Battery Pack Capacity Balancing Using Aging-Compensated Voltage Curves
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Solution Overview
Problem
Existing battery packs face challenges in accurately balancing battery capacities due to differences in self-discharge rates and internal resistance, leading to potential overcharging and safety risks, with current methods lacking a strong theoretical basis for determining voltage mismatches.
Innovation Solution
A method and device that obtain voltage and current information from battery packs, using aging voltage and capacity compensation parameters to determine if voltages are on the same curve fragment, calculating balanced capacities, and adjusting capacities to achieve balance, considering both open circuit and working voltages.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If voltage threshold evaluation is used to determine battery state consistency, then the evaluation process is simple, but measurement precision deteriorates due to internal resistance differences causing misjudgment
Solution Approach 1:
The patent transforms the evaluation from direct voltage comparison to capacity comparison by introducing the relationship between open circuit voltage and state of charge (SOC). It calculates available capacity from open circuit voltage using the SoC-OCV curve, then determines battery state consistency based on capacity differences rather than voltage differences, eliminating the misjudgment caused by internal resistance variations
Solution Approach 2:
The patent introduces open circuit voltage as an intermediary parameter. Instead of directly comparing working voltages which are affected by internal resistance, the system measures open circuit voltage (which reflects true state of charge), converts it to available capacity through the SoC-OCV relationship, and uses this capacity value for consistency evaluation, thus mediating between voltage measurement and accurate state assessment
2Measurement precision
If open circuit voltage is used to calculate available capacity, then battery state evaluation accuracy is improved, but device complexity increases due to additional measurements and calculations
Solution Approach 1:
The patent performs preliminary action by measuring open circuit voltage and calculating available capacity in advance, before the actual battery operation. The system stores the SoC-OCV curve data and pre-establishes the relationship between open circuit voltage and state of charge, so that during operation, it only needs to measure open circuit voltage and look up the corresponding capacity from the pre-stored curve, avoiding complex real-time calculations
Solution Approach 2:
The patent implements self-service by using the battery packs themselves to provide the open circuit voltage measurements needed for evaluation. Each battery pack's open circuit voltage is measured directly from its terminals, and the system automatically converts these measurements to capacity values using the stored SoC-OCV relationship, making the evaluation system self-contained and independent of external complex equipment
3Ease of operation
If traditional voltage-based balancing is used, then the balancing process is straightforward, but reliability deteriorates due to inability to accurately reflect true battery state differences
Solution Approach 1:
The patent changes the balancing parameter from voltage to capacity. Instead of balancing based on voltage thresholds, the system calculates available capacity for each battery pack using open circuit voltage and the SoC-OCV curve, then performs balancing based on capacity differences. This parameter change ensures that the balancing operation reliably reflects the true state of charge differences between battery packs, eliminating the unreliability caused by internal resistance variations
Data Source
AI summary
A method and a device for balancing a battery state are provided, in which the method includes executing a battery capacity balancing of a plurality of battery packs when voltage information of the plurality of battery packs is open circuit voltages or when balanced voltages of the plurality of battery packs are on the same curve fragment, such that balanced capacities of the plurality of battery packs can be calculated via aging voltage compensation parameters and/or aging capacity compensation parameters of the plurality of battery packs, and a capacity adjustment can be performed according to the balanced capacities. Therefore, the battery capacity balancing can be performed by obtaining voltages in different states, and the battery capacity of each battery pack can be accurately adjusted to achieve balance among the battery packs by taking the aging parameters of the battery packs into consideration.