Battery SoC Estimation Using Partial Derivative Coefficients
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Solution Overview
Problem
Existing rechargeable battery parameter estimation methods fail to accurately estimate the state of charge (SoC) due to offset errors in current measurements, which propagate errors in estimating the full charge capacity (FCC) and state of charge, leading to incorrect battery parameter estimation.
Innovation Solution
A rechargeable battery parameter estimation apparatus and method that calculate partial derivatives of the SoC with respect to offset errors and capacity errors, using derivative information to estimate these errors from voltage and current measurements, allowing for precise estimation even with offset errors in current measurements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If the Coulomb-counting method is used to estimate SoC, then the battery can be monitored online without suspension, but the estimation accuracy is greatly degraded by offset errors in current measurements
Solution Approach 1:
The patent implements a feedback mechanism where the estimated SoC is continuously compared with voltage measurements and current integration results. The system uses the open-circuit voltage relationship as a reference to correct cumulative errors from current measurement offsets, creating a closed-loop estimation system that maintains accuracy over time while enabling continuous monitoring.
Solution Approach 2:
The patent dynamically adjusts estimation parameters by switching between different measurement strategies based on battery operating conditions. When the battery is in idle state, it uses voltage-based SoC estimation; when in use, it uses current integration with periodic calibration, thereby adapting to different operational requirements to maintain both continuous monitoring and accuracy.
2Measurement precision
If the open circuit voltage method is used to estimate SoC, then the estimation accuracy is high, but the battery has to be suspended for a long period
Solution Approach 1:
The patent applies partial action by using voltage-based SoC estimation only when the battery is in idle state (not in use), rather than requiring complete suspension. During active use, it switches to current integration method, thereby obtaining sufficient calibration data without unnecessarily extending battery suspension time.
Solution Approach 2:
The patent performs preliminary SoC calibration using voltage measurements during idle periods before the battery enters active use. This preliminary action establishes an accurate initial SoC value that serves as a reference for subsequent current integration, eliminating the need for prolonged suspension during actual operation.
3Measurement precision
If current integration is performed over a long period to improve FCC estimation, then the influence of offset errors is reduced, but the propagation of errors in SoC estimation increases
Solution Approach 1:
The patent implements periodic calibration cycles where voltage-based SoC estimation is performed at regular intervals during battery idle states. These periodic actions reset cumulative errors from current integration, maintaining both FCC estimation accuracy and SoC reliability without requiring excessively long integration periods.
Solution Approach 2:
The patent performs preliminary current integration over calibrated periods bounded by voltage-based SoC measurements. This preliminary integration establishes accurate FCC estimates while limiting error propagation, as each voltage calibration resets the integration baseline before the next active period begins.
Data Source
AI summary
The rechargeable battery parameter estimation apparatus includes: a current measurement part for measuring a current flowing through a rechargeable battery, the current measurements having an offset error; a first coefficient calculation part for calculating a first coefficient, which is a partial derivative of an estimated value of an state of charge (SoC) of the battery with respect to the offset error; a second coefficient calculation part for calculating a second coefficient, which is a partial derivative of the estimated value of the SoC with respect to a capacity error, which is a difference of a typical full charge capacity from an actual full charge capacity of the battery; and an error estimation part for estimating the offset error and the capacity error from derivative information including the first coefficient and the second coefficient, the current flowing through the battery, and the estimated value of the SoC.