Direct Torque Control of PM Brushless AC Motors Having Non-sinusoidal Back-emf Waveforms

This paper describes the application of direct torque control (DTC) to a PM brushless AC machine whose back-emf waveform is non-sinusoidal, and compares its performance with that which is achieved when the back-emf waveform is assumed to be sinusoidal. It also demonstrates the utility of employing a sliding mode observer to estimate the back-emf waveform, and, thereby, to calculate the instantaneous electromagnetic torque and to minimise torque ripple. The effectiveness of this approach is validated by both simulations and measurements.