Offshore wind turbines are getting larger in terms of size and power output, resulting in lower rotation speed and higher torque at the rotor. As hydraulic transmissions are generally employed in high load systems, the case for compact hydraulic drive trains is becoming ever stronger. The hydraulic Delft Offshore Turbine (DOT) concept replaces drive train components with a single sea water pump, and pressurizes sea water to a central multi-megawatt electricity generation platform. This paper presents the first steps in realizing the DOT concept, and prototype tests are conducted with a single full-scale wind turbine with a hydraulic configuration. A hydraulic torque control strategy is developed and in-field test results are presented.

A hydrostatic transmission is commonly used in off road construction equipment for its high power density. It
can also be used in wind turbines for more reliable and cost effective transmission than a conventional gearbox.
A power regenerative test platform has been built at the University of Minnesota to understand the performance
of a hydrostatic transmission in a wind turbine. In this paper the use of an advanced control valve to characterize
the components of the test bed has been demonstrated. The electrohydraulic valve has precise control on pressure
and flow and gives more flexibility to the testbed.

Based on different motivations and driving forces for the electrification of hydraulics, this paper introduces and
explains the solutions and basic principles used for increasing the energy efficiency by electrification. The
following chapters explore these solutions and principles in depth. The key success factors for the electrification
of hydraulics are intelligent energy management and appropriate energy storage type and size. Particular
attention is paid to the energy storage systems giving an overview of their optimal application fields. The „Smart
Energy Mode“ energy management solution for industrial applications is then introduced. Afterwards, the Smart
Energy System Design is explained by way of an industrial and a mobile example. The paper concludes with a
remark concerning the current needs of automatic linking of different model-based tools. This ensures the
holistic approach required in this context.

One way to increase the compactness and power density of electro hydraulic power units is to increase the
rotational speed level. Hence, a high-speed electrical drive and a high-speed gear pump are connected.
Particularly, high-speed internal gear pumps are not state of the art and increasing rotational speed entails a lot of
challenges for the hydraulic system. This paper analyses the influence of different pump parameters for the speed
limit of internal gear pumps. Furthermore, a preliminary dimensioning of drive concepts is used to identify the
best concept in terms of power density.