Quasi Two-Level PWM Operation of an MMC Phase Leg with Reduced Module Capacitance

Abstract

The modular multilevel converter offers benefits for medium and high voltage power conversion due to indirect series connection of devices. The drawback is a large amount of capacitance that has to be installed in each module, often prohibiting its use in cost sensitive applications. This letter proposes a new operation mode of modular multilevel topologies that allows reducing the capacitance by at least an order of magnitude. To achieve this, the multilevel operation is sacrificed, but many advantages of indirect series connection, such as proper voltage sharing, small voltage steps, limited voltage slopes, modularity, and scalability remain.