Research On The Implementation Of The State-space Based Control Strategies Of VSCF Wind Turbine

With the need of reducing the cost of wind power, wind turbines are built largerand larger. The capacity of single turbine roars all the way up from Kilowatts toMegawatts, and even Upwind is designing the prototype of20MW. Of cause larger sizebenefits, it reduces the cost of manufacturing, transportation and maintenance. But stillit’s a double-edged sword. Larger size brings tougher engineering threats. The biggerthe rotor is, the severer unbalanced load it subjected from wind shear, turbulence andtower shade. In addition, the greater weight and longer range of the blade amplify loadscaused by misalignment. For these reasons, the traditional SISO control strategy nolonger meets the need. Stabilize the rotor speed becomes the basic goal, people desirestable power output, less variation of loads and vibration. Based on state-space, moderncontrol strategy makes this MIMO control possible.This paper studied on the modeling of VSCF wind turbine and linearization andbuilt the state-space equation of the wind turbine system. Integrated with analyses ofwind turbine operation control, implementation of modern control strategy on thissystem was carried out. Main attention was focused on the unbalanced load caused bywind shear, turbulence and tower shade, and the insufficient damp of power train issue.Traditional way of control for wind turbine employs a constant torque for generatorabove rated wind speed while using pitch control to regulate rotor speed，this result in aquite low damp of the drive train torsional mode which would invoke large fluctuationin drive train torque,and even oscillate the structure. Concerning this issue, this paperdesigned a Linear Quadratic Regulator to dynamically control the generator torque. Bymoving the poles corresponding to the first order drive train torsion mode further to theleft in the complex plane, the generator torque controller adds active damping to thismode.Focusing on the1P unbalanced load caused by wind shear, individual pitch controlstrategy was proposed by combining the Linear Quadratic Regulator (LQR). The resultsshowed that，the proposed strategy of individual pitch control can reduce the windturbine main components loads. Furthermore, in account of bad robustness using onlystate-space method, this paper combined gain-scheduled pitch control and ensured goodrobustness of the controller..