A New Breed of Optimized Symmetrical and Asymmetrical Cascaded Multilevel Power Converters

Multilevel voltage source power converters are the state-of-the-art and key elements for medium-voltage (MV) high-power applications. The cascaded multicell (CM) topologies reach higher output voltage and power levels, and also retain higher reliability due to their modular and fault-tolerant features. This paper initially proposes an optimized topology for symmetrical CM (SCM) multilevel converters. The superiority of the proposed SCM, as compared with the conventional CM converter structure, is that the number of required high-frequency power switches is reduced. Next, a new topology of an asymmetrical CM (ACM) converter, which is formed based on the proposed optimized modules of an SCM converter, is suggested. The advantage of the proposed new ACM converter in comparison with the traditional ACM topology is that the variety of the dc links with different voltage ratings reduces, which makes the proposed topology more modular. The simulation results and the experimental measurements taken from the laboratory prototypes are presented for the proposed converters in order to validate the effectiveness and the advantages of these converters as well as their control strategy.