Wind Generation - NPTEL

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Wind GenerationHistory of Wind-Mills:¾ The wind is a by-product of solar energy. Approximately2% of the sun's energy reaching the earth is converted intowind energy.¾ The surface of the earth heats and cools unevenly, creatingatmospheric pressure zones that make air flow from high- tolow-pressure areas.¾ The wind has played an important role in the history ofhuman civilization .¾ The first known use of wind dates back 5,000 years toEgypt, where boats used sails to travel from shore to shore.

Wind Generation-1¾ The first true windmill, a machine with vanes attached to anaxis to produce circular motion, may have been built as earlyas 2000 B.C.¾ In ancient Babylon. By the 10th century A.D., windmills withwind-catching surfaces having 16 feet length and 30 feetheight were grinding grain in the areas in eastern Iran andAfghanistan.¾ The earliest written references to working wind machines inwestern world date from the 12th century.¾ These too were used for milling grain. It was not until a fewhundred years later that windmills were modified to pumpwater and reclaim much of Holland from the sea.

Wind Generation-2¾ The multi-vane "farm windmill" of the American Midwest andWest was invented in the United States during the latter half ofthe l9th century.¾ In 1889 there were 77 windmill factories in the United States,and by the turn of the century, windmills had become a majorAmerican export.¾ Until the diesel engine came along, many transcontinental railroutes in the U.S. depended on large multi-vane windmills topump water for steam locomotives.¾ Farm windmills are still being produced and used, though inreduced numbers.¾ They are best suited for pumping ground water in smallquantities to livestock water tanks.

Wind Generation-3¾ In the 1930s and 1940s, hundreds of thousands of electricityproducing wind turbines were built in the U.S.¾ They had two or three thin blades which rotated at high speedsto drive electrical generators.¾ These wind turbines provided electricity to farms beyond thereach of power lines and were typically used to charge storagebatteries, operate radio receivers and power a light bulb.¾ By the early 1950s, however, the extension of the central powergrid to nearly every American household, via the RuralElectrification Administration, eliminated the market for thesemachines. Wind turbine development lay nearly dormant for thenext 20 years.

Wind Generation-3¾ A typical modern windmill looks as shown in the followingfigure.¾ The wind-mill contains three blades about a horizontal axisinstalled on a tower.¾ A turbine connected to a generator is fixed about thehorizontal axis.

Wind Generation-4¾ Like the weather in general, the wind can be unpredictable. Itvaries from place to place, and from moment to moment.¾ Because it is invisible, it is not easily measured without specialinstruments.¾ Wind velocity is affected by the trees, buildings, hills andvalleys around us.¾ Wind is a diffuse energy source that cannot be contained orstored for use elsewhere or at another time.

Classification of Wind-mills¾ Wind turbines are classified into two general types: Horizontalaxis and Vertical axis.¾ A horizontal axis machine has its blades rotating on an axisparallel to the ground as shown in the above figure.¾ A vertical axis machine has its blades rotating on an axisperpendicular to the ground.¾ There are a number of available designs for both and each typehas certain advantages and disadvantages.¾ However, compared with the horizontal axis type, very fewvertical axis machines are available commercially.

Classification of Wind-mills-1Horizontal Axis:¾ This is the most common wind turbine design.¾ In addition to being parallel to the ground, the axis of bladerotation is parallel to the wind flow.¾ Some machines are designed to operate in an upwind mode,with the blades upwind of the tower.¾ In this case, a tail vane is usually used to keep the bladesfacing into the wind.¾ Other designs operate in a downwind mode so that the windpasses the tower before striking the blades.¾ Some very large wind turbines use a motor-driven mechanismthat turns the machine in response to a wind direction sensormounted on the tower.¾ Commonly found horizontal axis wind mills are aero-turbinemill with 35% efficiency and farm mills with 15% efficiency.

Classification of Wind-mills-3Vertical Axis:¾ Although vertical axis wind turbines have existed for centuries,they are not as common as their horizontal counterparts.¾ The main reason for this is that they do not take advantage ofthe higher wind speeds at higher elevations above the ground aswell as horizontal axis turbines.¾ The basic vertical axis designs are the Darrieus, which hascurved blades and efficiency of 35%, the Giromill, which hasstraight blades, and efficiency of 35%, and the Savonius, whichuses scoops to catch the wind and the efficiency of 30%.¾ A vertical axis machine need not be oriented with respect towind direction.

