A Single Phase Induction Generator As Wind Generator – A New Concept and Design

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Experimentation is done on a standard …

Experimentation is done on a standard
induction motor, run as a single phase induction
generator. The guidelines obtained from the performance
of this trial machine are used to design and construct a
novel prototype single phase induction generator. This
novel design combines the concepts of ac tachogenerator,
ac servomotor and dc self excited generator. It can
generate at low sub synchronous speeds corresponding
wind speeds being of the order of two to three meters/sec.
Utility of this machine for converting wind power to
electrical power for household consumption is put forth as
a novel concept in this field. Details of construction and
mathematical design of a prototype machine are given.
The performance of the prototype machine is shown to
tally well with the design.

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  • 1. ACEEE International Journal on Electrical and Power Engineering, Vol. 1, No. 2, July 2010 A Single Phase Induction Generator As Wind Generator – A New Concept and Design Mrs. N.R. Kulkarni,1 Dr.(Mrs.) Y.S. Apte2 1 Associate Professor in Electrical Engg.Modern College of Engg.Pune,India nrkmcoe@gmail.com 2 Retired Professor,IIT,Mumbai,India yashoda.apte@gmail.comAbstract- Experimentation is done on a standard between the two windings takes place. Current ratingsinduction motor, run as a single phase induction of main and auxiliary windings were 2.4A and 0.68Agenerator. The guidelines obtained from the performance respectively. Tapings at 50% winding were taken outof this trial machine are used to design and construct a for flexibility of connections and provision of feedback.novel prototype single phase induction generator. Thisnovel design combines the concepts of ac tachogenerator, A good quality fan chosen by experimentation from aac servomotor and dc self excited generator. It can number of fans was mounted on the generator shaft.generate at low sub synchronous speeds corresponding From the analysis of the experiments done on thiswind speeds being of the order of two to three meters/sec. machine, it is concluded that designing a generatorUtility of this machine for converting wind power to based on the above concept would be worthwhile afterelectrical power for household consumption is put forth as implementing some improvements such as increase ina novel concept in this field. Details of construction and length and optimising parameters like number of i/p,mathematical design of a prototype machine are given. o/p winding turns and swg of conductor, rotorThe performance of the prototype machine is shown to resistance (i.e. material used for rotor bars), propertally well with the design. selection of stampings etc. The basic principle ofKey words –wind generator Tachogenerator, sub working of generator is given below.synchronous speed, push pull amplifier, prototypemachine etc III. BASIC PRINCIPLE OF WORKING OF SINGLE PHASE GENERATOR I. INTRODUCTION The basic principle of working of the proposed Section II presents some experiments conducted on a machine is that the o/p voltage is generated for anytrial machine and design of a prototype single phase speed > 0 and it increases with increasing rotor speedwind generator. In section III principle of operation of and frequency of output is the same as input frequencysingle phase Induction generator based on tacho as in AC tachogenerator.generator principle is elaborated. In Section IV Two windings are mounted at right angle to eachanalytical design of 1-ph. Induction generator is other i.e. in space quadrature. Rotor is squirrel cage i.e.described. In Section V peripheral circuit and bars with end rings creating a short-circuited secondaryexperimental setup is given. Section VI gives winding. Resistance of rotor winding is taken high soexperimental results, Excel and Matlab simulated that X/R is small. Due to this Zero speed