Virtual Resistor Based Second-Order Ripple Sharing Control for Distributed Bidirectional DC-DC Converters in Hybrid AC-DC Microgrid

The hybrid ac-dc microgrid, consisting of ac subgrid and dc subgrid, is a promising structure to interconnect ac and dc systems to provide high quality and reliable electric energy. However, in single-phase microgrid or unbalanced three-phase microgrid, second-order ripples of the dc subgrid can lead to significant power quality issues. The ripple mitigation function can be added to existing bidirectional dc-dc converters (BDCs) or dc active power filters. Considering these ripple sources can be distributed in the dc subgrid, it is essential to develop ripple mitigation control schemes for distributed BDCs. In this article, a virtual resistor based ripple mitigation strategy is proposed. Autonomous accurate ripple current sharing can be achieved for BDCs installed closely, enabling flexible parallel of ripple mitigation converters. A comprehensive parameter design method is developed to ensure the accurate sharing for closely installed BDCs. For dc subgrid with significant line impedance, the control scheme provides the opportunity for supervisory control to further enhance ripple current sharing and mitigation performance. Both simulation and experimental results validate that the control method and the parameter design method are effective.