High-accuracy current measurement with low-cost shunts by means of dynamic error correction

Abstract

Abstract. Measurement of electrical current is often performed by using shunt resistors. Thermal effects due to self-heating and ambient temperature variation limit the achievable accuracy, especially if low-cost shunt resistors with increased temperature coefficients are utilized. In this work, a compensation method is presented which takes static and dynamic temperature drift effects into account and provides a significant reduction of measurement error. A thermal model of the shunt resistor setup is derived for this purpose and a suitable calibration method is developed. The correction algorithm is based upon a digital filter bank and is optimized for microcontrollers with low computational complexity. It is implemented in laboratory test equipment for long-term studies on automotive lithium-ion cells. For a 600 A current pulse, it reduces the measurement error from 2 % to less than 0.1 %. Measurements with a real-life testing profile show a reduction of remaining measurement error by 60 %. Statistical results for 100 test systems and long-term drift measurements prove the reliability of the method. The proposed dynamic error correction algorithm therefore allows high measurement accuracy despite the use of low-cost shunt resistors.