Direct Measurement of the Current Derivative Using a Delta-Sigma Modulator for Sensorless Traction Motor Control

This paper discusses a new method of direct measurement of the current derivative applied to determine an electric motor inductance required for efficient and reliable control of sensorless AC electric drives. The method is based on the measurement of the voltage drop across a calibrated inductor implemented into the power circuit of the motor drive inverter. In order to increase accuracy and reduce transients and oscillations the measured voltage drop is processed using a delta-sigma modulator. The data stream generated by the modulator is then transferred to a microcontroller supported demodulation for further processing and filtering. The paper also presents the results of experimental investigations of three different shunt inductors. The results demonstrate a high accuracy and noise immunity of the proposed method.