Week-7 Challenge: DC Motor Control
1.A) BJT model is taken from Matlab, It is used for power switching applications.
The H Bridge Consists of 4 diode pairs,Two transistors are switched simultaneously causing positive and negative voltage to flow,
Initail Condition of Speed control of DC motor using BJT H bridge is run and the result is as below:-
a)Current shoots up in the intially high level and then becomes steady and after switching to -ve values it goes in the zero state
b)TO get steady flow of current the flow should be decrease and through duty cylce.Switching is happeing which cause shoot up.
1.B). The Four quadrant chopper dc drive is a DC-DC Convertor,
The DC motor is separately excited with a constant DC voltage source. The armature voltage is provided by an IGBT converter controlled by two PI regulators. The converter is fed by a DC bus obtained by rectification of a AC voltage source. In order to limit the DC bus voltage during dynamic braking mode, a braking chopper has been added between the diode rectifier and the DC7 block.
The first regulator is a speed regulator, followed by a current regulator. The speed regulator outputs the armature current reference (in p.u.) used by the current controller in order to obtain the electromagnetic torque needed to reach the desired speed.The current regulator controls the armature current by computing the appropriate duty ratios pulses of the four IGBT devices (Pulse Width Modulation) This generates the average armature voltage needed to obtain the desired armature current. In order to limit the amplitude of the current oscillations, a smoothing inductance is placed in series with the armature circuit.
- H-Bridge is circuit that controls a DC motor to go backward and forward.
- The 4 Quadrant chopper works in all the four modes like Forward motoring,reverse motoring and forward braking ,reverese braking
- In H -bridge current is transmitted from one switch to other to reverse the direction of motor while the polarity changes changes the direction in Chopper.
- Chopper have high switching frequency
2. 2quadrant Chopper model
In this chopper the average voltage will be always postive,the 2 channels should not be made on simulateously as it will result in short circuit
Eg:-Regenrative braking can use these type of chopper configuration
3.
BLDC MOTOR:-
BLDC stands for Brushless DC motor, it works on the principle that when a conductor which is carrying current is placed in magnetic field it will experience a force, in BLDC motor the current conductor remains stationary while the permanent magnet moves,since the conductor will also exert an opposing force in magnet to move hence equal and opposite force will be faced by magnet
In this design, the rotor is external. i.e. stator windings are located at the core while the rotor, carrying permanent magnets, surrounds the stator.
Construction:-
- Stator
- Permanent Magnets
- Poles
- Hall Sensors
Advantage of BLDC Motor:-
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· Torque is more |
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· Efficiency Better |
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· Durability |
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· Less noise
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