Download Speed Control of Three Phase Induction motor by Using PLC and VFD

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.
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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.
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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
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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[TV²] 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.
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