Abstract
This article proposes a new approach for dc-link second-order harmonic power cancellation in an online uninterruptible power supply based on a single-phase switched-capacitor dc/ac converter. The proposed topology has only one-stage power conversion from ac to dc to ac. The inverter output voltage contains five levels and the magnitude comes with a boost functionality. It has an advantage over the conventional structure in terms of number of power devices, small LC filter size, and less total harmonic distortion with better output waveforms. Because of the high-temperature operability and the faster switching speed of GaN semiconductor based power devices, cooling system size will further decrease, and with less reverse recovery, no snubber circuits are required. 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 and high modulation indices are proved to be feasible for second-order power cancellation in the dc link. Theoretical analysis, simulation, and experimental results are provided to validate the effectiveness of the topology and control of the proposed converter.