Effects of low switching frequency on synchronous AC drives

We present analytical results and numerical simulations that quantify effects of low switching frequency in AC drives. These results build on our related results for DC converters. Specifically, we reexamine the models of pulse-width modulated (PWM) inverters that are used in high efficiency AC drives. The standard modeling procedure assumes that the switching frequency of the PWM block is high enough, so that resulting supply waveform can be replaced by its first harmonic in control-oriented models. There are practically important cases when characteristics of available semiconductor switches (or of the heat removal system) limit the switching frequency, thus mandating a re-evaluation of standard models. We use tools from averaging theory to model the PWM policy known as space vector modulation, which is commonly used in high performance drives, and derive results that are relevant for a number of AC drives.

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