Week-7 Challenge: DC Motor Control
Study 1:-
Speed Control of DC Motor using BJT H-Bridge:-
Model:-
Under Help documentation speed control of a DC motor using BJT H-Bridge model is selected and opened using simulink workspace. then the model is run and the results are observed under the scope block
This Model contains BJT and diodes connected in parallel which in turn connected as H bridge network and are connected to the DC Motor
Pluse generator act as the signal to the BJT across the model so there by changing the pulse generator parameters the output of the model can be changed.
By default the pulse generator parameters are as shown below
The output observed under the scope is seen below
The Armature Current shoots up at intial stage and during the change over time there is spike in armature current and then it becomes stable.
Four Quadrant Chopper DC Drive:-
Model:-
Under Help documentation DC7- Four-Quadrant Chopper 200 HP DC Drive model is selected and opened using simulink workspace. then the model is run and the results are observed under the scope block
In this model AC to DC converter which is connected to the three phase Power supply and the output from the AC to DC converter is DC power which is provided to the four-quadrant chopper DC drive and speed reference and linear load torque is provided as input and output is motor and convertion and control and load toque and then the model is Run and the output is observed under the scope
Plot:-
Here the armature voltage and current are observed which is a step signal
In both the Graphs i.e, in DC7 chopper and in BJT H-Bridge DC Motor control the armature current there is a spike occurance during the change in quadrant is observed.
The DC7 chopper can be operated under four quadrant and hence it provides better efficiency and can operate at high power levels whereas the BJT can be operated at moderate power levels.
Study 2:-
Two Quadrant Chopper :-
In two quadrant chopper, the average voltage is always positive but the average load current can be either positive or negative, Here the switches CH1 and CH2 should not be turned on simultaneously since which may result in short circuit.These are used in regenerative braking and motoring.
when the chopper CH1 is turned ON the current flows from source to load and when it is off freewheeling diode starts conducting and when the chopper CH2 is ON the load current will be negative and current completes its path through the diode D2.
Model:-
Under Help documentation DC6- Two-Quadrant Chopper 200 HP DC Drive model is selected and opened using simulink workspace. then the model is run and the results are observed under the scope block
In the Model the supply voltage three phase 460 V 60 Hz is provided to a AC to Dc converter and then the converter output is provided as input to the two quadrant chopper DC Drive along with the speed reference and load torque and the output is provided to the scope and are observed.
Plot:-
Study 3:-
Operation of BLDC Motor:-
BLDC - Brushless DC Electric Motor which is also known as Synchronous DC Motor or Electronically Commutated Motor.
Since the commutation happens electronically due to the absence of brushes , thus the losses are minimized and the efficiency of this motor is high which ranges above 95%.
Brushless motor has permanent magnets that rotate around a fixed armature, eliminating problems associated with connecting current to the moving armature.
An electronic controller replaces the commutator assembly of the brushed DC motor, which continually switches the phase to the windings to keep the motor turning.
The controller performs similar timed power distribution by using a solid-state circuit rather than the commutator system.
Brushless DC motors has many advantages over brushed DC motors,
1) High torque to weight ratio
2) Increased efficiency producing more torque per watt
3) Increased reliability, reduced noise, longer lifetime by eliminating brushes and commutator erosion,
4) Elimination of ionizing sparks from the commutator and
5) Overall reduction in Electromagnetic Interference.
BLDC Motors has maintenance-free operation, high speeds, and operation where sparking is hazardous i.e, explosive manufacturing environment or could affect electronically sensitive equipment.