Battery Pack Voltage Dispersion Detection via Unloaded State Comparison
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Solution Overview
Problem
In battery packs for electric and hybrid vehicles, detecting dispersion in remaining capacities of cells is challenging, especially when the vehicle is under load, leading to inaccurate readings and potential over-discharge of auxiliary power sources, and existing methods are inefficient for long-term non-use scenarios.
Innovation Solution
A remaining-capacity dispersion detecting apparatus that senses total voltage before and after the battery pack becomes unloaded, comparing values to detect dispersion and adjust cell capacities, using a total voltage sensing section, storing section, and dispersion detecting section to equalize cell charges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of stationary object
If voltage readings are taken when the battery pack is under load to enable continuous monitoring, then monitoring coverage is improved, but measurement accuracy deteriorates due to voltage and current variations
Solution Approach 1:
The system performs remaining capacity detection periodically at specific moments when the battery pack transitions to an unloaded state, rather than attempting continuous monitoring under load. This periodic detection at appropriate intervals resolves the contradiction by capturing accurate data at optimal moments while maintaining monitoring coverage through systematic scheduling of detection events.
Solution Approach 2:
The system detects remaining capacity during the unloaded state that naturally occurs before the battery pack is fully activated for operation. By performing detection in advance during this brief unloaded period, the system ensures accurate measurements are captured before load conditions begin to affect voltage readings, thus maintaining both accuracy and monitoring coverage.
2Measurement precision
If dispersion detection is performed every time the vehicle is activated to ensure accurate remaining capacity readings, then measurement accuracy is improved, but startup time increases due to the time required to read voltages of all cells
Solution Approach 1:
The system performs a simplified voltage check during startup to determine if full dispersion detection is necessary, rather than always executing the complete time-consuming detection routine. This partial action approach maintains measurement accuracy by performing full detection only when needed (when voltage difference exceeds threshold) while reducing startup time by using a quicker assessment method for routine cases.
Solution Approach 2:
The system uses a lightweight, quick voltage comparison method as a preliminary check during startup, which serves as a disposable screening step. This inexpensive fast check determines whether the more time-consuming full dispersion detection is necessary, thus reducing overall startup time while maintaining detection accuracy when actually performed.
3Use of energy by moving object
If a timer powered by the low-voltage battery is used to measure elapsed time and avoid unnecessary dispersion detection, then energy consumption is reduced, but the low-voltage battery may become over-discharged
Solution Approach 1:
The system uses the existing voltage sensing infrastructure and control unit to perform the dispersion detection function, rather than introducing a separate timer-based system that would continuously draw power. The voltage sensing section and control unit already serve multiple functions, and adding the dispersion detection capability leverages these existing components to avoid creating a separate power-consuming subsystem.
4Measurement precision
If coolant temperature is used to estimate elapsed time for determining whether dispersion detection is needed, then detection accuracy for long-term nonuse is improved, but reliability deteriorates when the battery pack is left unused for extended periods
Solution Approach 1:
The system uses the total voltage sensing capability, which already serves the primary function of monitoring battery pack voltage for operation, to also perform the dispersion detection function. This multi-functional use of the voltage sensing section eliminates the need for separate estimation mechanisms based on coolant temperature, providing reliable detection across all time periods including long-term nonuse scenarios.
Data Source
AI summary
A remaining-capacity dispersion detecting apparatus for a battery pack having a plurality of cells includes a total voltage sensing section adapted to sense a total voltage which is a terminal voltage of the whole of battery pack; a storing section adapted to store a value of the total voltage when the battery pack becomes under unloaded condition from loaded condition; and a dispersion detecting section. The dispersion detecting section is adapted to detect a value of the total voltage at a time of activation before the battery pack becomes under the loaded condition from the unloaded condition, to compare the currently-detected total voltage value with the total voltage value previously stored by the storing section, and to detect a dispersion in respective remaining capacities of the plurality of cells in the case where a difference between the currently-detected total voltage value and the previously-stored total voltage value is greater than or equal to a predetermined value.