Pulse Width Modulation(PWM) working Principal using Matlab
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PWM

Introduction

Pulse Width Modulation(PWM) working Principal using Matlab.

PWM stands for Pulse Width Modulation. It is a type of digital modulation that is widely used for controlling the power delivered to electrical devices, such as motors, lights, and heaters.

In PWM, the duty cycle of a square wave is varied to control the average value of the waveform, which is proportional to the power delivered to the device. The duty cycle is defined as the proportion of time that the square wave is in the “on” state to the total time it takes to complete one cycle. By varying the duty cycle, the average value of the waveform can be adjusted, and therefore the power delivered to the device can be controlled.

PWM is used in many applications because it is a simple and efficient way to control the power delivered to a device, while also reducing the amount of electromagnetic interference generated by the device. For example, in motor control, PWM is used to control the speed of a motor by adjusting the duty cycle of the square wave that is applied to the motor. By adjusting the duty cycle, the average voltage applied to the motor can be adjusted, which in turn changes the motor speed.

In PWM, the frequency of the square wave is typically much higher than the bandwidth of the device being controlled. This results in a low-frequency signal that is filtered out by the device, while the high-frequency component of the signal drives the device. This results in low electromagnetic interference and improved power efficiency

PWM Components

  1. A Pulse Generator: This generates the square wave that serves as the base signal for the PWM waveform. The pulse generator can be a digital or analog circuit, and it produces a square wave with a fixed frequency and variable duty cycle.
  2. A Control Circuit: This circuit adjusts the duty cycle of the square wave in response to control signals from an external source, such as a microcontroller or a potentiometer. The control circuit can be an analog or digital circuit that implements a control algorithm to adjust the duty cycle based on the input signal.
  3. A Power Stage: This stage delivers the PWM signal to the load, such as a motor or a light. The power stage typically includes a power switch, such as a transistor or a MOSFET, and an output filter, such as a low-pass filter, to smooth out the PWM signal and produce a continuous average voltage that drives the load.
  4. A Load: This is the device that is being controlled by the PWM signal. The load can be a motor, a light, a heater, or any other device that requires power control.
  5. An optional Feedback Circuit: This circuit measures the response of the load to the PWM signal and provides feedback to the control circuit. The feedback circuit can be used to implement closed-loop control, where the duty cycle of the PWM signal is adjusted based on the load response, in order to maintain a desired setpoint.

Duty Cycle of PWM

The duty cycle of a PWM waveform is the proportion of time that the waveform is in the “on” state, relative to the total time it takes to complete one cycle. It is expressed as a percentage or as a fraction of the total cycle time.

For example, if the PWM waveform is “on” for half of a cycle, and “off” for the other half of the cycle, the duty cycle would be 50%. If the PWM waveform is “on” for a quarter of a cycle, and “off” for the other three quarters of the cycle, the duty cycle would be 25%.

The duty cycle of a PWM waveform can be adjusted to control the average value of the waveform and, therefore, the power delivered to the load. For example, if the duty cycle is increased, the average value of the waveform increases, and more power is delivered to the load. Conversely, if the duty cycle is decreased, the average value of the waveform decreases, and less power is delivered to the load.

In PWM applications, the frequency of the waveform is typically much higher than the bandwidth of the load, so the load only responds to the average value of the waveform. By adjusting the duty cycle, the average value of the waveform can be controlled, and the power delivered to the load can be adjusted.

Software Requirement

Matlab Software or Online Matlab

Matlab Code

clc;
clear all;
close all;
F2=input('Messsage frequency=');
F1=input('Carrie Sawtooth Frequency=');
A=5;
t=0:0.001:1;
c=A.*sawtooth(2*pi*F1*t);
subplot(3,1,1)
plot(t,c);
xlabel('time')
ylabel('Amplitude');
title('Carrier Sawtooth Wave');
grid on;
m=0.75*A.*sin(2*pi*F2*t);
subplot(3,1,2);
plot(t,m);
xlabel('Time');
ylabel('Amplitude');
title('Message Signal');
grid on;
n=length(c);
for i=1:n
if (m(i)>=c(i))
pwm(i)=1;
else
pwm(i)=0;
end
end

subplot(3,1,3);
plot(t,pwm);
xlabel('Time');
ylabel('Amplitude');
title('plot of PWM');
axis([0 1 0 2]);
grid on;

PWM Output

PWM5

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