Modelling of modular multilevel converter topology with voltage correcting modules

Modular multilevel converter (M2LC), which features modularity, scalability, reduced voltage rating of the switches and redundant switching operations, is becoming popular in medium to high-voltage applications. Circulating current, which is an inherent feature of the M2LC topology, increases both the converter losses and complexity of the control scheme. Recently, M2LC with voltage correcting modules (M2LC-VCM) is proposed as a method to minimize the circulating current. A mathematical model of the M2LC-VCM that is based on the sum of all the capacitor voltages in an arm is derived in the paper. The model can be used either as a tool for investigating the behaviour of the M2LC-VCM or designing the physical system. Simulated results of a three-phase five-level 2-MVA grid connected M2LC are presented with discussion to demonstrate the viability of the mathematical model.