Battery State of Charge Initialization via Open-Circuit Voltage
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Solution Overview
Problem
Existing battery management systems for hybrid and electric vehicles face challenges in accurately determining the state of charge and state of ageing of batteries, particularly due to errors in impedance models and the need for immediate correction of voltage drops during operation, which can lead to rapid battery ageing and potential damage.
Innovation Solution
A method that initializes and operates a battery management system by reading stored battery variables, measuring open-circuit voltage, and determining the state of charge using a combination of last stored and instantaneous values, with a plausibility check and weighted averaging, allowing for safe initialization and continuous monitoring without relying on impedance models.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If impedance models are used to correct voltage drops during operation, then the state of charge can be determined during operation, but measurement precision deteriorates due to errors in the impedance models
Solution Approach 1:
The patent applies preliminary action by measuring the open-circuit voltage during initialization (when no current flows) to obtain an accurate reference state of charge value before operation begins. This pre-measured accurate value is then used to correct or validate the impedance model-based calculations performed during operation, thereby maintaining measurement precision while enabling continuous monitoring.
2Productivity
If the battery management system is initialized with impedance model corrections, then continuous monitoring is enabled, but reliability decreases due to model errors affecting battery safety
Solution Approach 1:
The patent implements feedback by continuously comparing the state of charge values obtained from impedance models during operation with the accurate reference value obtained during initialization. When deviations exceed a threshold, the system triggers corrections or alerts, thereby maintaining reliability and battery safety while preserving continuous monitoring capability.
3Measurement precision
If only instantaneous open-circuit voltage measurement is used for state of charge determination, then measurement precision is high, but loss of information occurs because the last stored state of charge is not utilized
Solution Approach 1:
The patent merges the instantaneous open-circuit voltage measurement (which provides high precision) with the last stored state of charge value (which preserves historical information). By combining these two data sources during initialization, the system achieves both high measurement precision and retention of information, as the stored value serves as a reference that complements the instantaneous measurement.
Data Source
AI summary
A method for initializing and operating a battery management system is disclosed. The method comprises the following steps. First, start the battery management system. Next, read battery variables which are stored in a nonvolatile memory of the battery and comprise the last state of charge of the battery. Then measure the open-circuit voltage of the battery. Next, determine an instantaneous state of charge value on the basis of the measured open-circuit voltage. Then determine an estimated value of the state of charge of the battery as a function of both the stored last state of charge of the battery and the instantaneous state of charge value. Then initialize the state of charge in the battery management system using the determined estimated value of the state of charge. Finally, operate the battery management system with the initialized values.