Reducing Average Capacitor Voltage to Alleviate Current Stress in Modular Multilevel Converter

Modular Multilevel Converter (MMC) has gained significant traction as a prevalent topology within the realm of variable speed drives. However, during low-frequency operation, the voltage fluctuation of the submodule (SM) capacitors poses a significant challenge, jeopardizing the stable operation of the motor. To overcome this challenge, this paper suggests an improved control strategy that integrates an improved high-frequency injection approach with a decrease in the average voltage of the capacitors. This strategy can effectively reduce the voltage ripple of capacitors at low frequency operation and mitigate the current stress caused by high-frequency component injection. Consequently, MMC can operate reliably at low frequencies, ensuring enhanced safety and dependability. The effectiveness of this improved control strategy has been verified in PLECS.