Battery SOC Estimation With Coulomb Counting And Thermal Limits
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of electric batteries in vehicles, particularly in aircraft, are prone to significant errors due to calibration issues in current sensors, leading to inaccurate representation of the available charge, especially under varying operating conditions such as temperature and discharge current.
Innovation Solution
A method that decouples the calculation of stored charge and the influence of operating conditions by using coulometric counting for total charge and temperature-dependent non-extractable charge to determine available charge, simplifying calculations and providing reliable estimates of both stored and available charge states.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coulometric counting is used to monitor battery state of charge by integrating current over time, then the state of charge can be tracked during battery operation, but calibration errors in current sensors accumulate over time leading to significant errors in estimated state of charge
Solution Approach 1:
The patent implements periodic open-circuit voltage measurements at predetermined time intervals to recalibrate the state of charge estimate. Between these periodic measurements, coulometric counting continues to track charge changes. This periodic reset prevents error accumulation while maintaining continuous monitoring capability.
Solution Approach 2:
The patent uses open-circuit voltage measurements as a feedback mechanism to correct accumulated errors in the coulometric counting method. The measured open-circuit voltage provides a reference value that resets the state of charge estimation, creating a feedback loop that eliminates drift over time.
2Measurement precision
If the state of charge is determined using open circuit voltage and temperature measurements with a characteristic chart, then the state of charge can be accurately assessed, but this technique can only be used when the battery is not producing electrical current
Solution Approach 1:
The patent merges two previously separate methods: open-circuit voltage-based state of charge determination and coulometric counting. By combining these methods, the system achieves accurate state of charge measurement (from open-circuit voltage) while maintaining the ability to track charge changes during operation (from coulometric counting), thus resolving the limitation that prevented use during battery discharge.
Solution Approach 2:
The patent performs preliminary open-circuit voltage measurements to establish an accurate baseline state of charge before resuming coulometric counting during battery operation. This preliminary action ensures that the subsequent tracking during operation starts from an accurate reference point.
3Measurement precision
If the available charge state is determined using a Kalman filter with multiple measurements and complex calculations, then a more accurate available state of charge can be estimated, but the calculations required become very large and computationally intensive
Solution Approach 1:
The patent extracts and separates the calculation into simpler components: instead of using a full Kalman filter with multiple state variables and complex matrix operations, the invention uses a simplified approach that tracks only the essential charge state and applies straightforward corrections based on open-circuit voltage measurements and temperature-dependent adjustments. This extraction of essential functionality reduces computational complexity while maintaining accuracy.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This approach provides accurate and reliable estimates of both stored and available charge states, reducing calculation complexity and ensuring precise monitoring and control of battery performance under varying conditions.
Implementation Method 1
calculation, by an electronic processing and control system, of a total electric charge stored in the battery at a current instant, by coulometric counting
Data Source
Figure 1~2
Figure 3~4
AI summary
The invention relates to a method comprising the steps of: - calculating a total electrical charge (Qs) accumulated in a battery at the current time by Coulomb counting on the basis of a total electrical charge accumulated in the battery at a previous time (Qs,o) and on the basis of a current (i) supplied by the battery, - calculating a stored charge state (SOCs), equal to the total accumulated electrical charge (Qs) divided by a maximum total charge (Qs,max), - calculating an available electrical charge (Qa) on the basis of a difference between said total electrical charge (Qs) and a non-extractible electrical charge (Qs,minlim) which cannot be extracted from the battery because of its temperature (T), - calculating an available charge state (SOCa), equal to the available electrical charge (Qa) divided by a maximum available charge (Qa,max).