Week-7 Challenge: DC Motor Control

EV LIVE BATCH - 16

1). 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.

SOLUTION:

SPEED CONTROL OF A DC MOTOR USING BJT H-BRIDGE:

• In general is a simple circuit containing four switching element ,with the load at the centre ,in an H-bridge configuration.
• 
• When the gate signal is given the switch is Q1 and Q4 are turn on and the motor rotoes in forward direction
• D1 and D4 are in off condition
• during energing of the time period the D1 and D4 are in on condition at that time the switch Q1 and Q4 are off condition
• when the negative gate signal is given that the switch Q3 and Q2 are turn and the motor rates in reverse direction and the motor rototes in reverse direction and D3 and D4 are in off condition....

FOUR QUADRANT CHOPPER:

• The motor can be operated in all the four different model (forward motoring ,reverse motoring ,forward braking ,reverse braking )
• In this vehicle control is better
• The current values are chopper in not continous hence simulation are less
• Regenerative braking can be achived
• the signals given to the 4th quadranrt operation &discreate
• widely used in the automobile application for the control of DC motor speed and direction.....

H-BRIDGE MODEL:

• In this model we have only two model forward and reverse by changing the direction of motor
• In this vehicle control are less
• the current values is continous
• IN this regenerative braking is not possible
• here the signals are contionus
• the h-bridge is used in the electro-mechanical devices to control the speed and direction of the dc motor at low level speed.......

2) Develop a 2-quadrant chopper using simulink & explain the working of the same with the relevant results. (Refer to article - Multiquadrant operation of motor )

SOLUTION:

• The two-quadrant dc chopper allows bidirectional current and power flow with a unidirectional voltage supply.

• the 2 -quadrant chopper is chopper means it is a DC drive which decrease high voltage supply to low voltage demand supply.
• the motor current io is inductive current and therefore cannot change instantaneously
• the transistor Q1 and diode D1 together from a bidirectional current switches s1 and s2 .
• The 2-quadrant operation are quadrant 1 and quadrant 2, in quadrant 1 operation , turning on Q1 allows current and power to flow from battery to the motor
• motor terminal voltage vo & current io are greater than (or) equal to zero.....

QUADRANT 2:

SWITCH CH2 TURNED ON;

• Let us assume that the motor is running in the forward direction
• here switch CH2 operated ,switch CH and diode D4 conducts, output voltage......

SWITCH CH2 TURNED OFF;

• Here diode D4 and Diode D1 conducts ,output voltage V,becomes positive and the output current i,is negative , inductor release energy using diodes D4 and D! power flows load to source and as forward braking .
• this is also known as Regenerative braking.....

3) Explain in a brief about operation of BLDC motor.?

SOLUTION:

• The brushless DC motor as the current passing through the motor is alternating current which is converted and supplied from a DC source.
• it is also called as a self -synchronous motor,permanent magnetic synchronous motor,&electrically commuted motor
• The basic operation of BLDC motor are the switched direct from a DC source through a coil on the stator.
• The rotor is pulled on the round in a clockwise direction
• the current that flows in the direction that the magnetizes the stator and the rotor is turned clockwise direction.
• motor torque rate can be improved by increasing the coilsfrom single to three
• the electronic circuit is used to drive and control the coil current is called an inverter.
• The main feature of BLDC motor is that torque will be reduced as the speed will increased .......

ADVANTAGES OF BLDC MOTOR:

• Higher efficiency and reliablity
• lower noise
• smaller
• lighter
• high speed range
• longer life
• better speed torque characteristics......