Modulation scheme for delta-type current source rectifier to reduce input current distortion

To reduce the conduction loss, a novel three-phase current source rectifier, named Delta-type Current Source Rectifier (DCSR), has been proposed in previous research. This rectifier has delta-type connection on its input side, and its dc-link current can be shared by multiple devices at a time to reduce up to 20% conduction loss. A high-efficiency modulation scheme for DCSR has been proposed, where the conduction states involve more switches to share the dc-link current. However, it causes current distortion when the input voltages have intersections. In this paper, the phenomenon is analyzed in detail. The clamped voltage on the diode bridge will fluctuate at the voltage intersections, resulting in false current pulse and distortion. An improved modulation scheme is then proposed for DCSR to reduce the input current distortion without sacrificing much efficiency. Through experiment in a 7.5 kW prototype, its effectiveness is verified and the total harmonic distortion (THD) of the input current is reduced dramatically.