PWM Speed Control of ACSingle Phase Induction Motor Using ... - ijcee

International Journal of Computer and Electrical Engineering, Vol. 3, No. 6, December 2011

PWM Speed Control of ACSingle Phase Induction Motor Using MCUSeries Combined With TRIACTechnology R.Khan and M.M.S. Riyadh

Abstract—Single phase induction motor has been used widely in discipline industry and household where a simple motor starter can't let vary speed in starting and also running with mechanical load. This paper introduces a method for controlling the speed of an AC single phase induction motor. Combination of micro controller unit & TRIAC has been used. A single phase induction motor adjustable speed control is implemented with hardware setup and software program. The main feature used in PIC17C756 microcontroller to control speed is pulse width modulation technique. Voltage drop across two terminals of TRIAC MT1 and MT2 is controlled with its gate voltage. Gate is controlled by DIAC and its input is controlled by an R-C triggering circuit. In triggering circuit variable resistor is used to vary TRIAC gate voltage through DIAC. DIAC gate voltage, TRIAC input voltage and output voltage are also simulated by “Electronic Workbench” software. One chip and re-programmable ROM avoids nonlinearity and it can replace mechanical speed variation. Output voltage and capacity of the system can also be varied. Index Terms—Pulse width modulation, micro controller unit, triode for alternating current, diode for alternating current, silicon controlled rectifier, metal oxide semiconductor field effect transistor.

switching elements e.g. thyristors, MOSFET, solid state relays, or transistors [5]. PWM is a commonly used technique for controlling power to inertial electrical devices, made practical by modern electronic power switches [6]. The average value of voltage and current fed to the load is controlled by turning the switch between supply and load on and off at a fast pace. The longer the switch is on compared to the off periods, the higher the power supplied to the load is. Duty cycle describes the proportion of 'on' time to the regular interval or 'period' of time; a low duty cycle corresponds to low power, because the power is off for most of the time [7]. In this paper, the basic principles and operation of PWM inverters for ACMC applications using Induction Motor controller devices has been outlined [8]. PIC17C756 microcontroller, TRIAC and DIAC are used to control the speed of the DC motor. The performance of the proposed system in Electronic Workbench software has been evaluated in terms of duty cycle, PWM and output voltage.

II. INDUCTION MOTORS

I. INTRODUCTION

In an induction motor, power is supplied to the rotor by means of electromagnetic induction. If a single phase voltage is applied to the stator, current will start flowing. This current produces a magnetic field BS, which will rotate in a counter clock wise direction. Speed of the magnetic field’s rotation is given by (1),

An induction or asynchronous motor is a type of AC motor where power is supplied to the rotor by means of electromagnetic induction, rather than by slip rings and commutators as in slip-ring AC motors [1]. Single phase induction motor is the most familiar of all electric motors & they are similar to a 3-phase squirrel cage induction motor. It has a squirrel-cage rotor identical to a 3-phase motor and a single phase winding on the stator [2]. There are several methods for controlling the speed of DC motors. One simple method is to varying frequency and voltage of the motor. Another method is controlling SCR for DC motors convert AC power to direct current, with adjustable voltage [3]. In PWM method, pulse width modulation is used to regulate the current sent to the motor. Unlike SCR method which switch at line frequency, PWM controls produce smoother current at higher switching frequencies, typically between 1 and 20 kHz [4]. At 20 kHz, the switching frequency is inaudible to humans, thereby eliminating the hum which switching at lower frequency produces. However, some motor controllers for radio controlled models make use of the motor to produce audible sound, most commonly simple beeps. A PWM controller typically contains a large reservoir capacitor and an H-bridge arrangement of

nsync =

(1)

where f is the system frequency and P is the number of poles. This rotating magnetic field BS passes over the rotor bars and induces a voltage in them, which is given by (2) eind = (v B). l

(2)

where, vis the velocity of the rotor relative to the magnetic field and lis the length of conductor.There will be rotor current flow which would be lagging due to the fact that the rotor has an inductive element. The rotor current will produce a magnetic field at the rotor, BR. The interaction between both magnetic field would produce torque according to (3), τind = kBR BS

(3)

The resulting torque is counter clockwise. Since the rotor induced torque is counter clockwise, the rotor accelerates in that direction. In normal operation both the rotor and stator

Manuscript received October 3, 2011; revised December 12, 2011. The authors are with with Islamic University of Technology, Bangladesh (e-mail: [email protected]; e-mail: [email protected]).

