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DOI 10.4010/2016.1028 ISSN 2321 3361 © 2016 IJESC Research Article Volume 6 Issue No. 4 Simulation and Speed Control of 3-Phase Induction Motor Drives K.Anitha1, G.Santosh2, L.Suneel3, K.Spandana4, E.Raviteja5 Assistant Professor 1, UG Scholar2, 3, 4, 5 Department of Electrical and Electronics Engineering Lendi Institute of Engineering and Technology, Andhra Pradesh, India Abstract: Induction motors are the most widely used electrical motors due to their reliability, low cost and robustness. However, induction motors do not inherently have the capability of variable speed operation. Due to this reason, earlier dc motors were applied in most of the electrical drives. But the recent developments in speed control methods of the induction motor have led to their large scale use in almost all electrical drives. Out of the several methods of speed control of an induction such as pole changing, frequency variation, variable rotor resistance, variable stator voltage, constant V/f control, slip recovery method etc., the closed loop constant V/f speed control method is most widely used. In this method, the V/f ratio is kept constant which in turn maintains the magnetizing flux constant so that the maximum torque remains unchanged. During starting of an induction motor, the stator resistance and the motor inductance (both rotor and stator) must be kept low to reduce the steady state time and also to reduce the jerks during starting. On the other hand, higher value of rotor resistance leads to lesser jerks while having no effect on the steady state time. The vector control analysis of an induction motor allows the decoupled analysis where the torque and the flux components can be independently controlled (just as in dc motor). This makes the analysis easier than the per phase equivalent circuit. Keywords: space vector modulation, v/f control, transient analysis, slip, steady state analysis .Induction motor Electric motor drive, matlab, simulink I. INTRODUCTION Be it domestic application or industry, motion control is required everywhere. The systems that are employed for this purpose are called drives. Such a system, if makes use of electric motors is known as an electrical drive. In electrical drives, use of various sensors and control algorithms is done to control the speed of the motor using suitable speed control methods the rotor cuts the rotating flux .Hence torque is experienced and rotor rotates. Fig1: Internal parts of induction motor Earlier only dc motors were employed for drives requiring variable speeds due to ease of their speed control methods. The conventional methods of speed control of an induction motor were either too expensive or too inefficient thus restricting their application to only constant speed drives. However, modern trends and development of speed control methods of an induction motor have increased the use of induction motors in electrical drives extensively. II. INDUCTION MOTOR Principle: It is an asynchronous motor when 3ph supply is given to the stator, flux is induced in the stator and due to the mutual induction flux is transform from stator to rotor. The current is generated in the rotor due to short circuit copper bars in International Journal of Engineering Science and Computing, April 2016 III. SPEED CONTROL OF INDUCTION MOTOR DRIVES (METHODS) 1. V / f control or frequency control. 2. Changing the number of stator poles. 3. Controlling supply voltage. 4. Change in the resistance of stator and rotor circuit III. 1 V/F CONTROL OR FREQUENCY CONTROL We vary the stator voltage in such a way that the flux remains constant by simultaneously varying the supply frequency such that the ratio V/f remains constant. The AC supply is rectified and then applied to a PWM inverter to obtain a variable frequency, variable magnitude 3-ph AC supply. The electromagnetic torque developed by the motor is directly proportional to the magnetic field produced by the 4478 http://ijesc.org/ stator and the flux produced by the stator is proportional to the ratio of applied voltage and frequency of supply. Therefore, by varying the voltage and frequency by the same ratio, flux and hence, the torque can be kept constant throughout the speed range. This makes constant V/f method the most common speed control method of an induction motor III. 2 CHNAGING THE NUMBER OF STATOR POLES. In this case of speed controlling method , it is very complicated to change the stator poles where it is time taking and there is change in design of the induction motor .so in this method we cannot make any change in stator poles so, we rarely use this method. The waveforms of open loop PI controller of v/f ratio method: Fig 3 : variation of dc bus voltage versus time III. 3 CONTROLLING SUPPLY VOLTAGE A very simple and economical method of speed control is to vary the stator voltage at constant supply frequency. The three-phase stator voltage at line frequency can be controlled by controlling the switches in the inverter. As seen from the equation (3.10) the developed torque is proportional to the square of the stator supply voltage and a reduction in stator voltage will produce a reduction