Discontinuous Space Vector Modulation Schemes for Modular Multilevel Converters

In this article, a new, simple, and generalized discontinuous pulse width modulation (PWM)-based submodule capacitor voltage balancing approach is proposed and generated within the carrier-based PWM for modular multilevel converters (MMCs). In this scheme, different variants of zero-sequence voltage (ZSV) component is injected into the pulse width modulator so that each arm of the MMC is virtually clamped to positive or negative dc bus during a specific interval to achieve discontinuous modulation. A simple approach based on the location of the voltage vector mapping to a two-level space-vector diagram is presented to determine various ZSV components. The effectiveness of the proposed scheme with a voltage balancing algorithm is demonstrated through PLECS simulations and experimentally verified using a hardware-in-the-loop-based system. The performance of MMC with different ZSV injections is holistically evaluated to determine the best possible sequence over a wide range of modulation index.