International Journal of Computer Sciences and Engineering Open Access
Research Paper Volume-4, Special Issue-6, Aug 2016 E-ISSN: 2347-2693
Micro-Controller Based Soft Start for three Phase Induction Motor
Maharshi Ghosh [1*], Govind Kumar [2], Saurabh Kumar Ray [3],
Rohit Sharma [4], Prasanta Pattanayak[5] Amartya Roy [6]
[1,2,3,4,5,6]
Dept.of EEE, Pailan College of Management & Technology, Kolkata-104
Available online at: www.ijcseonline.org
Received: Jun/26/2016 Revised: July/08/2016 Accepted: July/26/2016 Published: Aug/12/2016
Abstract— This project attempts a new speed control technique for the A.C three-phase induction motor. It uses optimized
soft-start to start induction motor. At the time of starting Induction motor draws high amount of current (Starting Current) which
is 6 times of full load current, to prevent this starter is needed. Here we are using PIC18F4550 to control the soft-start. Input
control signal to PIC, which gives Digital output to DAC (Digital to analog converter). DAC converts digital input of PIC to
analog output. This analog output is given to Op-Amp, for maintain reference output, which in turn is gives supply to opto-
coupler for protection of Control Circuit. It presents a design of a low-cost; high-efficiency drive capable of supplying a three-
phase induction motor.
Keywords— Soft-start, Induction Motor, Micro-controller, Proteus, Digital to Analog Converter.
I. INTRODUCTION
An induction motor is similar to a poly-phase transformer
whose secondary is short circuited. Thus, at normal supply
voltage, like in transformers, the initial current taken by the
primary is very large for a short while. If an induction motor
is directly switched on from the supply, it takes 5 to 7 times
its full load current and develops a torque which is only 1.5
to 2.5 times the full load torque. This large starting current
produces a large voltage drops in the line, which may affect
the operation of other devices connected to the same line.
Hence, it is not advisable to start induction motors of higher
ratings (generally above 25kW) directly from the mains
supply.
Fig 1: - DOL starter
Various starting methods of induction motors are described
below: -
2. Auto-transformer Starter:
Auto-transformer starter is also known as auto-starters. They
1. Direct-on-line (DOL) starters: can be used for both star connected and delta connected
Small three 3 phase induction motor can be started direct-on- squirrel-cage induction motor. It is basically a three phase
line, which means that the rated supply is directly applied to step down transformer with different taps provided that
the motor. But, as mentioned above, here, the starting permit the user to start the motor at, say, 50%, 65% or 80%
current would be very large, usually 5 to 7 times the rated of line voltage. With auto-transformer starting, the current
current. The starting torque is likely to be 1.5 to 2.5 times the drawn from supply line is always less than the motor current
full load torque. Induction motors can be started directly on- by an amount equal to the transformer ratio.
line using a DOL starter which generally consists of a
contactor and a motor protection equipment such as a circuit
breaker. In order to avoid excessive voltage, drop in the
supply line due to large starting current, a DOL starter is
generally used for motors that are rated below 5kW.
© 2016, IJCSE All Rights Reserved 114
International Journal of Computer Sciences and Engineering Vol.-4(6), Aug 2016, E-ISSN: 2347-2693
The external resistance introduced is only for starting
purposes, and is gradually cut out as the motor gathers the
speed.
Fig 2: - Auto Transformer starter
3. Star-delta starter:
This method is used in the motors, which are designed to run
on delta connected stator. A two-way switch is used to
connect the stator winding in star while starting and in delta
while running at normal speed. When the stator winding is
star connected, voltage over each phase in motor will be
reduced by a factor 1/(sqrt. 3) of that would be for delta
connected winding. The starting torque will 1/3 times that it
will be for delta connected winding. Hence a star-delta
starter is equivalent to an auto-transformer of ratio 1/(sqrt. 3) Fig 4: - Ext. Resistance starter
or 58% reduced voltage.
II. SOFT START & PROPOSAL MODEL
A. Soft Starter Introduction
An induction motor connected directly to the power supply
draws a constant magnetizing current at full speed, no matter
what the load is. At anything less than full load, power factor
of the induction motor is less than its rated power factor
because the torque producing current decreases as the load
decreases, but the magnetizing current does not change. The
lighter the load, worse the power factor.
Motors selected from a standard range are almost always
chosen with a rated power in excess of maximum load
demand, with the result that in any installation the motors
seldom operate at their full rated load. Consequently, they
can never achieve their rated power factor even at a
maximum load demand. Moreover, if the load is variable.
