Adaptive SOC Reset Using Temperature and Charge Rate
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
Existing state of charge estimation algorithms for traction batteries in electrified vehicles often lead to errors over time due to variations in temperature and charge rate, making it difficult to accurately determine the battery's state of charge and potentially resulting in excessive or inadequate charge cycling.
Innovation Solution
A controller is programmed to generate an adaptive relaxation time and adaptive compensation voltage based on temperature and charge rate changes, updating the state of charge after a charge cycle by using a measured voltage difference, which allows for more accurate SOC estimation and operation of the traction battery.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If Amp-hour integration algorithms are used to estimate state of charge, then the state of charge can be estimated during operation, but errors accumulate over time leading to inaccurate estimation
Solution Approach 1:
The system performs a relaxation period after charging where the battery is allowed to rest and voltage is monitored. This preliminary action before final SOC determination allows the battery chemistry to stabilize, eliminating the accumulation of estimation errors that occur during active charging operations.
Solution Approach 2:
The system changes the measurement parameter from current-based Amp-hour integration during charging to voltage-based Open Circuit Voltage measurement after relaxation. By switching to OCV measurement after the battery has rested, the system obtains a more accurate SOC reading that does not suffer from the cumulative errors inherent in continuous current integration.
2Measurement precision
If a fixed relaxation time is used after charge cycle, then the state of charge can be updated, but temperature and charge rate variations cause estimation errors
Solution Approach 1:
The relaxation time is made dynamic rather than fixed. The system adjusts the relaxation duration based on real-time temperature and charge rate conditions. Higher temperatures or higher charge rates result in longer relaxation periods, while lower conditions allow for shorter relaxation times, optimizing both accuracy and response time across varying operating conditions.
Solution Approach 2:
The system changes the relaxation time parameter based on temperature and charge rate inputs. By making this key parameter adaptive rather than constant, the system maintains accurate SOC estimation across the full range of operating conditions without requiring overly conservative fixed relaxation times.
3Speed
If voltage measurement is taken immediately after charge cycle, then quick state of charge update is achieved, but voltage has not stabilized leading to inaccurate estimation
Solution Approach 1:
A voltage stabilization period is introduced immediately after the charge cycle completes. During this preliminary measurement phase, the system monitors voltage at multiple points to detect when the Open Circuit Voltage has stabilized. This ensures accurate voltage measurement without requiring an excessively long fixed wait time, thus balancing speed and precision.
Solution Approach 2:
The system uses feedback from continuous voltage monitoring during the relaxation period to determine when measurement can proceed. By checking whether voltage changes between successive measurements are below a threshold, the system dynamically determines the optimal measurement timing, ensuring accuracy while minimizing unnecessary delay.
Data Source
AI summary
An electrified vehicle includes a traction battery that is operated according to a state of charge of the traction battery. A controller is programmed to operate the traction battery according to the state of charge of the traction battery and, in response to completion of a charge cycle of the traction battery, generates an adaptive relaxation time and an adaptive compensation voltage of the state of charge that changes with a temperature and a charge rate of the traction battery. The controller is further programmed to, in response to expiration of the adaptive relaxation time after completion of the charge cycle, update the state of charge to a value corresponding to a voltage defined by a difference between a measured voltage of the traction battery and the adaptive compensation voltage.