Dual Converter using Thyristors

Dual Converter using
Thyristors

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Introduction
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
5V DC
12V step down
Bridge rectifier
Filter(470µf) 5v Regulator

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 - AT89S52/51

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

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.

 When logic zero is given as input to the LED then the light doesn’t 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.
Optocoupler (Opto-Isolator)

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)= 60*f/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;
• P=Pole 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 Transistors.
 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 SCR’s. 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 SCR’s 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 / (2*line frequency in hertz *capacitance in
farads). But as rule of thumb for 1 A current 1000uF is best. Thus it is
load dependent.
Formula

Application
 Dual converters are mostly used at industries where we requires
reversible D.C. Generally Dual Converters are used for Speed
Control of D.C. Motors etc.
 Main use of dual converter is to easily change the direction of the
motor and handle braking system of the motor.

Conclusion
 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 . This
single phase converter is achieved by using a pair of thyristor controlled
bridge. The use of SPMC in the design of dual converter that has full
controllability in both forward and reverses directions has been analysed.

Dual Converter using Thyristors

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