A 36-kV 12-Mvar T-STATCOM Based on Mixed Si-WBG Open End Winding Multilevel Converter

In 2021, Terna S.p.A. introduced a 36 kV connection standard for renewable energy plants (10-100 MW), optimizing costs, simplifying connections, and reducing substation space requirements. This allows multiple producers to connect to shared bays near 380-60kV/36kV substations, promoting efficiency and scalability in renewable energy integration. The initiative was prompted by the increasing demand for renewable energy plants to connect to the National Transmission Grid (RTN). To regulate AC voltage at the 36 kV Point of Connection (PoC), this paper proposes a transmission-type STATCOM with an open-end winding multilevel converter. The design uses silicon IGBTs in a five-level neutral point clamped (NPC) converter, switching at line frequency (50 Hz) to minimize switching losses, and SiC MOSFETs in a two-level converter, enhancing efficiency due to their low switching and conduction losses. The STATCOM includes a coupling transformer with an open-end secondary winding, eliminating the need for additional series filter reactors. This solution aims to facilitate the integration of wide-bandgap (WBG) devices in grid-connected renewable energy systems like SiC MOSFETs limited at 3.3kV, 1kA. Preliminary simulations show that the design, when applied to a 12 MVAR, 11 kV STATCOM connected to a 36 kV transmission line, exhibits high efficiency, compactness, and enhanced performance, paving the way for the adoption of WBG technology in renewable energy applications.