Modeling of MMC Based High Power DC-DC Converter Controlled Using Trapezoidal Modulation

The multi-terminal high voltage dc (HVdc) networks require isolated dc-dc converters for voltage matching, power flow control and fault protection. The dc-dc converters based on modular multilevel converter (MMC) are continuously gaining popularity. The trapezoidal modulation method in dc-dc converters provides controlled dv/dt stress, high dc voltage utilization and power transfer capability. The simulation based models are gaining interest in recent literature. However, more focus is required on the mathematical modeling aspect of these converters. This paper presents an averaged dynamic model of MMC working in the trapezoidal modulation. The developed model effectively captures both ac and dc side dynamics along with the internal dynamics of sub-module capacitors. The presented average model provides a simplified method of analyzing large converter system. The comparison between simulation and analytical model validates the performance of the developed model. A laboratory prototype is also developed to observe MMC operation in the trapezoidal modulation scheme.