AC-DC-AC Three-Phase Converter Based on Three Three-Leg Converters Connected in Series

A unidirectional ac-dc-ac three-phase dc-link converter is proposed in this paper. It is composed of three unidirectional ac-dc-ac three-leg converters. The three-leg converter is composed of a noncontrolled leg, two controlled legs, and a dc-link. A suitable model and control strategy of the system, including a synchronization method, are proposed. The synchronization method, associated with the pulse width modulation (PWM) strategy, imposes that the grid currents and load voltages have the same phase angle of the converter voltages. This method ensures sinusoidal grid currents and mitigate the zero-crossing distortions normally caused by the use of diodes. Simulation and experimental results are also presented for validation purposes.