Battery SOH Estimation Using Rest-Period OCV and Current Integration
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Solution Overview
Problem
Existing methods struggle to accurately determine the State Of Heath (SOH) of a battery at rest due to limitations in determining State Of Charge (SOC) changes and accounting for error components during rest periods.
Innovation Solution
A battery management system that measures battery current and voltage, calculates integrated current values, and determines SOC changes during rest periods, while also accounting for offset errors and rest times to weight the accuracy of SOH determination.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the OCV-SOC curve is used to determine SOC after a predetermined time has passed since the battery shifted from the cycle state to the rest state, then the SOC determination is free from hysteresis effects, but the response time is delayed and the battery cannot be monitored during the stabilization period
Solution Approach 1:
The patent segments the rest period into multiple time intervals (first rest period, second rest period, third rest period) with different determination methods. During the first rest period (stabilization phase), the system uses a different approach than during subsequent periods, allowing continuous monitoring while accounting for hysteresis effects in each segment
Solution Approach 2:
The patent dynamically adjusts the SOC determination method based on the battery's state and time elapsed. The system transitions from one determination approach during stabilization to another after stabilization, and continues to adapt during subsequent rest periods, optimizing both response time and accuracy dynamically
2Adaptability or versatility
If ampere counting or Kalman filter is used to determine SOC during the cycle state, then the method is suitable for dynamic conditions, but the accumulated offset error of the current sensor degrades accuracy over time
Solution Approach 1:
The patent implements feedback by using OCV-SOC curve determination during rest periods to correct and verify the SOC values obtained from ampere counting during cycle states. This feedback mechanism detects and compensates for accumulated offset errors in the current sensor by comparing against the hysteresis-free OCV-based measurements
Solution Approach 2:
The OCV-SOC curve determination during rest periods acts as an intermediary that bridges and corrects the accumulated errors from cycle state measurements. This intermediary measurement method provides a reference point that resets and validates the SOC tracking, eliminating the cumulative error problem
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
Enables accurate determination of SOH during rest periods by accounting for SOC changes and error components, improving the reliability of battery health assessment.
Implementation Method 1
it is more desirable to determine the SOC of the battery based on an OCV-SOC curve which is data defining a correlation between Open Circuit Voltage (hereinafter referred to as 'OCV') and SOC of the battery
Implementation Method 2
the voltage across the battery is not maintained constantly due to hysteresis generated by a cycle history in the cycle state
Data Source
AI summary
A battery management system includes a current sensor to measure a battery current through a battery, a voltage sensor to measure a battery voltage across the battery, and a control circuit. In response to a key-on signal during a first rest period of the battery, the control circuit determines a fixed rest time, a fixed Open Circuit Voltage (OCV) and a fixed State Of Charge (SOC), and determines an integrated current value of the battery current during a cycle period of the battery. In response to a key-off signal during the cycle period, the control circuit starts a second rest period of the battery. The control circuit determines an interest SOC corresponding to an interest OCV, i.e., the battery voltage during the second rest period. The control circuit determines a State Of Heath (SOH) of the battery based on the fixed SOC, the integrated current value and the interest SOC.