A comparative survey of power converter topologies for full-size converter operation of medium-voltage hydropower generators

This paper discusses the challenges for today’s power converter topologies when operating large synchronous motor-generators in pumped storage power plants, which is a medium-voltage high-power application. First, the available ratings and characteristics of the utilized power semiconductor switches are analyzed. Then, the practical limitations of classical multilevel voltage source converters are reviewed, particularly the individual maximum achievable operating voltage. Next, the usability of direct AC–AC converters is discussed. Due to their arbitrary scalability and excellent performance, modular multilevel converter topologies gain special attention in this paper. The characteristics of the two main arrangements, the modular multilevel converter and the modular multilevel matrix converter, are examined with respect to the torque-speed characteristic of the installed reversible-speed pump-turbines. A review of commercially available power converters for medium-voltage high-power drive applications and their specifications as well as the identification of promising power converter topologies for operation in large pumped storage power plants complete this comprehensive analysis.