Battery State-of-Charge Estimation via Voltage Logging
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Solution Overview
Problem
Current methods for determining the state-of-charge of a battery are complex and fail to accurately estimate SOC over a broad range of operation conditions, especially in non-equilibrium states and without the need for current shunts, which are cumbersome for small currents.
Innovation Solution
A method that combines coulomb counting during charging with open-circuit voltage measurements over specific time intervals to accurately estimate the total state-of-charge, eliminating the need for current shunts by using a data logger and user equipment to measure and process battery voltage data.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a shunt resistor is used to measure current from/to the battery, then current measurement is achieved, but the voltage drop detection becomes cumbersome for small currents
Solution Approach 1:
The patent extracts the current measurement function from direct voltage drop detection across a shunt resistor. Instead of measuring the small voltage drop directly, the system uses a voltage logger to measure battery terminal voltage and combines it with coulomb counting to determine state-of-charge, thereby avoiding the detection difficulty of small voltage drops.
Solution Approach 2:
The patent introduces an intermediary approach by using open-circuit voltage measurements and coulomb counting as intermediate steps to infer current flow and state-of-charge. Rather than directly measuring current through voltage drop, the system uses these intermediary measurements to calculate SOC without encountering the small signal detection problem.
2Measurement precision
If precise current and voltage measurements are used to determine SOC, then measurement accuracy is improved, but device complexity increases due to requiring shunt resistors and voltage detectors
Solution Approach 1:
The patent removes the shunt resistor component from the measurement system. By extracting the current measurement function and replacing it with voltage-based coulomb counting, the system achieves SOC determination without requiring the complex shunt resistor and voltage detector combination.
Solution Approach 2:
The patent uses a voltage logger to copy and record battery terminal voltage over time. This voltage data is then processed through coulomb counting algorithms to infer current flow and determine SOC, creating a simplified measurement system that copies the essential information needed without requiring direct current measurement hardware.
3Measurement precision
If a complicated model with multiple parameters is used to determine SOC, then SOC estimation accuracy is improved, but method complexity increases
Solution Approach 1:
The patent extracts only the essential parameters needed for SOC determination: battery terminal voltage and cumulative charge/discharge current. By removing unnecessary parameters from complex models, the system achieves accurate SOC estimation with a simplified approach using voltage-based coulomb counting.
Solution Approach 2:
The patent changes the measurement parameters from direct current and voltage to voltage-based coulomb counting. By transforming the measurement approach to integrate voltage measurements over time and calculate cumulative charge, the system achieves accurate SOC with fewer parameters and less computational complexity.
Data Source
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AI summary
The invention relates to a method and a system for calculating a total state-of-charge of a battery, wherein the method comprises wherein the method comprises calculating the total state-of-charge as a coulomb counting state-of-charge, upon determining that the battery is charging. Determining an off period, which is the time period that the battery has not received charge, upon determining that the battery is no longer charging. calculating the total state-of-charge as a constant state of charge being equal to the coulomb counting state-of-charge, upon determining that the off period is shorter than a first time interval Calculating the state-of-charge as a function of the constant state-of-charge and an open circuit voltage state-of-charge determined by means of the voltage across the poles of the battery, upon determining that the off period is shorter than a second time interval, and that the off period is longer than the first time interval. The method further comprises calculating the total state-of-charge by means of the open circuit voltage state-of-charge, upon determining that the off period is larger than the second time interval.