in speed. Therefore, continuous speed control may be obtained by adjustment of the stator voltage without any alteration in the stator frequency Fig:4 variation of torque versus time III.4 ADDING RHEOSTAT IN STATOR CIRCUIT In this method of speed control of three phase induction motor rheostat is added in the stator and rotor circuit due to this voltage gets dropped .In case of three phase induction motor torque produced is given by T ∝ sV22. If we decrease supply voltage torque will also decrease. But for supplying the same load , the torque must remains the same and it is only possible if we increase the slip and if the slip increase motor will run reduced speed. In this way we can control the speed of induction motor Fig :5 variation of stator current versus time SIMULINK DIAGRAM Fig:2 open loop control method PI controller for v/f ratio International Journal of Engineering Science and Computing, April 2016 Fig 6: variation of rotor speed versus time 4479 http://ijesc.org/ .SPEED CONTROL OF INDUCTION MOTOR BY VARYING STATOR AND ROTOR RESISTANCE Fig7: Speed control of induction motor Fig:11 Graph between rotor current verses time LOW ROTOR RESISTANCE LOW STATOR RESISTANCE Waveforms of low stator resistance: Fig12: Graph between speed and time Fig8: Graph between speed (n) and time (sec) 4 Fig13: Graph between torque and time Fig9:Graph between torque versus time Fig10: Graph between stator current and time. International Journal of Engineering Science and Computing, April 2016 Fig:14 Graph between rotor current verses time 4480 http://ijesc.org/ Finally, we would like to thank all the faculty members of the ELECTRICAL AND ELECTRONICS DEPARTMENT who made us to think in all possible ways to complete our project and making us to know the real zeal in which every student should inculcate during proceedings of project in REVIEW session. VII. REFERENCES [1] Gopal K. Dubey, “Fundamental Of Electrical Drives”, Narosa Publication House, Second Edition, 2011. [2] A. E. Fitzgerald, Charles Kingsley, Jr. And Stephan D. Umans, “Electrical Machinery”, McGraw-Hills Publications, Year 2002. Fig15 :Graph between stator current verses time These are the different characteristics of the induction motor for changing stator and rotor resistance without load torque. So we are totally analysing the speed and torque, current in the transient time. If we change the stator and rotor resistance, the peak values of stator and rotor currents changes. The peak value of the torque is also changes But, the response of the transient time is not changed because of not changing inductance. If there is any change in the inductance, then time constant value is changed due to that transient period of characteristics are changed. VI. CONCLUSION In V/f ratio control method we can control the speed of induction motor by changing the frequency. But in this case if we change the frequency the voltage at the secondary side also changes. So, for the low speeds the frequency of the supply voltages is small when compared to high speeds. So the supply voltage automatically decreased for maintaining V/f ratio constant. Therefore, the torque is decreased because the torque is directly proportional to square of the voltage. So, this is not a efficient method for speed control. Further we can conclude that we can change the resistance for the speed control of induction motor. In this method in order to get the maximum starting torque we can increase the rotor resistance. But in the running condition, the copper losses are increased due to having high resistance. So, the efficiency of the motor is decreased. So, we can conclude that it is also doesn’t play a major role in speed controlling and we need to further check for other method [3] “IEEE Standard Test Procedure for Polyphase Induction Motors and Generators”, volume 112, issue 1996 of IEEE, by IEEE Power Engineering Society. [4] Scott Wade, Matthew W. Dunnigan, and Barry W. Williams, “Modelling and Simulation of Induction Machine Vector Control with Rotor Resistance Identification”, IEEE transactions on power electronics, vol. 12, no. 3, may 1997. [5] D.W. Novotney, et al (editor), “Introduction to Field Orientation and High Performance AC drives”, IEEE IAS tutorial course, 1986. [6] Ramon Blasco Blasco Gimenez, “High Performance Sensorless Vector Control of Induction Motor Drives”,The University of Nottingham,December 1995. VII. ACKNOWLEDGEMENT: We would like to express our deep sense of gratitude to Mrs. Anitha Madam, Associate professor, Lendi institute of technology for his whole hearted co-operation, unfailing inspiration and valuable guidance. We also thank Mr.Sumit kumar,Associate Professor, department of electrical and electronics for extending his valuable support and encouraging in all unknown situations during our project which leads to completion of our project. We also thank our HEAD OF DEPARTMENT, Dr. Y. Narendra Kumar sir who has motivated in all possible ways and gave less pressure to the students which makes our project more clear and trying to know the roots of the project in which credits goes to him. International Journal of Engineering Science and Computing, April 2016 4481 http://ijesc.org/