Battery Available SOC Estimation Using Instantaneous Voltage
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Solution Overview
Problem
Existing methods for estimating the state of charge (SOC) of a battery fail to accurately account for the effects of temperature and current, particularly at high currents, leading to inaccuracies in determining the available SOC.
Innovation Solution
A method that determines the stored state of charge (SOC) using open-circuit voltage and temperature, measures instantaneous voltage, and calculates available SOC by the product of the stored SOC, the difference between instantaneous and minimum permissible voltage, and open-circuit voltage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If coulomb counting method is used to estimate state of charge, then the stored capacity information is obtained, but the available state of charge becomes inaccurate due to unaccounted internal impedance effects
Solution Approach 1:
The patent introduces an intermediary variable (instantaneous voltage) that mediates between the stored state of charge and the available state of charge. By measuring voltage and using it as a mediator to calculate the ratio of available to stored capacity, the system accurately accounts for internal impedance effects without requiring complex direct measurements of impedance or temperature-dependent capacity models.
Solution Approach 2:
The battery itself provides the necessary information for correction through its terminal voltage. The voltage measurement automatically reflects the combined effects of state of charge, internal impedance, temperature, and current without requiring external sensors or complex modeling. The system uses the battery's own electrical characteristics to self-correct the SOC estimation.
2Reliability
If high current is applied to test battery capacity, then the available capacity at operating conditions is revealed, but battery temperature increases making the test invalid for specific temperature points
Solution Approach 1:
The patent performs preliminary action by measuring the open-circuit voltage before applying load and correcting the SOC estimation in advance. By establishing the relationship between open-circuit voltage and stored capacity before high-current operation, the system can predict and correct for the upcoming voltage drop due to internal impedance, making the SOC estimation accurate even before temperature rise occurs.
Solution Approach 2:
The system uses real-time voltage measurement as feedback to continuously update the available state of charge estimation. The measured terminal voltage feeds back into the calculation to determine the ratio of available to stored capacity, dynamically adjusting the SOC estimation as conditions change during high-current operation without requiring temperature compensation.
3Measurement precision
If multiple parameters (temperature, current, voltage) are measured to account for internal impedance effects, then the available state of charge accuracy improves, but the system complexity and measurement requirements increase
Solution Approach 1:
The patent extracts only the essential measurement (terminal voltage) needed to account for internal impedance effects, eliminating the need to measure temperature, current, or directly measure internal impedance. By extracting and using only the voltage parameter, the system achieves accurate available SOC estimation while minimizing measurement complexity.
Solution Approach 2:
The terminal voltage measurement serves multiple functions simultaneously: it indicates the state of charge, reflects the internal impedance effects, accounts for temperature variations, and provides the correction factor for available capacity. This single universal measurement replaces what would otherwise require multiple separate sensors and measurements.
Data Source
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AI summary
The invention relates to a method for estimating the state of charge of a battery, the method comprising the following steps: • - determining the stored state of charge; • - determining the open-circuit instantaneous voltage of the battery according to a predetermined map and the stored state of charge; • - measuring the instantaneous voltage across the terminals of the battery; • - determining the available state of charge according to the stored state of charge, the instantaneous voltage, the open-circuit instantaneous voltage and the minimum acceptable voltage; • - the minimum acceptable voltage being predetermined by design.