Battery State of Charge Estimation Error Correction
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Solution Overview
Problem
Conventional battery state of charge estimation methods, such as current integration and open circuit voltage estimation, face accuracy issues due to error accumulation over time and high-frequency noise, respectively, when used separately, and weighting their results with a single weight worsens estimation accuracy.
Innovation Solution
An apparatus and method that combines current integration and open circuit voltage estimation methods using a Kalman filter-based error model to calculate and subtract estimation errors, improving accuracy by accounting for errors in charge/discharge current and terminal voltage detection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the calculation interval is shortened to improve estimation accuracy with the current integration method, then estimation accuracy improves, but high frequency noise increases with the open circuit voltage estimation method
Solution Approach 1:
The patent combines the current integration method and open circuit voltage estimation method into a unified estimation system. The current integration unit and open circuit voltage estimation unit work together, with the open circuit voltage serving as a reference to correct errors in the current integration method, thereby achieving accurate estimation without excessive noise while maintaining computational efficiency.
2Device complexity
If a single weight is used to combine estimation results from both methods, then the device complexity is reduced, but estimation accuracy worsens
Solution Approach 1:
The patent employs dynamic weighting where the weight assigned to the open circuit voltage estimation method varies based on the state of charge and operational conditions. The weighting unit adjusts the weight dynamically, assigning higher weight to the open circuit voltage method when the battery is in certain states (e.g., low SOC) where current integration error accumulates more significantly, and lower weight when the battery is in other states. This dynamic adjustment optimizes estimation accuracy without requiring complex manual tuning.
3Stability of the object's composition
If the open circuit voltage estimation method is used to avoid error accumulation, then long-term stability improves, but short-term estimation accuracy deteriorates due to limited sensitivity to state of charge changes
Solution Approach 1:
The patent implements a feedback mechanism where the open circuit voltage estimation serves as a reference to correct the current integration method's accumulated errors. The error correction unit uses the open circuit voltage measurement to identify and compensate for drift in the current integration-based state of charge estimation, thereby maintaining both long-term stability and short-term accuracy. The system continuously adjusts the estimation based on the feedback from open circuit voltage measurements.
Data Source
AI summary
An apparatus and method for battery state of charge (SOC) estimation can reduce the estimation error in the battery SOC. The apparatus includes a charge/discharge current detection unit, a terminal voltage detection unit, a first estimation unit that estimates a first SOC by integrating the charge/discharge current value, a second estimation unit that estimates an open circuit voltage value from the charge/discharge current value and the terminal voltage value and estimates a second SOC from the open circuit voltage value, a first difference calculation unit that calculates a SOC difference between the first SOC and the second SOC, an error estimation unit that estimates, based on the SOC difference, an error as a state quantity of an error model by using the error model, and a second difference calculation unit that calculates a SOC of the battery by subtracting the error from the first SOC.