Battery SoC Estimation Using Coulomb Counting and Lookup Tables
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Solution Overview
Problem
Conventional battery management systems experience abrupt changes in estimated state of charge (SoC) when transitioning from normal to end-of-discharge or fully-charged states due to independent error sources in coulomb counting and lookup table methods, leading to inaccurate battery state estimation and potential device failure.
Innovation Solution
A battery management controller that combines coulomb counting with a remaining-capacity lookup table to estimate SoC, using analog-to-digital conversion circuitry, memory, and a processor to search for parameter values corresponding to voltage, current, and temperature, and calculates full available charge capacity to smooth transitions and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If coulomb counting method is used for SoC estimation in normal charging/discharging states, then the estimation is suitable for normal operation, but errors occur and cause abrupt changes when transitioning to end-of-discharge or fully-charged states
Solution Approach 1:
The patent combines coulomb counting method and lookup table method into a unified SoC estimation framework. The processor switches between methods based on battery state, but more importantly, it merges the results by using the lookup table to correct cumulative errors from coulomb counting, thereby maintaining both normal operation accuracy and endpoint precision
Solution Approach 2:
The patent changes the estimation parameters dynamically based on battery state. In normal states, it uses coulomb counting with accumulated charge/discharge data. When approaching end-of-discharge or fully-charged states, it switches to lookup table parameters based on voltage, current, and temperature, thereby adapting the estimation parameters to match the battery's operational phase
2Measurement precision
If lookup table method is used for SoC estimation in close-to-end-of-discharge or fully-charged states, then the estimation is more accurate for these states, but errors exist and cause abrupt transitions when switching from coulomb counting
Solution Approach 1:
The patent implements feedback by continuously monitoring battery voltage, current, and temperature, and using this information to query the lookup table. The lookup table results are fed back to correct the coulomb counting accumulation, ensuring that the SoC estimation remains continuous and reliable across state transitions. The system constantly adjusts the estimation based on real-time battery parameters
Solution Approach 2:
The patent performs preliminary action by pre-calculating and storing capacity relationships in the lookup table during battery manufacturing or initial charging cycles. This pre-stored data includes the relationship between voltage, current, temperature, and remaining capacity, which is prepared in advance to enable accurate endpoint estimation without real-time calculation delays
3Measurement precision
If independent estimation methods are used for normal and endpoint states, then each method can be optimized for its specific state, but the independent error sources cause abrupt SoC changes during transitions
Solution Approach 1:
The patent introduces the lookup table as an intermediary between coulomb counting and the final SoC value. Instead of directly switching between independent methods, the lookup table acts as a mediator that provides correction factors based on voltage, current, and temperature. This intermediary smooths the transition by blending the cumulative coulomb counting data with the state-specific lookup table data, eliminating abrupt changes
Data Source
Figure 1A~1B
Figure 2A
Figure 2B
AI summary
In a battery management controller, analog-to-digital conversion circuitry converts analog signals, indicative of a battery voltage, a battery current, and a battery temperature, to digital signals. A memory stores a remaining-capacity lookup table that includes multiple groups of data. Each group of data includes a voltage, a current, a temperature, and a parameter associated with a remaining capacity corresponding to the voltage, the current and the temperature. A processor searches the lookup table for a current parameter value and an end-of-discharge parameter value based on the digital signals, and estimates a full available charge capacity of the battery based on the current parameter value and the end-of-discharge parameter value. The processor also counts the amount of charges flowing through the battery based on a battery current. The processor further estimates an available state of charge of the battery according to the full available charge capacity and the amount of charges.