Model-based analysis of control strategies for a variable speed wind turbine

Relative to constant-speed systems, variable-speed wind turbines offer increased energy capture. The maximum energy capture is accomplished by controlling the power drawn so that the rotor operates at peak aerodynamic efficiency. These systems also improve the dynamic behavior of the wind turbine, reduce stresses and prolong the lifetime of the system. Advances in power electronics have made variable-speed control feasible, with many systems fielded. The objective of this project is to investigate the operation of a wind turbine at variable speed, and to determine its advantages. The system is modeled by simulating the wind input, based in the Sandia National Laboratories wind model (SNWind v.1.0), the 20 kW NREL variable speed wind turbine, a squirrel cage induction machine, and the two speed controllers. The speed controller input is the rotor speed based on constant Cp at optimum tip speed ratio based algorithm. The field orientation principle (vector control) and the constant Volts/Hertz (scalar) control form the basis of the generator control models. The performance of the two control and uncontrolled systems is evaluated and compared during steady-state and transient operation. Energy capture and torque loads of both systems are the factors that determine the systems\u27 performance. The results of this thesis show that the field oriented control wind turbine produces more energy than the constant speed wind turbine, and it offers the capability of reducing the loads on the machine without affecting the energy captured