Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 161 IMPROVINGSTARTINGCHARACTERISTICS OF SQUIRREL- CAGE MOTOR BY USING V/F CONTROL METHOD Assist. Lecturer Hashmia Sh. Dakheel Assist. Lecturer Zainab B. Abdulla University of technology University of technology hash_sh76@yahoo.co btbt_n@yahoo.com Received 3 March 2015 Accepted 21 January 2016 ABSTRACT:- This paper presents one of the most successful method controllers of 3-phase squirrel-cage IM motor which is employing V/F method with application of pulse width modulation (PWM), this dynamic model is implemented using Mat Lab simulation program. The improved techniques of suggested model presents high performance of improving the starting characteristics (starting current , starting torque) of the double comparison with single-cage IM using PWM techniques at constant V/F control. Simulation results refers to the characteristics of double-cage better than single cage and shows that the satisfy performance and good response of this model. Keywords:- Induction motor IM, single, double cage, V/F control and PWM technique. الخالصة:- يقدم هذا المقال واحدة من اهم طرق السيطرة الناجحة للمحرك ثالثي االطوار ذات القفص السنجابي والذي يعمل بطريقة V/F مع تطبيقات لمضمن عرض الحزمة ((PWM هذا النموذج الديناميكي يعمل باستخدام برنامج المحاكاةMat Lab . خصائص البدء )تيار البدء، عزم البدء( للمحرك ثنائي القفص مقارنة حسينعالي لتللنموذج المقترح تقدم االداء ال محسنةالتقنيات ال نتائج المحاكاة تشير الى .ثابتة V/F عند مسيطر باستخدام تقنية مضمن عرض الحزمة االطوار ثالثي المحرك احادي القفص مع حسن واالستجابة الجيدة لهذا النموذج.ان الخصائص لثنائي القفص هي افضل بكثير من احادي القفص وتبين االداء الم -:TRODUCTION IN-1 The construction of three- phase induction motors haven’t any mechanical commutations therefore these types of the motors are use in most of industrial application. [5], [6], [2], [9]. The induction motor has large speed range, high robustness and efficiency, low manufacturing cost. [6],[10].The cage-type machine of induction drives have applications in the industry that include:- textile mills , papers, fans, pumps , air-conditioners, heat pumps , rolling mills and wind generation systems, vehicles, home applications , machines tools robotics .The range power of these machines cover fractional and horse-power to megawatts. In this time there is most application in the process control because the energy saving aspect to variable- frequency drives. [2].All these applications have drastic move away from analogue motor control to precision digital control that use variation processors digital control of induction motor results led to more efficient operation of the motor gives lower power dissipation and longer life wide. Today the various control techniques of induction motor are generating variable frequency supply that V/F is the constant ratio of voltage to Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 161 frequency. [6].This technique is known as V/F control principles is good understood with the introduction of solid-state inverters, the constant V/F control become widely.[1]. Nowadays the advances development of power electronics technology and high speed computers with associated high speed microcontrollers A.C. drive system have been available alternative to D.C. machines for variable speed applications. The induction motors have merits over the other types of industrial motors. [2]. the important of machines control algorithm fast-switching power semiconductors devices, most precise (pulse width modulation) increases particularly interest. Recently the pulse width modulations have large variety in methods that which a survey was given. The large utilization the ac machine drives application, of the dc bus voltage is extremely important leds to obtain the maximum output torque at all operating conditions. [8]. There are many limitations of variable speed drives represents longer space, low speed ,poor efficiencies so, by using the power electronics to achieve the variable speed drive into a high efficiency, smaller size and high reliability. The advance in improving of control system using frequency has been designed by combinations of PWM controller. [10].This study presents the implemented system to develope the starting characteristics of induction motor for constant V/F of the motor, the comparison is done between single and double-cage induction motor drives by using PWM techniques which improve the performance of induction motor by eliminating the current harmonics of the motor. 2-DOUBLE-CAGE IM:- The field control techniques can be used to control the torque developed of induction machine from flux regulation. In induction motor for variable speed drives to obtain minimize losses; the rotor resistance should be designed as low values. In construction with a general purpose induction motor, there is honked to compromise the design of the rotor cage in order to achieve adequate starting torque. In large machines (mill drive systems), high rotor current flows in rotor, therefore the rotor cage is also design large. [4]. The construction of squirrel-cage winding includes of layers short circuited bars by end rings .The upper bars have higher resistance and smaller cross-sectional area than the lower bars [7]. The effective resistance (Reff ) and leakage inductance of double-cage rotor vary with frequency because at the low rotor-frequencies corresponding to small slips, reactance can be neglected and the rotor resistance reaches that of the two layers in parallel.