Six switches solution for single-phase AC/DC/AC converter with capability of second-order power mitigation in DC-link capacitor

This paper proposes an approach for DC-link second-order harmonic power cancellation in single-phase AC/DC/AC converter with reduced number of switches. The proposed six-switch converter has two bridges with three switches in each of them, where the middle switch in each bridge is shared by the AC/DC rectifier and DC/AC inverter. A small size DC-link capacitor can be achieved through coordination control of rectifier and inverter to cancel the second-order oscillation power. Maximum available phase difference between rectifier's and inverter's modulation references is investigated to be dependent on their modulation indices of the six-switch converter, and high modulation indices are proved to be feasible for second-order power cancellation in the DC-link based on the phase difference analysis. Both reduced switch numbers and DC electrolytic capacitor size can be achieved using the proposed converter. Simulation results are provided to validate the effectiveness of the topology and control of the proposed six-switch AC/DC/AC converter.