Design and experiment of modular multilevel converter prototype with 49-level output voltages

There is a large number of submodules in modular multilevel converters (MMC), but it is difficult to control or even organize these submodules. They are connected with multiple controllers through a great quantity of high-throughput IOs which make the complexity and costs of MMC much high. A prototype of MMC with 49-level output voltages is designed and implemented. Measurement and control signal multiplexers are applied to reduce the number of optical fiber channels. Controllers are connected through a double-bus structure to meet the speed requirement of real-time control signals and the capacity requirement of non-real-time data. Experimental results show the THD of output waveforms is low, the power step respond is quick, and the power tracking is accurate. The results verify the feasibility of the proposed strategy. © 2013 Chinese Society for Electrical Engineering.