IGCT-Based Direct AC/AC Modular Multilevel Converters for Pumped Hydro Storage Plants

This paper presents a direct AC/AC modular multilevel converter (MMC) for pumped hydro storage power plants utilizing synchronous machines with variable speed operation. Due to the straightforward voltage and power scalability of the MMC topology, the machine-side transformer can be avoided over a wide power range. Moreover, the proposed use of reverse conducting integrated gate-commutated thyristor (RC-IGCT) semiconductor technology offers even higher converter efficiencies as well as great robustness against failures. General system design considerations are made, such as grid-side active/reactive power capability, harmonic performance, power losses etc. The converter closed-loop control stability against grid faults is discussed through dynamic performance simulation tests. Finally, measurements from a medium voltage converter illustrate the cell start-up and discharge operation.