A Generic Six-Step Direct PWM (SS-DPWM) Scheme for Current Source Converter

This paper aims to explore the pulsewidth modulation (PWM) schemes for three-phase current source converter, and a generic six-step direct PWM (SS-DPWM) scheme is proposed. In the SS-DPWM, one line cycle is divided into six 60° intervals, so called as ¿six-step.¿ During each interval, only two of the three references, referred to as the
Master
and
Slave
references, respectively, compare with the carriers to directly generate the required switching patterns instead of using the transformation from bilogic signals to trilogic ones, as used in the conventional sinusoidal PWM (SPWM). In this paper, the variety of the
Slave
reference for each interval is identified, and many sets of modulating waveforms are presented for the SS-DPWM, resulting in very flexible and expanded modulations. The mechanism of the SS-DPWM is also presented to develop its modulating characteristics, and it is shown that, comparing with the conventional SPWM, the SS-DPWM has lower switching frequency, higher dc current utilization ratio, and in-phase transfer between the line currents and their references. A prototype has been built in the lab and the validity of the theoretical analysis is verified by the experimental results.