Decentralized Loss Balancing Control for Modular Multilevel Converter

Abstract

Loss balancing control of semiconductor devices in submodules (SMs) is critical for the reliable performance and long-term operation of the Modular Multilevel Converters (MMC) due to the significant uneven loss distribution between top and bottom semiconductor devices within one submodule (SM). To extend the lifetime of MMCs, this paper proposes a decentralized loss balancing control strategy for the MMC in combination with the decentralized self-aligned phase-shifted pulse width modulation (PWM) (self-aligned carriers) and capacitor voltage balancing method. This loss balancing approach, which is integrated into the capacitor voltage balancing, is proposed to control the loss distribution of the SMs by adjusting the capacitor voltage reference. The key approach is that each SM local controller regulates its own voltage and loss distribution by utilizing information from itself and adjacent SM controllers. Simulation results demonstrate the viability of the proposed control scheme in association with self-aligned phase-shifted carriers.