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Iff the load in ann induction inccreases, its sliip increases, and a r speed fallls. Since the rotor speed iss slower, theree is the rotor no more m relative motion betw ween the rotorr and the stator mag gnetic fields. Greater G relativve motion prod duces a strongger rotorr voltage ER which in tuurn produces a larger rotor curreent IR. With a larger rotor current, rotorr magnetic fieeld BR also a increasess. However thhe angle of th he rotor curreent and BR changes as a well. Since rotor slip is larger, the rotor uency rises, and rotor reaactance increeases. The rotor frequ curreent lags furthher behind thee rotor voltag ge, and the rotor mag gnetic field shiifts the currennt. Fig. 2 show ws the inductiion operrating at a fairrly high load.. The increasee in BR tends to increease the torqque, while inncrease in an ngle δ tends to decrrease the torquue. The overalll induced torrque increasess to supp ply the motor’s increased looad.

magnetic field BR and BS rotates at syynchronous sppeed, m w while the rotor itself turns at a slower speeed. m The voltage induced in a rotor of ann induction motor deepends on the speed of rotoor relative to thhe magnetic fields. fi Sllip speed,nslipp is as the diifference betw ween synchroonous sppeed and rotorr speed. nslip =nsync nm

(4)

where, nm is mechanical shaft w s speed of o motor. Sllip is reelative speed expressed onn a percentagge basis, which is giiven by (5) s=

%

(

=

(5) (

%

If the rotor tuurns at synchrronous speed, s = 0, while if the rootor is stationnary, s = 1. All normal motor speedss fall soomewhere betw ween those tw wo limits. IIII. TORQUE-SPEED CHARAC P CTERISTICS A net magnetic field,, Bnet is produced p by the magnetization current, IM. The maagnitude of the m m magnetization current andd hence of Bnet is dirrectly prroportional to the voltage E1. If E1 is connstant, then thhe net m magnetic field,, Bnet in the motor m is consstant. In an actual a m motor, E1 variies as the loaad changes, because b the stator s im mpedances cauuse varying voltage v drops with varying load. H However, thesee drops in thee stator winddings are relattively sm mall, so E1 is approximately a y constant withh changes in load. l At no load, the t rotor slip is i very small, and so the rellative m motion betweeen the rotor and a the magnnetic field is very sm mall, and rotoor frequency is i very small.. This conditiion is shhown in Fig.1. Since the rootor motion is small, the vooltage ER induced in the rotor iss very small and the resuulting cuurrent IRis smaall. Because thhe rotor frequency is very small, s thhe reactance of o the rotor is nearly zero, and the maxiimum rootor current IR is almost in phase p with the rotor voltagge ER. Thhe rotor curreent thus produces a small magnetic m field BR at ann angle just slightly greaater than 9000 behind thee net m magnetic field,, Bnet. The innduces torque, which keepps the rootor running iss given by (6) τind = kBR Bnet

Fig. 2. Magnnetic field in an innduction under heeavy loads

IV. TORQUEE-SPEED CURV VE Th he induction motor m torque--speed charactteristics curvee is show wn is Fig.3. The T induced toorque of the motor m is zeroo at syncchronous speeed. The torquee-speed curvee is nearly lineear betw ween no load and a full load. There is a maaximum possibble torqu ue that cannoot be exceedeed. This torqu ue is pull-out or breaakdown torquee, is 2 to 3 tim mes the rated full load torqque of th he motor. Thhe starting torrque of the motor m is slighhtly largeer than its fuull load torquue, so this motor m will sttart carry ying any load that it can suppply at full po ower.

(6)

Fig. 3. Inductioon Motor Torquee-Speed Characterristics Curve

Th he torque on the motor foor a given sliip varies as the t squaare of the appplied voltage. If the rotor of o the inductiion moto or is driven faster than ssynchronous speed, then the t direcction of the innduced torquee in the mach hine reverses. If the motor m is turninng backward rrelative to thee direction of the t mag gnetic fields, thhe induced torque will stop p the motor veery rapid dly and will try t to rotate itt in the other direction. Sinnce reveersing the direction of magnnetic field rotaation is simplyy a mattter of switchhing any twoo stator phasses. The act of switching two phaases in order tto stop the mo otor very rapiddly

Fig. 1. Magnetic M field in an induction undder light loads

Since the rottor magnetic field is very small, the indduced toorque is also quite q small. Itss magnitude iss given by (7) τind = kBRBnet sin δ

(7)

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is called pluggiing. The poweer converted too mechanical form inn an induction motor is giveen by (8) Pconv = τindωm

VIII. HAR RDWARE VIEW W

(8)

w where,ω e angular velocity of the mootor. m is the PWM Motorr Control PWM is a method m for biinary signals generation, which w haas two signal periods p (high and low).Thee width, W off each puulse varies beetween 0 and the period,T..A PWM signnal is geenerated by using u the timeer and the coomparator [9].. The coontroller consstantly checkss for zero crossings through the coomparator. If the conditionn is true the output o pin wiill be clleared and thee timer will start. s The tim mer counts upp to a ceertain value. If I it reaches a predefined value v it is stoopped annd reset for thhe next cyclee. The outputt pin will alsoo set. Thhis cycle will w repeat byy waiting foor the next zero crrossing[10].