onwardresults with prototype machine and waveforms generating action takes place and single phase motoringobtained. Section VII concludes with highlighting the action is eliminated. Most of the literature on inductioncontributions of this work. Future scope is described at generators [5,6,7,8,9,10] reports generation at high orthe end. super synchronous speeds making it useless for small scale household generation where wind speeds are low. II. TRIAL ON PROTOTYPE MACHINE When i/p is given to reference winding the magnetic A typical single phase induction motor of rating 230 field produced along its axis can be represented asV, 3 Amp and 300 watt was taken for converting it to a equivalent to two clockwise and anticlockwise fields ofsingle phase generator for testing the novel concept of same magnitude and rotating in same directions. So thegenerating a voltage of constant frequency and torque produced is zero at standstill condition wheremagnitude proportional to all speeds including the sub the torque of each component is equal and opposite .synchronous speeds. This concept is taken from For any other speed (given by driving torque) theworking principle of tachogenerator. Two windings, resultant torque due to the two components is nonzeromain and auxiliary of the machine were rewound at and is negative due to x/R ratio of the rotor keptsmallerquadrature in space so that no magnetic coupling 6© 2010 ACEEEDOI: 01.ijepe.01.02.02
  • 2. ACEEE International Journal on Electrical and Power Engineering, Vol. 1, No. 2, July 2010than1(generating action).It is balanced against the The input flux density B is taken as reference vector asdriving torque giving steady speed. shown in fig I. with arbitrary magnitude and phase A simple explanation of the operation with angle zero. Then flux Фin is of magnitude = B*area of aapproximate phasor diagram is given below followed slot*4 (As 4 slots are used for input winding at oneby design of generator. Alternating flux Φin = Φm sinwt side) and same phase angle zero.is produced due to current carried by reference or input Flux density in tooth and core is calculated to keepcoil which is excited with ac voltage of frequency w them within allowed limit.radian/sec.When rotor is rotated with speed N rpm , Flux density of tooth Bth wb/m2 =B*Single slotvoltage is induced in rotor bars (V grb) under each half of pitch/Slot tooth widththe reference/ input winding i.e. in the single turn rotor Flux density in corecoil with its axis along the quadrature axis. Directions Bc wb/m2= (Ф/2)/((Ls/100)*(Thmin/100))of current in rotor bars under the two halves areopposite as linear speeds are in opposite directions. Excitation frequency is taken as an adjustable designThey form a single coil carrying the current and parameter Ampere turns (AT) required for gapcreating flux in quadrature. Atgi=B*800000*2*Lg/100 [4] The operation of ac tachogenerator is similar to a dctacho generator because the excitation flux and the Total ampere turns ATi = 1.25*Atgi taking intogenerated rotor flux are at quadrature in space in both. account those for the magnetic material path.EmfThe magnitudes of the voltages generated in the rotors induced per turn isof both are proportional to speed. However the fluxes Emf/turn Et= 4.44*Ф*f volts (rms).being ac in the ac tachogenerator no brushes are Total emf induced in input winding Ei= Et *No ofrequired to obtain output but the output voltage due to turns Magnetising Current (rms) required for the giventhe generated quadrature flux can be taken from stator Ampere turns Im = (ATi/Ti)/√2 Magnetising reactanceby transformer action. for the given magnetising path Xmi =Induced emf in input winding/ Im = Ei / Im IV.DESIGN OF GENERATOR Lm = Xmi/ (2*π*f)Choice of prototype machine Input winding resistance and output winding resistance, Material for stampings CRGO Ri and Ro respectively can be measured.Input winding leakage reactance Xli is assumed 15% of Xmi Maximum flux density for 1.6 wb/m2 CRGO Total input impedance = Ri +jXli Diameter (OD) of stator 