A Three-Phase Isolated Rectifier using Current Unfolding and Active Damping Methods

This paper discusses a three-phase isolated rectifier with integrated buck functionality, derived from an unfolding three-phase inverter and a 7-level forward converter. Its operating principle is based on current shaping and unfolding methods. The circuit consists of 10 diodes, 3 low-frequency bidirectional switches and 8 high-frequency switches. It operates as a current source converter and requires only 3 filter capacitors at the ac input and a dc filter inductor at the dc output. Parasitic inductances from the ac grid enable direct connection to the utility. This paper discusses the basic operating principle and control method of the proposed inverter. It proposes a new unsymmetrical modulation method that can reduce switching frequency while maintaining the accuracy of current sampling. Also, an active damping method is used to overcome intrinsic oscillation due to unfolding operation. Finally, experimental verification is carried out to confirm stable operation of the proposed three-phase isolated rectifier.