Modeling and control of a wind turbine as a distributed resource in an electric power system

Abstract

Deregulation of electric utilities has led to consideration of new distributed resources (DRs) such as wind turbines. The DR dynamics have to be studied carefully to avoid unpredictable outputs and unknown interferences as well as to make sure that consistent and efficient power is supplied according to the load requirements. The objective of this thesis is to make a contribution to the ongoing wind turbine research in the areas of modeling, control and implementation of wind turbines as DRs in deregulated electric power systems. A model of complete open-loop wind turbine system consisting of a rotor, a gearbox and a three-phase ac generator was developed, and it was used as a basis for the design of a controller for the wind turbine. The wind turbine (rotor and gearbox) transfer function was derived and its performance was studied using the MATLAB Program. The electric generator was modeled using the synchronous generator model in the MATLAB Power System Blockset. This thesis provided a different approach to wind turbine modeling and control design methodology. All the results were in close agreement with results from other studies. The main strategy of the controller was to regulate the rotor angular speed and the power demand to match the required profiles. This thesis focused on controller design to maintain a constant shaft angular speed and constant power production for a variable-pitch, constant-speed horizontal-axis wind turbine. A simple wind turbine model was linearized about an operating point and it was used to systematically perform trade-off studies between minimization parameters. The robust nature of the PID controller was illustrated and optimal operating conditions were determined. Wind turbine economics was also studied in order to evaluate the economic feasibility of using wind turbines as DRs. Continued research illustrates that the optimum wind turbine has not yet been build and most of the remaining work lies in how the wind turbine is controlled. Additional design and control strategy improvements can be expected as experience is gained with wind turbine operations.