New current control scheme for the Vienna rectifier in discontinuous conduction mode

The Vienna rectifier (VR) is used in applications that require unidirectional, non-isolated, three-phase AC to DC conversion with constant output voltage and sinusoidal input currents. However, because of the unidirectional topology, the input currents become discontinuous at small output power values. As a consequence, the relationship between rectifier input voltage and duty cycle changes compared to continuous conduction mode. Therefore, if no additional measures are taken, the rectifier input currents will be distorted. This work describes a new control scheme that allows operation of the VR with sinusoidal input currents in discontinuous conduction mode (DCM). The limits of operation are described, concerning maximum mains voltage, maximum midpoint current and minimum resistance to the mains in DCM. Further, the noise emission in DCM is compared to continuous conduction mode (CCM) operation. Finally, the proposed scheme is experimentally verified on a hardware prototype.