Application of an Advanced Repetitive Controller to Mitigate Harmonics in MMC With APOD Scheme

In a modular multilevel converter (MMC), the second and other even-order harmonics in the circulating currents are mainly due to the fluctuations in the capacitor voltages in the sub modules of the MMC. The increased circulating currents affect the system performance and threatens the safety operation of power devices. To mitigate the circulating currents, this article puts forward the application of an advanced repetitive controller with alternate phase opposition and disposition pulse-width modulation technique. The proposed controller was operated in tandem with a proportional integral controller for better results of circulating current harmonic suppression and then the stability analysis was analyzed by the Popov criteria. This method is very simple to implement and suitable for multiple harmonic mitigation. Computer simulations and experimental results on a prototype shows that the proposed controller is effective and easy to implement for MMCs.