Hybrid-Electric Vehicle Battery Capacity Estimation via Controlled Charge Cycles
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Solution Overview
Problem
Hybrid-electric vehicles face challenges in accurately estimating the capacity of their traction batteries due to unpredictable energy usage and discharge patterns during drive cycles, which affects energy management and fuel efficiency.
Innovation Solution
A system and method where a controller operates the engine and electric machine to continuously discharge or charge the traction battery based on predetermined thresholds, allowing for accurate estimation of battery capacity by monitoring state of charge and current integration during specific operational modes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If various algorithms are used to estimate battery capacity during normal operation, then battery capacity estimation can be performed, but the estimation accuracy deteriorates due to unpredictable energy usage and discharge patterns
Solution Approach 1:
The system performs preliminary actions by continuously charging the battery to a target state of charge before capacity estimation, and allowing rest periods for voltage stabilization. This preparatory charging and resting ensures the battery is in a known, stable state before measurement, eliminating the uncertainty caused by unpredictable energy usage patterns during normal operation.
Solution Approach 2:
The system implements periodic capacity estimation cycles during which the battery is charged to a target state of charge, allowed to rest, and then measured. This periodic approach creates regular intervals where predictable conditions are established, enabling accurate estimation while maintaining normal unpredictable operation during other times.
2Measurement precision
If the battery is continuously charged and discharged to estimate capacity, then accurate capacity estimation can be achieved, but vehicle performance and energy management are affected
Solution Approach 1:
The system applies partial action by charging the battery only to a target state of charge (not necessarily full charge) and allowing rest periods rather than continuous charging. This partial approach achieves sufficient voltage stabilization for accurate measurement without the excessive action of continuous charging, thereby maintaining vehicle performance.
Solution Approach 2:
The system uses the battery's own self-discharge characteristics during rest periods to naturally stabilize voltage without external intervention. This self-service approach allows the battery to reach a stable state for measurement without requiring continuous external charging or discharging, thus avoiding impacts on vehicle performance.
3Productivity
If state of charge thresholds are used to control charging and discharging, then energy management can be optimized, but the system complexity increases
Solution Approach 1:
The system changes the parameter being monitored from multiple complex variables to a single state of charge threshold parameter. By base capacity estimation on state of charge thresholds rather than multiple simultaneous parameters, the system achieves optimized energy management with simpler controller programming and fewer computational requirements.
Data Source
AI summary
An electrified vehicle includes a powertrain that includes an engine and an electric machine. The vehicle includes a traction battery that is charged and discharged by operation of the engine and the electric machined. The vehicle includes a controller programmed to operate the engine and the electric machine to satisfy a driver power demand. The controller is also programmed to initiate an estimated of a capacity of the traction battery under predetermined conditions. The controller operates the engine and the electric machine to satisfy the driver power demand and charge and discharge the traction battery in a predetermined manner to create conditions favorable for estimating the capacity.