Single Phase Induction Motor Speed Control

Single Phase Induction
Motor Speed Control

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Introduction
Single Phase Induction Motor
Speed Control
 Induction motors are widely used in many residential, industrial,
commercial, and utility applications. Single-phase induction motors are
widely used in home and industrial appliances . This project is designed to
control the speed of a single-phase induction motor using an easy
operating knob, which is commonly used in home automation application.
The main advantage of these motors is their ability to operate from a
single-phase power supply.

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Block Diagram

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Hardware Requirements
 Op-amp
 Opto-isolators
 SCRs
 Voltage Regulator
 Transformer
 Diodes
 LED
 Resistors
 Capacitors
 Lamp

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Types of Single Phase Induction Motor
 Split phase induction motor,
 Capacitor start inductor motor,
 Capacitor start capacitor run induction motor,
 Shaded pole induction motor.

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Power Supply

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About Power Supply
 The 230V AC supply is first stepped down to 12V AC using a step
down transformer.
 This is then converted to DC using bridge rectifier.
 The AC ripples is filtered out by using a capacitor and given to the
input pin of voltage regulator 7812.
 At output pin of this regulator we get a constant 12V DC which is
used for different ICs in this project.

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Induction Motor

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Induction Motor
 The single-phase induction machine is the most frequently used motor
for refrigerators, washing machines, clocks, drills, compressors, pumps,
and so forth.
 The single-phase motor stator has a laminated iron core with two
windings arranged perpendicularly.
 One is the main winding
And
 The other is the auxiliary winding or starting winding .

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 This “single-phase” motors are truly two-phase machines.
 The motor uses a squirrel cage rotor, which has a laminated iron core with
slots.
 Aluminium bars are moulded on the slots and short-circuited at both ends
with a ring.
Induction Motor

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Soft Starter
 A soft starter is another form of reduced voltage starter for A.C.
induction motors.
 The soft starter is similar to a primary resistance or primary
reactance starter in that it is in series with the supply to the motor.
 The current into the starter equals the current out.
 The soft starter employs solid state devices to control the current
flow and therefore the voltage applied to the motor.

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Soft Starter
 Soft starters are connected in series with the line voltage applied to the
motor, or can be connected inside the delta loop of a delta connected
motor, controlling the voltage applied to each winding.
 Voltage control is achieved by means of solid state A.C. switches in series
with one or more phases. These switches comprise either:
a. Triac b. Diode & SCR c. Two SCRs

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SCR - Silicon Controlled
Rectifier
 A Silicon Controlled Rectifier (or Semiconductor Controlled Rectifier) is a
four layer solid state device that controls current flow.
 An SCR can be seen as a conventional rectifier controlled by a gate signal.
 It is a 4-layered 3-terminal device.
 When the gate to cathode voltage exceeds a certain threshold, the device
turns 'on' and conducts current.

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 The operation of a SCR can be understood in terms of a pair of tightly
coupled Bipolar Junction Transistors.
 SCR has Three States:
• Reverse blocking mode, Forward blocking mode, and Forward conducting
mode.
SCR - Silicon Controlled Rectifier

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Comparator
 Op amps & comparators look very similar.
 But a comparator gives a logic output indicating the relative potentials
on its two inputs.
 An op amp amplifies the differential voltage between its two inputs –
and is designed always to be used in closed-loop applications.
 Potential dividers are connected to the inverting and non inverting
inputs of the op-amp to give some voltage at these terminals.

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 Supply voltage is given to +V and –V is connected to ground.
 The output of this comparator will be logic high (i.e., supply voltage) if
the non-inverting terminal input is greater than the inverting terminal
input of the comparator.
 If the inverting terminal input is greater than the non-inverting
terminal input then the output of the comparator will be logic low
(i.e., gnd).
Comparator

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Working Principle
 To start the motor with low current, two anti-parallel SCRs connected in
series with an induction motor to the utility supply. When the project is in
operation, the firing angle is adjusted according to the requirement, which
leads to changed intensity of a lamp or speed control of an induction
motor. An op-amp operates in comparator mode that compares with zero
voltage pulses to develop a saw-tooth voltage.
 This saw tooth waveform is further compared against a varying voltage by a
potentiometer for the level comparator to develop delayed pulses for
triggering the SCRs. A lamp is provided in this project in place of an
induction motor for demonstration purpose.

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Advantages
 Single phase motor is that it requires a two wire supply
 Single-phase motors are less expensive to manufacture than other
motors.
 Capacitor-start motors are good general purpose motors and they are
ideal for most occasions.
 The single phase motors are simple in construction, cheap in cost,
reliable and easy to repair and maintain.

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Disadvantages
 Single phase motor are that their power is limited.
 They do not have good starting torque and they have a
complex starting switch in some cases.
 Speed control of induction motors are difficult.
 At low loads, the power factor drops to very low values

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Applications
 Single phase motor finds its application in
 Vacuum Cleaner
 Fans
 Washing machine
 Centrifugal pump
 Blowers
 Small toys

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Further Enhancement
 The project can be enhanced by using six SCRs, two connected in back
to back for each phase for a three phase load and the same project can
also be enhanced to run motor in both the directions.

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Conclusion
 Single phase power system is widely used in domestic purpose,
commercial purpose and to some extent in industrial purpose. As the
single phase system is more economical and the power requirement
in most of the houses, shops, offices are small, which can be easily
met by single phase system. The single phase Induction motors are
simple in construction, cheap in cost, reliable and easy to repair and
maintain.

Single Phase Induction Motor Speed Control

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