10.5 cm The resistances of rotor are calculated for rotor winding (same as trial machine) around direct axis as Rrd and for rotor winding around quadrature axis as Rrq each of the two windings taken Length of stator was chosen 40 cm as single turn winding.So the current I rd in rotor as Ls (four times of trial winding around the direct axis given by transformer machine) action is Length of air gap kept Lg 0.055 cm Ird= Induced emf per turn/resistance Rrd Diameter of rotor Dr 6.29 cm Ird =Ird transferred to stator side = Ird /No of input turns Number of stator slots 24 A. Rotor Side Calculations Stator slot pitch SSP 1.15 cm As per the principle tachogenerator, generated Stator slot depth SSD 1.525 cm voltage by reference flux (Primary generation) in rotor bar is Thickness below the slot Thmin 1.3 cm Vgrb =d Фin/dt=d (B *A)/dt Number of Rotor slots 18 Where A=Area engaged by flux, B=corresponding flux Rotor tooth width RTW 0.6 cm density = Bm *sinwt. So Crossectional area of rotor 0.12 cm2 Vgrb =d (Bm *sinwt *A)/ dt = d (Bm *sinwt *S*L)/dt slot Where S = length of arc of stator engaged by flux rotor bar material Brass So Vgrb =Bm*L ( d (sinwt*S)/dt)= Bm*L*V *sinwt Following are the steps of design done in Window’sExcel sheet. where V= velocity of rotor bar. 7© 2010 ACEEEDOI: 01.ijepe.01.02.02
  • 3. ACEEE International Journal on Electrical and Power Engineering, Vol. 1, No. 2, July 2010Vgrb = Bm*V*L sinwt Xci is input capacitor connected across input winding. It is chosen practically in such a way that input Thus generated voltage has two components of 90 waveforms have good sinusoidal shape though thedegree phase difference amplifier input is a square wave.Generated voltage in turn Vgrt =2Bm*V*L sinwt Current in input capacitor Vin /XciB. Quadrature / Output Side Calculations Total current in the input circuit =Iin=Ii+Ic The output side capacitor is designed to maximize Idc=Iin/1.11 Average output voltage is Voavg Totalthe output voltage due to resonance.Xmo is magnetising resistance at output side =Ro+ R’rdreactance referred to output in output circuit Approximate Output power= ((Voavg-Vb)*Vb)/(Ro+R’rd)Xmo= Xmi*(To/Ti) 2 Vb is the loading battery voltage.Magnetising reactance referred to rotor side is Input power=Idc*Vinp/2Xmr= Xmo = Xmo/ (To2) Parameters considered for optimising the output in the excel design sheet areAt resonating condition Xmo =Xco i) The Input winding & Output winding turnsCapacitive reactance referred to rotor side Xco‘= Xco/(To2) ii) Rotor winding resistance iii) Frequency of reference input iv) Capacitance across the output winding.Output resistance referred to rotor side Ro = Ro/ (To2) The density of the excitation flux is adjusted so as toFor no load condition and with the resonating capacitor obtain output voltage of the specified value required foracross the output Emq = Vgrt (Neglecting the charging a 12 volts battery. Out of the 24 slots in theapproximation because of the output winding resistance stampings 8 and 16 slots are used for input winding andRo)Then the output current referred to rotor side Ior output winding respectively. Those are at quadrature in=Emq/ (Ro+jXco) space. Total turns accommodated in these slots areOutput voltage referred to rotor side Vor= Ior *Xco’ 136(68+68) with 34 conductors in a slot for inputOutput voltage Vop = Vor*To winding and 400(200+200) with 50 conductors in a slotThe flux density in quadrature axis Bmq is for output winding. Resistances of these windings areBmq=B*Emq /Ei 6.0 ohm and 12 ohm respectively. Rotor is squirrel Vgrd i.e. Voltage generated in rotor bar (secondary cage. Rotor bar resistance is 0.0064ohm. The resistancegenerated voltage) around direct axis has two of the single turn rotor winding of the cage rotor aroundcomponents similar to the primary generation direct axis and quadrature axis winding are 0.0016 &0.0032 respectively. The chosen material for rotorVgrd1= Bmq*v*L*sinwt Total Vgrd = 2Vgrd1 bars is brassTotal impedance of rotor circuit Zrd=Rrd+XmrCurrent due to Vgrd generated in