Design of a FCS MPC-based three-phase four-leg bidirectional VSC for application in ac or dc microgrids

Abstract

This work proposes a design methodology for a three-phase four-leg voltage source converter operating as an interface between an ac and dc systems. This design includes the LC-filter parameters calculation when using Finite Control Set Model Predictive Control (FCS-MPC). This converter may operate as an ac grid former for an ac grid of 220Vrms line-line or as an dc grid former for a bipolar dc grid of ±190V. When using FCS-MPC, the switching frequency is not fixed, which leads to a more complex design of the converter filter. In this work, a new method is given to guarantee that the input current ripple is limited to a predetermined level when the converter is operating as a dc-grid former, and the output voltage ripple is limited for the ac grid-former operation. To validate the proposed methodologies, simulation results are shown.