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Dual Converter using Thyristors


Dual converter is a power electronics control system to get either polarity DC from AC rectification by forward converter and reverse converter . It can run a DC motors in either direction with speed control too. – PowerPoint PPT presentation

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Title: Dual Converter using Thyristors

Dual Converter using Thyristors
Dual Converter using Thyristors
  • 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.

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

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

Power Supply
230 V AC 50 Hz
Bridge rectifier
5v Regulator
12V step down
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...

Internal Structure of Microcontroller -
Features of Microcontroller
  • Compatible with MCS-51 Products
  • 8K Bytes of In-System Programmable (ISP) Flash
  • 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

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.

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.

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

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

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.

Silicon Controlled Rectifier (SCR)
  • The operation of a SCR can be understood in terms
    of a pair of tightly coupled Bipolar Junction
  • SCR has three states
  • Reverse blocking mode, forward blocking mode, and
    forward conducting mode

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.

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.

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.

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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