Sensor aids accurate range assessment for the BMW i3

17th September 2014
Nat Bowers

An integrated automotive sensor interface, from ams, has been utilised by BMW in the battery sensor of the i3 series EVs. The battery management system (BMS), which monitors the voltage and current of the 400V li-ion battery powering the electric motors, uses the AS8510 to provide extremely accurate measurements. This enables an accurate estimation of the range the vehicle can cover before the battery is completely discharged.

Energy storage and battery life optimisation are essential for EVs to provide customers with sufficient range and reliability. The BMS requires accurate current and voltage measurements to make a highly accurate calculation of a li-ion battery’s state of charge. Utilising the AS8510 and a special calibration scheme, the sensor system in the BMS is able to measure current to an accuracy of just ±0.5% and voltage to an accuracy of better than ±0.1%.

Operating over a temperature range from -40 to +125°C, the AEC-Q100 qualified AS8510 integrates data acquisition front ends which include two independent 16-bit sigma-delta ADCs. One channel measures current across a shunt resistor from milliamps up to 1kA and provides a digital output via a serial peripheral interface. The second channel can capture three different voltage sources simultaneously with current samples.

Easing the design of the i series’ current and voltage measurement system, the AS8510 features zero-offset architecture, low noise, high linearity, multi channel architecture and low drift. The device supports the functional safety compliance efforts of car manufacturers according to ISO26262.

Bernd Gessner, Vice President and General Manager, Automotive Business Unit, ams, comments: "The techniques for monitoring the state of charge and the state of health in electric vehicle batteries are constantly being refined and improved, and BMW has set a new benchmark in battery management system design in the new i3 model. ams is proud to have supported BMW’s advanced implementation of ultra-accurate battery parameter measurement in the demanding environment of a vehicle drivetrain."

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