Real-time stator resistance estimation for electrical drives : a control perspective

Sammanfattning: The automotive industry is in the middle of a rapid transition towards electrical machines. This transition leads to a higher interest in electrical machine management. In this thesis a stator resistance estimation scheme for field oriented controlled motors is proposed and tested in both simulations and experiments. The proposed scheme uses a DC-current injection in the stationary reference frame with injection in one of the axes. Ohm’s law is used to estimate the stator resistance. The DC-component of the current is found by a zero-crossover detection scheme which calculates the average current over one electric period. The DC-current values is then eliminated from the feedback currents to the field oriented control to minimise disturbances in these controls. The injection is controlled by simple PI-regulators in both axes of the stationary frame to compensate for the cross-coupling between the α and β axis currents. Simulations shows that the accuracy of the estimated resistance improves and the speed of resistance estimation increases when the injection control is applied in both axis. However a continuous implementation of Ohm’s law is highly oscillatory. To prevent this an accumulator is introduced which averages the estimated resistance over several electrical periods. The trade off using this accumulator is that the speed of detection decreases to achieve higher accuracy. Torque oscillations are inevitable when a DC-current component is injected in the motor. But torque oscillations are solely dependent on the injected DC-current level. The experiments show promising initial results in both DC-current estimation and injection control. However future test are required to further improve the accuracy of the resistance estimation.