Project 1
Design and Develop a PWM-controlled fan load with a DC motor
The project is defined to design a Fan model controlled by a PWM- signal and the aerodynamic load acting upon the fan blades hindering the rotational speed of the motor.
For the construction of the model, various blocks from the simscape environment are used.
A DC motor is used as an energy converter to convert electrical energy to rotational energy. The DC motor consists of permanent magnets, which are fixed and produce a permanent magnetic field and The motor armature consists of individual electrical coils connected together in a circular configuration around its metallic body producing a North-Pole then a South-Pole then a North-Pole etc, it is called the rotor.
Whenever the coils are connected to the electrical supply through brushes, the current flows in the electric coils producing the magnetic field around it. The magnetic field interacts with the stationary magnetic fields, the opposite poles attract each other, and unlike poles repel each other. Thus creating a torque force within the motor. If the current is increased the electromagnetic field produced becomes stronger and it results in higher torque.
The motor speed is directly proportional to the back emf of the motor. Back emf is the rate at which the magnetic flux is opposed or the opposition to the flow of current in the coil.
The motor is controlled with the help of a power electronic converter. H-bridge, the four-quadrant converter is used to control the motor. H- bridge consists of semiconductor switches and a diode parallel to these switches. The FET switches of the converter are closed and opened with the help of PWM signals.
The width of the PWM pulse determines how long the switch should close and thus it improves the average voltage which increases the speed of the motor. If the duty cycle is reduced then the average voltage is also reduced decreasing the motor speed.
PWM control voltage block is connected to the controlled voltage source, which in turn gets the input from the pulse generator. These pulses are converted into voltage signals by the controlled voltage block. Depending upon the voltage pulse the duty cycle is decided by a controlled PWM voltage block. Which sends these pulses to the FET switches of the conveter.
The h_ bridge and motor is grounded but the PWM is not grounded. When the motor is OFF that is when the brake is applied then the regenerative braking is utilized where the motor acts as a generator feeding the power back to the source.
Now the rotational speed of the motor is being sensed by the rotational mechanical sensor. The Angular speed (rad/s) of the sensor is being converted to torque (Nm). For this, a subsystem is created using PS gain and PS product block.
Torque = C * (Angular speed )^2
The torque converted is sourced to the ideal torque source block, which is considered as the aerodynamic drag. It applies the torque to the shaft of the rotor.
The speed, torque and rpm behavior output of the motor is shown using the scope.