A Generalized Thyristor-Based Valve Design for Realizing Zero-Voltage-Operated Director Switches in Hybrid Modular Multilevel Converters

With the growing demand for renewable energy integration, hybrid modular multilevel converters (HMMCs) have gained significant attention. These converters employ high-voltage insulated-gate bipolar transistors (IGBTs) as director switches (DSs), which are realized by stacking multiple devices. This approach complicates the design and increases conduction losses. As an alternative, this paper introduces a generalized thyristor-based DS structure (TB-DS). The TB-DS benefits from series-connected thyristors as the main DS current path, supported by an auxiliary circuit that enables the turn-OFF commutation. This approach significantly reduces DS conduction loss and the complexity of stack voltage control in conventional DSs. The operating principle of the proposed TB-DS is demonstrated on detailed simulations of two established HMMCs: the extended overlap alternate arm converter (EO-AAC) and the three-level hybrid modular multilevel converter (HMMC₃). The results show a potential for a 57.3% reduction in DS losses and a 16.8% reduction in total converter loss for the EO-AAC; while the TB-DS HMMC₃ achieves a 43.7% reduction in DS losses and an 18.7% total converter loss reduction compared to its IGBT-DS counterpart. Finally, a scaled-down laboratory prototype of the proposed TB-DS is constructed to validate its actual switching performance experimentally, rather than relying on hardware-in-the-loop (HIL) simulation results.