Speed Compensation in Hydraulic Wind Turbine Control

The combination of hydraulic drivetrains and wind turbines impose control challenges due to their inherent dynamic behaviour. At the same time, the increase in system performance due to controller improvements causes a considerable impact on the turbine's performance. In such wind turbines, the system is controlled through pressure. Based on aerodynamic, hydraulic and mechanical parameters and measurements, the pressure is regulated for the rotor achieve maximum aerodynamic efficiency at steady state. However, the reference pressure might be inaccurate due to the difficulty in determining exact component's parameters and wind measurement, leading to a suboptimal rotor speed. The wrong pressure reference is a consequence on most control methods that are based on the classic K omega(2) law. In this paper, a control structure is presented where the turbine rotor speed error is used to compensate the pressure reference calculated by the K omega(2) law. The proposed structure can lead to optimal operation despite the components parameter uncertainties. Nevertheless, it uses wind speed measurement, which also contain uncertainties. The proposed method with rotor speed compensation is compared to the classic K omega(2) law. Their performance is assessed through system simulation with added uncertainties in system efficiency and in wind speed measurement. Experimental tests are shown to confirm the simulated system behavior and the actuation of the speed compensation. The presented control method allows for faster system response and better tracking of optimal rotor operation point under certain conditions. It is confirmed that the system can increase the energy extraction from the wind however, the system overall efficiency is not necessarily improved.