Analysis of Effect of Grid Harmonics and Unbalance on DAB-Based Three-Phase Single-Stage AC-DC Converter and Solutions

In this article, the actions of the dual active bridge (DAB)-based three-phase single-stage ac-dc converter under the nonideal grid conditions and corresponding solution are researched for the first time. The average state-space model of the converter is built first. Then the effect of grid harmonics and unbalance on the three-phase grid current are analyzed and it reals the grid current harmonics, and unbalance is caused by the distorted grid. In order to solve this problem, a proportional-resonant (PR) + reduced parallel repetitive control closed-loop controller of grid current in the two-phase stationary frame is proposed. The parameter constraint and frequency-domain characteristics of the proposed compound controller are analyzed in detail. The detailed experimental results verify the correctness of the theoretical analysis and the feasibility of the proposed closed-loop controller.