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Publication Date

2012-12-05

Availability

UM campus only

Embargo Period

2012-12-05

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PHD)

Department

Mechanical Engineering (Engineering)

Date of Defense

2012-11-05

First Committee Member

Singiresu S. Rao

Second Committee Member

Qingda Yang

Third Committee Member

Jizhou Song

Fourth Committee Member

Gang Wang

Abstract

Energy is the basis for economic development and it is important to have a reliable supply of energy for the sustainable development of any country. With the rapid growth of the global economy, the energy crisis is aggravating substantially. It is, therefore, of great interest to develop reliable renewable energy resources that can take up a relatively large proportion of the growing energy needs with the crucial features of energy security, environment protection and economic development. Since the beginning of the twenty first century, countries all over the world and international organizations have invested tremendous amount of funds for the development of new energy systems. As a competitor to the conventional energy sources, wind energy is considered to be an important source for a diversified energy portfolio, particularly, because it is a clean energy source with an inexhaustible supply. Wind energy has become one of the fastest growing renewable energy systems with promising prospects for large scale commercialization. This work presents an integrated optimum design of horizontal axis wind turbine and doubly fed induction generator system with multiple objectives and multiple design constraints. The design of horizontal axis wind turbine rotors for maximum power generation is considered, using the blade element momentum aerodynamic modeling, in this exploratory study. The rotor is assumed to operate over a specific range of wind velocity and the restrictions imposed upon the behavior of the structure involve limitations on aerodynamic axial induction factor and blade stresses that allow the turbine blade rotation while satisfying the strength requirements. The blade element momentum theory and Prandtl’s tip root loss approximation are used to develop the aerodynamic computational model and beam finite elements are used to idealize the rotor blade. The sequential quadratic programming method has been used to solve the multivariable nonlinear constrained optimization problem. Based on the structural design of the turbine, the power versus speed characteristic of the horizontal axis wind turbine is determined, which is subsequently used to develop a speed control strategy for the induction generator so as to make the wind turbine reach its maximum efficiency of power generation. The vector control of the doubly fed induction generator system for decoupling active and reactive power is presented, and the proportional and integral control of the rotor-side and the grid-side converters is outlined. A sudden step change in wind velocity is assumed for the simulation of the doubly fed induction generator system in order to predict the power output of the wind turbine system. The control of doubly fed generator system is carried out to improve the quality of power flow to the grid. Because many of the parameters associated with the wind turbine system such as wind velocity, variation of wind velocity with altitude, and fabrication/installation quantities like rotor height, blade dimensions and airfoil shape, are uncertain or random, a nonlinear constrained stochastic optimization problem of the wind turbine systems design is also formulated. The design variables corresponding to the optimum blade design are found to capture the maximum annual power at any specific location of the wind turbine system. The mean value plus a constant number of standard deviations of the annual power generated by the turbine is considered as the objective for maximization. In order to be able to handle the uncertainty problem without a precise knowledge of the random parameters, in terms of probability distributions and/or characteristics such as mean values and standard deviations, a fuzzy approach is also presented for the optimum design of wind turbine systems. Since most practical engineering design problems involve several conflicting objectives to be considered, a multi-objective optimization method is introduced in this work with the consideration of maximization of the power generated by the wind turbine along with the minimization of overshoot and settling tine of the transient response of the induction generator. To handle conflicting multiple objectives, appropriate membership functions of the objective functions, constraints and design variables are defined, and a method of solving a fuzzy multi-objective wind turbine system optimization problem using nonlinear programming techniques is presented.

Keywords

Probabilistic optimization; Fuzzy optimization; Wind turbines

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