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Transactions on Engineering and Sciences Volume 4, Issue 2, April-June 2016 ISSN: 2347-1964 (Online) 2347-1875 (Print) Speed Control of Three Phase Induction motor by Using PLC and VFD Bishnu Prasad Satpathy1 Dinesh Kumar2 Manish3 Manoj Kumar Bhargard4 S. S. Hirve5 1,2,3&4Student, 5Assistant Dept. of EEE, Bharati Vidyapeeth Deemed University College of Engineering, Pune. Professor, Dept. of EEE, Bharati Vidyapeeth Deemed University College of Engineering, Pune. Abstract: This paper suggests the use of PLC and VFD combination for control the speed of a 3 phase induction motor. The combination provides an efficient approach for getting a motor with continuous running. It is cost effective method along with huge amount of energy saving. Zero impact of overvoltage and under voltages, also economical, reliable and have a greater life.VFD is a communication between PLC and a 3 phase induction motor. It carries out instruction of PLC through a medium PC (Personal computer). Programme is installed in PC which enable human operator to control entire operation. Key words: plc, vfd, cost effective, economical, induction motor, personal computer. I. A. INTRODUCTION Variable Frequency Drive It is a device in electrical system which performs the conversion of single phase or three phase supply of fix frequency into three phase supply with variable frequency. It is used for the application of variable speed requirement .Due to smooth operation it has widely used in circumstances of different speeds. It can be controlled either manually or automatically. In over application it is controlled automatically by using PLC. It helps the operator to vary the speed of motor automatically. The operation is carried out by using PLC (Programmable Logic Controller). Reversing, switching and braking are additional function performed by VFD.For connecting switches and push buttons different I/O’s terminals are given. A port for serial communications is also provided which allow VFD to be controlled and monitored by computer. B. Driving operation Operates in all the four quadrants i.e. perform the operations like motoring, breaking, generating, accelerating and decelerating. Figure 1: VFD internal structure II. PLC (PROGRAMMABLE LOGIC CONTROLLER) It is used in electrical system to improve the reliability and efficiency of electrical equipment (electrical motor) in automation processes. To obtain accurate result PLC is interfaced with converter, PC (Personal computer) and other electrical equipment. In this application PLC of Allen Bradley is used which communicate with VFD and in turn it control 3 phase induction motor. A control programme is developed to get required operation of motor and VFD. A. Figure 2: PLC used in setup CPU (Processor): Figure 3: Block diagram of PLC It is brain of PLC. It executes various logic and control function. Consists of a number of data processing equipments that facilitates I/O processing. 64 Techscripts Transactions on Engineering and Sciences Volume 4, Issue 2, April-June 2016 B. ISSN: 2347-1964 (Online) 2347-1875 (Print) Memory: Contains all the programmes. Holds the complete data of PLC Coordinates I/O operations. C. I/O Module: Provides connections to the process that is to be controlled. III. OVERVIEW OF THE PROPOSED MECHANISM A. V/F method Variation in supply frequency leads to change in speed. Product of flux and supply frequency is directly proportional to induced stator voltage. When stator drop is consider zero then E≈V V f. If an induction motor is to be operated at different frequencies with practically constant values of power factor, efficiency, a constant absolute slip, overload capacity and, then with the iron unsaturated, it is essential that the supply voltage V be varied with the change in frequency accordingly. Both output voltage and frequency vary as the speed if the automatic correction is provided. Figure 4: Torque speed characteristics of induction motor As induction motor follow the relation T V/F So for constant v/f ration a constant torque can be achieved. However, this control scheme focus to ensure that any particular torque can be obtained at the same flux as operating at normal frequency and voltage. Ns = 120f/p From above relation the induction motor speed can be changed by varying the frequency of supply given because poles are inbuilt and cannot contribute in speed control. So for constant v/f ratio torque developed is constant in entire operation. It is the only focus of this method. Fig.4 shows the speed-torque characteristics of the IM with VF control. Figure 5: Torque speed characteristics with v/f control IV. Figure 6: Complete setup EXPERIMENTAL SETUP Figure 7: Block diagram of complete setup. Power Flex 4M AC drive of Allen Bradley is cost effective & smallest .which provides powerful control of speed. 