Classification of Wind-mills-4¾ Because the shaft is vertical, the transmission and generatorcan be mounted at ground level allowing easier servicing and alighter weight, lower cost tower.¾ Although vertical axis wind turbines have these advantages,their designs are not as efficient at collecting energy from thewind as are the horizontal machine designs.¾ There is one more type of wind-mill called Cyclo-gyro windmill with very high efficiency of about 60%. However, it is notvery stable and is very sensitive to wind direction. It is alsovery complex to build.

Classification of Wind-mills-5¾ The following figures show all the above mentioned mills.

Main Components of a wind-mill¾ Following figure shows typical components of a horizontal axiswind mill.

Main Components of a wind-mill-1Rotor:¾ The portion of the wind turbine that collects energy from thewind is called the rotor.¾ The rotor usually consists of two or more wooden, fiberglass ormetal blades which rotate about an axis (horizontal or vertical) ata rate determined by the wind speed and the shape of the blades.¾ The blades are attached to the hub, which in turn is attached tothe main shaft.Drag Design:¾ Blade designs operate on either the principle of drag or lift.¾ For the drag design, the wind literally pushes the blades out ofthe way.¾ Drag powered wind turbines are characterized by slowerrotational speeds and high torque capabilities.

Main Components of a wind-mill-2Lift Design:¾ The lift blade design employs the same principle that enablesairplanes, kites and birds to fly.¾ The blade is essentially an airfoil, or wing.¾ When air flows past the blade, a wind speed and pressuredifferential is created between the upper and lower bladesurfaces.¾ The pressure at the lower surface is greater and thus acts to"lift" the blade.¾ When blades are attached to a central axis, like a wind turbinerotor, the lift is translated into rotational motion.¾ Lift-powered wind turbines have much higher rotational speedsthan drag types and therefore well suited for electricitygeneration.

Main Components of a wind-mill-3¾ Following figure gives an idea about the drag and lift principle.¾Tip Speed Ratio:¾The tip-speed is the ratio of the rotational speed of the blade tothe wind speed.¾The larger this ratio, the faster the rotation of the wind turbine rotorat a given wind speed.

Main Components of a wind-mill-4¾ Electricity generation requires high rotational speeds.¾ Lift-type wind turbines have maximum tip-speed ratios ofaround 10, while drag-type ratios are approximately 1.¾ Given the high rotational speed requirements of electricalgenerators, it is clear that the lift-type wind turbine is mostpractical for this application.¾ The number of blades that make up a rotor and the total areathey cover affect wind turbine performance.¾ For a lift-type rotor to function effectively, the wind must flowsmoothly over the blades.¾ To avoid turbulence, spacing between blades should be greatenough so that one blade will not encounter the disturbed,weaker air flow caused by the blade which passed before it.¾ It is because of this requirement that most wind turbines haveonly two or three blades on their rotors.

Main Components of a wind-mill-5Generator:¾ The generator is what converts the turning motion of a windturbine's blades into electricity.¾ Inside this component, coils of wire are rotated in a magneticfield to produce electricity.¾ Different generator designs produce either alternating current(AC) or direct current (DC), and they are available in a largerange of output power ratings.¾ The generator's rating, or size, is dependent on the length of thewind turbine's blades because more energy is captured bylonger blades.¾ It is important to select the right type of generator to matchintended use.

Main Components of a wind-mill-6¾ Most home and office appliances operate on 240 volt, 50 cyclesAC.¾ Some appliances can operate on either AC or DC, such as lightbulbs and resistance heaters, and many others can be adapted torun on DC.¾ Storage systems using batteries store DC and usually areconfigured at voltages of between 12 volts and 120 volts.¾ Generators that produce AC are generally equipped with featuresto produce the correct voltage of 240 V and constant frequency50 cycles of electricity, even when the wind speed is fluctuating.¾ DC generators are normally used in battery chargingapplications and for operating DC appliances and machinery.¾ They also can be used to produce AC electricity with the use ofan inverter, which converts DC to AC.

Main Components of a wind-mill-7Transmission:¾ The number of revolutions per minute (rpm) of a wind turbinerotor can range between 40 rpm and 400 rpm, depending on themodel and the wind speed.¾ Generators typically require rpm's of 1,200 to 1,800.¾ As a result, most wind turbines require a gear-box transmissionto increase the rotation of the generator to the speeds necessaryfor efficient electricity production.¾ Some DC-type wind turbines do not use transmissions.¾ Instead, they have a direct link between the rotor and generator.¾ These are known as direct drive systems.¾ Without a transmission, wind turbine complexity andmaintenance requirements are reduced.¾ But a much larger generator is required to deliver the samepower output as the AC-type wind turbines.

