Novel Insight into the Output Current Ripple for Multilevel and Multiphase Converter Topologies

When it comes to the computation / estimation of the switching losses in a multilevel converter, it is crucial to know the instantaneous value of the output current. If the average output current value is used instead, there is a non negligible error when the quality of the output current waveform is low. This paper addresses this issue with a generic and versatile fast numerical method for phase-disposition PWM that produces the exact switching pattern, hence the exact inductor flux, without having to run time-domain switched simulation(s), as the calculations are performed for the minimal set of points required to fully determine the inductor flux ripple at the switching instants

Virtual Submodule Concept for Fast Semi-Numerical Modular Multilevel Converter Loss Estimation

During the design phase of a modular multilevel converter (MMC), an accurate loss evaluation of the submodule (SM) plays an important role. In this paper, a method based on the analytical description of the MMC key waveforms that allows to directly obtain the average semiconductor and capacitor losses that each SM will experience is introduced, under different operating conditions or control schemes. To verify the proposed concept, the results are compared with the losses obtained from a switched model with closed-loop control, where the analytical MMC key waveforms are approached in steady state. The proposed method provides a great flexibility and a significant reduction of the simulation / computational time otherwise needed to evaluate SM losses under various operating conditions