A Direct Three-Phase AC to DC Rectifier with a High-Frequency Open Delta Transformer Isolation

This paper proposes a new direct three-phase AC-DC rectifier with high-frequency open-delta transformer isolation. The three-phase input voltages are modulated by two AC to AC converters to generate a high-frequency link at 20 kHz. The high-frequency link is then interfaced to a 12-pulse rectifier by means of a high-frequency open-delta transformer arrangement. The resultant output voltage is shown to be high quality and its magnitude is controllable via phase shift modulation. Moreover, the proposed modulation allows the high-frequency converter to achieve soft switching. The output DC voltage can be regulated via a simple duty cycle control. The overall three-phase input currents are of high quality and near unity power factor due to the cancellation of 5^th and 7^th harmonics. The proposed approach substitutes the bulky line-frequency transformer with a high-frequency transformer, thereby achieving higher power density. Simulation results demonstrate the validity of the concept. Experimental results on a laboratory prototype system demonstrate the feasibility of the proposed approach.