The use of a Digital Fluid Power Transmission (DFPT), in a 5 MW offshore wind turbine is investigated in this thesis. The focus is to design a controller for the DFPT system to maximise the energy extraction. Mechanical and electrical requirements to the wind turbine are investigated to set up requirements for the system operation. The system consists of a DFPT, a generator and back-to-back converter, thus non-linear models of these systems are developed. To maximise the amount of energy extracted from the wind turbine, control systems for the DFPT, the generator and the grid side of the back-to-back converter are developed. The system performance is evaluated given a wind profile with a mean wind speed of 8 m/s and compared to a conventional wind turbine model (NREL). It was found that the DFPT system was able to perform comparable to the NREL in tip-speed-ratio tracking with an RMS error of 0.06. The stresses on the rotor axis of the DFPT and NREL reference turbines showed the DFPT added approximately 24.000 stress cycles, hence a relative larger accumulated fatigue damage compared to the NREL. A more detailed analysis of the mechanical structure must be conducted to estimate the expected lifetime.