EV Battery Pack OCV Estimation for Fast Power Limit Control
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Solution Overview
Problem
Existing battery management systems in electrified vehicles face challenges in accurately estimating the state of charge (SOC) and power limits due to the time required for open circuit voltage (OCV) stabilization, especially at colder temperatures and with larger battery cell counts, which affects regulatory compliance and computational demands.
Innovation Solution
A vehicle system estimates OCV using voltage measurements and a decay parameter that is a function of the last deactivation voltage and time, employing non-linear regression models to improve accuracy, allowing for rapid and precise SOC and power limit estimation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the system waits for OCV stabilization before estimation, then measurement precision improves, but loss of time increases
Solution Approach 1:
The system performs preliminary voltage measurements during the stabilization period and uses decay parameters to predict the final OCV value before complete stabilization occurs. This allows the estimation to be made in advance of full equilibrium, reducing waiting time while maintaining accuracy through compensatory calculations.
Solution Approach 2:
The system changes the estimation approach by introducing decay parameters that account for the transient behavior of battery voltage during stabilization. By modeling the voltage decay characteristics, the system can extrapolate the equilibrium OCV from intermediate measurements, transforming the problem from waiting for stabilization to actively predicting the stabilized value.
2Measurement precision
If the system uses traditional OCV stabilization waiting, then measurement precision improves, but productivity decreases
Solution Approach 1:
The system performs preliminary calculations using decay parameters and intermediate voltage measurements to estimate OCV before complete stabilization. This preliminary estimation enables the vehicle control system to determine SOC and power limits faster, improving vehicle activation readiness while maintaining estimation accuracy through the decay compensation model.
Solution Approach 2:
The system skips the complete stabilization waiting period by using decay parameter modeling to predict the final OCV value. This rushing through of the stabilization process allows the system to obtain accurate estimates faster, directly improving productivity by reducing the time to vehicle readiness without sacrificing measurement precision.
3Loss of time
If the system measures OCV immediately after deactivation, then loss of time decreases, but measurement precision worsens due to voltage decay
Solution Approach 1:
The system changes from direct OCV measurement to a predictive estimation approach using decay parameters. By measuring voltage at intermediate times and applying decay compensation calculations, the system can obtain accurate OCV estimates immediately after deactivation without waiting for stabilization, thus reducing time loss while maintaining precision through the decay model.
Solution Approach 2:
The decay parameter acts as an intermediary that bridges the gap between immediate voltage measurements and the true equilibrium OCV value. By using this intermediary parameter to compensate for voltage decay effects, the system can accurately estimate OCV at any time point after deactivation, enabling immediate measurement with preserved precision.
Data Source
AI summary
An electrified vehicle (EV) includes a battery pack, one or more sensors, and a vehicle controller. The battery pack includes a plurality of battery cells and is operable to provide at least a portion of propulsion power of the EV. The vehicle controller is configured to charge and discharge the battery pack according to power limits defined at activation of the EV by an estimated open circuit voltage (OCV) for each of the battery cells that is based on voltages measured by the one or more sensors after a last deactivation of the EV and a decay parameter that is a function of the voltages and a duration since the last deactivation.