A 
turbine (2) driven 
electric power production 
system  (1), —said 
turbine (2) arranged for being driven by a fluid (3) having a fluid speed (v) varying in time, —said 
turbine (2) connected to a hydrostatic displacement pump (6) further connected to a hydrostatic displacement motor (8) as part of a 
closed loop hydrostatic 
transmission system (7), —said motor (8) arranged for driving an electrical generator (9) supplying 
AC power (10) at a frequency (fg) near a given desired frequency (fdes), characterized by a 
closed loop system arranged for controlling a volumetric displacement (13) of the hydrostatic motor (8), comprising —a fluid speed meter (11m) arranged for producing a speed 
signal (11s) representing a speed (v) of said fluid (3), and —a rotational speed meter (12m) arranged for providing a rotational speed 
signal (12s) representing a rotational 
speed measurement (ω) of said turbine (2), —a motor 
displacement control system (15) for continuously receiving said speed 
signal (11s) and said rotational speed signal (12s) and arranged for calculating a 
control signal (16), —a volumetric 
displacement control actuator (17) on said hydrostatic motor, arranged for receiving said 
control signal (16) for continuously adjusting a volumetric displacement (d) of said hydrostatic motor (8) for maintaining a set turbine 
tip speed ratio (tsrset) and thereby providing an improved power efficiency of the power production system (1) during fluctuations in said fluid speed (v).