Battery SOC Calibration via OCV Estimation and Current Integration
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Solution Overview
Problem
Current methods for estimating the state of charge (SOC) of batteries, such as current integration, suffer from accuracy issues due to measurement errors over time, and methods like OCV-SOC curve estimation require batteries to be in a no-load condition, making it impossible to measure SOC during charging or discharging.
Innovation Solution
A method and battery management system that measures terminal voltage and current, estimates open-circuit voltage (OCV) using an equivalent circuit model, and calibrates the SOC based on voltage and current data, allowing for SOC calibration irrespective of the battery's charge or discharge state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If current integration method is used to estimate SOC, then SOC can be estimated continuously during charging and discharging, but accuracy deteriorates over time due to measurement errors
Solution Approach 1:
The patent combines current integration method with OCV-based calibration method into a hybrid SOC estimation system. The current integration provides continuous estimation during operation, while OCV measurements provide periodic calibration points to correct accumulated errors, achieving both continuous monitoring and high accuracy.
Solution Approach 2:
The system uses OCV measurements as feedback to detect and correct errors in current integration-based SOC estimation. By comparing the SOC value from current integration with the reference SOC from OCV-SOC curve, the system identifies measurement errors and applies corrections to maintain accuracy.
2Measurement precision
If OCV-SOC curve method is used to estimate SOC, then accuracy is maintained without current sensor errors, but measurement is impossible during charging or discharging due to no-load requirement
Solution Approach 1:
The system performs OCV measurements during periods when the battery is not under load (idle periods) to obtain reference SOC values. These preliminary OCV-based SOC estimates are stored and used to calibrate the current integration method when the battery enters charge or discharge modes, enabling accurate SOC estimation during operation.
Solution Approach 2:
The patent uses a lookup table (LUT) containing OCV-SOC correspondence data as an intermediary. During idle periods, OCV measurements are converted to SOC values using the LUT. During charge/discharge, the system uses this calibrated SOC information to correct current integration results, bridging the gap between accurate but limited OCV method and continuous but error-prone current integration method.
3Measurement precision
If battery is kept in no-load condition for OCV measurement, then accurate SOC calibration is possible, but system productivity decreases due to operational interruption
Solution Approach 1:
The system performs OCV measurements periodically during idle periods rather than requiring continuous no-load conditions. This periodic calibration approach allows the battery to resume normal charge/discharge operations quickly, minimizing productivity loss while maintaining sufficient calibration frequency to ensure accuracy.
Solution Approach 2:
The system applies OCV calibration only partially - during idle periods when no load is applied - rather than requiring continuous calibration. This partial application of the calibration method is sufficient to correct errors accumulated during charge/discharge operations without excessively interrupting system productivity.
Data Source
AI summary
Disclosed is a method and a battery management system for calibrating a state of charge of a battery. The method includes measuring a terminal voltage and a current of the battery, storing a measured voltage value indicating the terminal voltage and a measured current value indicating the current in a memory, updating a state of charge of the battery based on the measured current value, estimating an open-circuit voltage of the battery based on a first number of measured voltage values and a first number of measured current values in the order stored in the memory, storing an estimated voltage value indicating the open-circuit voltage in the memory, and calibrating the updated state of charge with a reference state of charge when a calibration condition is satisfied by a data set in which a second number of estimated voltage values sequentially stored in the memory are arranged in sequential order.