Battery Cell Balancing with Parasitic Wire Resistance Compensation
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Solution Overview
Problem
Battery management systems face inaccuracies in state estimation due to parasitic cell connection resistance, which distorts terminal voltage measurements during cell balancing, leading to inaccurate determination of state-of-charge and available power.
Innovation Solution
A method and system to extract parasitic resistance of battery connection wires by controlling pack current and applying balancing current in opposite directions, allowing for accurate determination of parasitic resistance through linear equations, and using these resistances to estimate battery state.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If cell balancing is performed to improve battery performance and lifespan, then battery reliability is improved, but measurement precision deteriorates due to parasitic resistance distorting terminal voltage measurements
Solution Approach 1:
The patent replaces direct voltage measurement with an equivalent electrical measurement approach. Instead of measuring terminal voltage directly during balancing (which is distorted by parasitic resistance), the system measures the voltage across the cell terminals when no balancing current flows, then calculates the actual cell voltage using the measured parasitic resistance and balancing current. This substitution of measurement timing and method eliminates the distortion effect while maintaining the benefits of cell balancing.
Solution Approach 2:
The patent changes the operating parameters for measurement by performing voltage measurements at different current conditions. Specifically, it measures voltage when pack current is zero (no load condition) and when pack current equals balancing current (balanced condition), then uses these parameter differences to calculate parasitic resistance. This parameter change approach allows separation of parasitic resistance effects from actual cell voltage, resolving the measurement precision issue while maintaining reliability improvements from balancing.
2Device complexity
If parasitic resistance is not extracted and compensated, then device complexity is low, but state estimation accuracy deteriorates
Solution Approach 1:
The system performs self-characterization by automatically extracting its own parasitic resistance parameters during normal operation. The BMS uses its existing measurement capabilities to measure voltages under different current conditions, calculates parasitic resistance values, and then uses these extracted parameters to compensate future measurements. This self-service approach improves state estimation accuracy without requiring external calibration equipment or additional hardware complexity.
Solution Approach 2:
The patent performs preliminary extraction of parasitic resistance parameters before they are needed for accurate state estimation. By continuously or periodically measuring and calculating parasitic resistance values in advance, the system prepares compensation data that can be immediately applied to improve SOC and power estimation accuracy. This preliminary action ensures accurate measurements are available whenever needed without adding operational complexity.
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
Improves battery state estimation accuracy by compensating for parasitic resistance, enabling precise determination of cell terminal voltages and states-of-charge, and detecting potential corrosion or connection faults.
Implementation Method 1
determining a total parasitic resistance of the battery connection wires based on the total voltage drop and the balancing current
Data Source
AI summary
When balancing cells in battery packs, the voltage induced by the balancing current across the parasitic wire resistance distorts the measured cell voltage, leading to inaccurate cell state estimation. A method and battery management system to extract a parasitic resistance of battery connection wires connecting a cell of a battery to a cell balancing circuit is disclosed. The parasitic wire resistances for a battery pack are extracted through the coordinated operation of a pack-level current source and cell-level balancing circuit. A voltage drop is imposed and measured across the parasitic resistances while maintaining zero current in the immediate battery cell. Maintaining zero current in the immediate battery cell avoids possible extraction error resulting from voltage drop across the battery cell impedance due to battery cell current flow.