Performance and control of a back to back MMC-HVDC for asynchronous ac networks interconnection

Modular Multilevel converters (MMC) is one of the categories of the voltage source converters (VSC); it has all the VSC advantages over the classical current source converters (CSC), in addition, the multilevel technique and modular construction of the MMC makes it one of the most promising power converter topology for high voltage and high power applications in the near future. This paper discusses the principle of operation of the MMC and its control strategies including the modulation technique and the capacitor voltages balancing algorithm. Using MATLAB/SIMULINK software, the performance of the MMC is studied in a complete back to back High voltage direct current (HVDC) model connecting two asynchronous ac networks. A control strategy is applied for controlling dc link voltage, ac network voltage, active power and reactive power flow. Moreover, a fault analysis is carried out which shows that the MMC-HVDC system can remain in stability under faults conditions and rapidly restore its pre-fault status after fault clearance.