A Redundant SM Structure for Fault-Tolerant Capability of Hybrid Modular Multilevel Converters

This paper presents a novel redundant submodule (SM) structure for hybrid modular multilevel converters (hybrid MMCs) that enables rapid fault recovery without introducing conduction losses or requiring charging time. Conventional hot reserve fault-tolerant methods cause conduction losses and circulating currents, while cold reserve methods require a charging period before activation, limiting their effectiveness in fast fault recovery. To address these limitations, the proposed redundant SM maintains its capacitor charge during normal operation without incurring additional cost or losses. This allows for immediate insertion upon fault detection without extra components that increase conduction losses. As a result, it can be immediately inserted after a fault occurs without requiring additional components that could increase conduction losses or delay activation. This redundancy mechanism can effectively handle faults in full-bridge submodules (FBSMs), half-bridge submodules (HBSMs), or both simultaneously. The proposed method's performance under different fault scenarios is analyzed, and simulation results confirm the effectiveness of the proposed approach.