A Dual-Perspective Analysis of IGBT Open-Circuit Faults in Hybrid Modular Multilevel Converters: Unified Characteristics and Diagnoses

The hybrid modular multilevel converter (HMMC) comprising both full-bridge submodules (SMs) and half-bridge SMs has drawn extensive attention for its cost-effective DC fault ride-through capability. However, IGBT OCF diagnosis-a prerequisite for fault isolation and fault reconfiguration, is critical to the reliability of HMMCs, while relevant research remains scarce. Furthermore, varied OCF scenarios within HMMC further complicate fault diagnosis. To fill this gap, this article first conducts a dual-perspective analysis of IGBT OCFs in HMMCs, covering single and multiple OCF scenarios in an SM. Two unified characteristics are yielded: 1) Unified Characteristic I, derived from the mode-type perspective and reveals that IGBT OCFs cause specific mode-type conversions of the faulty SM; 2) Unified Characteristic II, derived from the switching-function perspective, indicates that the faulty SM maintains a specific switching function. Therefore, a unified characteristics-driven strategy is proposed, including a detection stage and a localization stage. In the detection stage, the suspected faulty SM is selected via Unified Characteristic II and its status is then ascertained using Unified Characteristic I. Upon the identification of a fault, other suspected faulty SMs are screened, with their statuses determined in the ensuing localization stage. Hardware-in-the-loop (HIL) experiments validate the effectiveness of the proposed strategy.