Week-7 Challenge: DC Motor Control
NOTE: EV Live session Batch 16 :
Q1. A. Explain a MATLAB demo model named ‘Speed control of a DC motor using BJT H-bridge’.
B. Comment on the armature current shoot-up from the scope results.
C. Refer to the help section of ‘The Four-Quadrant Chopper DC Drive (DC7) block’. Compare it with the H-bridge model.
ANS:
The below model is of Speed control of a DC motor using BJT H-bridge.
- BJT when used in power switching it used as IGBT.
- In above model field winding is suopoly by300 V supply weareas Armature winding is supply by240 V supply through IGBT
- Four freewheeling diode and Four IGBT are used to control the speed of DC motor
- this IGBT are operate in such a way that when Q1 and Q4 are in ON condition the Q2 and Q3 are in OFF conditionand D2,D3 are act as free-wheeling diode & when Q2 and Q3 ON D1 D4 are act as free-wheeling diode and Q1 Q4 OFF
- When Q1 and Q4 are ON the positive supply fed to motor and motor operate in forward motoring mode and when Q2 and Q3 ON negative supply fed to motor and motor in reverse motoring mode.
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Comment on the armature current shoot-up from the scope results.
As we discuss above when Q1 and Q4 are ON the positive supply fed to motor and motor operate in forward motoring mode and when Q2 and Q3 ON negative supply fed to motor and motor in reverse motoring mode. at time of this switch changing the negative torque reuirement is high theare fore current shut up to full fill this requirement.
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C. Refer to the help section of ‘The Four-Quadrant Chopper DC Drive (DC7) block’. Compare it with the H-bridge model.
ANS:
This is model of The Four-Quadrant Chopper DC Drive (DC7) block’
Comparison between The Four-Quadrant Chopper DC Drive (DC7) block’ and H-bridge model.
- in the DC7 block operatin is done in four mode namely forward motoring , forward braking , reverse motoring , reverse braking but in H-bridge model. the operation in done in two mode forword motoring and reverse motoring only.
- the regenerative braking is possible in The Four-Quadrant Chopper DC Drive (DC7) block’ but in h-bridge its not possible .
- In H-brige we control the vlg given to the load but inThe Four-Quadrant Chopper DC Drive (DC7) block’ interuption of signal under control of another
- in The Four-Quadrant Chopper DC Drive (DC7) block’ the speed and current regulator(PI regulator) are use to control the armature current and to stabilised system
- therefore as use of diff controller and regulator the efficiency of The Four-Quadrant Chopper DC Drive (DC7) block’ is more as compared to H-bridge model
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Q2)Develop a 2-quadrant chopper using simulink & explain the working of the same with the relevant results. (Refer to article - Multiquadrant operation of motor )
ANS:
The model Of Two Qudrant chopper given below
- In Two Quadrant chopper TWo swiches are ued with Two diode one is freewheeling ather is D2
- The switching of switches are such a way that the bothe swicheches should not be turn on at a time as it cause short circuit
- In this chopper voltage is always positive as freewheeling diode is connected across load but load current may be positive or negative
- When CH1 is ON the current flows from sourse to load and inductor store energy.
- When CH1 OFF the voltage `V_0` will equql to `V_s` as free-Wheeling diode start conducting
- When CH2 ON The direction of load current get reversed it flowing towards sourse through D2
- For Regenerative breaking and motoring this type of chopper are used
- THis is scope output of above model
- We can see the voltage is always positive and current value is positive as well as negative
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Q3. Explain in a brief about operation of BLDC motor.
ANS:
- BLDC motor works on the principle similar to that of a brushed DC motor. 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 a BLDC motor the stator is usually a series of electromagnets made of magnetic cores around which are wound wire coils.The rotor on the other hand, is composed of several permanent magnets arranged end to end, with opposite poles facing each other.
- When current flows through the coil of a brushless motor, a magnetic field generated. The magnetic field reacts with that of the rotor’s permanent magnet next to it, producing either an attraction or repulsive force. In a typical brushless DC motor operation, two coils are energized at the same time. One coil attracts a part of the rotor, while the other repulses it. This causes the rotor to move.
- For continuous motion, the next coil must energize, while the previous coil loses magnetism. The magnetic field then literary rotates around the stator, while the rotor practically chases it. This causes a continuous revolution of the rotating part of the motor.