Branch energy balancing of double wye DC-DC Modular Multilevel Converter

Modular Multilevel Converter (MMC) topology is an interesting solution for number of medium and high voltage applications. Key advantages over another multilevel topologies include flexibility of scaling in voltage and simple implementation of redundancy. In this publication control of DC-DC MMC is discussed. Analyzed converter consists of six branches connected in double wye structure. It enables bidirectional power transfer and step-up or step-down voltage conversion. The scope of the paper is branch energy balancing of the converter. Balancing system is derived from the analysis of branch powers during steady state operation. Operation of the control system is verified in the hardware in-the-loop (HIL) simulator provided by OPAL-RT Technologies. Complete control loop realized on hierarchical system was implemented. The system is composed with a top-level controller (based on ABB AC 800PEC) and a number of cell controllers build with Texas Instruments DSP (C2000 F28035).