Battery SOC Estimation Using OCV Pre-Charge and Discharge Control
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Solution Overview
Problem
Existing state-of-charge (SOC) estimation methods for storage batteries, particularly lithium iron phosphate batteries used in electric vehicles, suffer from inaccuracies due to variations in C-rates during charge and discharge, leading to errors in open-circuit voltage (OCV) and subsequent SOC estimation, especially during fast charging.
Innovation Solution
A state-of-charge estimation device that includes a storage unit to log charge and discharge history, a determination unit to assess battery state, a control unit to adjust charge and discharge, and an OCV acquisition unit to estimate SOC using specific OCV-SOC curves, minimizing OCV errors by controlled power exchange between batteries.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If OCV-based SOC estimation is performed during fast charging, then charging speed is improved, but measurement precision deteriorates due to C-rate variations causing OCV errors
Solution Approach 1:
The system performs preliminary charge/discharge actions before SOC estimation to standardize the battery state. By charging or discharging the battery by a predetermined amount before measuring OCV, the system eliminates the influence of previous C-rate variations, ensuring accurate SOC estimation even during fast charging operations
Solution Approach 2:
The system changes the operational parameters by controlling charge/discharge currents at standardized rates (first and second predetermined currents) before measurement. This parameter standardization removes the harmful effect of variable C-rates on OCV, enabling precise SOC estimation during fast charging without sacrificing charging speed
2Measurement precision
If charge/discharge history is stored and analyzed, then SOC estimation accuracy is improved, but device complexity increases
Solution Approach 1:
The system uses the battery's own charge/discharge history and electrical characteristics to perform self-diagnosis and SOC estimation. By utilizing internally generated data (charge/discharge currents and OCV measurements) rather than requiring external complex measurement systems, the invention achieves high accuracy while maintaining simple device structure
Solution Approach 2:
The system implements feedback by storing charge/discharge history and using it to determine subsequent charge/discharge control strategies. This feedback mechanism enables the system to adaptively standardize battery states before measurement, improving SOC estimation accuracy through a simple cyclic process rather than complex external systems
Data Source
AI summary
A state-of-charge estimation device includes: a storage unit that stores the charge and discharge history of a storage battery; a charge and discharge determination unit that determines whether the storage battery is in a charged state or a discharged state; a charge and discharge control unit that discharges the storage battery by a predetermined amount when the charge and discharge determination unit determines that the storage battery is in a charged state, and charges the storage battery by a predetermined amount when the charge and discharge determination unit determines that the storage battery is in a discharged state; an open-circuit voltage acquisition unit that acquires the open-circuit voltage of the storage battery; and a state-of-charge estimation unit that refers to a charge and discharge curve to estimate the state of charge of the storage battery from the open-circuit voltage acquired by the open-circuit voltage acquisition unit.