A distributed PWM strategy for modular multilevel converter

The modular multilevel converter (MMC) has become a potential candidate for medium/high-power applications including high-voltage direct current (HVDC) transmission, adjustable speed drive, and static var compensation systems. One of the technical challenges associated with the control of an MMC is the choice of pulse width modulation (PWM) strategy along with a submodule (SM) capacitor voltage balancing algorithm without imposing high computational burden on the controller and/or unnecessary switching transitions among the SMs. This paper proposes a distributed PWM strategy with an improved SM capacitor voltage balancing algorithm which aims at reducing the computational burden of the controller, the electro-magnetic interference and the switching frequency. The validity of the proposed PWM strategy and the SM capacitor voltage balancing algorithm is confirmed by simulation and experimental results.