Normalized Voltage Calculation for Battery State of Charge
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Solution Overview
Problem
Existing battery management systems face challenges in accurately determining the state of charge and health of battery cells, particularly in lithium sulphur and lithium ion batteries, due to variations in current flow during charge and discharge cycles, which complicates the interpretation of voltage measurements.
Innovation Solution
A battery management system that includes a cell monitoring device to measure current and voltage at multiple times and a controller to calculate normalized voltages, independent of the current flow, allowing comparison to reference profiles to estimate state of charge and health, using normalization factors that account for resistance and temperature changes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Productivity
If voltage measurements are taken during charge/discharge cycles with varying current flow, then battery performance monitoring is enabled, but measurement precision deteriorates due to current variations affecting voltage interpretation
Solution Approach 1:
The patent transforms the measured voltage and current into a normalised voltage parameter that is independent of current flow magnitude. This parameter transformation allows voltage measurements taken during varying current conditions to be compared against reference profiles, thereby maintaining measurement precision for state of charge determination while enabling continuous monitoring during dynamic charge/discharge cycles
Solution Approach 2:
The patent introduces normalised voltage as an intermediary parameter between the raw voltage measurement and the state of charge determination. This intermediary accounts for the effects of varying current and resistance, allowing accurate state of charge estimation without requiring constant current conditions
2Adaptability or versatility
If current flow varies during charge and discharge cycles, then battery usage flexibility is improved, but state of charge determination accuracy deteriorates
Solution Approach 1:
The system changes the parameter from raw voltage to normalised voltage, which is calculated by adjusting the measured voltage based on the measured current and resistance characteristics. This parameter change enables accurate state of charge determination regardless of whether the battery is charging or discharging at varying current rates
Solution Approach 2:
The patent implements a dynamic calculation approach where the normalised voltage is continuously adjusted based on real-time measurements of current and resistance. This dynamic adaptation allows the system to maintain measurement accuracy throughout varying charge/discharge cycles without requiring fixed operating conditions
Data Source
AI summary
A battery management system for determining a time series of normalised voltage of at least one battery cell corresponding to a time period during which a first current flows through the at least one battery cell. The battery management system comprises a cell monitoring device configured to measure a current flowing through the at least one battery cell and a voltage of the at least one battery cell at a plurality of different times during the time period; and a controller configured to determine a normalised voltage of the at least one battery cell for each of the plurality of different times, in dependence on the measured current and measured voltage corresponding to that time, wherein the determined normalised voltages at the plurality of different times form a times series of normalised voltage, wherein the normalised voltage at each of the plurality of different times corresponds to an estimate of a voltage of the at least one battery cell if a second constant current were flowing through the battery cell throughout the time period, where the second constant current is different to the first current.