Chapter 6 Power Electronic Converters

This chapter describes some approaches to applying frequency-selective averaging to modeling the dynamic behavior of pulse-width modulated (PWM) and line-commutated converters. We start with the case that is considered practical when the switching frequency is considerably (say two orders of magnitude) higher than the highest frequency of the waveform being synthesized at the converter’s output (say low frequency AC or even DC). As expected, the modeling procedure is reasonably straightforward, and only issues such as unbalance in polyphase AC systems could make it challenging. In the second section, we look at the case when the switching frequency is closer to the highest frequency being synthesized or observed, colloquially labeled as low-frequency switching (the labels clearly refer to relative separation among frequencies and not to their actual values). A different type of challenge is encountered in the third section when modeling systems with semi-controllable switches (such as thyristors) or converters in which uncontrollable switches (such as diodes) play a key role. In the final section, we briefly review the application of four different nonlinear control design procedures to the nonlinear dynamic phasor model derived in the preceding section and observe the versatility and utility of dynamic phasors models.