Analysis and Control of Modular Multilevel Converters using Discontinuous Modulation

This paper proposes a simple and generalized approach of an adaptive zero-sequence voltage injection to control the modular multilevel converter with reduced switching losses and capacitor voltage ripple. In this method, a simple approach based on the location of the voltage vector mapping to a two-level space-vector diagram is presented to determine various zero-sequence voltage components. A generalized control structure is established to conduct the perform studies among different ZSV components. Moreover, a real-time electro-thermal model is developed in PLECS platform to analyze the thermal loading on power devices. The performance and effectiveness of the proposed approach is analyzed through detailed hardware-in-the-loop experimental studies. Finally, the performance of MMC with different zero-sequence voltage injections are holistically evaluated to determine the best possible sequence in terms of reduced capacitor voltage ripple and power losses.