Maintaining the Integrity of the Specifications:
Fig 3: - Star-Delta starter B. Soft Starter Introduction
4. External Resistance Staring:
Slip-ring motors are started with full line voltage; as external
resistance can be easily added in the rotor circuit with the
help of slip-rings. A star connected rheostat is connected in
series with the rotor via slip-rings as shown in the fig.
Introducing resistance in rotor current will decrease the
starting current in rotor (and, hence, in stator). Also, it
improves power factor and the torque is increased. The Fig 5: - Proposed system
connected rheostat may be hand-operated or automatic.
As, introduction of additional resistance in rotor Fig 5 suggest, giving supply to PIC microcontroller, which
improves the starting torque, slip-ring motors can be started gives controlled output to DAC (Digital to Analog
on load. Converter). DAC converts digital input of PIC to analog
output. This analog output is given to Op-Amp which in turn
gives supply to opto-coupler for protection of control circuit
© 2016, IJCSE All Rights Reserved 115
International Journal of Computer Sciences and Engineering Vol.-4(6), Aug 2016, E-ISSN: 2347-2693
form high voltage supply. It presents a design of a low-cost;
high-efficiency drive capable of supplying a three-phase a.c.
induction motor. Finally, complete content and
organizational editing before formatting. Please take note of
the following items when proofreading spelling and
grammar:
III. SIMULATION AND EXPERIMENTAL SETUP
Table 1: - Ratting of Experimental Induction motor
K.W(H.P) .75(1)
VOLTS 415±6%
FREQUENCY 50 Hz Fig 7: - Experimental setup 1
FRAME 80
PHASE 3 The model for this soft-start has been made successfully.
R.P.M 1450 The induction motor has been replaced with the bulb and a
prototype has been made. The prototype has been run on
AMPS 2.1
PROTEUS successfully. In experimental setup 2 (Fig 8) full
RATING CONT hardware circuit and setup will be given
INSULATION- AMBIENT B-40c
TEMPERATURE
CONNECTION STAR
IV. MODEL VALIDATION
The software stimulation has been done in proteus. The pic
programming has been first made in C Language then has
been made into hex code. In proteus the 3 phase induction
motor is not available. So in the place of 3 Phase IM we
have used three Bulbs. Each bulb represents each phase of
Induction motor.
Fig 8: - Complete hardware circuit
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V. RESULTS AND DISCUSSION
Some of the values from entire 256 bits are given in Table
Fig 6: - Proposed simulated system 2. Starting current and speed of the motor is gradually
increase to its final values of current and speed (in no load
condition). In auto transformer of Star delta peak of starting
current is 6Amps (1 hp motor) but in this model reduce that
peak current. Fig 8 shows the characteristics of different
starting current of using different starting topology.
© 2016, IJCSE All Rights Reserved 116
International Journal of Computer Sciences and Engineering Vol.-4(6), Aug 2016, E-ISSN: 2347-2693
Table 2: - Experimental table [5] Lukitsch, W,J (4-6 May 1999). Soft Starter Vs AC
Drivers Understand the Differences. IEEE Textile,
Fiber and Film Industry Technical Corfe rence, p. 5.
[6] Sastry, V.V., Prasad, M.R. and Sivakumar, T.V (Nov.
1997). Optimal soft starting of voltage-controller-fed
1M drive based on voltage across thyristors. IEEE
Transactions on Power Electronics, Vol. 12, pp. 1041
- 1051.
Characteristics of DAC are not linear some some noise is
happened in time of experiments.
Fig 9: - Comparison chart
ACKNOWLEDGMENT
Thanks to Department of Electrical & Electronics
Engineering, Pailan College of Management & Technology.
Special thanks to Prof. (Dr.) Nirmalendu Chatterjee, Ex-
Professor of Electrical Engineering Department, Jadavpur
University.
REFERENCES
[1] J. A. Kay, R. H. Paes, G. Seggewiss, and R. G. Ellis,
“Methods for the Control of Large Medium-Voltage
Motors: Application Considerations & Guidelines,”
IEEE Trans. Industry Applications, Vol. 36, No. 6, pp.
1688-1696, November/ December 2000.
[2] A. K. Mukhopadhyay, “Matrix Analysis of Electrical
Machines”, New Age International Limited
Publishers, 2003, ch. 7, pp.77-104.
[3] I. F. Akyildiz, X. Wang, and W. Wang, “Wireless Mesh
Networks: A Survey”, Computer Networks and ISDN
Systems, Vol.47, Issue-2, 2005, pp.445-487.
[4] Blaabjerg, F., Pedersen, lK., Rise, S., Hansen, H.-H.
and Trzynadlowski ,A. M. (Sept.-Oct. 1997). Can Soft
Starter Help Save Energy. IEEE Industry Applications
Magazine, Vol. 3, pp. 56 - 66.
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