Week-7 Challenge: DC Motor Control

1Q. Run MATLAB demo ‘Speed control of a DC motor using BJT H-bridge’. Modify the model such that armature current doesn’t shoot up when motor changes direction from forward to reverse. 

Speed control of a DC motor using BJT H-bridge Model

After running the default setting we get the following result:

           Here in the above graph, the simulation time is one second is applied the motor speed is increasing at 0.5 seconds that is the half time of the total time the speed and current value is also changing and the speed is reversing but the values are same like positive one thousand and negative one thousand this means that the motor still running in one thousand the only change here is the direction is changed.

          In Armature current the current is smooth but when switching there was an overshoot in the middle because of switching loss. There are two switching losses one is hard switching and soft switching. Here in this model, we have hard switching which made an overshoot in the armature current.

           Now to resolve this we will give some proper duty cycle to the switches so that both sets of switches will work smoothly without any losses.

With 75% of the duty cycle, the switches are getting disturbed. we will decrease the pulse width so the armature current is smooth.

 Graph after decreasing the duty cycle to 30%:

With 30% of the duty cycle, the switching operation is smooth and the armature current does not have any overshoot.

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Q2.Refer to the help section of ‘The Four-Quadrant Chopper DC Drive (DC7) block’. Compare it with the H-bridge model.

The above image is the Simulink model of The Four-Quadrant Chopper DC Drive (DC7) block.

It is an AC to DC rectifier passes the current to four-quadrant chopper it controls the armature current according to the given input.

1st Quadrant:

                     S1 and S4 Both voltage and current across and through the load are positive rotating the motor in the forward direction( Forward motoring).

2nd Quadrant:

                     S2 and D4 are on the initial energy of the motor are stored in the armature inductance, the voltage across the inductor increases. When S2 turns off D3 and D4 are turned on (forward breaking regenerative breaking).

3rd Quadrant:

                     S3 and S2 are on (Reverse motoring).

4th Quadrant:

                     S4 is turned on the voltage across the armature inductance increase (Reverse breaking)

The main advantages of this DC Drive are that it can control all four quadrants of operation with Hbridge forward motoring, forward regenerating, reverse motoring, reverse regenerating. Due to high switching frequency DC-DCconverters, a lower armature current ripple is obtained the four switching device are required which increase the complexity of the drive system.

 H-bridge model:

In general, an H-bridge is a rather simple circuit, containing four switches with the load at the center in H-like configuration. The switches to work for only two-quadrant.

The switching S1 to S4are usually bipolar or FET transistor in some high- voltage application IGBTs are used. S1 and S2 never be connected together otherwise it will create a short circuit with input supply. s3 and s4 also never be connected together.

H-bridge circuits are used in motor drive, robotics technology. the advantages are very high efficiency very low loss the circuit can be placed in a small place.

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Q3. Make a suitable EV model using the DC7 block and make a result report.

1. The AC voltage source and AC to DC converter are replaced by a DC Voltage source of 100V.

2. The SP input is replaced with the workspace drive cycle file.

Drive cycle link below

https://docs.google.com/spreadsheets/d/1zr5JJuzHA8UD0zhK-wf5NlU9Da31aCo7clbAI1hrj3A/edit#gid=0

3. The linear load torque block is replaced with the subsystem model according to load Characteristics

T=24.7+0.0051*w_m

Output Graph:

From our EV model, we can see that the non-linear load is matching motor load.

Reference:

https://skill-lync.freshdesk.com/en/support/solutions/articles/43000571899-how-to-model-dc7-four-quadrant-chopper-200-hp-dc-drive

https://www.mathworks.com/help/physmod/sps/powersys/ref/fourquadrantchopperdcdrive.html