Control of a Wind Driven Doubly Fed Induction Generator During Grid Faults

Master's Thesis from the year 2013 in the subject Engineering - Power Engineering, grade: none, - (Faculty of engineering-Minia university - Electrical engineering department), course: Electrical engineering (Renewable energy), language: English, abstract: Wind electrical power systems are recently getting lot of attention, becausethey are cost competitive, environmental clean and safe renewable powersource, as compared with fossil fuel and nuclear power generation. A specialtype of induction generator, called a doubly fed induction generator (DFIG),is used extensively for high-power wind applications. They are used moreand more in wind turbine applications due to ease controllability, highenergy efficiency and improved power quality.This thesis aims to develop a method of a field orientation scheme forcontrol both the active and reactive powers of a DFIG driven by a windturbine.The proposed control system consists of a wind turbine that drives aDFIG connected to the utility grid through AC-DC-AC link. The maincontrol objective is to regulate the dc link voltage for operation at maximumavailable wind power.This is achieved by controlling the and axescomponents of voltages and currents for both rotor side and line sideconverters using PI controllers. The complete dynamic model of theproposed system is described in detail. Computer simulations have beencarried out in order to validate the effectiveness of the proposed systemduring the variation of wind speed. The results prove that , better overallperformances are achieved, quick recover from wind speed disturbances inaddition to good tracking ability.Generally, any abnormalities associated with grid asymmetrical faults aregoing to affect the system performance considerably. During grid faults,unbalanced currents cause negative effects like overheating problems andmechanical stress due to high torque pulsations that can damage the rotor shaft, gearbox or blade assembly. Therefore, the dynamic model of theDFIG, driven by a wind turbine during grid faults has been analyzed anddeveloped using the method of symmetrical components. The dynamicperformance of the DFIG during unbalanced grid conditions is analyzed anddescribed in detail using digital simulations.A novel fault ride-through (FRT) capability is proposed (i.e. the ability ofthe power system to remain connected to the grid during faults) with suitablecontrol strategy in this thesis. In this scheme, the input mechanical energy ofthe wind turbine during grid faults is stored and utilized at the moment offault clearance, instead of being dissipated in the resistors of the crowbarcircuit as in the existing FRT schemes. [...]