Thyristors-Based Sub-Module with Hybrid Devices for Low-Loss Realization of Modular Multilevel Converter

This paper presents a new low loss sub-module (SM), benefiting from hybrid switching devices, i.e., thyristors and IGBTs. Employing two cross-connected thyristors, along with a commutation chain-link made up of a stack of full-bridge SMs and an inductor allows for reliable thyristor switching operation of the new SM, thus leveraging thyristor's low conduction loss for realizing the state-of-the-art modular multilevel converters (MMCs). The new SM, called thyristorbased SM (TBSM), not only reduces the total loss of the MMC by 40 %, but also allows to employ IGBTs with low current rating for its commutation chain-link, since the IGBTs of its commutation chain-link conducts the TBSM's current for a significantly short interval, e.g. a few hundred micro-seconds per switching cycle. Therefore, these features enable a more compact cooling system design and reduces the semiconductors' upfront cost of the MMC. Finally, the operating principle of the TBSM, along with the simulation results for a case study are presented before the power loss comparisons are benchmarked.