Pitch-Controlled Variable-Speed Wind Turbine Generation

1 Pitch-Controlled variable -SpeedWind Turbine GenerationFebruary 2000 NREL/CP-500-27143E. Muljadi and ButterfieldPresented at the 1999 IEEE Industry ApplicationsSociety Annual MeetingPhoenix, ArizonaOctober 3-7, 1999 National Renewable Energy Laboratory1617 Cole BoulevardGolden, Colorado 80401-3393 NREL is a Department of Energy LaboratoryOperated by Midwest Research Institute Battelle BechtelContract No. DE-AC36-99-GO10337 NOTICEThe submitted manuscript has been offered by an employee of the Midwest Research Institute (MRI), acontractor of the US Government under Contract No. DE-AC36-99GO10337. Accordingly, the USGovernment and MRI retain a nonexclusive royalty-free license to publish or reproduce the publishedform of this contribution, or allow others to do so, for US Government report was prepared as an account of work sponsored by an agency of the United Statesgovernment.

2 Neither the United States government nor any agency thereof, nor any of their employees,makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy,completeness, or usefulness of any information, apparatus, product, or process disclosed, or representsthat its use would not infringe privately owned rights. Reference herein to any specific commercialproduct, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarilyconstitute or imply its endorsement, recommendation, or favoring by the United States government or anyagency thereof. The views and opinions of authors expressed herein do not necessarily state or reflectthose of the United States government or any agency electronically at for a processing fee to Department of Energyand its contractors, in paper, Department of EnergyOffice of Scientific and Technical Box 62 Oak Ridge, TN 37831-0062phone: : : for sale to the public, in paper, Department of CommerceNational Technical Information Service5285 Port Royal RoadSpringfield, VA 22161phone: : : ordering: on paper containing at least 50% wastepaper, including 20% postconsumer waste1 Pitch-Controlled variable -SPEEDWIND Turbine GENERATIONE.

3 Muljadi ButterfieldNational wind Technology CenterNational Renewable Energy Laboratory (NREL)1617 Cole BoulevardGolden, CO 80401, - wind energy is a viable option tocomplement other types of pollution-free the early development of wind energy, themajority of wind turbines were operated at constantspeed. Recently, the number of Variable-Speed windturbines installed in wind farms has increased andmore wind Turbine manufacturers are makingvariable- speed wind paper covers the operation of Variable-Speed wind turbines with pitch control. The systemwe considered is controlled to generate maximumenergy while minimizing loads. The maximization ofenergy was only carried out on a static basis andonly drive train loads were considered as aconstraint.

4 In medium wind speeds, the generatorand power converter control the wind Turbine tocapture maximum energy from the wind . In thehigh wind speed region, the wind Turbine iscontrolled to maintain the aerodynamic powerproduced by the wind Turbine . Two methods toadjust the aerodynamic power were investigated: pitch control and generator load control, both ofwhich are employed to control the operation of thewind analysis and simulation shows that thewind Turbine can be operated at its optimum energycapture while minimizing the load on the windturbine for a wide range of wind TERMSWind Turbine generator, renewable energy, Pitch-Controlled , variable INTRODUCTIONThe development of wind Turbine powergeneration has been expanding during the past 10 global market for the electrical power produced bythe wind Turbine generator (WTG) has been increasingsteadily, which directly pushes the wind technology intoa more competitive arena.

5 Recently, there have beenpositive trends shown by the utilities to offer renewableenergy to customers. Many customers who areenvironmentally conscious now have the option ofsubscribing to clean energy such as wind energy fromthe power provider. The European market has shownan ever-increasing demand for wind wind Turbine Generation has beengaining momentum, as shown by the number ofcompanies joining the Variable-Speed WTG Generation is claimed to have a betterenergy capture and lower loading. The effect ofturbulence on energy capture and power fluctuations invariable- speed wind turbines is affected by the overallcontrol algorithm used [1-4]. The method ofcontrolling the generator strongly affects the electricalpower generated by the generator [2].

6 Different typesof generators are used for Variable-Speed Generation fordirect drives [2-3]; however, control algorithms forwind Turbine operation are not discussed in goal of this project is to study the behavior ofthe wind Turbine generator operated under variablespeed with pitch -control capability under turbulentwinds. The basic comparison between a constant-speedwind Turbine and a Variable-Speed wind Turbine will alsobe explained. The constant- speed wind turbinePower Converter+ GeneratorPitchable BladeGear BoxUtility(60 Hz)WindLow speed shaftHigh speed shaft Figure 1. Physical diagram of the system2operation is a very simple case that can be used as abaseline. The Variable-Speed algorithm was chosenbased on the maximum energy and steady-state limit ofthe wind Turbine .

7 The steady-state limit is based on theCP-TSR curve provided. Thus in the steady statecalculation, wind gust and wind shear are notconsidered. It turns out that using the steady state limitis a good approximation in the lower wind speeds, asshown by the performance ratio and energy captured bythe wind concept that is fundamental to the controldynamics is that the speed change is relatively slowbecause of the large inertia involved. This makes itdifficult to use the power converter to control the speedin highly variable wind applications. pitch control isrelatively fast, however, and can be better used toregulate power flow especially when near the highspeed 1 shows the system under wind Turbine is connected to a Variable-Speed windturbine.

8 The generator output can be controlled tofollow the commanded power. The wind Turbine has apitchable blade to control the aerodynamic power. Thedashed line indicates that the pitch angle can becontrolled. It is shown that there is a mechanicalcomponent (such as a gearbox ) between the high-speedshaft and the low- speed shaft. The low- speed shaft isdriven by the Turbine blades, which generatesaerodynamic power. The high- speed shaft is loaded bythe electric generator in the form of electrical paper is organized as follows: The nextsection is devoted to the condition of the wind third section is devoted to the method of the fourth section, the discussion and analysis ispresented, and in the fifth section, the conclusion wind Turbine CHARACTERISTICSThe wind Turbine can be characterized by its CP -TSR (curve as shown in Figure 2), where the TSR is thetip- speed ratio; that is, the ratio between the linearspeed of the tip of the blade with respect to the windspeed.

9 It is shown that the power coefficient CP varieswith the tip- speed ratio. It is assumed that the windturbine is operated at high CP values most of the a fixed-frequency application, the rotor speed of theinduction generator varies by a few percent (based onthe slip) above the synchronous speed while the speedof the wind may vary across a wide Figure 2, the change of the CP-TSR curve as thepitch angle is adjusted is also shown. In low to mediumwind speeds, the pitch angle is controlled to allow thewind Turbine to operate at its optimum condition. In thehigh wind speed region, the pitch angle is increased toshed some of the aerodynamic Equation 1, the tip- speed ratio for a fixedspeed wind Turbine varies across a wide rangedepending on the wind speed .

10 The power captured bythe wind Turbine may be written as Equation 2. FromEquation 2, it is apparent that the power productionfrom the wind Turbine can be maximized if the system is(4) (3) )(RPM K = P = P3 PTARGET3mTARGET3 pTARGETTARGET speedrotorRPM_data Turbine windcomputed = KPTSRat CpCp)Cp(max power Target =P :whereTARGETTARGETTARGET==(m/s) velocity wind = Vturbinewindoftcoefficien = Cpm2 ( areaswep =A m3(kg/density air = :where (2) = Pmech)t) VR m = Rmeter/sec wind theof speedlinear = Vmeter blade theof radius = Rradian/sec mechanical speedrotor = m :where(1)TS Cp for different pitch RATIO (TSR)Cp (Power Coefficient)Angle = 0 degAngle = 6 degAngle = 10 degFigure 2.