22-06-2011, 02:12 PM
Doubly-Fed Induction Generator for Variable Speed Wind Energy Conversion Systems- Modeling & Simulation
Abstract— The aim of this paper is to present the complete modeling and simulation of wind turbine driven doubly-fed induction generator which feeds ac power to the utility grid. For that, two pulse width modulated voltage source converters are connected back to back between the rotor terminals and utility grid via common dc link. The grid side converter controls the power flow between the DC bus and the AC side and allows the system to be operated in sub-synchronous and super synchronous mode of operation. The proper rotor excitation is provided by the machine side converter. The complete system is modeled and simulated in the MATLAB Simulink environment in such a way that it can be suited for modeling of all types of induction generator configurations. The model makes use of rotor reference frame using dynamic vector approach for machine model.
Index Terms—doubly-fed induction generator (DFIG), pulse width modulation (PWM), dynamic vector approach, utility grid, wind energy conversion systems,
I. INTRODUCTION
The conventional energy sources are limited and have pollution to the environment. So more attention and interest have been paid to the utilization of renewable energy sources such as wind energy, fuel cell and solar energy etc. Wind energy is the fastest growing and most promising renewable energy source among them due to economically viable [1-8]. In India, the total installed capacity of wind power generation is 8754 MW in the year 2008.By the end of 2012, the total installed capacity is going to be reached to 12000 MW according to ministry of new and renewable energy, India and total installed capacity of wind energy is estimated to be more than 160 GW [WWEA] all around the world. There were several attempts to build large scale wind powered system to generate electrical energy. The first production of electrical energy with wind power was done in 1887 by Charles brush in Cleveland, Ohio.DC generator was used for power production and was designed to charge the batteries. The induction machine was used at the first time in 1951.
Manuscript received July 4, 2009. This work was supported in part by the National Mission on Power Electronics Technology under the Departmnet of Information Technology; India under the Project Wind Energy Harnessing
Many applications of wind power can be found in a wide power range from a few kilowatts to several megawatts in small scale off-grid standalone systems or large scale grid-connected wind farms. Recently Enercon constructed a wind turbine of 4.5 MW with rotor diameter of 112.8 meters. Due to lack of control on active and reactive power, this type of dispersed power generation causes problems in the electrical connected system. So this requires accurate modeling, control and selection of appropriate wind energy conversion system.
During last two decades, the high penetration of wind turbines in the power system has been closely related to the advancement of the wind turbine technology and the way of how to control. Doubly-fed induction machines are receiving increasing attention for wind energy conversion system during such situation. because the main advantage of such machines is that, if the rotor current is governed applying field orientation control-carried out using commercial double sided PWM inverters, decoupled control of stator side active and reactive power results and the power processed by the power converter is only a small fraction of the total system power. So doubly-fed induction machine with vector control is very attractive to the high performance variable speed drive and generating applications [1-4]. With increasing penetration of wind-derived power in interconnected power systems, it has become necessary to model the complete wind energy systems in order to study their impact and also to study wind power plant control. In this paper, an attempt to develop a dynamic model of induction machine which can be simulated as both motoring and generating mode when testing control strategies. Through the model developed in this paper can be used for simulating all types of induction generator configurations. The choice of synchronous rotating reference frame makes it particularly favorable for the simulation of doubly-fed configuration in transient conditions. The induction machine is modeled in vectorized form in the synchronous reference frame. The speed is adjusted by the turbine pitch control to maximize the power generated at a given wind speed. A complete simulation model is developed for such machine under variable speed operation using MATLAB Simulink environment. Section I describes the modeling of wind turbine for different wind velocities.
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