Abstract

The purpose of this paper is to develop a model and propose control strategies to mitigate dc-link current ripple for current-source grid-connected converter (CSGCC) under unbalanced grid conditions. Based on the model of instant active power under unbalanced grid conditions, this paper proposes the optimized negative-sequence current references for eliminating the double-frequency oscillations on active power at ac side of CSGCC. Both the single CSGCC and the paralleled CSGCCs are considered in this paper. In order to track the asymmetric current references more accurately while maintaining LC resonance damping, the hybrid current controller is proposed by combining the closed-loop fundamental current controller under double synchronous frames and the closed-loop high-bandwidth harmonic current controller under stationary frame. The design of the hybrid current controller is analyzed. Finally, the experimental results are shown to verify that the control strategies can mitigate the dc-link current ripple effectively, and also provide good LC resonance damping performance for grid currents.

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