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. Back

INTRODUCTION SINGLE PHASE RECTIFIER:

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 Thyristor Read the value of the Input voltage If value =0v Delay =(firing angel) Output the triggering pulse Back Y N

Basic inputOutput of zero cross Triggering at zero ◦ Triggering at 30 ◦

Triggering at 60 ◦ Triggering at 90 ◦ Triggering at 120 ◦

Bridge circuit construction Thyristor test : We chose the thyristor to work on which is TIC 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 Interface Thyristors and zero cross 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 = 135˚at α = 90˚ at α = zero˚ at α = 45˚

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˚ L=455mh and R= 16Ω, Ф= at α = zero˚ at α = 45˚ at α = zero˚

L= 70 mh, R= 16Ω, Ф= 53.9˚ L=455mh and R= 16Ω, Ф= 83.61˚ at α = 90˚ at α = 135˚

at α = 45˚ at α = zero˚ at α = 135˚ at α = 90˚ following figures show the input current at different firing angle, input voltage (Vin)= 20 v and R= 16Ω, L= 70 mh, Ф= 53.9˚ :

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 = 90˚at α = 135˚ at α = 45˚

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 = 90˚at α = 135˚ at α = 45˚

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 Hzat Fc= 159 Hz at Fc= 79 Hzat 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).