In this paper hydraulic PTOs featuring accumulators for use at WECs with oscillating buoyant bodies are studied. The PTO analysed comprises two cylinders connected with switchable check valves to accumulators in high and low pressure. The power extracted from the WEC and smoothed in the accumulators is used to drive variable displacement motors with attached generators. Due to valve switching, motor switching and system pressure variation the system has three degrees of freedom. Only one degree of freedom (here: valve switching) is needed for an optimized damping force to overcome the limited WEC efficiency with fixed force damping. The other two degrees of freedom can be used for improving the PTO performance. In this paper system pressure variations are investigated closely for improving the general PTO behaviour in terms of good efficiency, smooth power output and low component loading for reliable operation. For this, different control concepts (closed loop pressure or power control, additional feedback loops, additional open-loop/feed-forward controls) are analysed. In an analytical part recommendations for parameter settings are deduced from PTO parameters enabling general rules for the control parameterisation. In the simulation part, the former results are validated with a simulation model.