[3]. 3-INDUCTION MOTOR MATHEMATICAL MODEL :- At start condition the rotor resistance of squirrel- cage induction motor is very large compared to rotor resistance at running (fixed and small). The rotor current has frequency equal the supply frequency, hence, the starting torque per ampers is very poor ,because at standstill the starting current flows in the rotor is very large in magnitude and very large angle behind the rotor induced e.m.f in the rotor .The starting torque represents in equation:- [11] TS=K1E2I2COSφ2 (1) Where:- TS = starting torque, E2 = e.m.f induced in rotor per phase at standstill, I2 =rotor current at starting, Φ2 = angle between rotor e.m.f and the rotor current, K1= constant Figure (1) shows equivalent circuit of double-cage induction motor. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 161 The starting current of the squirrel cage IM is (5 to 7 ) times of the the full load current and the starting torque is 1.5 times the full load torque, therefore these types of motors are not used in where applications of heavy loads [11]. 4-V/F CONTROL AND IMPROVE STARTING CHARACTERISICS OF IM:- In a squirrel cage rotors in a squirrel cage rotors no resistance can be inserted at the starting as this done wound-rotor can be developed in many a way.[11].The various schemes all make use of the inductive effect of the slot-leakage flux on the current distribution in the rotor bars. [7]. The voltage applied to the stator is proportional the torque developed on the shaft of the motor and directly proportional to the angular velocity and the product of stator flux. This led the stator the flux produced by proportional to the ratio of V/F(applied voltage and frequency of supply). The torque can be remain constant at all speed range at ratio of voltage to frequency constant .the ratio V/F makes the most common speed control of an induction motor. The torque developed is proportional to the (Voltage/Frequency).The ratio must be constant although we vary the voltage and frequency ,with various speed rang the torque produce in induction motor will remain constant, figure (2) shows the torque-speed characteristics of IM with V/F control .The (voltage and frequency) ratio reaches the maximum value at the base speed. [6]. The torque- speed characteristics of the V/f control reveal the following:- 1-the current at starting is low. 2-the stable operating region of the motor is increased instead of simply ruing at its rated speed, the motor can be run typically from 5% of the synchronous speed up to the base speed. The torque generated by the motor can be kept constant throughout this region. 3-since almost constant rated torque is variable over the entire operating ranges the speed range of the motor becomes widely user can be set the speed as per the load requirement, thereby achieving the higher efficiency. [6]. 5-IMPROVING MODEL OF IM BY USING INVERTER:- The desired sinusoidal voltage can be produced by pulse width modulation at a particular frequency to the squirrel cage of IM inverter is controlled, A PWM provides higher performance because more efficient and typically.[10]. Figure (3) shows the block diagram of induction motor using bridge and inverter rectifier to improve the starting of IM, figure (4) shows the block diagram of induction motor by using (PWM) that proposes in this study, and figure (5) shows the construction of the modeling use in this study.[12]. This study presents the model that is designed in order to compare between double-cage and single- cage IM by using the power electronics elements. So this model consists of 3- phase full bridge rectifier which is designed using (6A10BL) power diodes, the second part of model is three full bridge inverter which is PWM, the output of PWM is filtered by ( 300µf, 900V) capacitor which is used to filter the harmonics of IM and three- phase induction motor is the last part of the model. 6-RESULTS SIMULATION:- Simulation results were obtained at constant V/F control of induction motor drives that is fed by inverter with single and double squirrel cage by using pulse width modulation refers to:- Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 161 1- The mechanical characteristic ( torque-speed) of the single and double-cage rotors of induction motor shows in figure (6) at constant V/F. these results indicate to a higher starting torque of double –cage than single-cage rotor, but the double-cage has a smaller maximum torque , these results can be shown in table (1) . 2-Tthe double- cage rotor consists of two layers (upper and lower),the simulation results refers to higher starting torque characteristic in upper-layer comparison than lower-layer which can be shown in figure (7) and table (2). The summation of two components curves led to torque- speed characteristics. 