IJETT-V4I4P253.pdf

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International Journal of Engineering Trends and Technology (IJETT) - Volume4Issue4- April 2013

ISSN: 2231-5381 http://www.ijettjournal.org Page 776

Speed Control of Induction Motor using

CycloconverterB. SAI SINDURA #1, B. N . KARTHEEK *2,

# Department of Electrical and Electronics Engineering, K L UniversityVaddeswaram, Guntur, AP, India

* Asst Professor Department of Electrical and Electronics Engineering, K L University

Vaddeswaram, Guntur, AP, India

Abstract This method is used to control the speed of the

induction motor .The speed control by this method is simple andcan be made economical by using different methods to control theoperation of cycloconverter which in turn controls theperformance of motor. The formula for speed for inductionmotor is Ns=120f/p. from this formula we can conclude that thespeed of the motor can be varied in two ways, one is by changingthe number of poles and the second method is by changing thefrequency. The speed control through the first method isuneconomical and the number of poles cant be varied underrunning conditions and the size of the machine also becomesbulky. These problems can be overcome by the second method. Inthis method the frequency can be varied under runningconditions also and there is no change in the size of the motor. Inthis method the frequency changing device is cycloconverter. Acycloconverter is a power electronic device used to convert

constant voltage constant Frequency AC power to adjustablevoltage adjustable frequency AC power without a DC link . Inamong all the methods this method is simple, reliable andeconomical. The various speed of induction motor is obtained byvarying the supply frequency by using cycloconverter.

Keywords- Cycloconverter, Split Phase Induction Motor

I. I NTRODUCTION

Speed control of induction motor isnecessary in industrial applications. There areseveral methods for the speed control of inductionmotor.Cyclo-converters are used in very largevariable frequency drives with ratings from fewmegawatts up to many tens of megawatts. Acycloconverter is controlled through the timing ofits firing pulses, so that it produces an alternatingoutput voltage. It can also be considered as a staticfrequency changer and typically contains silicon-controlled rectifiers.The development of the

semiconductor devices has made it possible tocontrol the frequency of the cycloconverteraccording to the requirement and deliver a largeamount of controlled power with the help ofsemiconductor switching devices like Thyristors,MOSFETs in order to get alternating output ofvariable frequency. The quality of the outputwaveform improves if more switching devices areused. Split-phase induction motors are widely usedin many applications due to their energy efficientcharacteristics. Improvements in its performancemean a great saving in electrical energy

consumption. Thus, a cycloconverter has the facilityfor continuous and independent control over both itsoutput frequency and voltage. Cycloconvertereliminates the use of flywheel because the presenceof flywheel in machine increases torsional vibrationand fatigue in the component of power transmissionsystem.

II. S INGLE - PHASE TO SINGLE -PHASE CYCLO -CONVERTER

The single-phase to single-phasecycloconverter with mid-tap transformer typeconverter is shown in Fig.1.

As shown in fig.1. in this type ofarrangement midpoint tap transformer is use toobtain variable voltage and variable frequency.Waveforms shown are obtained by varying thenumber of cycle covered by positive and thenegative converters and firing angle.

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Fig.1 Single Phase Mid-tap Transformer Type Cycloconverter

III. WORKING

The frequency can be varied by varying theconduction period for each mosfet. The gate pulsefor SCR can be provided by either by using firingcircuit. Here for positive half cycle of input orsupply.T1, T2 are forward biased, T1 is given

pulse. For negative half cycle of input or supplyT1, T2 are forward biased. T1 is given pulse. Foranother positive half cycle T2 is given pulse. Foranother negative half cycle T2 is given pulse. Byusing cycloconverters we can vary voltage andfrequency. As AC motor characteristics require theapplied voltage to be proportionally adjustedwhenever the frequency is changed in order todeliver the rated torque this method is also calledvolts/hertz.. For optimum performance, somefurther voltage adjustment may be necessary

especially at low speeds, but constant volts per hertzare the general rule. This ratio can be changed inorder to change the torque delivered by the motor.

The input voltage, Vs is an ac voltage at afrequency, fi, as shown in Fig.2 (A). All thethyristors are fired at =0 firing angle, i.e.thyristors act like diodes. Note that the firing anglesare named as P for the positive converter and N for the negative converter. The frequency of Vo can

be changed by varying the number of cycles the positive and the negative converters work. It canonly change as integer multiples of input frequencyin Single Phase to Single Phase Cycloconverter. Forexample, to obtain the input frequency four timesthe output frequency as shown in fig.2 (B) fired

positive group and negative group converteralternately.

