Project 1

Ans- In pulse width modulation speed control the motor with a series of 'ON-OFF' pulses and varying the duty cycle, the fraction of time that the output voltage is 'ON' compared to when it is 'OFF', of the pulses while keeping the frequency constant.The power applied to the motor can be controlled by varying the width of pulses and causes varying the average DC voltage applied to the motors terminals. By changing or modulating the timing of these pulses the speed of the motor can be controlled, ie, the longer the pulse is 'ON' the faster the motor will rotate and likewise if the shorter pulse is 'ON' the slower the motor will rotate.

If wider the pulse width, the more average voltage applied to the motor terminals, hence the stronger the magnetic flux inside the armature windings and the faster the motor will rotate and the amplitude of the motor voltage remains constant so the motor is always at full strength. The result is that the motor can be rotated much more slowly without it stalling.

This Shows the work for the design of the fan speed control system using Pulse Width Modulation by establishing a connection between an H-Bridge circuit and a Dc motor. A fan type load equation has been used here to analyze the output. The speed of the fan is varied according to the input voltage using PWM technique.

By changing the timing of these pulses the speed of the motor can be controlled. A stepwise change in the speed variation is given and the full load speed is observed. In this model, all input ports of the H-Bridge block except the PWM port are connected to ground. As a result, the H-Bridge block behaves as follows:

• When the motor is on, the H-Bridge block connects the motor terminals to the power supply.
• When the motor is off, the H-Bridge block acts as a freewheeling diode to maintain the motor current.

Torque exerted by fan represented by T

Load torque T proportional to square of speed w^2 and K is the proportionalty constant.

T= Kw^2

By varying the electrical parameter of motor voltage and current we are controlling load torque or load speed.

For fan load we use a subsystem to the left side there is w and it is multiplying by product block then it is become w^2

Then gain block is used that is the constant of proportionality 8.8e-8 Unit of this gain block is N*m/(rad^2/s^2).Output of this subsystem is fed to the Aerodynamic block(Ideal torque source block). This ideal torque source block is going to apply torque on the shaft of DC motor.

For getting the speed we used Motion sensor. Value of the motion sensor w is given to the subsystem w and the value of the torque is given to the aerodynamic block and therefore completing the loop.

Controlled voltage source is connected to the controlled PWM voltage and H-bridge is connected through PWM voltage.

Pulse generator block used as input to the controlled voltage source.

The Controlled PWM Voltage block represents a pulse-width modulated (PWM) voltage source. We can model electrical or physical signal input ports by setting the Modeling option parameter to either:

• Electrical input ports— The block calculates the duty cycle based on the reference voltage across its ref+ and ref- This option is the default.
• PS input— Specify the duty cycle value directly by using an input physical signal port. The H-Bridge block represents an H-bridge motor driver. The block has the following two Simulation mode options-

PWM- The H-Bridge block output is a controlled voltage that depends on the input signal at the PWM port. If the input signal has a value greater than the Enable threshold voltage parameter value, the H-Bridge block output is on and has a value equal to the value of the Output voltage amplitude parameter. If it has a value less than the Enable threshold voltage parameter value, the block maintains the load circuit using one of the following three Freewheeling mode options.

H-bridge used to change the direction of motor. We can use a H-Bridge motor driver for the DC motor which helps in reversing the polarity of the motor to run it in the reverse direction. So by the help of H-bridge we can implement the Regenerative brakinng in system.

PWM signals are provided to the H-bridge, and output of H-bridge is given to the Dc motor through the current sensor and voltage sensor.

The DC motor is driving the fan load, we are taking the speed output from the Dc motor through the motion sensor. And pass it to the subsystem.

Parameters Screen short,Graph,Scope and project Model is provided.