Single Phase Induction Motor Speed Control

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Single Phase Induction Motor Speed Control
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Single Phase Induction Motor Speed Control
Introduction

• 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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Single Phase Induction Motor Speed Control
Block Diagram
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Single Phase Induction Motor Speed Control
Hardware Requirements

• Op-amp
• Opto-isolators
• SCRs
• Voltage Regulator
• Transformer
• Diodes
• LED
• Resistors
• Capacitors
• Lamp

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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
Power Supply
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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
Induction Motor
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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
Induction Motor

• 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.

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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
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

c. Two SCRs
b. Diode SCR
a. Triac
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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
SCR - Silicon Controlled Rectifier

• 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.

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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
Comparator

• 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).

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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
Applications

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

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Single Phase Induction Motor Speed Control
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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Single Phase Induction Motor Speed Control
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.

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