3-The current-speed characteristics that obtained of simulation program indicates to starting and rated currents for single-cage are higher than double-cage, those results can be shown in figure (8) and table (3). 4- In figure (9) and (10) shows the torque- speed curves of single and double-cage rotor respectively for several excitation frequencies of three phase induction motor operating with its air gap flux remain constant at all rated condition value for all values of slips, These curves shows that the value of the torque remains the same at given value of the slips speed for any value of speed, these results can be seen in table (4) and (5) respectively. 5-The simulation results of the torque-speed curves for single and double-cages motor respectively shown in figure (11) and (12)that use excitation voltage based on stator V/F of air gap magnetic flux constant at rated value and rotor currents gives the same pull out torque. The curve of speed of magnetic field is low has much higher value of pull out torque and this speed is properly with magnetizing voltage (Em) so that stator curve will be determined by stator terminal voltage and the stator winding resistance so the stator current remains constant when terminal voltage is fixed at all slips speed, these results can be shown in table (6) and (7). 6-Figure (13) and (14) shows the starting torque and current for different starting frequencies for single and double-cage motor respectively, the simulation results can be shown in table (8), (9). With a low frequency start, the rotor reactance is low , hence the induced rotor current are much closer in phase to the voltage so giving high torque with high power factor and consequently minimum starting current magnitude. -CONCLUSION:-7 By use of double-cage rotors, squirrel-cage motors can be designed to have the good starting characteristics resulting from high rotor resistance at start and at the same time good running characteristics resulting from low rotor resistance at running. The design of double-cage rotor is necessarily somewhat of a compromise and the motor lacks the flexibility of the wound-rotor machine with external rotor resistance. The current demanded by the induction motor for a direct-on line stator fixed frequency has a magnitude of approximately six times the normal full load current. With a fixed- frequency source, this starting current can only be reduced by voltage reduction. However, using the inverter drives it is possible to start at low frequency, and then raise the frequency to accelerate the motor. -REFERENCES:-8 Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 161 [1] Alfredo Munoz-Garcia Thomas A. Lipo and Donald W.Novotny, "A New induction motor V/F control method capable of high- performance regulation at low speeds", IEEE Transactions on industry applications, vol. 34, no.4, July/August 1998,pp 813-820. [2] C. Saravanan, A.Mohamed Azarudeen and S.Selvakumar, "Performance of three phase induction motor using modified stator winding ", Global Journal of researches in Engineering Electrical and Electronics Engineering, vol.12, Issue 5 version 1, April 2012. [3] C.U. Ogbuka, and M.U.Agu, "A Modified Closed Loop V/F Controlled Induction Motor Drive",the Pacific Journal of Science and Technology, May 2009, Vol.10, NO.1, pp 52. [4] J. K. Seok and S.K.S ul, "Pseudorotor- flux- oriented control of an induction machine for Deep- Bar-Effects compensation ", IEEE Transactionon industry applications, vol. 34, no. 3 may/June, 1998. [5] Mohamed Y. Kaikaa , Fatima Badaa, Abdelmalek Khezzar, Mohamed Boucherma, "Analytical analysis of rotor slot harmonics in the line current of squirrel cage IM", Journal of Electrical Engineering, vol. 57, no. 1,2006, 12-19. [6] M.S.Aspalil, Asha R 2 , P.V.Hunagund 3 , "Three phase induction motor drive using IGBTS and constant V/F method", International Journal of Advanced Research in Electrical, Electronics and Instrumentation Engineering vol. 1, Issue 5, November 2012. [7] M. Y. Kaikaa, F. Babaa, A. Khzzar and M. Boucherma, "Analytical Analysis of Rotor Harmonic in the Line Current of Squirrel Cage Induction Motors", Journal of Electrical Engineering, Vol.57, N0.1, 2006,PP 12-19. [8] R. Linga Swamy and P. Satish Kumar, "Speed control of space vector modulated inverter driven induction motor", Proceedings of the International mult conference vol.II, March, Hong Kong, 2008 [9] SafdarFasal TK and Unnikrishnanl, "A Performance study of PI controller and Fuzzy logic controller in V/F control of three phase IM using space vector modulation ", transactions on Electrical and Electronics Engineering (ITSI-TEEE), vol.1, Issue 2, 2013. [10] Shilpa V. Kailaswar, prof. R .A. Keswani, "Speed control of three phase induction motor by V/F method for Batching Motion System ", International Journal of Engineering Research and applications (IJERA), vol.3, Issue 2, March-April 2013 ,pp1732-1736. [11]Thanga Raj, S.P.Srivastava and Pramod Agarwal, " Induction motor design with limited harmonic current using practical swarm optimization", International Journal of Electrical and Computer Engineering, 3:15 2008, pp 1000. [12] Thida Win, Nang Sabai and Hnin Nandar Maung, "Analysis of Variable frequency three phase induction motor drive", World Academy of Science, Engineering and Technology, 18, 2008, pp 647-650. Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 166 Table (1): Torque-Speed characteristic Table (2): Torque-Speed characteristic in single and double-cage IM. in double-cage IM Table (3): Current-Speed characteristic Table (4): Torque-Speed with constant In single and double-cage. Air gap. Table (5):Torque-Speed of double-cage Table (6):Torque-Speed of single with with constant air gap. constant V/F Double-cage Single-cage V/F torque Speed torque Speed 0.13 160 0 135 0 0.13 170 200 150 200 0.13 175 400 170 400 0.13 180 600 175 600 0.13 193 800 197 800 0.13 212 1000 225 1000 0.13 220 1200 240 1200 0.13 235 1400 265 1400 0.13 212 1600 240 1600 Upper-cage Lower-cage Torque speed torque speed 132 0 16 0 120 200 18 200 110 400 23 400 96 600 25 600 80 800 34 800 65 1000 42 1000 53 1200 53 1200 42 1400 65 1400 20 1600 92 1600 Torque (N-m) Speed (rev/min) F(HZ) 30 450 15 65 90 30 258 1100 45 132 1700 60 Current speed current Speed 165 200 78 200 163 400 74 400 160 600 70 600 157 800 67 800 140 1000 65 1000 130 1200 57 1200 108 1400 54 1400 70 1600 45 1600 double-cage Single cage Speed (rev/min) Torque (N-m) F(HZ) 390 68 15 740 132 30 1160 200 45 1500 264 60 Speed (rev/min) Torque (N-m) F(HZ) 450 545 15 700 500 30 1076 265 45 1700 124 60 Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 161 Table (7):Torque-Speed of double-cage Table (8):Starting torque and current with constant V/F . in single-cage Table (9):Starting torque and current in double-cage Figure (1): Equivalent circuit of double-cage IM Speed (rev/min) Torque (N-m) F(HZ) 1565 265 60 1100 278 45 785 285 30 380 1060 15 Starting torque Starting current K values 232 72 0.1 270 114 0.2 258 125 0.3 232 145 0.4 210 158 0.5 193 165 0.6 170 174 0.7 167 180 0.8 Starting torque Starting current K values 178 40 0.1 230 55 0.2 225 61 0.3 210 63 0.4 190 65 0.5 187 68 0.6 182 72 0.7 175 75 0.8 170 78 0.9 165 83 1 R1 X1 X2 R2/S X3 R3/S Xm V1 Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 161 Figure (2):Torque- Speed characteristic of induction motor Figure (3):Block diagram of system Figure (4):Block diagram of IM by using PWM . Maximum torque VS/ωe=constant VS/ωe=constant 0 0.5 1 Frequency (ωe/ ωb) rated curve Torque (Te/Tem) =consta nt Maximum torque AC –to DC Converter (to any DC voltage) DC to AC Converter (to any frequency) AC Motor AC to DC Converter IM Inverter (PWM) Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 161 Figure (5): The construction of the model Fig. (6):Torque- Speed characteristic Fig. (7):Torque- Speed characteristic in single and double cage. in lower and upper cage. Figure (8): Current- Speed characteristic. Figure (9): Torque- Speed of single cage with constant air gap 0 200 400 600 800 1000 1200 1400 1600 1800 0 50 100 150 200 250 300 Speed (rev/min) T o rq u e ( N .m ) Single-Cage Design Double-Cage Design 0 200 400 600 800 1000 1200 1400 1600 1800 0 20 40 60 80 100 120 140 Speed (rev/min) T o rq u e ( N .m ) Lower Cage Upper Cage 0 200 400 600 800 1000 1200 1400 1600 1800 0 20 40 60 80 100 120 140 160 180 Speed (rev/min) S ta to r C u rr e n t (A m p e re s ) Single-Cage Design Double-Cage Design 0 50 100 150 200 250 300 350 0 200 400 600 800 1000 1200 1400 1600 1800 Torque (N.m) S p e e d ( re v /m in ) Torque speed curves, single cage, with constant airgap flux f = 60 Hz f = 45 Hz f = 30 Hz f = 15 Hz Al-Qadisiyah Journal For Engineering Sciences, Vol. 9……No. 2 ….2016 111 Figure(10):Torque- Speed of double- Figure (11):Torque-Speed of single- Cage motor with constant air gap cage motor with constant V/F Figure (12):Torque - Speed of double-cage Figure(13):Starting torque and current motor with constant V/F . related to frequency of single-Cage motor Figure (14):Starting torque and current related frequency of double-cage motor 0 50 100 150 200 250 300 350 0 200 400 600 800 1000 1200 1400 1600 1800 Torque (N.m) S p e e d ( re v /m in ) Torque speed curves, double cage with constant airgap flux f = 60 Hz f = 45 Hz f = 30 Hz f = 15 Hz 0 200 400 600 800 1000 1200 0 200 400 600 800 1000 1200 1400 1600 1800 Torque (N.m) S p e e d ( re v /m in ) Torque speed curves, single cage with constant v/f f = 60 Hz f = 45 Hz f = 30 Hz f = 15 Hz 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 50 100 150 200 250 300 K Values Starting torque and current related to frequency for single cage motor Starting Torque Starting Current 0 200 400 600 800 1000 1200 1400 0 200 400 600 800 1000 1200 1400 1600 1800 Torque (N.m) S p e e d ( re v /m in ) Torque speed curves,double cage with costant v/f f = 60 Hz f = 45 Hz f = 30 Hz f = 15 Hz 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1 0 50 100 150 200 250 K Values Starting torque and current related to frequencyfor double cage motor Starting Torque Starting Current