ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 5, October 2012
A Review on Speed Control Techniques of Single
Phase Induction Motor
Atul M. Gajare1, Nitin R. Bhasme2
Abstract - In this paper, various types of speed control methods
for the single phase induction motor are described. This research
paper explains speed control of single phase induction motor by
means of frequency ,its implementation and test result also the
power conversion section in the given speed drive is consisting
IRF840 N-channel MOSFET as a switching element. These
MOSFET (four in number) are used in H-bridge configuration to
form inverter to supply a.c. current to the motor. The driver
circuit for this H-bridge inverter is made up of C124 transistors
and MJE 13002 transistors. H-bridge inverter is supplied with
300v power supply and for driver and frequency control circuit,
12V power supply is given. Here, IC SG3525A is used as pulse
width modulation IC for frequency control purpose. So,
constructed system the frequency range is 16 to 57 Hz at constant
voltage for changing the speed of induction motor.
Keywords: driver circuit, induction motor, variable speed drive,
frequency control circuit.
I.
INTRODUCTION
Induction motors are widely used in many residential,
industrial, commercial, and utility applications. Single-phase
induction motors are widely used in home appliances and
industrial control. A variable-frequency drive (VFD) is a system
for controlling the speed of a rotational or linear alternating
current (AC) electric motor by controlling the frequency of the
electrical power supplied to the motor. A variable frequency
drive is a specific type of adjustable-speed drive. Variablefrequency drives are also known as adjustable-frequency drives
(AFD), variable-speed drives (VSD), AC drives, micro drives or
inverter drives [7].The multispeed operation and multipurpose
operation are provided by controlling the speed of these motors.
In the previous days, the variable speed drives had various
limitations such as larger space, poor efficiencies, lower
speed and etc. But, the invention of power electronics devices
change the situation so now, variable speed drive are
constructed in smaller size, high efficiency and high reliability
[2].
Variable-frequency drives are used in a wide number of
applications to control pumps, fans, hoists, conveyors, and
other machinery.
II.
SPEED CONTROL
There are two speed terms are synchronous speed and rated
speed used in the electric machine. Synchronous speed is the
speed at which a motor's magnetic field rotates. Synchronous
speed is the motor's theoretical speed if there was no load on
the shaft and friction in the bearings. The two factors affecting
synchronous speed are the frequency of the electrical supply
and the number of magnetic poles in the stator. The
synchronous speed is given by
Where,
f = Frequency in Hz
P = Number of Poles
The rotor speed of an Induction machine is different from the
speed of Rotating magnetic field. The shaft speed (rotor speed)
of induction motor when driving load will always be lass than
the synchronous speed. The percent difference in synchronous
speed and shaft speed is called slip as shown in equation
Ns = Synchronous speed
Nr = Rotor speed
Below relation states that synchronous speed of induction
motor is directly proportional to the frequency and inversely
proportional to the number of poles of the motor .Since the
number of poles is fixed by design, the best way to vary the
speed of the induction motor is by varying the supply
frequency.
In this paper, sections 2 explain the basic concept of speed
The speed of the motor shaft with rated voltage and line
control and v/f ratio control, generic topologies, control
technique of speed control. This paper SPIM has been control frequency applied at full load is so called base speed. By
by frequency control method by using PWM control circuit and changing the frequency to the motor above or below 60Hz; the
motor can operate above or below base speed.
H-bridge inverter.
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ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 5, October 2012
III. MOTOR DRIVEN LOAD CHARACTERISTICS
A. Volts - Per - Hertz Ratio
This term describes a relationship that is fundamental to the
The behavior of torque and horsepower with respect to speed
operation of motors using adjustable frequency control. An ac partially determine the requirement of motor drive system.
induction motor produces torque by virtue of the flux in its
rotating field. Keeping the flux constant will enable the motor
to produce full load torque. Below base speed, this is
accomplished by maintaining a constant voltage-to-frequency
ratio applied to the motor when changing the frequency for
speed control. For 460 and 230 Volt motors, the ratio is 460/60
= 7.6 and 230/60 = 3.8. If this ratio rises as the frequency is
decreased to reduce the motor speed, the motor current will
increase and may become excessive. If it reduces as the
frequency is increased, the motor torque capabilities will
decrease. There are some exceptions to this rule which are
described below.
The base speed of the motor is proportional to supply
frequency and is inversely proportional to the number of stator
poles. So, by changing the supply frequency; the motor speed
can be changed. Above base speed, this ratio will decrease
when constant voltage (usually motor rated voltage) is applied
to the motor. In these cases, the torque capabilities of the motor
decrease above base speed.
