Time-varying feedback gains for power circuits with active waveshaping

This paper presents a line interfaced inverter that employs a dc-dc converter to actively shape its ac current waveform. The duty cycle applied to this converter to control the current is determined in a closed loop fashion. The incremental dynamic response of the power circuit is found to be highly dependent on the ac voltage and current waveforms and therefore varies on a 60 Hz basis. With fixed feedback gains this variance would give closed loop poles that moved during the cycle. To avoid the problems that a time-varying system response would cause, a novel control scheme is proposed. This scheme uses periodically varying feedback gains to counteract the power circuit´s time dependent response in a way that gives closed loop poles that do not move. Results of a Parity Simulation are included to verify the validity of this approach.