Multiport DC–DC–AC Modular Multilevel Converters For Hybrid AC/DC Power Systems

Hybrid ac/dc power systems will rely on power electronics to enable controlled energy exchange between different dc and ac systems. Multiport dc-dc-ac (MP-DC2AC) converters offer the ability to exchange power between two dc systems and an ac system using a single converter structure. Potential benefits include reduced energy conversion stages and a more compact station footprint. To date, limited information is available on modeling, operation, and control of MP-DC2AC converters suitable for HVDC and MVDC applications. This paper helps to fill this gap by presenting a generalized modeling and control framework for two yet unexplored MP-DC2AC modular multilevel converters. Based on derived analytical models of internal power transfer mechanisms, a dynamic controller is proposed that allows independent control of port power flows while keeping capacitor voltages regulated. Results are validated by extensive time-domain simulations. A comprehensive comparative analysis between four different MP-DC2AC topologies is carried out.