Main Components of a wind-mill-8Tower:¾ The tower on which a wind turbine is mounted is not just asupport structure.¾ It also raises the wind turbine so that its blades safely clear theground and so it can reach the stronger winds at higherelevations.¾ Maximum tower height is optional in most cases, except wherezoning restrictions apply.¾ The decision of what height tower to use will be based on thecost of taller towers versus the value of the increase in energyproduction resulting from their use.¾ Studies have shown that the added cost of increasing towerheight is often justified by the added power generated from thestronger winds.¾ Larger wind turbines are usually mounted on towers rangingfrom 40 to 70 meters tall.

Main Components of a wind-mill-9¾ Towers for small wind systems are generally "guyed" designs.¾ This means that there are guy wires anchored to the ground onthree or four sides of the tower to hold it erect.¾ These towers cost less than freestanding towers, but requiremore land area to anchor the guy wires.¾ Some of these guyed towers are erected by tilting them up.¾ This operation can be quickly accomplished using only a winch,with the turbine already mounted to the tower top.¾ This simplifies not only installation, but maintenance as well.Towers can be constructed of a simple tube, a wooden pole or alattice of tubes, rods, and angle iron.¾ Large wind turbines may be mounted on lattice towers, tubetowers or guyed tilt-up towers.

Operating Characteristics of wind mills¾ All wind machines share certain operating characteristics, such ascut-in, rated and cut-out wind speeds.Cut-in Speed:¾ Cut-in speed is the minimum wind speed at which the blades willturn and generate usable power.¾ This wind speed is typically between 10 and 16 kmph.Rated Speed:¾ The rated speed is the minimum wind speed at which the windturbine will generate its designated rated power.For example, a "10 kilowatt" wind turbine may not generate 10kilowatts until wind speeds reach 40 kmph.¾ Rated speed for most machines is in the range of 40 to 55 kmph.

Operating Characteristics of wind mills-1¾ At wind speeds between cut-in and rated, the power output froma wind turbine increases as the wind increases.¾ The output of most machines levels off above the rated speed.Most manufacturers provide graphs, called "power curves,"showing how their wind turbine output varies with wind speed.Cut-out Speed:¾ At very high wind speeds, typically between 72 and 128 kmph,most wind turbines cease power generation and shut down.¾ The wind speed at which shut down occurs is called the cut-outspeed.¾ Having a cut-out speed is a safety feature which protects thewind turbine from damage.¾ Shut down may occur in one of several ways. In some machinesan automatic brake is activated by a wind speed sensor.

Operating Characteristics of wind mills-2¾ Some machines twist or "pitch" the blades to spill the wind.¾ Still others use "spoilers," drag flaps mounted on the blades orthe hub which are automatically activated by high rotor rpm's,or mechanically activated by a spring loaded device whichturns the machine sideways to the wind stream.¾ Normal wind turbine operation usually resumes when the winddrops back to a safe level.Betz Limit:¾ It is the flow of air over the blades and through the rotor areathat makes a wind turbine function.¾ The wind turbine extracts energy by slowing the wind down.

Operating Characteristics of wind mills-3¾ The theoretical maximum amount of energy in the wind that canbe collected by a wind turbine's rotor is approximately 59%.¾ This value is known as the Betz limit. If the blades were 100%efficient, a wind turbine would not work because the air, havinggiven up all its energy, would entirely stop.¾ In practice, the collection efficiency of a rotor is not as high as59%. A more typical efficiency is 35% to 45%.¾ A complete wind energy system, including rotor, transmission,generator, storage and other devices, which all have less thanperfect efficiencies, will deliver between 10% and 30% of theoriginal energy available in the wind.

Mathematical Expression GoverningWind Power¾ The wind power is generated due to the movement of wind.¾ The energy associated with such movement is the kinetic energyand is given by the following expression:12Energy KE m v2Wherem Air mass in Kg Volume (m3) x Density (Kg/m3) Q x ρQ Dischargev Velocity of air mass in m/sHence, the expression for power can be derived as follows:dEPower dt

Mathematical Expression GoverningWind Power-1{}{}1 d m v22 dt1 dρ Q v2 2 dtdQ 21 ρ vdt2dQHere, Rate of discharge (m3/s) A (m2) v (m/s)dtWhere, A Area of cross section of blade movement.1Power ρ A v 32