Fig.2 (A) Input Voltage Waveform of Single Phase to Single PhaseCycloconverter

Fig.2 (B) Output Voltage Waveform for Zero Firing Angle of Single Phase toSingle Phase Cycloconverter (Input Frequency is Four Times Output

Frequency)

IV: MODELING OF SPLIT PHASE INDUCTIONMOTOR

Split phase induction motors are usuallyconstructed with two windings on the stator sideand squirrel cage winding in the rotor side. Theauxiliary winding is used to produce a rotating fieldto start the motor. The axis of the auxiliary windingis placed 90 electrical ahead of the main windingas shown in Fig.3. The simulation of the motor is

presented in the stationary d-q frame to facilitate theapplication of the inverter. Since the axis of themain and auxiliary windings are already orthogonal,the stationary d-q axes are chosen aligned with the

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orthogonal axes of the physical windings. Thesquirrel cage rotor is represented by equivalent twocoils transformed to the stationary d-q axis asshown in Fig.3.

Fig.3 Modeling of Split Phase Induction Motor

Stator windings covers two windings namely themain and auxiliary coils have different number ofturns and different mutual reactance. Therefore, atransformation is made to transfer the auxiliarywinding to an equivalent winding with the samenumber of turns as that of the main coil. The new

variables referred to the equivalent coil are given asfollows:-

r mss i Li Ls r mss i Li Ls r r sm i Li Lr

r r sm i Li Lr

The current equation of the motor can be written inthe d-q stationary frame as follows:

mr s

r msr s

L L L L L

i2

mr s

smr sr

L L L L L

i2

mr s

smr sr

L L L L L

i 2

The equations of motion are given by:

)( r smr sm pe ii Lii LPT

Ler T T dt d

J

Where; r r ss ,,, are the d-q stator and rotor flux

linkage, respectively, r r ss iiii ,,, are the statorand rotor currents, r r ss L L L L ,,, are the statorand rotor inductances, mm L L , are the magnetizinginductances,

r =Rotor speed, electric rad/sec,Te =Developed torque,

LT =Load torque,

J =Rotor moment of inertia,

V: SIMULATION RESULT

Simulink model of split phase inductionmotor and single phase to single phasecycloconverter is shown in Fig.3. The objective ofthis paper is to analyse the speed of induction motor

performance. The stator of a split phase inductionmotor has two windings, the main winding and

mr s

r msr s

L L L L L

i2

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auxiliary winding. Since, the d-q axis model of aninduction motor is only valid for sinusoidal inputvoltage. Fig4 and Fig5 shows output phase voltagesand currents for input frequency is 2 times theoutput frequency of the single-phaseCycloconverter.

Fig.3. Cycloconverter Fed Split Phase Induction Motor

Fig.4 (a) Source Voltage (b) Output Voltage (c)Output current Waveform of Single Phase to Single

Phase Cycloconverter When Input Frequency is TwoTimes Output Frequency.

Fig.5 (a) Main winding and auxiliary winding current(b) Rotor Speed (c) Load and Electromagnetic Torque

Waveform of Single Phase Induction Motor, When Input Frequency to the Cycloconverter is Two Times

Output Frequency

VI: CONCLUSION

From this work and result analysis, it is observedthat speed of an induction motor can be efficientlycontrolled by using Cycloconverter. The role ofCycloconverter in speed control of induction motoris to vary the supply frequency which in turn,changes the speed of motor. In the present work, theSimulation of speed control of motor at different

frequencies by using Cycloconverter is simulatedand waveforms are discussed.

REFERENCES

1. Vinamra Kumar Govil, Yogesh Chaurasia Modeling & Simulation ofPWM Controlled Cycloconverter FED Split Phase Induction MotorInternational Journal of Advanced Research in Electrical, Electronicsand Instrumentation Engineering, Vol. 1, Issue 3, September 2012.

2. E A Lewis Cycloconverter Drive Systems Power Electronics andVariable Speed Drives, Conference Publication No. 429, IEEE, 1996.

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3. Abhishek Pratap Singh, V. K. Giri Simulation of Cycloconverter FedSplit Phase Induction Motor International Journal o f EngineeringScience and Technology, Vol. 4, No.01, January 2012, pp. 367-372.

4.

Abhishek Pratap Singh, V.K. Giri Modeling and Simulation of SinglePhase Cycloconverter International Journal of Engineering Scienceand Technology, Vol. 2, I ssue2, March/April, 2012, pp. 346-351.

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IJETT-V4I4P253.pdf