rotor circuit is Igrd V. PERIPHERAL CIRCUITS AND LABORATORY SETUPIgrd=Vgrd/Zrd, Ird =Ei /Rrd As the optimizing frequency happens to be not equal to 50 Hz, the excitation voltage needs to be generated. A low frequency generator from laboratory Erd is used for this purpose. As its output current is very Ird low (about 100 mA) a three stage amplifier was designed. Switching mode, square wave input and push-pull type stages are chosen for the design in order B mq Im Bin Vgrt to keep loss in transistors low to avoid their heating. Electrical motor is used to drive the generator for Igrd Vgrd laboratory experiments. The linear wind speeds Fig I. Phasor diagram required to create rotational speeds of the following table are in the range of 2.5m/s to 5m/s for the chosenInput current Ii=I’rd +I’grd+Im fan of diameter 1m and this small generator of dia. 6.29cm and length 40cmAt input side there are 138 turns centre tapped. So inputvoltage Vin = 2Ei+Zi*Ii VI. EXPERIMENTAL OBSERVATIONS The capacitor C i across the input winding is chosen practically for good sinusoidal form of Vin across the 8© 2010 ACEEEDOI: 01.ijepe.01.02.02
  • 4. ACEEE International Journal on Electrical and Power Engineering, Vol. 1, No. 2, July 2010input winding. Capacitor connected across i/p winding experimentation for feedback and loading (12VCi=1100 microF, Capacitor connected across o/p battery) and the waveforms are given below in FigII.winding Co = 122 microF Observations taken on this It is observed from above mentioned readings andsystem with no load on output are given in Table No waveforms that output increases with speed more thanI(i). Waveforms are observed and they are good. The proportionately and results are matching with excelobservations tallied well with the corresponding sheet design results. In closed loop circuit the feedbackvariables of design sheet. The system performance was capacitor was chosen to give maximum output voltage.enhanced further by giving feedback The feedback As it was expected the output voltage is larger in thisdesign could not be done in excel sheet as the software case. Waveform across (Vcf and Vo) and (Vcf and Vin )cannot do circular computation. So feedback design were observed in order to measure relative phasewas done by practical trials. It was then verified by angles. Both the pair have common point as earthingMATLAB simulation.Again feedback capacitor Cf was point of DSO. So one from each pair is taken aschosen practically to maximize output voltage. This C f negative while calculating phase difference between Vois 50 microF (100+100 microF in series)The results of and Vin as shown in Table No I.(ii) TABLE NO I(I) OBSERVATIONS FOR OPEN LOOP SYSTEM Sr.No Speed Vip Vcc Freq Idc Vop 1 800 7 3.92 18.5 0.75 4 2 1200 7 3.92 19.4 0.75 8 3 1500 7 3.92 22.9 0.75 14 4 1550 8 3.95 23.4 0.75 16 5 1690 8 3.95 23.9 0.75 25 6 1750 8 3.95 24 0.65 26 7 1925 8 3.95 26.2 0.65 28where Vip = Peak input voltage Vcc = Battery voltage required for amplifier Freq = Input frequency I dc = Amplifier output current/current in the half input winding ,Vop = Peak output voltage TABLE NO I.(II) OBSERVATIONS FOR FEEDBACK AND LOADING 12 V BATTERY Angle Sr Speed freq Idc Vop Vip Ifb IL Vcc Angle Angle bet bet Vin betVi&V No rpm Hz Vout Amp Volts Volts A mA Volts and Vcf o and Vcf 1 1350 19.3 0.7 15 7 0.085 0 3.9 54 21 33 2 1350 19.3 0.725 12 7 0.05 5 3.9 54 21 33 3 1500 20.8 0.7 20 7 0.1 0 3.9 72 15 63 4 1500 20.8 0.725 12 7 0.08 15 3.9 72 15 57 5 1650 22.5 0.7 32 7 0.14 0 3.9 80 15 65 6 1650 22.5 0.75 12 7 0.08 24 0.3 80 21 59 7 1750 23.0 0.7 33 7 0.15 0 3.9 90 16 74 8 1750 23.0 0.7 12 7 0.08 25 3.9 90 24 66Matlab Simulation turns required for magnetic path, leakage flux density, air gap length, Rrd etc which cannot be measured The Excel model is fitted to the practical observations accurately.by minor adjustment of the parameters like ampere 9© 2010 ACEEEDOI: 01.ijepe.01.02.02
