Batteries are
indispensable for electric vehicles and other mobile devices that require
electrical power. Complex battery management systems (BMS) are needed to
estimate, for example, the range and durability of the battery. Therefore, they
determine the state of charge for each cell on the basis of Current (Coulomb
Counting) and Voltage. As BMS calculations 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 energy themselves.
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.
The systems use
ultrasound pulses to measure and evaluate the density of the negative anode
which changes with the state of charge of the cell.
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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