Incorporating deadbeat and low-frequency harmonic elimination in modular multilevel converters

This study shows that modular multilevel converter (MMC) can implement deadbeat control and harmonic elimination together. MMC, under single-phase deadbeat control, tracks the current reference exclusively, so that it is: (i) safe from large destructive currents of ac faults; and (ii) free from the odd harmonics generated by the non-linearities of MMC. As a deadbeat control cannot filter even harmonics on the dc-side, harmonic elimination has to be done by joint feedback-feedforward methods. However, the cost saving from capacitor size reduction, made possible by the harmonic elimination, comes to naught when large ac fault currents charge the capacitors to voltage levels destructive to insulated-gate bipolar transistors. Deadbeat, in preventing the flow of large fault currents, safeguards capacitor size reduction made possible by the harmonic elimination methods. Redundant protection by the methods enhances reliability. Claims are validated by simulations by SIMULINK of MATLAB.