Measuring battery status with ultrasound: cheaper, more reliable than BMS

December 01, 2017 // By Christoph Hammerschmidt
To determine the durability and health status of a battery as well as the resulting driving range of the vehicle, complex battery management systems (BMS) are in use. Such systems they are rather prone to error. In the SoCUS project, the Fraunhofer R&D Center for Electromobility Bavaria is developing cost-effective sensor systems that can be integrated directly into the battery and can measure the state of charge more accurately than commercially available systems.

Available BMS detect the state of charge for each cell based on current and voltage. As the calculations of such systems are based on default values, they are prone to error. Especially with frequent partial charge and certain battery cell types, no precise measurement of the state of charge is possible. In addition, these systems consume some of the battery energy themselves.

The approach developed by Fraunhofer ISC makes it possible to measure the state of charge using ultrasonic pulses. The density of the negative anode - which changes with the state of charge of the cell - is measured and evaluated directly.

This method combines several benefits: Since there is a linear relation between state of charge and measurement signal, the evaluation is simpler and more accurate than known technologies. A measurement unit can monitor several battery cells at the same time and detects the state of charge only during charging and discharging, a permanent control is not necessary. This saves additional energy and costs. Since the ultrasound signal correlates directly with the mechanical properties of the cell, aging processes are better taken into account. This allows more specific conclusions about the remaining capacity and thus, the performance of the battery.

The new sensor system is suited for all kinds of battery types but has been especially tested for lithium-ion batteries. Typical fields of application are electric vehicles, stationary storage systems, and drones.

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