  • 5. ACEEE International Journal on Electrical and Power Engineering, Vol. 1, No. 2, July 2010 Then magnitude and phase angles of all variablesmatched well with Excel results. The same model isthen simulated in Matlab to observe dynamicperformance.The waveforms of various variables matched withthose observed in practical and saved by photograph ofthe display on oscilloscope.It is easy to verify dynamicperformance of machine by Matlab simulation. Soverification of results of experimentations for openloop is done by Matlab simulation as well as by Excel. Fig.II. Vop &Vinp for1500 rpm TABLE NO II. OPEN LOOP OUTPUT VOLTAGE FOR PRACTICAL OBSERVATION, MATLAB, EXCEL SIMULATION r.No Speed Freq Vinp Vop Angle between Vin and Vo In rpm In Hz Matlab Excel Observe Matlab Excel Observed Matlab Excel Observed Design Design d values Design Design Values Design Design Values 1 1150 18.5 7.0 7.1 7.0 9.0 9.0 9.0 72 74 72 2 1350 19.2 7.0 6.9 7.0 13.0 13.06 13.5 90 81 108 3 1500 20 7.0 8.53 7.0 15.5 15.3 15 72 89 72 VII. CONCLUSION 7)H.L. Rai, Prof. Singh, Prof S.S. Murthy “Simplified approach for the analysis of single phase IE (I) JOURNAL – As mentioned above the theoretical and practical Vol 79 Feb 1999 pp 167-171results tallied well. This developed confidence in the 8)Abdin E.S., Xu. W. ’‘Control Design and Dynamicstrategy of design in which theoretical design and performance analysis of wind turbine- induction generatorpractical design was alternately used as per unit”. IEEE transactions on Energy Conversion, Vo 15, No1 March 2000 pp 91-96convenience and verified at every stage by the other. 9)Bog Dow, S Borowy, Ziyad M Salameh “DynamicThe present research establishes that the innovative response of standalone wind energy conversionconcept of using a single phase externally excited low system with battery energy storage to a wind gust” IEEEfrequency; induction machine working on a. c. transactions on Energy Conversion, Vo 12, No1 March 1997tachogenerator principle is useful for household wind 10)M.Godoy Simoes, Sudipta Chakraborty, Robert Woodgeneration as it operates at low wind speeds and over a Induction generator for small wind energy system IEEElong enough range of speeds giving constant frequency power Electronics Society News Letter –Third edition 2006output. The machine is suitable as a household unit pp 19-22because of its low inertia and low maintenance N.R. Kulkarni was born on 07 December, 1963. She receivedrequirements. This is the first successful trial of this the B.E. (Electrical) in1985 from WCE, Sangli, India, M.E.kind as found from recent literature survey. (Electrical) in1998 and is pursuing Ph.D. (Electrical Engg)degree, Currently, she is Associate professor in REFERENCES Electrical Engineering Department, Modern college of Engg Pune. Her areas of interest include electrical machines, wind1)Hugh Piggott “Wind power workshop” Centre for energy conversion, power quality, and control systems.Alternative Technology publication 19972)Paul Gipe “Wind power for Home and Business” Amazon Y.S.Apte was born on 25 September 1939. She.com new edition2004 received the B.E. (Electrical) from WCE, Sangli,3)I.J.Nagrath & M. Gopal “Control System Engineering” India in 1961, M. Tech (Electrical) in1966 andNew age international publisher 3rd edition 19994)M.G.Say “Performance and design of alternating current Ph.D. degrees in1976from IIT, Mumbai, Indiamachines” CBS publisher & Distributers, New Delhi 3rd respectively. She was associated with IIIT,Edition, reprint 2002. Mumbai for 30 years and She is working as R&D5)S.S. Murthy, H.C.Rai, A.K.Tandon “A novel self excited Dean in Modern College of Engg. Pune She hasself regulated single phase Induction Generator” part-I &II many publications in the areas of MultivariableIEEE transactions Energy Conversion, Vol 8, No3September 1993 pp 377-388 control system. Her areas of interest include6)S.P. Singh, Dr. B Singh and Dr. M.P. Jain, ”Optimisation Multivariable control system & machine analysis,of a Self – excited Cage Induction Generator Design” IE (I) system reliability and renewable energy.JOURNAL: Vol 76 May 1995 pp 18-22 10© 2010 ACEEEDOI: 01.ijepe.01.02.02