Autonomous Power Ripple Suppression Scheme for Grid-Connected Multiport Converters Under Unbalanced Grid Conditions

The active power decoupling technique is a promising solution for grid-connected converters under unbalanced grid conditions due to its advanced merits in simultaneously achieving negative-sequence current elimination and active power ripple suppression. However, an extra power decoupling circuit, along with a complex power ripple tracking controller, should be designed for these purposes. Given this, this article proposes an autonomous power ripple suppression scheme that achieves both active power ripple suppression and negative-sequence current elimination based on a grid-connected multiport converter. In the proposed scheme, negative-sequence current elimination is implemented at the ac port, and the dc-port power is controlled to be constant to suppress active power ripples. Thus, the differential power ripples are autonomously buffered by the ripple port. Besides, the multiport converter is decomposed into an upper-port converter and a lower-port converter to ease the modulation design under time-varying dc-link voltages. With the proposed scheme, balanced three-phase grid currents and ripple-free dc output voltage are simultaneously obtained under unbalanced grid conditions without extra power ripple controllers. Experimental results are presented to demonstrate the effectiveness of the proposed scheme.