Abstract: Pump-turbine units are kind of hydropower facilities with both pump and power generation abilities，

they are used mainly in pumped-storage plants and also in water-managing projects. Conventional units operate with

fixed-speed. To make power control quick and flexible and to extend operation ranges of turbines as well as improve

their efficiency，more and more units change to variable-speed operations following the development of frequency

converters. Benefits of variable speed operations，two solutions and their frequency converters as well as control

schemes for realizing variablespeed were introduced.

    Key words: variable speed pumped-storage；benefits of variable speed operations；solutions for realizing

variable speed；frequency converters；control schemes