Improved Power Loss Balance Control for Modular Multilevel Converters Based on Variable Capacitor Voltage Deviation Predefined Value under SM Malfunction

When it concerns the reliable working of the modular multilevel converter (MMC), the power loss balance control cannot be ignored. Under the submodule (SM) malfunction condition, each arm of the MMC operates in an asymmetrical status, resulting in unbalanced power loss in every arm of MMCs, which affects the converter operation's reliability. This essay proposes a variable capacitor voltage deviation predefined value-based power loss balance control (VCVDPV-PLBC), which could optimize faulty arms' power losses by regulating capacitor voltage deviation predefined value to change power devices' switching loss in MMCs under SM malfunction. On this basis, the coupling relationship between SM's switching frequency and the capacitor voltage deviation predefined value is revealed. The raised VCVDPV-PLBC could effectually prolong the service life of power devices in faulty arms and strengthen the reliability of MMC system under the malfunction of the SM. The validity of the raised VCVDPV-PLBC was proved by simulation results with specialized software PSCAD/EMTDC and experimental studies with small-scale MMC setup.