Increase of maximum output-voltage in 3-phase buck PWM by discontinuous-switching-modulation

The discontinuous-switching-modulation scheme has been developed and practically applied to the 3-phase voltage-source-inverters to improve the de-voltage utilization factor. The discontinuous-switching-modulation is, however, easily applicable to 3-phase current-source-inverters/rectifiers by applying the delta-current-modulation scheme that had been developed by one of the authors. This paper shows that the maximum controllable de-voltage of the 3-phase buck-type PFC rectifiers can be increase by 15% compared to the conventional continuous-switching-modulation scheme by means of the discontinuous-switching-modulation. Because the de-voltage increase while the switching is interrupted in 1/3 fundamental period, both the de-current and the average switching frequency decrease in discontinuous-switching-modulation. Thus, the conduction losses (produced by the switching devices and the de-inductor) as well as the switching losses decrease. As a result, the efficiency increases. The theory of the discontinuous-switching-modulation in the 3-phase buck PFC rectifier is described in detail and the validity is confirmed through experimental results obtained from a four kW-class setup.