Week-7 Challenge: DC Motor Control
1)
*** Explain a MATLAB demo model named 'speed control of a DC motor using BJT H-bridge.
BJT H-bridge:
The Bipolar Junction Transistor when used for power switching applications, operated as an IGBT and when it is conducting a forward voltage Vf is developed between collector and the emitter, therefore the IGBT block can be used to model BJT.
H-bridge consistes of 4 BJT/Diode pairs, two transistors are switched simultaneously.
When q1 and q4 are fired a positive voltage is applied to the motor and diodes d2 and d3 operate as free wheeling diodes when q1 and q4 are switched off.
When q2 and q3 are fired a negative voltage is apllied to the motor and diodes d1 and d4 operate as free wheeling diodes when q2 and q3 are switched off.
The first step is to run the MATLAB demo model named 'speed control of a DC motor using BJT H-bridge.
The second step is to comment on the armature current shoot-up from the scope results.
By using the help section we can import the MATLAB demo model given in the question.
The model shown above will open up in the simulink window.
Run the model as it is and observe the results and the graphs obtained.
*** Comment on the armature current shoot-up from the scope results.
In the simulink model we can see a pulse generator block on right-down, here we can change the pulse width as per our need.
Enter the pulse width as 75% and 35% respectively and run the simulink for two times and the results are obtained in a graph.
From the graphs or resluts otained we can observe that when there is an decrease in the pulse width the steap value of the armature current also decreases.
*** Refer to the help section of 'The Four-Quadrant Chopper DC drive (DC7) block'. Compare it with the H-bridge model.
By using the help section we can import the model given in the question.
The model opens up in the simulink window.
After importing the given model the model shown above will open up in a simulink window.
After importing just run the model as it is and observe the graphs or reluts carefully.
In the obove obtained graph we can see that the scope shows the motor armature voltage and current, the four IGBT pulses and the motor speed respectively.
COMPARISON:
THE FOUR-QUADRANT CHOPPER DC DRIVE (DC7) BLOCK DC DRIVE USING BJT H-BRIDGE
(1) The field windings are seperately excited in this method. The field windings are seperatele excited in this method.
(2) The D motor operates in all four quadrants-forward This type works only in forward motoring and reverse motoring, reverse motoring, forward braking and reverse motoring.
braking.
(3) This symbolizes the mechanical and power electronics It is just controls the DC motor speed.
components.
(4) Efficiency is more. Efficiency is less.
(5) The torque is proportional to speed. The torque is proportional to the square of the speed.
3) Explain a brief about operation of BLDC motor.
BLDC motor - Brushless DC motor.
The brushless DC motor also known as an elctronically commutated motor or synchronous DC motor, is a synchronous motor using a direct current electric power supply.
It uses an electronic closed looped controller to switch DC currents to the motor windings producing magnetic fields which effictively rotate in space and which the permanent magnet rotor follows.
CONSTRUCTION:
The construction of the brishless motor system is typically similar to a permanent magnet synchronous motor, but can aslo be a switched reluctance motor or an induction motor.
The advantage of a brushless motor over brushed motor are high power to weight ratio, high speed, nearly instantaneous control of speed and torque, high efficiency and low maintenance.
The brushless motors are used in computers, variety of vehicles from aircraft to a normal automobile, etc......