Protecting modular multilevel converters (MMC) against ac fault by deadbeat control

The paper shows that deadbeat control and harmonic elimination by feedforward and feedback can be implemented by MMC. In tracking the current reference, MMC is: (i) safe from large destructive of ac faults; (ii) free from the odd harmonics generated by the nonlinearities of MMC. As deadbeat control cannot filter the even harmonics on the dc side, their elimination has to be done by feedback and feedforward methods developed by many researchers, including the authors. However, the cost saving from capacitor size reduction, made possible by the even harmonic elimination methods, comes to naught when large ac fault currents charge the capacitors to voltages destructive to IGBTs. Deadbeat in preventing the voltage levels from rising ensures that cost saving from capacitor size reduction is feasible. Claims are validated by simulations by SIMULINK of MATLAB.