AN-NAJAH NATIONAL UNIVERSITY

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AN-NAJAH NATIONAL UNIVERSITY DEPARTMENT OF
ELECTRICAL ENGINEERING Investigation On a
Microcontroller-Triggered Single Phase Thyristor
Bridge
PREPARED BY SARI YAISH
HASHEM ASMAH
INSTRUCTOR PROF. MARWAN
MAHMOUD 2008/2009
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The Project Idea

• Is to build a single phase full controlled
  bridge rectifier ,use it to supply different
  types of load and to make investigations about
  the improvement of its grid current .

Back
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INTRODUCTION

• SINGLE PHASE RECTIFIER

Back
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• Properties
• for continuous operations
  for discontinuous operations
• Two quadrant operation is possible.
• The thyristors are triggered at an interval of ?
  .
• It can be used in continuous mode depend on the
  firing angle.

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Applications

• This circuit is widely used in single phase dual
  converters (ups).
• It is also used to control the speed of DC
  motors.
• Can be used as power electronic lab unit.

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Triggering operation

• 555 Timer Astable Multivibrator
• Circuit

• 555 Timer Monostable Multivibrator Circuit

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• Unijunction Transistor Relaxation Oscillator
  

• Pulse transformer
•  

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• We used the idea of zero cross detector
• We used PIC 16F877 to do the triggering program .

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The basic circuit
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START
Read the value of the Input voltage
If value 0v
N
Flow Chart
Y
Delay (firing angel)
Output the triggering pulse
Thyristor
Back
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Basic input
Output of zero cross
Triggering at zero?
Triggering at 30?
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Triggering at 90?
Triggering at 60?
Triggering at 120?
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• Bridge circuit construction
• Thyristor test
• We chose the thyristor to work on which is TIC
  116.
• 8 A Continuous On-State Current
• 400 V to 800 V Off-State Voltage.
• Max IGT of 20 mA.

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• Circuit operation
• For this circuit the source is
• Sinusoidal voltage source.
• When it is positive T1 and T2
• Can be triggered, when it is negative T3 and
  T4 can be triggered.
• Current through the load remains unidirectional .
• Varying the firing angle provide a variable
• Output DC voltage.
• When Vs change from a positive to a negative
• value, the current through the R-load
• becomes zero at instant wt p , but in
  RL-Load
• The current does not fail.

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• Triggering Transportation
• Now our project is divided into two parts the
  first part consists of the control part (the zero
  cross and the PIC) and the second part consists
  of the thyristors bridge ,then we need to connect
  the two parts by using a suitable interface .
• PIC Interface
  Thyristors
• and zero cross
  bridge
• Several circuit has been built in order to make
  connection one them work properly but the
  others faild.

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• The failure methods

Direct connection between the PIC and the Bridge
Make connection between PIC and bridge by using
MOS 3020
using photo coupler between anode and gate
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• The successful method
• In this method transistor photo isolator
  (4n25) has been used to make the following
  connection
• transistor photo isolator (4n25)

connection between PIC and bridge By using
transistor photo isolator (4n25)
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The complete circuit
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(No Transcript)
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• Investigation about the input and output
  characteristics
• This stage is divided into different parts
• Pure resistive load.
• R-L load.
• DC motor speed control.
• Filtering the grid current.
• I- Pure resistive load
• In this part we apply resistive
• load on the output of the bridge
• and we get the waveforms from the
• oscilloscope.

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• following figures show the output voltage at
  different firing angle, input voltage (Vin) 20 v
  and R 16?

a zero
a 45
a 135
a 90
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• following figures show the input current at
  different firing angle, input voltage (Vin) 20 v
  and R 16?

at a 45
at a zero
at a 135
at a 90
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• II- RL-Load
• In this part we apply R-L load on the output
  of the bridge and we get the waveforms from the
  oscilloscope.
• We will apply two loads
• R 16O, L 70 mh, ? 53.9
• R 16O, L 455mh, ? 83.61
• note the load angel can be calculated by
  the following equation

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The following figures show the output voltage at
different firing angle, input voltage (Vin) 20
v

• L 70 mh, R 16?, ? 53.9

• L455mh and R 16?, ? 83.61

at a zero
at a zero
at a 45
at a 45
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• L 70 mh, R 16?, ? 53.9

• L455mh and R 16?, ? 83.61

at a 90
at a 90
at a 135
at a 135
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• following figures show the input current at
  different firing angle, input voltage (Vin)
  20 v and R 16?, L 70 mh, ? 53.9

at a zero

• at a 45

at a 135
at a 90
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• The following figures show the input current at
  different firing angles, input voltage (Vin) 20
  v, L 455 mh and R 16?, ? 83.61

at a 45
at a zero
at a 90
at a 135
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• III- DC motor speed control
• The single phase bridge also can be used to
  control the speed of DC motor by changing the
  value of output voltages and this can be achieved
  by changing the firing angel.
• can be noted that the equivalent circuit of
  the DC motor consist of resistor, inductor and
  battery, the battery affects the form of output
  and input current.

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• The following figures show the output voltage of
  DC motor

at a 45
at a zero
at a 135
at a 90
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• The following figures show the input current of
  DC motor

at a zero
at a 45
at a 90
at a 135
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• IV- Filtering the grid current
• From the previous partwe note that the input
  current of the bridge at different load contains
  a lot of high harmonics component , this
  components have very bad effects on AC machines
  like motors, transformers that connect to the
  network supply the bridge, also the
  communication devices around the bridge so, at
  this part the input current will be improved by
  using filter on the input side of the rectifier.
• the grid
  current

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• To remove these harmonics an LC resonance
  circuit has been used.
• the cut off frequency of this circuit can be
• calculated by the following equation
• at least we want to remove the harmonic which
  have 350 and 450 Hz.
• Practically the values which have been calculated
  are not available in our market because we need
  to use non polar capacitor with high capacity and
  high voltages, also we face problems in finding
  the suitable value of inductors.

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• After we fail to improve the input current by
  using the previous circuit, we try to achieve
  this improvement by using low pass filter
  circuit.
• The cut off frequency of this circuit is given by
  the following equation

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• The input current waveforms after filtering are
  shown in the following figures

at Fc 398 Hz
at Fc 159 Hz
at Fc 79 Hz
at Fc 53 Hz
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• benefits
• Improve our skills in designing electronic
  circuits and interfaces by using the simple
  electronic components (resistors, capacitors,
  transformers and diodes), and more complicated
  components like photo couplers.
• Learn how to use the measurement devices and how
  to take accurate measurement by using multimeter
  and oscilloscope .
• Have a basic idea about how to use microprocessor
  (PIC), building its basic and program it
  successfully.
• Have a good acknowledgment about the basic
  power electronics component (thyristor).
• Understanding the concepts of power electronic
  like triggering (firing angel), thyristor turn

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• Future suggestions
• Varying the firing angle of the thyristor of
  this circuit by using potentiometer (this need
  high level of calibration for the thyristor
  firing angle with the PIC analog to digital by
  programming ).
• Using this circuit in industrial application
  but for huge applications the thyristor should be
  changed to be more suitable and stand with high
  currents.
• Use this circuit to build a complete
  uninterrupted power system ( UPS) .