Gas turbine control system and method for single-shaft combined cycle plant

A gas turbine control system for a single-shaft combined cycle plant comprising a gas turbine, a steam turbine, a generator, and a condenser for condensing exhaust steam from the steam turbine, wherein the gas turbine, the steam turbine, and the generator have rotating shafts thereof coupled together, the gas turbine control system further comprising:

• a first command-generating section for generating a first gas turbine output command on the basis of the output of the generator and an output of the steam turbine;
• a second command-generating section for generating a second gas turbine output command using a parameter reflecting an output of the gas turbine;
• and
• a selection section for selecting and outputting the first gas turbine output command or the second gas turbine output command depending on whether or not the condenser is in a reverse-washing/normal-washing switching period.