Yes it is possible, as is said in my last reply,the use of a static frequency converter (SFC) which is inserted between the grid and the stator is a well known solution to achieve an adjustable speed machine (refer to type D in Figure below) . Adjustable speed drive systems have already been applied in the past to hydro power plants. Up to now they have mainly been used for start -up purposes of pumps or pump -turbines. The used converters were therefore rather small in respect of converter power output (< 30 MVA). 