A Novel PWM Technique for MMCs with High Frequency Link and Natural Capacitor Balancing for Grid-Interfacing of Renewables

This paper presents a new pulse width modulation (PWM) technique for a high-frequency link Modular Multilevel Converter topology for grid-integrated renewables. The topology generates a multilevel output voltage with low harmonic distortion, increased reliability, and design flexibility due to the modular nature of the converter. A central full-bridge converter is connected to multiple High Frequency Link modules via high frequency transformers. Each module produces its own isolated DC voltage, and modules are inserted or bypassed to synthesize large AC voltages. The proposed PWM technique equalizes module utilization without increasing losses, and retains inherent capacitor voltage balancing. Simulation results using SIMULINK models show that the proposed modulation scheme results in better performance than conventional schemes such as level-shifted carrier PWM, phase-shifted carrier PWM, hybrid schemes or nearest-level modulation.