This torque formula implies that the torque is directly
proportional
to the horse power rating and inversely
At approximately 30 Hertz and lower, the Volts-per-Hertz
proportional
to
the speed.
ratio is not always maintained constant. Depending on the type
of load, the voltage may be increased to give a higher ratio, in
In real applications, various kinds of loads exist with
order for the motor to produce sufficient torque, especially at different torque-speed curves. The type of load that a motor
zero speed. This adjustment is usually called "Voltage Boost".
drives is of the most important one application considerations
At base speed and below, the Volts-per-Hertz ratio can be when applying any type of inverter. Generally, loads can be
adjusted lower to minimize motor current when the motor is grouped into three different categories explain below
lightly loaded. This adjustment, which lowers the voltage to the
A. Constant Torque Load
motor, will reduce the magnetizing current to the motor.
Constant torque loads require the same amount of torque at
Consequently, the motor will produce less torque which is
low speeds as at high speeds. Torque remains constant
tolerable. This control is the most popular in industries and is
throughout the speed range and the horsepower increases and
popularly known as the constant V/f control.
decreases in direct proportion to the change in speed. Figure 2
The VFD is a system made up of active/passive power shows the constant torque load characteristics of induction
electronics devices; figure 1 shows electronic speed control of motor. If the speed drops to 50 percent, then the power required
the motor supply frequency. The basic concept of these drives, to drive the operation will drop to 50 percent while the torque
figure 1, is that a rectifier converts the fixed frequency supply remains constant.
to d.c. (which converts commercial power into a direct current).
A d.c. link stage smoothes the rectified output to a stable d.c.
voltage (or current).This d.c. is then inverted to provide a
synthesized a.c. waveform at the motor terminals. The
frequency and power of the a.c. supply delivered to the motor is
controlled by inverter [3].
Figure 2. Constant Torque Load Characteristic
Figure 1. Basic Block Diagram of VFD
This type of load characteristics includes most compressors,
conveyors, reciprocating pumps.
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ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 5, October 2012
B. Constant Horsepower Load
This is characteristic of grinders, turret lathes and winding
reels. Specifically, the torque required of the load will decrease
as the speed is increased, or vice versa. Hence, the product of
torque and speed, which is horsepower, is approximately
constant as the speed changes. This type of loading is usually
applied above base speed. Figure 3 shows the constant horse
power load characteristics of induction motor. As an example,
an empty reel winding a coil will require the least amount of
torque, initially, and will be accelerated to the highest speed.
IV.
GENERIC TOPOLOGIES
Variable frequency drives can be classified according to the
following generic topologies.
A. Voltage-Source Inverter (VSI) Drives
In a VSI drive, the diode-bridge rectifier plus full bridge
IGBT based inverter used. A dc link capacitor is required to
supply the reactive power needed by the motor . The vast
majority of drives are VSI type with pulse width modulation
(PWM) voltage output. The circuit topology shown in figure 5.
Figure 5. Voltage source Inverter drives
Figure 3, Constant Horsepower load characteristics
B. Current-Source Inverter (CSI) Drives
As the coil builds up on the reel, the torque required will
In a CSI drive, the DC output of the SCR-bridge converter
increase' and the speed will be decreased. Energy savings can stores energy in series-reactor connection to supply stiff current
be achieved by varying the speed of the motors and the driven input to the inverter. CSI drives can be operated with either
load using a commercially available variable frequency drive.
PWM or six-step waveform output. Current source inverter
drives block diagram shown in figure 6
C. Variable Torque Load
With a variable torque load, the loading is a function of the
speed. This is a characteristic of centrifugal pumps and fans.
Specifically, as the speed is increased or decreased, the torque
required of the load will change with the square of the speed,
while the power is the cube of the speed. Figure 3 shows the
variable torque load characteristics of induction motor. As an
example, with a 100% torque load at 100% speed, when the
speed is reduced to 50%, the square of the speed is 0.5 x 0.5 or
0.25 and the load torque will be 25% of full load torque in Fig.
below
Figure 6. Current Source Inverter Drive
Figure 4. Variable Torque Load Characteristics
C. Six-Step Inverter Drive
Six-step drives can be either VSI or CSI type and are also
referred to as variable-voltage inverter drives. There is no need
for a divided dc bus. A special PWM topology needs to be
implemented to achieve the maximum possible converter
utilization for a two-phase output voltage (balanced or
unbalanced). This topology uses a six pack IGBT module to
control a two-phase induction motor. The circuit topology as
shown in figure 7
35
ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 5, October 2012
V.
