Reactive Component Reduction in Modular Multilevel Matrix Converters through Iterative Design-Simulation Cycles

Modular multilevel matrix converter (M3C) is being considered for high power motor drive systems, wind plant interfaces and, low-frequency AC (LFAC) transmission systems. From a design perspective, the power circuit of the M3C converter is mainly composed of capacitors, inductors, and semiconductor switches that need to be dimensioned to meet performance requirements. However, the design relationships between the reactive components and circuit operating conditions are highly nonlinear due to the multiple frequencies and switching processes that take place in the power converter. Some of the techniques proposed in the literature make exclusive use of extensive, time-consuming simulations to choose parameters within a relatively narrow design space. On the other hand, simplified design equations that ignore interactions among the multiple frequencies in current and/or voltage waveforms lead to very large errors. This paper proposes a hybrid approach that uses simplified analytical design equations coupled with a time-domain simulation approach in a cyclic-iterative manner. The proposed approach is quick-converging, leading to 53% reduction in capacitor value and 34% reduction in inductor value compared to the analytical design solutions. Furthermore, using an active control to regulate circulating currents, ripple and efficiency performance metrics are further improved. Simulation results using averaged circuit models implemented in EMTP are presented to verify the proposed approach for a candidate LFAC application.