Week-7 Challenge: DC Motor Control

1] Run MATLAB demo ‘Speed control of a DC motor using BJT H-bridge’. Modify the model such that armature current doesn’t shoot.

ANSWER:-

For speed control of a DC motor using BJT Hbridge the following command is typed in MATLAB command window.

power_Hbridge

Following images show the model with output of 75% duty cycle.

The output for 75% is as follows


After changing the duty cycle to 45%

The output for 45% duty cycle


The duty cycle can not be less than 30%. For 29% duty cycle we see following results




2] Refer to help section of ‘The Four-Quadrant Chopper DC Drive (DC7) block’. Compare it with H-bridge model.
ANSWER:-
For The four Quadrant chopper Dc Drive we use the following command in matlab
dc7_example
Following figure shows the DC7 four quadrant chopper drive during speed requlation


The following is the output graph


The following figure shows the model demo of speed control of a dc motor using BJT H-bridge


The output graph is seen below


Comparission is as follows


3] Make a suitable EV model using DC7 block and make result report.
ANSWER:-
excel sheet inluded for drive cycle
following shows model and its ooutcome



4] Explain in a brief about operation of BLDC motor.
ANSWER:-

A brushless DC motor consists of a stator and a rotor. The stator is the stationary part and the rotor is
the part that rotates within the stator. The working of a BLDC motor is as follows.

In this motor, the permanent magnets attach to the rotor. The current-carrying conductors or armature windings are located on the stator. They use electrical commutation to convert electrical energy into mechanical energy.

The main design difference between a brushed and brushless motors is the replacement of mechanical commutator with an electric switch circuit. A BLDC Motor is a type of synchronous motor in the sense that the magnetic field generated by the stator and the rotor revolve at the same frequency.

Brushless motor does not have any current carrying commutators. The field inside a brushless motor is switched through an amplifier which is triggered by the commutating device like an optical encoder.

The layout of a DC brushless motor can vary depending on whether it is in “Out runner” style or “Inrunner” style.

• Outrunner – The field magnet is a drum rotor which rotates around the stator. This style is preferred for applications that require high torque and where high rpm isn’t a requirement.
• In runner – The stator is a fixed drum in which the field magnet rotates. This motor is known for producing less torque than the out runner style, but is capable of spinning at very high rpm.