An Active Voltage Balancing Technique for Series Connection of Semiconductor Devices in Modular Multilevel Converters

Series connection of semiconductor devices facilitates the development of higher-voltage submodules in modular multilevel converters (MMCs) using commercially available lower-voltage semiconductor devices. However, if left uncontrolled, series-connected semiconductors may experience unequal voltage sharing after each switching event. This unequal distribution lead to semiconductor damage and system failure. This paper proposes a novel method for the series connection of semiconductor devices. The proposed solution utilizes an active snubber circuit (ASC) and a unique control system that ensure controlled voltage sharing among the semiconductors. The solution is mainly intended for MMCs operating at low switching frequencies. The efficacy of the proposed solution is verified through simulations in the MATLAB/Simulink environment.