IX. RESU ULT TA ABLE I:RESULT T AT NO-LOAD

RCUIT ELEMEN NTS V. CIR

M PIC17C756 Microcontrolller, MAC2233A TRIAC, MOC 30011 TRIAC Driver, D DIAC,, Transformerr, Rectifier Brridge, LC CD Displayy, Rewritablee Cartridge Fuse, Indiicator LiightResistor, Capacitor. C RCUIT DIAGRA AM VI. CIR

VII.

L FLOW CHART

F Fig.4. Voltage vs sspeed at no-load T TABLE II: RESULLT AT ON-LOAD

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and if TRIAC MT T1-MT2 acrosss drop decreaases motor inpput voltaage increases. When the m motor runs at no-load, ratted RPM M reaches at 65V only. W When the moto or runs at loaad, RPM M reaches at raated value graadually.Electro onic Workbennch softw ware has beenn used to evaluate the resullts. By hardwaare impllementation and a program tthe two appro oaches the sam me result. The propposed system m can avoid d non linearrity prob blems on speedd control and mechanical sp peed variationn.

XII.

Fig. 5. Voltage vs speed at no-looad

X X.

FUTTURE WORKS

Mathematical M m model can bee obtained fro om the graph of the motor m speed response. Froom the matheematical moddel, using MATLAB improved mootor speed can n be obtained by using controller package e.g. PID controlller, fuzzy loggic H voltagge and poweer can also be conttroller, etc. Higher obtaained by usingg IGBT. Fullyy automatic PLC based speeed conttroller also cann be designed for better reliiability.

INPUT-OUTPUT WAV VEFORM

REFEREENCES [1]

S. J. Chapman,, Electric Machiinery Fundamen ntals, McGraw-H Hill, 2005, pp. 381-3885. [2] V. K. Mehta andd R. Mehta, Objecctive Electrical Technology, T S.Chaand, 2007, pp. 637-6338. [3] I. M. Gottlieb, Electric E Motors and Control Tecchniques, McGraawHill, February 1,, 1994. [4] I. M. Gottlieb, Practical P Electricc Motor Handboo ok, Newnes, Octoober 8, 1997. [5] F. B. Crocker annd M. Arendt, E Electric motors, their t action, conttrol and application,N New York, D. Vaan Nostrand Com mpany. [6] B. P. Lathi,Moddern Digital andd Analog Comm munication Systeems, Oxford University Press, 2007, ppp. 260-263. [7] http://en.wikipeddia.org/wiki/Dutyy_cycle. [8] J. A. Houldswoorth and W.B. R Rosink, Introduction to PWM Speed Control System for f Three Phase AC motors, Elecctronic Componeents and ications, Voll.2, No.2, Februarry 1980. [9] D.A.Grant, J.A.H Houldsworth, K.N N.Lower, “A new w high-quality PW WM AC drive,” IEEE E Transactions, V Vol. IA-19, No 2, 1983. [10] J.E.Gilliam, J.A.Houldsworth, L L.Hadley, “Variab ble Speed Inducttion Motor with Inteegral Ultrasonic PWM Inverter,”” IEEE Conferennce, APEC,pp. 92-96,1988.

XI.

R. Khan receivved B.Sc in Electtrical and Electroonic Engineering froom Islamic Univeersity of Technoloogy (IUT) in 2010. He is student of o M.Sc Eng. In the institute of Reenewable Energy y of University of Dhaka. Currently, He is workiing as a lecturerr in Electronic Engineeering department of Electrical and E Green Universsity of Banglad desh. His reseaarch interests includde power systemss, power electronnics and renewable eenergy.

CONCLUSIONSS

In this paperr, microcontrooller PIC17C7756 has been used foor PWM adjuustable speedd control. Thhe circuit caan be diivided in thhree moduless. The firstt module is the traansformer andd rectifier. Att the end of thhis stage theree is a reectified AC wave w at 120 Hz at half of thhe original vooltage peeak-peak. Thee next modulee is zero crosss detection ciircuit. Too test this moodule MCU iss needed withh program runnning [88]. The designnated output pin p of the MC CU is expectted to haave a pulse at a 120 Hz. MOC M and TR RIAC are thee last m modules.TRIAC C has three teerminals (MT1, MT2 and Gate). G Itss voltage dropp across MT1 and MT2 caan be controlleed by coontrolling its gate g voltage. In the circuitt gate is contrrolled byy DIAC. DIA AC input is controlled by an R-C trigggering ciircuit [9]. In trriggering circuuit there is a variable v Resisttor to vaary TRIAC gate g voltage trough DIAC C. As TRIA AC is coonnected in series with Motor input so, if TRIAC MT1M M MT2 across drrop increases Motor input voltage decrreases

M. M. S. Riyyadhreceived B.S Sc in Electrical and a Electronic Enggineering from Isslamic Universityy of Technology (IIUT) in 2010. Hee worked at Huaw wei Technologies (BD) Ltd. as a BSS B Engineer. Noow, a he is servingg as a Lecturerr in Electrical and Electronic Enngineering departtment of Universsity of Informationn Technology an nd Sciences (UIT TS). His research interests includee power electronnics, biomedical im maging, LTE techn nology.

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