Single-phase rectifier with PWM control

Project report

SUBJECT: DC Converters

Sonali j. Chavda M.E-1 (I.E)ROLL NO- 252Department of Electrical Engineering MSU

ACKNOWLEDGEMENTWe have immense pleasure in successful completion of this work title “

SINGLE PHASE RECTIFIER WITH PWM CONTROL ”. The special environment at MSU that always supports educational activities, facilitated my work on this project.

We greatly appreciate the motivation and understanding extended for the project work, by Mr.MODI SIR & DAMLE SIR who responded promptly and enthusiastically. We are indebted to all of them, who did their best to bring improvements through their suggestions..

SINGLE PHASE RECTIFIER WITH PWM CONTROL

AIM: To control the output voltage of Single phase bridge rectifier with

PWM control.

APPARATUS:

SR NO. NAME OF COMPONENTS RATING QUANTITY

1. 555 timer IC 15 V, 10 mA ONE2. RESISTOR 560 ohm ONE3. RESISTOR 1 kilo-ohm TWO4. CAPACITOR 0.01 microfarad ONE5. CAPACITOR 0.1 microfarad ONE6. DIODE IN4007 FIVE7. RESISTOR 10 kilo-ohm ONE8. TRANSISTOR BC547 ONE

CIRCUIT-DIAGRAM:

V1

17 Vpk 50 Hz 0°

R1

10kΩQ1

BC547BP

D61N4007GP

D21N4007GP

D11N4007GP

D31N4007GP

A1

555_VIRTUALGND

DIS

OUTRST

VCC

THR

CON

TRI

R2

1kΩ

R3

1kΩ

R4560Ω

C10.01µFC2

0.1µF

R550kΩKey=A 80%

D5

1N4007GP

V212 V

THEORY:

The output voltage of a full wave bridge rectifier can be controlled with pulse width modulation signal.

The above figure shows how the rectified output of a full wave bridge rectifier can be contolled by combining it with the pwm signal. The average output voltage can be controlled by varying the duty cycle of the PWM signal. Thus, the output power across the load is also varied.

The PWM signal is given to the base of the switching element which becomes on and off, As the rectified output is passed from the switching element output voltage waveform is chopped.

Here, in this project the PWM is produced by the 555 timer IC.

What is a Pulse Width Modulation (PWM) Signal?

A Pulse Width Modulation (PWM) Signal is a method for generating an analog signal using a digital source. A PWM signal consists of two main components that define its behavior: a duty cycle and a frequency. The duty cycle describes the amount of time the signal is in a high (on) state as a percentage of the total time of it takes to complete one cycle. The frequency determines how fast the PWM completes a cycle (i.e. 1000 Hz would be 1000 cycles per second), and therefore how fast it switches between high and low states. By cycling a digital signal off and on at a fast enough rate, and with a certain duty cycle, the output will appear to behave like a constant voltage analog signal when providing power to devices.

Below are some graphs demonstrating PWM signals with different duty cycles.

25% Duty Cycle

50% Duty Cycle

NE555 timer IC:

A 555 timer will produce a pulse when a trigger signal is applied to it. The pulse length is determined by the amount of time it takes to charge and discharge a capacitor connected to a 555 timer.

Description of the 555 timer pins:

Pin 1 GND Ground ConnectionPin 2 Trigger 555 timer triggers when

this pin transitions from voltage at VCC to 33% v voltage at VCC. Output pin goes high when triggered

Pin 3 Output Output pin of 555 timerPin 4 Reset Resets 555 timer when

lowPin 5 Control Voltage Used to change

Threshold and Trigger set point voltages and is rarely used

Pin 6 Threshold Used to detect when the capacitor has charged. The Output pin goes low when the capacitor has charged to 66.6% of VCC.

Pin 7 Discharge Used to discharge the capacitor

Pin 8 VCC 5V to 15V supply input

BLOCK DIAGRAM:

The PWM Generation Circuit:

The capacitor C1 charges through the path R1, Rx, and R2. The lower half of POT R3 ie; Ry is out of the scene because the diode D1 by-passes it. When the voltage across the capacitor reaches 2/3 Vcc, the internal upper comparator flips its output which makes the internal flip flop to toggle its output. As a result the output of the astable multivibrator goes low. In simple words, the output of the astable multivibrator remains high until the charge across C1 becomes equal to 2/3 Vcc and here it is according to the equation Ton=0.67(R1+Rx+R2)C1.Since the internal flip flop is set now, the capacitor starts discharging through the path R2,Ry into the discharge pin. When the voltage across the capacitor C1 becomes 1/3 Vcc, the lower comparator flips its output and this in turn makes the internal flip flop to toggle its output again. This makes the output of the astable multivibrator high. To be simple, the output of the astable multivibrator remains low until the voltage across the capacitor C1 becomes 1/3 Vcc and it is according to the equation Toff = 0.67(R2+Ry)C1.

Ton = 0.67(R1+Rx+R2)C1Toff= 0.67(R2+Ry)C1Total time period of the output waveform “T” is according to the Equation :

T = Ton + ToffTherefore, T = 0.67(R1+Rx+R2+R2+Ry)C1

                        T= 0.67(R1+2R2+Rx+Ry)C1

We know that Rx+Ry = R3

Therefore, T = 0.67(R1+2R2+R3)C1 F = 1/(0.67(R1+2R2+R3)C1) 

PROCEDURE:

1. Complete the connection as per the circuit diagram.2. Switch on the supply voltage.3. Check the voltage waveform across the load resistor with help of CRO.4. Switch off the supply voltage.

WAVE FORMS:

Supply voltage

Voltage across load resistor

PWM output on pin 3 of 555 timer IC

Connection of the circuit

Wave forms obtained on CRO on pin 3 of 555 timer IC

CONCLUSION:

In this project work an attempt has been made to implement and test a circuit for a fully uncontrolled single phase converter. The circuit is fabricated using components such as resistors, capacitors and some standard IC chips. The circuit is first fabricated on bread board and then tested. It is concluded that full wave rectifier output voltage can be controlled by pulse width modulation. The circuit successfully generated complementary pulses as desired and the waveforms recorded for future realistic studies.