Battery State of Charge Estimation via Voltage-Current Correction
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Solution Overview
Problem
The estimation accuracy of the state of charge in secondary batteries is compromised by hysteresis in the voltage-derived method and integration errors in the current-derived method, leading to unreliable battery state estimation.
Innovation Solution
A method that estimates a third state of charge by combining voltage-derived and current-derived state of charge estimates, with correction based on the reliability of each method, shifting the battery state to a non-hysteresis region for accurate electric current-derived state of charge correction.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If voltage-derived state of charge estimation is used, then the state of charge can be estimated with reference to voltage value, but the estimation accuracy deteriorates in hysteresis regions where open-circuit voltage values differ significantly between charging and discharging
Solution Approach 1:
The patent changes the estimation parameter from voltage-based to current-integration-based when operating in hysteresis regions. The control unit identifies hysteresis regions and switches to using current integration values for SOC estimation, avoiding the voltage hysteresis problem while maintaining accurate estimation.
Solution Approach 2:
The patent introduces current integration values as an intermediary parameter to estimate SOC in hysteresis regions. By using the relationship between current integration and SOC change, the system bypasses the unreliable voltage measurement in hysteresis regions and achieves accurate estimation through the intermediary current-based measurement.
2Reliability
If electric current integrated value is used for state of charge estimation, then the estimation is less susceptible to hysteresis influence, but integration errors from current sensor become larger as integration period increases
Solution Approach 1:
The patent implements periodic correction of current integration values using voltage-derived SOC estimates. When the battery exits the hysteresis region, the system periodically corrects the accumulated current integration errors by comparing with voltage-based SOC, thereby maintaining long-term accuracy without continuous high-frequency measurements.
Solution Approach 2:
The patent uses feedback control by comparing voltage-derived SOC and current-derived SOC, then correcting the current integration baseline based on the voltage measurement when in non-hysteresis regions. This feedback mechanism eliminates accumulated integration errors while maintaining the benefits of current-based estimation during hysteresis operation.
3Measurement precision
If voltage-derived state of charge is used in non-hysteresis region, then accurate estimation can be obtained, but this method cannot be reliably used in hysteresis regions where voltage values do not uniquely correspond to state of charge
Solution Approach 1:
The patent implements dynamic switching between voltage-based and current-based estimation methods based on real-time detection of hysteresis region entry and exit. The control unit continuously monitors battery state and adapts the estimation method accordingly, ensuring high accuracy in non-hysteresis regions while maintaining reliability in hysteresis regions through method switching.
Data Source
AI summary
A method for estimating a state of charge of a battery includes: estimating, by an electronic control unit, a third state of charge used for control of the battery based on a first state of charge and a second state of charge, the first state of charge being a state of charge estimated with reference to an electric current integrated value obtained by integrating detected electric current values of the battery, the second state of charge being a state of charge estimated with reference to a detected voltage value of the battery; and correcting, by the electronic control unit, the first state of charge based on the second state of charge estimated when the state of charge of the battery is in the non-hysteresis region.