Battery Charge State Correction via No Load Voltage Feedback
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Solution Overview
Problem
Coulomb counting, used to estimate battery charge state in electric vehicles, accumulates errors over time, leading to inaccurate fuel gauge readings due to discrete current measurements, which cannot reliably indicate the remaining battery energy.
Innovation Solution
Determining a set of relationships between no load voltages and known good charge states, updating the estimated charge state when the battery is in a no load state, and using interpolation if no exact match is found, to correct for accumulated errors and improve accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If Coulomb counting is used to estimate battery charge state, then the fuel gauge can display energy remaining, but accumulated error increases over time reducing accuracy
Solution Approach 1:
The system uses voltage measurements as feedback to correct the Coulomb counting estimate. By periodically measuring battery voltage and comparing it against a lookup table of voltage-charge state relationships, the system adjusts the estimated charge state to compensate for accumulated counting errors, thereby maintaining accurate fuel gauge readings over time
Solution Approach 2:
The patent replaces the purely computational Coulomb counting method with a hybrid approach that incorporates physical voltage measurements. This substitution of measurement methodology allows the system to overcome the limitations of discrete current integration by using direct voltage-based charge state determination as a correction mechanism
2Device complexity
If discrete current measurements are used in Coulomb counting, then the system can operate with simple instrumentation, but small errors accumulate over time
Solution Approach 1:
The patent introduces voltage measurement as an intermediary that bridges the gap between simple current sensing and accurate charge state determination. The voltage-charge state lookup table acts as a mediator that translates easily measurable voltage into accurate charge state information, allowing the system to maintain both simplicity and precision
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 method enhances the accuracy of battery charge state estimation by correcting for errors in Coulomb counting, providing a more reliable indication of the battery's energy level, thereby improving the fuel gauge's accuracy.
Implementation Method 1
rechargeable battery system
Data Source
AI summary
Improved battery charge state determination. The estimated charge state of a battery comprising a plurality of series connected cells is updated using Coulomb counting during battery operation, for example, while operating an electric vehicle motor. The estimated charge state may be coupled to a fuel gauge. When the battery is in a no load state, a no load voltage measurement is made. During testing, a set of relationships between battery no load voltages and associated known good charge states have been determined. The measured no load voltage is compared to the set of no load voltages associated with known good charge states. A known good charge state associated with the measured no load voltage is used to update the estimated charge state, thereby providing a more accurate indication of the actual battery charge state, thus providing a more robust and accurate fuel gauge.