Modeling of PWM inverter-supplied AC drives at low switching frequencies

Presents analytical results, numerical simulations, and experiments that quantify effects of low-switching frequency in ac drives supplied by pulsewidth modulated (PWM) power electronic inverters. Specifically, the paper re-examines models of PWM inverters in cases when the switching frequency is only an order of magnitude higher than the fundamental of the ac waveform being synthesized. While the case of permanent magnet synchronous motor is studied in detail, the presented modeling procedure is applicable to other ac drives. Analytical results derived in the paper build on related results for do converters, and address the case of the PWM switching policy denoted as space vector modulation in industrial practice. Conventional modeling procedures assume that the PWM switching frequency is high enough so that the resulting waveform can be replaced by its first harmonic in control-oriented models. This paper provides analytical formulas in terms of the system parameters that quantify the deviations introduced by a slow PWM switching frequency.