Week-7 Challenge: DC Motor Control

Q1) A}

1. From the given model it is observed that the model consists a motor (5HP 240V 1750RPM field:300V), which is connected to a 240V supply with four BJT and diodes, which acts as full bridge rectifiers.
2. The model is known as H-Bridge because the connection of the BJT’s and diodes are inn such a way that switches the polarity of the voltage applied to the motor.
3. From the table we can similarly compare with the speed control model of the DC motor.
4. >When Q1, Q4 are connected the motor moves right.
5. When Q2, Q4 are connected the motor left.

S1	S2	S3	S4	RESULT
1	0	0	1	Motor moves right
0	1	1	0	Motor moves left
0	0	0	0	Motor coasts
1	0	0	0
0	1	0	0
0	0	1	0
0	0	0	1
0	1	0	1	Motor Brakes
1	0	1	0
X	X	1	1	Short circuit
1	1	X	X

Scopes are attached accordingly to get the graphs of IGBT current, diode current, speed of the motor in (rpm), armature current in (A) and load torque in (N-m).

The torque is calculated by using the relation between the torque and speed of a motor.

Q1) B)

Result :-

1} The default value of pulse width 75 is reduced to 50 and then the model is simulated :-

The scope consisting the speed of the motor armature current and load torque of the motor is given below. From the result we can see that T=0.5 pf the simulation the motor changes direction and the current shoot is reduced accordingly. Due to the reduced pulse width, the speed of the motor and the load torque is also reduced.

2} The pulse width is reduced from 50 to 25 and then the model is simulated :-

The scope consisting the speed of the motor, armature current and load torque of the motor is given below. From the result it is seen that, the current does not shoot up when the motor changes direction T=0.5s of the simulation. The speed of the motor and the load torque in of the moto are low.

CONCLUSION:- we conclude that, when the duty cycle of the pulse generator block is low then the speed, current and load torque is also low accordingly.

Q1) C)

Comparison of Four- Quadrant chopper DC7 block vs H-bridge model:-

1. In Four- Quadrant chopper Regenerative Braking is possible, but H- Bridge Regenerative Braking is not possible.
2. Four- Quadrant chopper can operates in all four modes, but H- bridge can operate in two modes (Forward and Reverse).
3. In Four- Quadrant chopper Two PI regulator is used to obtain electromagnetic torque needed to reach the desired speed and control the armature current and stabilize the system, but in H- bridge model PI regulator is not used.
4. Four- Quadrant chopper model gives better efficiency and high energy(power) storage than H-bridge model.
5. H- bridge is a electronic circuit that switches the polarity of voltage applied to the load and four-Quadrant chopper is electronic switch that is used to interrupt one signal under the control of another.

Q3)

BLDC MOTOR:-

• Brushless dc electric motor also known as electronically commutated motors.
• A brushless Dc motor is a permanent magnet synchronous electric motor which is driven by direct current electricity and it accomplishes electronically controlled commutation system instead of a mechanically commutation system.
• BLDC motors are also referred as trapezoidal permanent magnet motors.

Working of BLDC Motor:-

• BLDC motor works on the principle similar to that of a conventional DC motor, i.e., the Lorentz force law, which states that whenever a current carrying conductor placed in a magnetic field it experiences a force.
• As a consequence of reaction force, the magnet will experience an equal and opposite force. In case of BLDC motor, the current carrying conductor is stationary while the permanent magnet moves.
• When the stator coils are electrically switched by a supply source, it becomes electromagnet and starts producing the uniform field in the air gap. Though the source of supply is DC, switching makes to generate an AC voltage waveform with trapezoidal shape.
• Due to the force of interaction between electromagnet stator and permanent magnet rotor, the rotor continues to rotate.
• Based on the signal from sensor, the controller decides particular coils to energize. Hall-effect sensors generate Low and High signals whenever rotor poles pass near to it.
• These signals determine the position of the shaft.

Applications:-

1. Computer hard drives
2. Electric vehicles, hybrid vehicles
3. Industrial robots, CNC machine tools
4. Fans, Pumps and Blowers.

Q2)

Two Quadrant Chopper model using simulink:-

1. Let us take the two MOSFET blocks and diodes blocks and connect it as shown in circuit diagram.
2. Then DC voltage source is connected as shown in the figure. Let the voltage of DC voltage source be 24 volts.
3. Let us consider a series RLC branch and select it as inductor L, thus the block work as load.
4. To consider LE load in motor load, and dc voltage source of 12 volt is also connected in series with inductor.
5. The pulse generator block is used to create gate pulse. The not gate is used in the model so that the two MOSFET will not get closed at the same time otherwise short circuit will occur. Due to use of not gate, when one MOSFET is ON the other MOSFET will get off and when other MOSFET is ON the first MOSFET will get off.
6. The amplitude of pulse generator is kept 10 so that we can clearly see the pulses at scope and let the period be 0.02 seconds and let pulse width be 50%.
7. The voltage waveform is not going less than zero. The minimum value of voltage is zero and maximum value is always in the positive direction.
8. In current waveform, the current increases and decreases. The current may be positive as well as negative.
9. And the pulse amplitude is 10 thus from pulse waveform we can see that the pulse amplitude is 10.