Analysis and design of a novel, single-stage, three-phase AC/DC step-down converter with electrical isolation

A novel, single-stage, three-phase AC/DC step-down converter with electrical isolation has been presented. The front semi-stage, which is a three-phase AC/DC buck-boost converter, is operated in discontinuous conduction mode (DCM) to achieve unity power factor, pure sinusoidal input current and low total harmonic distortion of input current. The rear semi-stage, which is a DC/DC forward converter, is operated in continuous conduction mode at heavy load and is operated in DCM at light load for step-down voltage conversion. Also, the proposed converter has low voltage stress across the DC-link capacitor. In addition, the sixth times line frequency ripple component of DC-link voltage can be eliminated. Thus, smaller DC-link capacitor is required. Furthermore, the steady-state analysis of voltage gain and boundary-operating condition are discussed. The selections of inductors and capacitors are presented. Finally, simulated and experimental results are supplied to verify the theoretical analysis.