65 Techscripts Transactions on Engineering and Sciences Volume 4, Issue 2, April-June 2016 ISSN: 2347-1964 (Online) 2347-1875 (Print) Table 1: VFD specifications used in the experiment Motor rating Output AC Voltage range Continuous AMP 0.4KW(0.5 H.P) 3 phase,0-240 0-230V 2.3A Overload Amp 3.45,60sec The PLC used in this project is Allen Bradley Micro Logix 1400 series. The main parts of this PLC are CPU, Power Supply, output Module and input Module. Table2: PLC specifications Number of I/O Power supply voltage Power supply inrush Current Power consumption 20 inputs and 12 outputs (10 digital 2 analog) 24V DC 24V DC: 15 A for 20 ms 60W Table 3: Motor Specifications KW RPM Voltage Frequency Ambient Temperature Ampere Efficiency V. 0.37 (.5hp) 2820 415±10% 50+5% 50ºC 1.1 88.6% CONDUCTION OF EXPERIMENT Allen-Bradley PLC & Power Flex 4M VFD, a 3 IM moving freely is controlled by software(ladder logic) installed in CPU of plc and frequency of input supply was varied and speed of motor was tabulated. The complete data of experiment (which shows the relation between frequency and motor speed) is given by following observation table. Table 4: Observation Input supply frequency in Hz 4 9 14 19 24 29 34 39 Figure 8: Frequency input vs. speed output Figure 9: Rotor resistance starting Motor speed in rpm 230 520 840 1140 1395 1709 2000 2250 Figure 10: Reduced voltage starting 66 Figure 11: Starting with vf control. Techscripts Transactions on Engineering and Sciences Volume 4, Issue 2, April-June 2016 ISSN: 2347-1964 (Online) 2347-1875 (Print) From the above fig[9] it can be concluded that when the 3phase IM is started with rotor resistance starter motor produces high starting torque and starting current gets reduced due to high rotor resistances but because of the same cu ;losses become high which affect the efficiency. Fig.10 shows reduced voltage starting characteristics represent that reduced voltage provide much reduced torque because[TV²] thus starting current gets reduced but constant torque cannot be achieved using this method which is required for many industrial applications. Fig.11. VF control which provides a smooth control of the speed of induction motor at a constant value of torque. Reduced speed provides a huge amount of energy savings. By using VFD, maintenance cost is affected largely because lower speed results in longer life for bearing and motor. A speed reduction in 20% results in energy savings of 50%.By using VFD thermal and mechanical stress can be reduced on motor and belts during start, which is not possible in any other method of speed control of three phase induction motor. VI. CONCLUSION The present work describe a mechanism to monitor VFD by PLC.A complete study of each and every equipment along with their specifications is done. Software platform namely Allen Bradley ladder logic programming RS Linx is implemented. A 0.5 Hp 3-phase IM was taken for experimental setup. The drive used in this set-up offered various control modes of motor operation. A PLC program is made and verified in RS Linx software. A thorough study of operation of combination of PLC and VFD has imparted a good idea about automation systems in industries. REFERENCES [1] Ashfaq Husain (2002),”Electric machines” by Dhanpat Rai Publications co.(pvt)Ltd. Educational and Technical Publishers. [2] “Electrical Machinery” by Dr.P.S.Bimbhra, Khanna Publishers. (2013 edition) [3] “Electrical Machines 3rd edition (2011) ” by S.K.Bhattacharya by TATA MecGraw Hill Publishers. [4] Theory and performance of Electrical Machines (2012 edition)” by J.B.Gupta by Kataria Publishers. [5] “Programmable Logic Controller Principles and Applications (2013 edition)” by John W.Webb.Ronald A.Reis by PHI Publishers. [6] “Power Electronic (2008 edition)” by M.D.Singh & K.B.Khanchandani by TATA McGraw Hill Publishers. [7] “PLC Programming for Industrial Automation(2007 edition)” by Kevin Collins by Exposure Publishers. 67 Techscripts