In this paper we propose a suitable reference wave for Pulse Width Modulation (PWM) AC Drives. Staircase reference waves whose levels are calculated to eliminate certain harmonics are studied and a certain staircase reference waveform with L levels is constructed. When L is made very large in limit, this staircase waveform approaches a continuous one which is called Quasine (Quasi + Sine). This approach compared to the classical harmonic elimination method has the advantage that the magnitude of non-triplen harmonics is reduced. A computer program by TURBO PASCAL 6 was developed to enable us to have a comparison between the harmonic contents of output voltage for various reference waveforms.