A hydroelectric power generation apparatus comprising: - a hydro turbine having a rotary turbine shaft; - an asynchronous generator comprising a rotor shaft that is mechanically connected with said turbine shaft to be rotatably actuated by said turbine shaft, a rotor winding that is solidly connected to said rotor shaft, and a stator winding that is operatively coupled to said rotor winding; - an AC-AC converter, which has a first port that is electrically connected with said stator winding and a second port that is electrically connectable with an electric power distribution grid, said AC-AC converter comprising electronic means (44, 45, 46) to transmit electric power from said first input port towards said second port, and viceversa; wherein said electronic means comprises a first switching stage, a capacitive stage and a second switching stage, which are electrically connected in parallel, wherein said electronic means are adapted to operate in a mode, according to which: - said first switching stage receives a first AC voltage at a first frequency (f 1) and converts said first AC voltage in a DC voltage that charges said capacitive stage; - said second switching stage converts said DC voltage into a third AC voltage at a second frequency (f 2); wherein said electronic means are adapted to operate in another mode, according to which: - said second switching stage receives said third AC voltage at said second frequency (f 2) and converts said third AC voltage in said DC voltage; - said first switching stage converts said DC voltage in said first AC voltage at said first frequency (f 1); wherein said second operating frequency (f 2) is predefined and higher or equal than said first operating frequency (f 1), which is variable; wherein said AC-AC converter is of the active front end type having a symmetrical circuital structure comprising said first switching stage that includes said first port, said capacitive stage and said second switching stage that includes said second port, characterised in that said hydroelectric power generation apparatus further comprises a gear mechanism mechanically coupled with said turbine shaft and said rotor shaft, said gear mechanism increasing the rotational speed of the movement transmitted by said turbine shaft to said rotor shaft. - a hydro turbine having a rotary turbine shaft; - an asynchronous generator comprising a rotor shaft that is mechanically connected with said turbine shaft to be rotatably actuated by said turbine shaft, a rotor winding that is solidly connected to said rotor shaft, and a stator winding that is operatively coupled to said rotor winding; - an AC-AC converter, which has a first port that is electrically connected with said stator winding and a second port that is electrically connectable with an electric power distribution grid, said AC-AC converter comprising electronic means (44, 45, 46) to transmit electric power from said first input port towards said second port, and viceversa; wherein said electronic means are adapted to operate in a mode, according to which: - said first switching stage receives a first AC voltage at a first frequency (f 1) and converts said first AC voltage in a DC voltage that charges said capacitive stage; - said second switching stage converts said DC voltage into a third AC voltage at a second frequency (f 2); - said first switching stage receives a first AC voltage at a first frequency (f 1) and converts said first AC voltage in a DC voltage that charges said capacitive stage; - said second switching stage converts said DC voltage into a third AC voltage at a second frequency (f 2); wherein said electronic means are adapted to operate in another mode, according to which: - said second switching stage receives said third AC voltage at said second frequency (f 2) and converts said third AC voltage in said DC voltage; - said first switching stage converts said DC voltage in said first AC voltage at said first frequency (f 1); - said second switching stage receives said third AC voltage at said second frequency (f 2) and converts said third AC voltage in said DC voltage; - said first switching stage converts said DC voltage in said first AC voltage at said first frequency (f 1); wherein said second operating frequency (f 2) is predefined and higher or equal than said first operating frequency (f 1), which is variable; wherein said AC-AC converter is of the active front end type having a symmetrical circuital structure comprising said first switching stage that includes said first port, said capacitive stage and said second switching stage that includes said second port, characterised in that said hydroelectric power generation apparatus further comprises a gear mechanism mechanically coupled with said turbine shaft and said rotor shaft, said gear mechanism increasing the rotational speed of the movement transmitted by said turbine shaft to said rotor shaft.