CONTROL PLATFORMS
Various speed control techniques implemented by modernage VFD are mainly classified in the following three categories
A. Scalar Control (V/f Control)
In this type of control, the motor is fed with variable
frequency signals generated by the PWM control from an
inverter. Here, the V/f ratio is maintained constant in order to
get constant torque over the entire operating range. Since only
magnitudes of the input variables – frequency and voltage – are
controlled, this is known as “scalar control”. Generally, the
drives with such a control are without any feedback devices
(open-loop control). Hence, a control of this type offers low
cost and is an easy to implement solution.
Figure 7, Six-Step Inverter Drive
D. Load Commutated Inverter (LCI) Drives
In such controls, very little knowledge of the motor is
In a LCI drive, a special CSI case, the DC output of the SCR- required for frequency control. Thus, this control is widely
bridge converter stores energy via DC link inductor circuit to used.
supply stiff quasi-sinusoidal six-step current output of a second
B. Vector Control
SCR-bridge's inverter and an over-excited synchronous
This control is also known as the “field oriented control”,
machine.
“flux oriented control” or “indirect torque control”. In general,
E. Cycloconverters
there exists three possibilities for such selection and hence,
Cycloconverter topologies are AC/AC converters that have three different vector controls. They are:
no intermediate DC link for energy storage. In this
 Stator flux oriented control
configuration, a.c. signal is directly converted to a controlled
 Rotor flux oriented control
voltage and frequency ac signal. In this case, the motor torque
 Magnetizing flux oriented control
and current can be controlled and a wide range of speed
As the torque producing component in this type of control is
variation can be obtained. However, 12 more diodes are used in
controlled only after transformation is done and is not the main
this configuration. The circuit topology of cycloconverter as
input reference, such control is known as “indirect torque
shown in figure 8.
control”.
The most challenging and ultimately, the limiting feature of
the field orientation, is the method whereby the flux angle is
measured or estimated. Depending on the method of
measurement, the vector control is divided into two
subcategories: direct and indirect vector control.
In direct vector control, the flux measurement is done by
using the flux sensing coils or the Hall devices. This adds to
additional hardware cost and in addition, measurement is not
highly accurate. Therefore, this method is not a very good
control technique. The more common method is indirect vector
control. In this method, the flux angle is not measured directly,
but is estimated from the equivalent circuit model and from
measurements of rotor speed, the stator current & the voltage.
Figure 8. Single Phase ac/ac Cycloconverter
F. Doubly Fed Slip Recovery Systems
A doubly fed slip recovery system feeds rectified slip power
to a smoothing reactor to supply power to the AC supply
network via an inverter, the speed of the motor being controlled
by adjusting the DC current.
Figure 9. Direct Vector Control
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ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 5, October 2012
VI.
Figure 12. Block Diagram of Single Phase Induction Motor Using
Inverter
Figure 10. Indirect Vector Control
C.
SPEED CONTROL OF SPIM USING FREQUENCY
CONTROL
Direct Torque Control (DTC)
The heart of this technology is its adaptive motor model.
This model is based on the mathematical expressions of basic
motor theory. This model requires information about the
various motor parameters, like stator resistance, mutual
inductance, saturation co efficiency; etc Torque vector
controlled drives are capable of controlling the stator flux and
torque more accurately than vector controlled drives, while the
controller complexity is reduced considerably. Field orientation
is achieved without rotor speed or position feedback using
advanced motor theory to calculate the motor torque directly
without using modulation. The controlling variables are motor
magnetizing flux and motor torque. The external speed set
reference signal is decoded to generate the torque and flux
reference. Thus, in the DTC, the motor torque and flux become
direct controlled variables and hence, the name – Direct Torque
Control. The advantage of this technology is the fastest
response time, elimination of feedback devices, reduced
mechanical failure. The disadvantage is due to the inherent
hysteresis of the comparator, higher torque and flux ripple
exist.
The design considerations for speed control system using
frequency control have been divided into three parts such as
PWM control circuit, driver circuit and H-Bridge inverter.
Variable speed drive by using frequency control method is
commonly used to control and change the speed of the singlephase induction motor. It can vary the desired speed by
changing the frequency using the variable resistance. Due to
compact integrated circuit to obtained low cost high
performance speed control. In this project, two separate power
supply has been used which is 240 VD.C. and 12 VD.C. The
240 V D.C. was used to feed to H-bridge inverter while 12
VD.C was used in PWM control circuit and driver circuit as
shown in figure 13.
Figure 13. H Bridge Inverter
Figure 11. Direct Torque Control
Only two MOSFET are able to switch ON and OFF at the
same time. The four MOSFET will receiving the triggering
pulses from the driver circuit to turn ON and OFF continuously.
There have six operation of the switching MOSFET.
37
ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 5, October 2012
The operations of this inverter are
T1-T2 ON: Both create short circuits across the DC source
and are invalid.