Mathematical Expression GoverningWind Power-2¾ We know that for given length of blades, A is constant and so isthe air mass density ρ.¾ Hence we can say that wind power is directly proportional to(wind speed) 3.At sea level, ρ 1.2 Kg/m3. Therefore,1Power (1.2) A v 32Power (0.6) v 3 Power Density in watts/m2Area

Mathematical Expression GoverningWind Power-3¾ Let us construct a chart relating the wind speed to the powerdensity and the output of the wind turbine assuming 30%efficiency of the turbine as shown in the following table.Wind SpeedkmphWind speed Power Densitym/sWatts/m2Turbine Output30% efficiency10.2780.004Wind SpeedkmphWind speed Power Densitym/sWatts/m2Turbine Output30% 13

Mathematical Expression GoverningWind Power-4¾ The following plot gives the relationship between wind speed inKMPH and the power density.Wind Speed Vs Power Density30000.000Power Density in 000.0000.00020.00040.00060.00080.000 100.000 120.000 140.000-5000.000W ind speed in KMPH

Mathematical Expression GoverningWind Power-5¾ In the last column of the table, we have calculated the output ofthe turbine assuming that the efficiency of the turbine is 30%.¾ However, we need to remember that the efficiency of theturbine is a function of wind speed. It varies with wind speed.¾ Now, let us try to calculate the wind speed required to generatepower equivalent to 1 square meter PV panel with 12%efficiency.¾ We know that solar insolation available at the PV panel is 1000watts/m2 at standard condition.¾ Hence the output of the PV panel with 12% efficiency would be120 watts.

Mathematical Expression GoverningWind Power-6¾ Now the speed required to generate this power by the turbinewith 30% efficiency can be calculated as follows:¾ Turbine output required 120 Watts/m2¾ Power Density at the blades 120/ (0.3) 400 watts/m2¾ Therefore, the wind speed required to generate equivalent powerin m/s 400 1 / 3 8.735805 m/s 31.4489 kmph. 0.6 ¾ We have seen that the theoretical power is given by thefollowing expression:Ptheoretica l1 ρ A v32

Mathematical Expression GoverningWind Power-6¾ However, there would be losses due to friction and hence, theactual power generated would be smaller.¾ The co-efficient of power is defined as the ratio of actual powerto the theoretical power. That is,PactualCp Ptheoretica l¾Another important ratio we need to know is the tip speed ratio.It is defined as the ratio of tip speed of blade to wind speed. That is,Tip Speed of Blade ω radius (radians sec ond ) meters TR Wind Speedvelocity(meters sec ond )In general, Cp is of the order of 0.4 to 0.6 and TR is of the order of 0.8.

Grid Connection¾ We have seen in the previous section the generation of electricalpower by the flow of water through turbines.¾ The generated electrical power could be dc or ac depending onthe type of generator.¾ After the power is generated, it needs to be transmitted anddistributed to consumers by connecting it to the grid.¾ Following figure shows how the grid connection is done. It hasthe following sections:a)b)c)d)The rectifier.The capacitor.Switches.Inductor.

Grid Connection-1¾ The rectifier is required if the generated power is ac byalternator or induction generator.¾ The capacitor is required to smooth the generated power.¾ Switches are required to convert the power to ac to match thegrid frequency .¾ inductors are required to develop the 4D6D2RectifierD4InverterD82

Grid Connection-2GridVinvVL1L1 Vgrid2C112L2In the above figure,di LvL L dt1i L v L dtLAlso

Grid Connection-3Alsodi L v L vinv v grid dtLLThe above equation can be realized as follows:VgridGain-1Ig*d/dtdig*/dtLVgrid -VinvfeedbackcontrollerPWMVinv

Grid Connection-4¾ The starting reference is the grid voltage Vgrid.¾ The current Ig* proportional to the grid voltage is fed through adifferentiator giving dIg*/dt.¾ This is equivalent to a value given in equation (3). Multiplyingthis value by L gives (Vinv – Vgrid).¾ Adding this to Vgrid taken directly from the grid gives Vinv.¾ This is compared to the actual Vinv measured at the output ofthe inverter.¾ If the error is zero, then the voltage across the grid and thevoltage at the output of the inverter are same and hence can beconnected to each other.¾ If there is an error signal then the controller changes the dutycycle of PWM such that the error signal becomes zero.

Grid Connection-5¾ Harnessing wind power by means of windmills can be tracedback to about four thousand years from now when they wereused for milling and grinding of grains and for pumping ofwater.¾ However there has been a renewed interest in wind energy inthe recent years as it is a potential source of electricitygeneration with minimum environmental impact [1].¾ According to present growth the accumulated world wideinstalled wind electric generation capacity will reach to 50GWat the end of year 2005[2].¾ India has the fifth position in the generation of wind electricgeneration.

