State of Charge Estimation with Voltage Correction
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Solution Overview
Problem
Existing methods for determining the state of charge of electric energy stores, especially during longer operating times, suffer from large deviations due to measuring errors.
Innovation Solution
A method that determines the maximum and minimum state of charge for each electric energy store cell by using current, capacitance, and open-circuit voltage measurements, while accounting for measuring inaccuracies and service life changes in capacitance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If power integration method is used to determine state of charge during operation, then state of charge can be estimated continuously, but large deviations occur due to measuring errors especially in longer operating times
Solution Approach 1:
The patent uses feedback by continuously comparing the integrated state of charge with open-circuit voltage measurements and correcting the integration results based on the difference. This feedback mechanism compensates for accumulated measuring errors over time, maintaining accuracy during longer operating periods.
Solution Approach 2:
The patent performs preliminary calibration by determining correction values for the integration method during initial operation or when open-circuit voltage can be measured. These pre-determined correction values are then applied during subsequent operation to compensate for measuring errors before they accumulate significantly.
2Measurement precision
If current measuring inaccuracy is not considered, then calculation is simpler, but state of charge determination becomes less accurate
Solution Approach 1:
The patent changes the parameters used in calculation by introducing correction values that account for current measuring inaccuracy. Instead of using raw current measurements directly, the method transforms them by applying correction factors derived from open-circuit voltage comparisons, thereby improving accuracy while managing complexity through systematic parameter transformation.
3Measurement precision
If capacitance at beginning of service life is used for all calculations, then initial accuracy is high, but accuracy decreases as the energy store ages
Solution Approach 1:
The patent applies dynamics by making the capacitance value time-dependent and adaptive. Instead of using a fixed capacitance value from the beginning of service life, the method dynamically adjusts the capacitance parameter based on the actual state of the energy store, allowing accurate state of charge determination throughout the entire service life including aging effects.
Data Source
AI summary
The invention relates to a method for determining the state of charge of an electric energy store comprising electric energy store cells and at least one sensor,in which method: in a first method step, operating parameters of the electric energy store are determined;in a second method step, at least one maximum state of charge and at least one minimum state of charge are determined as a temporal integral for each electric energy store cell on the basis of a current (I), a current measuring inaccuracy (ΔI), at least one capacitance, a correction value for the minimum state of charge (formula (IA)), and a correction value for the maximum state of charge (formula (IB)) of the electric energy store cells;the correction value for the minimum state of charge (formula (IA)) is determined by means of a minimum state of charge (formula (IIA)) on the basis of a filtered minimum open-circuit voltage (formula (III)) of the electric energy store;the correction value for the maximum state of charge (formula (IB)) is determined by means of a maximum state of charge (formula (IIB)) on the basis of a filtered maximum open-circuit voltage (formula (III)) of the electric energy store;wherein a maximum state of charge (SOCmax) of the electric energy store is the maximum of the maximum states of charge (formula (IVA)) of all the electric energy store cells, and a minimum state of charge (SOCmin) of the electric energy store is the minimum of the minimum states of charge (formula (IVB)) of all the electric energy store cells.