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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
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 .
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INTRODUCTION
 SINGLE PHASE RECTIFIER:
Back
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.
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.
Triggering operation
•555 Timer Astable Multivibrator
Circuit:
•555 Timer Monostable Multivibrator
Circuit:
•Unijunction Transistor Relaxation
Oscillator :
Pulse transformer:
We used the idea of zero cross detector
We used PIC 16F877 to do the triggering program .
The basic circuit :
START
Read the value of the
Input voltage
If value =0v
N
Y
Delay =(firing angel)
Output the triggering
pulse
Thyristor
Back
Basic input
Triggering at zero◦
Output of zero cross
Triggering at 30◦
Triggering at 90◦
Triggering at 60◦
Triggering at 120◦
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.
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 = π , but in RL-Load
The current does not fail.
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
and zero cross
Interface
Thyristors
bridge
 Several circuit has been built in order to make connection one them work properly
but the others faild.
 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
 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)
The complete circuit:
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.
 following figures show the output voltage at different firing angle, input voltage
(Vin)= 20 v and R= 16Ω:
α = zero˚
α = 45˚
α = 90˚
α = 135˚
 following figures show the input current at different firing angle, input voltage
(Vin)= 20 v and R= 16Ω:
at α = zero˚
at α = 45˚
at α = 90˚
at α = 135˚
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= 16Ω, L= 70 mh, Ф= 53.9˚
 R= 16Ω, L= 455mh, Ф= 83.61˚
note: the load angel can be calculated by the following equation:
The following figures show the output voltage at different firing angle, input voltage
(Vin)= 20 v:
L= 70 mh, R= 16Ω, Ф= 53.9˚
at α = zero˚
at α = 45˚
L=455mh and R= 16Ω, Ф= 83.61
at α = zero˚
at α = 45˚
L= 70 mh, R= 16Ω, Ф= 53.9˚
L=455mh and R= 16Ω, Ф= 83.61˚
at α = 90˚
at α = 90˚
at α = 135˚
at α = 135˚
•following figures show the input current at different firing angle, input
voltage (Vin)= 20 v and R= 16Ω, L= 70 mh, Ф= 53.9˚ :
at α = zero˚
at α = 45˚
at α = 90˚
at α = 135˚
 The following figures show the input current at different firing angles, input voltage
(Vin)= 20 v, L= 455 mh and R= 16Ω, Ф= 83.61:
at α = zero˚
at α = 45˚
at α = 90˚
at α = 135˚
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.
 The following figures show the output voltage of DC motor:
at α = zero˚
at α = 45˚
at α = 90˚
at α = 135˚
 The following figures show the input current of DC motor:
at α = zero˚
at α = 45˚
at α = 90˚
at α = 135˚
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
 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.
 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:
 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
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
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) .