Dual Converter using Thyristors

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Dual Converter using Thyristors
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Dual Converter using Thyristors
Introduction

• A.C. motors have the great advantages of being
  relatively inexpensive and very reliable.
• Induction motors in particular are very robust
  and therefore used in many domestic appliances
  such as washing machines, vacuum cleaners, water
  pumps, and others.
• The induction motor may be regarded as
  practically a constant-speed machine, the
  difficulty of varying its speed economically
  constitutes one of its main disadvantages.
• This drawback is overcome by using a thyristor
  controlled cyclo converter that enables the speed
  to be lowered in steps by Microcontroller
  triggering a SCR bank of 8nos in F/2 F/3.

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Project Block Diagram
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Hardware Requirements

• Microcontroller
• Crystal Oscillator
• SCRs
• Opto- isolators
• Transformer
• Diodes
• LED
• Switches
• Capacitors
• Resistors
• Operational amplifiers
• Lamp or a 12 volt DC motor

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Software Requirements

• Keil Compiler
• Keil an ARM Company makes C compilers, macro
  assemblers, real-time kernels, debuggers,
  simulators, integrated environments, evaluation
  boards, and emulators for ARM7/ARM9/Cortex-M3,
  XC16x/C16x/ST10, 251, and 8051 MCU families.
• Languages Embedded C or Assembly

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Power Supply
230 V AC 50 Hz
Bridge rectifier
5v Regulator
Filter(470µf)
5V DC
12V step down
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Which Microcontroller is Used in this Project?

• A 40 pin microcontroller from 8051 family is used
  in this project.
• It is a smaller computer
• Has on-chip RAM, ROM, I/O ports...

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Internal Structure of Microcontroller -
AT89S52/51
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Features of Microcontroller

• Compatible with MCS-51 Products
• 8K Bytes of In-System Programmable (ISP) Flash
  Memory
• Endurance 10,000 Write/Erase Cycles
• 4.0V to 5.5V Operating Range
• Fully Static Operation 0 Hz to 33 MHz
• 256 x 8-bit Internal RAM
• 32 Programmable I/O Lines
• Three 16-bit Timer/Counters
• Eight Interrupt Sources
• Full Duplex UART Serial Channel
• Interrupt Recovery from Power-down Mode
• Watchdog Timer
• Dual Data Pointer

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Optocoupler (Opto-Isolator)

• Opto coupler is a 6 pin IC. It is a combination
  of 1 LED and a diac. Pin 5 is not generally used
  and when light falls on the diac then it switches
  ON the diac.

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Optocoupler (Opto-Isolator)

• When logic zero is given as input to the LED then
  the light doesnt fall on diac so the diac is off
  means the current does not flow through the diac.
• When logic 1 is given as input to the LED then
  light emitted by LED falls on diac so it starts
  conducting i.e., now there will be current
  flowing through the diac.

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Three Phase Induction Motor

• It consists of the fixed stator or frame, a
  three-phase winding supplied from the three-phase
  mains and a turning rotor.
• There is no electrical connection between the
  stator and the rotor
• Stator and rotor are made of highly magnetizable
  core sheet providing low eddy current and
  hysteresis losses

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Stator And Rotor

• The stator winding consists of three individual
  windings which overlap one another and are offset
  by an electrical angle of 120
• Synchronous Speed (Ns) 60f/p
• Rotor in induction machines with squirrel-cage
  rotors consists of a slotted cylindrical rotor
  core sheet package with aluminium bars which are
  joined at the front by rings to form a closed cage

• Ns Synchronous Speed/ minute
• F frequency
• PPole pair Number

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Silicon Controlled Rectifier (SCR)

• 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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Silicon Controlled Rectifier (SCR)

• 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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LM358 Series Amplifier

• The LM358 series consists of two independent,
  high gain internally frequency compensated
  operational amplifiers which were designed
  specifically to operate from a single power
  supply over a wide range of voltages.
• Operation from split power supplies is also
  possible and the low power supply current drain
  is independent of the magnitude of the power
  supply voltage.

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Features Of LM358

• Available in 8-Bump micro SMD chip sized package.
  
• Large dc voltage gain 100 Db.
• Wide power supply range

• Single supply 3V to 32V
• or dual supplies 1.5V to 16V

• Very low supply current drain (500
  µA)-essentially independent of supply voltage.

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Working Principle

• The project uses zero voltage reference ,8 Opto
  isolators(MOC3021) are used for driving 8 SCRs.
  Triggering pulses so generated by the MC as per
  the program written provides input condition to
  the Opto isolator that drive the respective SCR
  to get conducting for 20ms from 1st bridge and
  next 20ms from the 2nd bridge to get the output,
  total time period of one AC cycle of 40ms which
  is 25 Hz.

• Thus F/2 is delivered to the load while switch 1
  is closed. Similarly for F/3 the conduction takes
  place for 30ms in the 1st bridge and next 30ms
  from the next bridge, such that a total time
  period of 1 cycle comes to 60ms which in turn in
  F/3 while switch -2 is operated. Fundamental
  frequency of 50Hz is available by triggering on
  pair from the 1st bridge for 1st 10ms and for the
  next 10msfrom the next bridge while both the
  switches are kept in OFF condition. Reverse
  current flowing in the gates of the SCRs are
  Opto isolator output.

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What is the Formula for Calculating Smoothing
Capacitor Value?

• There is some approximated formula .Peak to peak
  ripple voltage Load current in amps / (2line
  frequency in hertz capacitance in farads). But
  as rule of thumb for 1 A current 1000uF is best.
  Thus it is load dependent.

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