EV Battery SOC Calibration Using On-Board Discharge Scheduling
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Solution Overview
Problem
Current methods for state of charge (SOC) calibration of electric vehicle batteries are complex, expensive, and prone to errors, requiring time-consuming conditioning to avoid flat regions of the OCV-SOC curve, leading to vehicle downtime.
Innovation Solution
A method and discharge circuit that determine a predicted time duration for SOC calibration, scheduling a time slot to discharge the battery to a steep part of the OCV-SOC curve using an on-board discharge circuit without external connection, allowing for accurate recalibration during predicted downtime, such as during vehicle parking.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If traditional SOC calibration methods are used requiring external discharging systems and time-consuming conditioning, then measurement precision is improved, but loss of time increases significantly
Solution Approach 1:
The vehicle's own traction motor is utilized as the discharge load for SOC calibration, eliminating the need for external discharging systems. The control unit manages the motor to discharge the battery to the steep part of the OCV-SOC curve during predicted downtime, enabling the vehicle to perform its own calibration service without external assistance.
Solution Approach 2:
The system predicts future downtime periods and schedules SOC calibration to be performed during these predetermined time slots before they occur. By analyzing historical data and predicting when the vehicle will be stationary, the system proactively schedules calibration tasks to be completed during these windows, avoiding delays to operational schedules.
2Measurement precision
If complex SOC estimation functions are implemented, then measurement precision is improved, but device complexity increases
Solution Approach 1:
The system replaces complex mechanical/electrical calibration equipment with a software-based control unit that manages motor operation for calibration. Instead of using sophisticated external measurement devices, the control unit uses the vehicle's existing motor and battery management systems to perform calibration, substituting complex hardware with intelligent control algorithms.
3Measurement precision
If battery conditioning is performed to reach suitable SOC-OCV curve points, then measurement precision is improved, but loss of time increases
Solution Approach 1:
The system changes the operating parameters of the battery by controlling the motor to discharge the battery to specific SOC ranges corresponding to the steep part of the OCV-SOC curve. Instead of passive conditioning that waits for natural voltage stabilization, the system actively adjusts the discharge state to reach optimal calibration points, significantly reducing the time required to achieve accurate measurement conditions.
Data Source
AI summary
A method for performing SOC calibration for an electrical energy storage system of an electrified vehicle is described The method includes determining a predicted time duration needed to complete a SOC calibration, scheduling a time slot sufficient for completing the SOC-calibration according to the predicted time duration, the scheduled time slot being during a predicted downtime for the electrified vehicle, wherein when at the scheduled time slot: discharging the electrical energy storage system to a steep part of an open circuit voltage versus SOC curve of the electrical energy storage system by an on-board discharge circuit within an acceptable time duration without connecting the electrical energy storage system to a discharging system external to the vehicle; once at an open circuit voltage with gradient with respect to SOC exceeding a threshold indicative of a steep part of the open circuit voltage versus SOC curve, measuring an electrical energy storage system voltage to re-calibrate the SOC of the electrical energy storage system.