charge-discharge of the battery. ECU determines which control method is used according to a predetermined determination condition for determining which of the first control method and the second control method is suitable for equalization in the present situation, and controls the equalization unit.