T3-T4 ON: Both create short circuits across the DC source
and are invalid.
T1-T4 ON: Applies positive voltage (Vs) to the load. The
positive current (IL) passes through T1-T4 and the negative
current (-IL) is through D1-D4.
T2-T3 ON: Applies negative voltage (-Vs) across the load.
The positive current (IL) flows through D2-D3 and returns
energy to the DC source. The negative current (-IL) flows
through T2-T3 and draws energy from the supply.
T1-T3 ON: Applies zero volts across the load. The positive
current’s path is T1-T3 and the negative current’s path is D1 T3.
T2-T4 ON: Applies zero volts across the load. The positive
current’s path is through D2-D4 and the negative current’s path
is T2-T4.
The circuit for the H-bridge inverter output was showed in
Figure 14.
Figure 15. Timing Diagram
Figure shown the results of single phase induction motor
when it was running at different frequency. In the test, the
lowest frequency is 16 Hz at 480 rpm while the highest
frequency is 57 Hz at 1690 rpm.
Figure 14. H Bridge Output
Pulse width modulation use technology and use sophisticated
power electronics to accomplish the same frequency and
voltage control.
PWM control circuit is used to provide the pulses by varying
resistor and fed to two driver circuits. The driver circuit is used
to divide four to two pulses of PWM control circuit. And then
the pulses of driver circuit are driven the H-bridge inverter. By
this way, the H-bridge inverter produces the alternating current
to the motor. The timing diagram of the frequency control
system is shown figure 15.
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Figure 16. Calculated Results Between Frequency (Hz) Vs RPM
ISSN 2249-6343
International Journal of Computer Technology and Electronics Engineering (IJCTEE)
Volume 2, Issue 5, October 2012
REFERENCE
[1] W.I.Ibrahim,.M.T.Raja,Ismail,M.R.Ghaz ali,” Development of Variable
Speed Drive for Single Phase Induction Motor Based on Frequency
Control”,
[2] Mr. Aung Zaw Latt, Dr. Ni Ni Win,” Variable Speed Drive of Single Phase
Induction Motor Using Frequency Control Method”, International
Conference on Education Technology and Computer, 2009.
[3] D S Henderson, “Variable Speed Electric Drives - Characteristics and
Applications”“Adjustable Frequency Control (Inverters) fundamentals
application Consideration”, Bulletin C870A.
[4] Theodore Wilidi.1997. Electrical Machine Drives and Power System
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[5] Farzan Rashidi, "Sensorless Speed Control of Induction Motor Derives
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[6] Negm, M. M. M, "Torque optimized speed control of a 3-phase induction
motor", IEEE International Conference on Power System Technology,
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[7] Ali S. Ba-thunya Rahul Khopkar Kexin Wei Hamid A. Toliyat,“Single Phase
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[8] Rakesh Parekh., 2003. AC Induction Motor Fundamentals. Microchip
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[9] Muljadi, Y. Zhao, T. Liu and T.A. Lipo, "Adjustable ac Capacitor for a
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[10] Mircea Popescu,” Induction Motor Modelling For Vector Control Purposes,”
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[11] E. R. Collins, Jr., "Torque and slip behavior of single-phase induction
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[12] A.S.ZEIN EL-DIN and A.E.EL-SABBE,” A Novel Speed Control
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Figure 17. Test Results Between Frequencies (Hz) Vs RPM
Figure 18. Response Between Test Results and Calculated Result at
Various Value of Resistance
VII.
[14] Nasar, S. A., 1987. Handbook of Electric Machines, McGraw-Hill Publishing
Company Limited.
CONCLUSION
The use of a Variable Speed Drive for a speed control
application usually offers an energy efficient and
environmentally friendly solution. The best opportunities for
energy savings, with subsequent economic savings, arise
through the laws which govern the operation of centrifugal fans
and pumps. Simple and straight forward VSD’s, such as the
PWM inverter drives, are available for applications where the
speed control accuracy is not critical. This compact inverter had
its hardware reduced to a minimum through the use of H-bridge
inverter. The variable speed drive with variable frequency
control method will offer new, low-cost solutions for light
commercial and consumer applications. The frequency range of
the constructed circuit is 16 Hz to 57 Hz at constant voltage for
changing the speed of induction motor between theoretical
limits of 480 rpm to 1690 rpm if 50 Hz, single-phase AC
motors are used.
Author’s Details
Atul M. Gajare1 M.E. Student, Government College of Engineering,
Aurangabad. atul.gajare@gmail.com
Nitin R. Bhasme2 Asst. Professor Government College of Engineering,
Aurangabad.
39