Direct Torque Control of a Doubly-Fed Induction Generator for Variable Speed Wind Turbines
ABSTRACT This paper presents the analysis and design of a Direct Torque Control (DTC) of a Doubly-Fed Induction Generator applied to a wind generation system as an alternative to the classical field-oriented control (FOC) widely used in drive control. The aims of the control system are the control of the reactive power interchanged between the generator and the grid and the control of the power drawn from the wind turbine in order to track the wind turbine optimum operation point. DTC appeared as a control concept for squirrel cage motor drives. In this paper, DTC concept is applied to control a wound rotor induction generator by means of a rotor connected VSI. Torque and rotor flux control are used to control in an indirect way active and reactive power, respectively.
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ABSTRACT: This paper proposes a hybrid ac/dc micro grid to re- duce the processes of multiple dc-ac-dc orac-dc-ac conversions in an individual ac or dc grid. The hybrid grid consists of both ac and dc networks connected together by multi-bidirectional converters. AC sources and loads are connected to the ac network whereas dc sources and loads are tied to the dc network. Energy storage systems can be connected to dc or ac links. The proposed hybrid grid can operate in a grid-tied or autonomous mode. The coordi- nation control algorithms are proposed for smooth power transfer between ac and dc links and for stable system operation under var- ious generation and load conditions. Uncertainty and intermittent characteristics of wind speed, solar irradiation level, ambient tem- perature, and load are also considered in system control and oper- ation. A small hybrid grid has been modeled and simulated using theSimulink intheMATLAB.The simulationresults showthatthe system can maintain stable operation under the proposed coordi- nation control schemes when the grid is switched from one oper- ating condition to another.IEEE Transactions on Smart Grid 01/2011; 2:278-286.
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ABSTRACT: Predictive direct control has been proposed and well developed because of its combination of simplicity and excellent steady-state and transient performance. This paper presents a predictive direct control strategy of doubly fed induction generator (DFIG) for grid synchronization. In no-load mode, predictive direct virtual torque control (PDVTC) is employed to meet the grid synchronization conditions. In grid-connected mode, the stator is connected to the grid, predictive direct power control (PDPC) is utilized with the purpose of flexible active and reactive power regulation. Furthermore, a rotor position sensorless scheme is proposed to make the control structure simpler during the grid synchronization process. The whole system is very simple and robust while the smooth and fast grid synchronization is achieved.Energy Conversion Congress and Exposition (ECCE), 2011 IEEE; 10/2011
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ABSTRACT: Undoubtedly, energy has a significant role in economic growth and technical developments. Renewable energy resources are becoming more important in recent years due to their tremendous contributions to the independence of power generation industry from traditional fossil energy resources. Wind energy has been outstanding among renewable energy resources since continuous harvestable potential on the earth is approximately around 106 MW. Concerning the variable nature of wind energy, the variable speed machines, especially doubly fed induction generators (DFIG) are one of the considerations for wind energy conversion systems (WECS). Their implementation in renewable energy conversion systems is dramatically increasing due to their numerous advantages such as low cost and small size, the elimination of external DC source, the ability to produce maximum power under various wind and rotational speeds, the capability of controlling active and reactive power, and the opportunity to employ cheaper and smaller convertors and controllers. This paper is an extensive review of researches in the past 30 years on DFIG. The study starts with describing general perspective on wind energy and commonly used generators in wind conversion. Then it presents more details on DFIGs operational modes, utilizations, their modeling and simulation. It is followed by DFIG control methods and overviews of different employed electrical and mechanical controlling methods. Finally the review on the mutual impact of DFIG on power networks and vice versa, including wind uncertainty, power and frequency stability, power and voltage quality, operation under steady state, dynamic and fault conditions, and protections is given. Based on the review DFIG has advantages in terms of electrical, mechanical, and economic perspectives. It can be concluded that the DFIG has the most promising future for WECSs in power generation to complement the conventional systems.Renewable and Sustainable Energy Reviews 11/2013; 27:692-708. · 5.63 Impact Factor