Comparison of Naturally Sampled PWM techniques in ultrahigh speed drives

Naturally Sampled Pulse Width Modulation (NS-PWM) is the most favourable form of modulation, because natural sampling does not introduce distortion or a delayed response. Three different NS-PWM techniques, the Sinusoidal, the Sinusoidal with third-harmonic reference injection and the Space Vector Modulation are studied and compared by simulation in ultrahigh speed drives, where the frequency ratio is low owing to the necessarily high fundamental frequency. It was found that all techniques are proned to generate DC current in the stator windings independently of considering or neglecting the dead-time of switches. Furthermore subharmonic flux and current components with considerable amplitudes can also be generated.