Mixed Dead-Time Effect Suppression Strategy for Modular Multilevel Converters

Dead time is necessary for the coupled power switches to prevent shoot-through, especially in the modular multilevel converters (MMCs) with a large number of power switches. This paper proposes a dead-time effect suppression strategy for MMCs with nearest level modulation. The operational principles of MMCs are first analyzed. According to the operational features of MMCs, the method that removes a switching signal from the coupled switches and the reduced switching frequency voltage balancing algorithms (RSFVBAs) are mixed in the proposed method. In the intervals that are furthest away from the zero-crossing points (ZCP) of arm currents, the single switching signal method can completely eliminate the dead-time effect (DTE). Alternatively, the DTE is suppressed by the RSFVBA in intervals that are close to the ZCP. By the combination of the two methods, the dependence of the DTE suppression method on currents is reduced and the influences of ZCP are also released without degrading the normal operation performance of MMCs. Moreover, the output performance of MMCs is improved and the voltage stress on the arm inductor dramatically decreases. Finally, the validation of the method is verified by the simulation results with the professional tool Matlab/Simulink.