Grid Connection-6¾ In India Wind power plants have been installed in Gujarat,Maharashtra, Tamilnadu and Orissa where wind blows at aspeeds of 30Km/hr during summer [3] but India has lot ofpotential for generation of wind power at other places inAndhra Pradesh, Madhya Pradesh, Karnatka and Kerala.¾ The total estimated wind power potential in India is about45195MW[4].¾ Wind electric systems directly feeding to the local load areknown as the isolated wind energy system .¾ The wind energy system that are connected to grid are knownas grid connected system .

Grid Connection-7¾ Wind is not available all the time for the generation of electricpower¾ power output of wind turbine is proportional to the cube of thevelocity of wind and the power output is optimal for a particularwind velocity.¾ So Large wind electric generator (WEG) systems are connectedto utility grid where they feed the power to grid.¾ The connection of cage rotor Induction Generator to grid againcause the problems in terms of drawing large magnetizingcurrent from grid at very low power factor.¾ Under the low wind conditions when the machine draws onlyreactive power from grid and stator power factor is very poor.

Grid Connection-8¾ Lagging power factor is compensated by connecting capacitorbanks across the line.¾ Depending on the active power generated these capacitors areeither cut-in or cut out to regulate the power factor.¾ The switching of capacitors may cause the over voltage inpower system [1].¾ So various techniques for connecting the WEG to grid hasbeen proposed [2,5,6].¾ The stand -alone system can be better utilized by using loadmatching techniques [7].

Wind Energy Regions in India¾ India has several on shore and off shore wind energy sites.¾ India has a lot of scope in terms of harnessing wind power usingthese sites.¾ The state wise estimated wind power potential in India is shownin table1 (Gross potential is based on assuming 1% of landavailability for wind power generation in potential areas.)SiNo.StateGross Potential(MW)TotalCapacity(MW) Technical(31-09-04)Potential 803Karnataka 6620274.21120

Wind Energy Regions in India-1SiNo.StateGrossPotential(MW)Total Capacity (MW) TechnicalPotential 958Tamilnadu30501683.617509West Bengal4501.145010Others29903.1-11Total (AllIndia)451952884.7512875

Wind Energy Regions in India-2¾ WEG of 2 MW capacity is installed in suzlon (Tamilnadu) isthe largest power rating in India.¾ Maximum WEG installations are in Tamilnadu of capacityabout 1639MW.¾ Maximum gross estimated Wind potential is in Gujarat of9675 MW.¾ The map of India is shown below indicating the various windenergy sites in India.

Wind Energy Regions in India-3

Wind Energy Regions in India-4Limitations of Present day WEG ‘s:¾ Most of the present day WEG ‘s are the constant speedinstallations.¾ These WEG’S have some limitations as given belowA-Poor Energy Capture¾ This is due to low aerodynamic efficiency of WEG and thevariation in efficiency over the entire operating range.Power output of turbinePt .5 Cp ρ A v3ρ Air density, A swept area, v wind velocity, Cp is calledthe power coefficient and is dependent on the linear velocityof the blade tip (Rω) and the wind velocity (v).The ratio, known as the tip-speed ratio, is defined asλ Rω/vwhere R is the radius of the turbine

Wind Energy Regions in India-5¾ From fig 1 it is observed that the power coefficient is maximumfor a particular tip ratio. So power capture is not optimum atother wind velocity.

Wind Energy Regions in India-6B-Reactive Power Consumption¾ Since most WEG ‘s employ induction generators aselectromechanical energy converters these WEG ‘s drawreactive power from grid for excitation.¾ This leads to additional T&D losses and changes in voltagestability margins.C- Unstable grid frequency¾ Most WEG ‘s have their blade design based on expected speedof the IG (grid frequency).¾ The aerodynamic efficiency greatly reduces when the gridfrequency is not maintained a constant at the specified level dueto the changes in the tip speed ratio.

Wind Energy Regions in India-7¾ By considering above-mentioned problems it is preferable torun WEG at variable speed.¾ A variable speed WEG enables enhanced power capture ascompared to constant speed WEG.¾ The rotor speed can be made to vary with changing windvelocity so the turbine always operates with max Cp within thepower and speed limits of the system.¾ Various control schemes are used for both Isolated WEG andgrid connected WEG running at variable speed.

