Prototype design and experimental verification of modular multilevel converter based back-to-back system

This paper presents the design and control methods for a modular multilevel converter (MMC) based back-to-back (BTB) system. A 20kW, 50Hz three phase downscaled prototype is constructed to show the working principles, hardware design procedures, and control circuits implementation. In this prototype, there are two MMC stations, namely the inverter and the rectifier, each consisting of 18 full-bridge (FB) sub-modules (SMs). Each station is controlled by an independent controller. Moreover, the management and communication methods of these sub-modules are also illustrated. Further, the control principles for the MMC based BTB system are presented as well to achieve power regulation and balance all the SM capacitor voltages. Finally, experimental results are given to verify the validity of the circuit design and show the effectiveness of the control methods.