Control design, implementation, and evaluation for an in-field 500 kW wind turbine with a fixed-displacement hydraulic drivetrain

Abstract

Abstract. The business case for compact hydraulic wind turbine drivetrains is becoming ever stronger, as offshore wind turbines are getting larger in terms of size and power output. Hydraulic transmissions are generally employed in high-load systems and form an opportunity for application in multi-megawatt turbines. The Delft Offshore Turbine (DOT) is a hydraulic wind turbine concept replacing conventional drivetrain components with a single seawater pump. Pressurized seawater is directed to a combined Pelton turbine connected to an electrical generator on a central multi-megawatt electricity generation platform. This paper presents the control design, implementation, and evaluation for an intermediate version of the ideal DOT concept: an in-field 500 kW hydraulic wind turbine. It is shown that the overall drivetrain efficiency and controllability are increased by operating the rotor at maximum rotor torque in the below-rated region using a passive torque control strategy. An active valve control scheme is employed and evaluated in near-rated conditions.

Integration of Hydraulic Wind Turbines for Seawater Reverse Osmosis Desalination

“…In contrast, SWRO technologies are units which are typically operated under relatively constant and stationary conditions. The application of wind powered SWRO desalination follows previous work where the integration of wind turbine technology in combination with hydraulic systems for power conversion has been studied for hydraulic offshore wind turbines [7]- [9]. This paper elaborates on the modelling, simulation and comparison of two potential configurations of SWRO with Fig.…”

“…This ability to manipulate the pressure in the water pump discharge will directly influence the pump torque which in turn, may be used for closed loop control of the rotor speed in below rated operating conditions. This configuration has been proposed for tidal energy desalination in [10], and the control strategy has been analysed and implemented in wind turbines that incorporate a hydraulic-drivetrain and Pelton turbine [9].…”

“…For a constant displacement pump, the relation between the pump torque and the rotational speed depends directly on the pressure across the pump as presented in (6). The system pressure is given by both the osmotic pressure and the membrane characteristics as a function of the volumetric flow rates according to (7), (8), (9), and (11) resulting in the following relation:…”

“…Both strategies are shown in the torque-speed graph of Fig .5, where it is shown that for low rotor-speeds a minimum torque is required to overcome the osmotic pressures and only after 6.5 or 7.0m/s the rotor is able to operate with the desired variable speed relation for optimal aerodynamic efficiency. Other control strategies to manipulate the system pressure in hydraulic wind turbines have been presented in [9], [19].…”

Passive shape shifting: A compliant design approach for full film bearings

“…Finally, pumps are an example of an application where both the load and velocity can change significantly. 11 When variable operating conditions are considered in the design of a bearing, more often than not the geometry of the bearing is the limiting factor for the performance, since not every bearing geometry excels in every aspect. This means the bearing designer usually resorts to designing for an average or maximum operating point in the range.…”