Switched Capacitor Battery Impedance Measurement
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Solution Overview
Problem
Conventional battery impedance measurement methods in automotive applications, particularly with lithium ion cells, face challenges due to high current discharge leading to battery depletion and power dissipation, which limits measurement frequency and accuracy, especially at high temperatures.
Innovation Solution
A device and method utilizing a switched capacitor network between a battery and an energy storage to alternately flow current, reducing current consumption by using an essentially rectangular current waveform, allowing for more efficient energy storage and reuse, thereby minimizing battery discharge and power dissipation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a sinusoidal current is drawn from the battery for impedance measurement, then the impedance measurement can be performed, but the battery is discharged to a non-negligible extent and high power dissipation occurs
Solution Approach 1:
The patent introduces an energy storage device (capacitor) as an intermediary between the measurement device and the battery. The capacitor stores energy during the charging phase and releases it during the discharging phase, enabling the measurement device to draw current from the capacitor rather than directly from the battery. This mediator allows the battery to remain in a relatively stable state while still enabling accurate impedance measurements.
Solution Approach 2:
The patent employs periodic charging and discharging cycles of the capacitor. During the first phase, the capacitor is charged from the battery; during the second phase, the capacitor discharges to provide measurement current. This periodic action allows the system to accumulate energy over time and reuse it, significantly reducing the continuous drain on the battery and minimizing power dissipation while maintaining measurement accuracy.
2Measurement precision
If high current is drawn from the battery to sense significant voltage variation, then the voltage variation can be detected, but the impedance measurements discharge the battery and cause power dissipation
Solution Approach 1:
The patent performs preliminary energy accumulation by charging the capacitor before the actual impedance measurement takes place. The capacitor is pre-charged from the battery during a dedicated charging phase, storing sufficient energy to support the measurement process. This preliminary action ensures that when measurement current is required, it can be drawn from the pre-charged capacitor rather than directly from the battery, enabling voltage variation detection without immediate power dissipation from the battery.
Solution Approach 2:
The patent implements an energy recovery mechanism where the capacitor that was charged from the battery is then discharged back to the battery or reused in subsequent measurement cycles. Instead of allowing the energy to be dissipated as heat during measurement, the system recovers the energy by directing the discharge current back to the battery or storing it for future use, thereby reducing net power dissipation while maintaining the ability to detect voltage variations.
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
This approach reduces current consumption by approximately 64% and achieves a current reduction of about 27% compared to conventional sinusoidal methods, enhancing measurement frequency and accuracy while minimizing battery depletion and temperature variations.
Implementation Method 1
a switched capacitor network coupled between the first terminals and the second terminals
Data Source
AI summary
A device for battery impedance measurement includes a switched capacitor network, a controller configured to operate the switched capacitor network to cause an alternating current to flow between a battery and an energy storage; and measurement circuitry configured to measure the alternating current flowing to or from the battery and a voltage across the battery.