Wind Energy Regions in India-8Isolated WEG:A- Load Matching¾ When wind driven self excited Induction generator (SEIG)running at variable Speed.¾ it is essential that the power output of the generator increasewith increasing power input to the prime mover.¾ which in the case of wind turbine varies approximately as thecube of the wind speed.¾ If this load matching is not planned properly, the generatorwould either over speed at high wind speed or come out ofexcitation at low wind speeds.

Wind Energy Regions in India-9¾ since the output voltage and frequency of the generator varieswith wind speed for many applications requiring constantvoltage.¾ some kind of power electronic controller is needed betweenthe generator and load. Fig shows a scheme employing aPWM inverter to obtain the voltage of required magnitude andfrequency at the load terminal.¾ Loads are connected through control switch, which couldappropriately be activated by monitoring the wind speed asshown in the fig2.

Wind Energy Regions in 1Firing andcontrolcircuitLoad2Voltage sensingControlInput

Wind Energy Regions in India-11B- Scalar Control of IG :¾ Scalar control of IG means control of magnitude of voltage andfrequency so as to achieve suitable speed with an impressed slip.¾ Scalar control disregards the coupling effect on the generator;that is, the voltage will be set to control the flux and thefrequency in order to control the torque.¾ If the IG is primarily in stand-alone operation, reactive powermust be supplied for proper excitation.¾ The overall scheme of control is shown below in fig3.

Wind Energy Regions in India-12Battery Start upVd M calculatorωrVa,b,cia,b,c*ScalarControlVsVs*Vd* ψ*Te*

Wind Energy Regions in India-13¾ The capacitor bank is bulk uncontrolled source of reactivecurrent.¾ The static VAR compensator is an inverter providing acontrolled source of reactive current.¾ Machine torque and flux input will be used in this applicationto regulate both DC link voltage at the capacitance C andgenerator voltage supplied for the AC load.¾ These regulators have to reject the disturbances produced byload and speed variations.¾ A DC link voltage regulator has been implemented to achievehigh enough DC link voltage for proper current controlledinverter operation.¾ The regulator input is the difference between the DC linkreference and measured value.

Wind Energy Regions in India-14¾ At the generator side terminal current and voltages aremeasured to calculate the magnetizing current needed for thegenerator,¾ The instantaneous peak voltage is compared to the statorvoltage reference, which generates a set point for flux throughthe feedback loops on the inverter side.¾ This system requires a charged battery startup. That can berecharged with an auxiliary circuit after the system isoperational.¾ Since stator voltage is kept constant the frequency can bestabilized at about 50Hz for the AC load,¾ but some slight frequency variation is still persists and therange of turbine shaft variation should be within the criticalslip in order to avoid instability.¾ Therefore AC loads should not be too sensitive for frequencyvariation in this stand- alone application.

Wind Energy Regions in India-15C- Vector Control of IG¾ The decoupled flux and torque control of IG is known asvector control.¾ For an IG operating in stand- alone mode, a procedure toregulate the output voltage is required as shown in the fig4.¾ The DC link voltage across the capacitor is kept constant andmachine impressed terminal frequency will vary with variablespeed.¾ Since the frequency of generated voltage depends on the windspeed (rotor speed).¾ the product of the rotor speed and the flux linkage should beremain constant so that the terminal voltage will remainconstant.

Wind Energy Regions in India-16¾ where the maximum rotor speed corresponding to maximumsaturated flux linkage.¾ The system starts up with a battery connected to the inverter.¾ Then, as the system DC link voltage is regulated a highervalue across the capacitor, the battery will be turned off by thediode and the DC load can be supplied across the capacitor.¾ The machine terminals are also capable of supplying the powerto an auxiliary load at variable frequency.

Wind Energy Regions in India-17Battery Start up Flux slip unitVector estimationωria,b,ccosθVR and 2to3phasevds*ψψs* ψmax ωmin/ωrVd* ψssinθvqs*ψ* Iqs*iqsnψsStator fluxDecouplerids*ids3phase to 2Phase.iaibic

Wind Energy Regions in India-18Generator Connected to Grid:A -Scalar Control¾ A current –fed link system for grid connection with constantV/Hz is depicted in fig5.¾ The DC link current allows easy bi-directional flow of power.¾ Although the DC link current is unidirectional.¾ A power reve

producing wind turbines were built in the U.S. ¾They had two or three thin blades which rotated at high speeds to drive electrical generators. ¾These wind turbines provided electricity to farms beyond the reach of power lines and were typically used to charge storage b

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