Week-7 Challenge: DC Motor Control

1.

when the pulse width is reduced from 75% to 50%, the sudden rise in the negative current in armature after 0.5 sec is significantly reduced. below images explain show the change.

2.

Comparing four quadrant chopper with H bridge.

Chopper characteristics:

1. Regenerative braking is possible.

2. The current values are chopped not continuous hence simulation takes less time.

3. Widley used in automobiles to control DC motor speed and direction.

4. To change to direction of motor current signals are interrupted with one another.

H- BRIDGE characteristics :

1. Regenerative braking is not possible but dynamic braking can be achieved.

2. The current values are continuous.

3. Widley used in robotics and electro-mechanical devices to control DC motor speed and direction.

4. To change the direction of motor only the polarity of the current is changed.

so a four quadrant chopper is preffered for automobiles as regenerative braking is possible.

3.

The following graph is input as a driving cycle for the DC7 example. this is the motor RPM vs time graph.

a 400 volt DC battery source is added to the model, replacing the AC source.

The motor characteristic equation is changed to T = 24.7 + 0.0051*w^2

math operations are used to create this equation in the model.

the final model looks like this.

after running the model the results are

duty cycle of IGBT 1,4 and 2,3 are mirror image of each other, there is a change armature current in response to the change in motor RPM.