Week-7 Challenge: DC Motor Control

Ans

H-bridge

speed control of a dc motor using BJT H-bridge

Aim- To control the speed of a dc motor using an H-bridge

Software used- Matlab Simulink

THeory-

In this model, there are four section

1- H-bridge-

This is the main section of this device because this only converts and controls the power input of the motor

It converts AC supply to DC supply and fed to the motor. This is being used in the saturation region for this operation.

In this, there is four bipolar junction transistors are being used as shown below and this is being controlled

by another circuit. At a time two opposite transistors are in one position and two opposite transistors are

turned off.

. .

These are two conditions when this transistor is being on

This one is for one direction of rotation or a positive cycle

This is for the opposite direction of rotation or negative cycle

so with this, we are getting a four-quadrant operation

And also we can control the output power by controlling the base input of the transistor.

Here diodes are used to conduct when suddenly BJT gets turned off and due to induction

present in the motor current cannot be zero suddenly then these diodes are conducting.

Powerful-

This uses a variable-step solver to solve Simpower blocks. This is shown below.

Separately excited motor-

This is a DC motor which is having a field winding excited by a separately Dc supply

as shown below

Measurement of speed and torque and feedback back to the DC motor and scope is used to

show torque and speed and armature current as shown below

Control circuit-

This is the main controller for the DC motor which makes and transistor turned on or off

as we want we will send a signal to the base of the transistor so that the transistor should be in

situation region and supply power to the motor

Below is the circuit for speed control of a DC motor using BJT.

I have paste 'power_Hbridge' in the command in the command section and press enter.

And I have got the result in scope which we can observe by double click on the scope

Output

Below are the output speed, armature current and load torque characteristics

observe.

B)

the armature's current shoot-up from the scope results-

when we will zoom this we will get the below result in it and it is due to ripple content present

in the input supply. We are not getting pure dc input to the armature

At the starting when the motor is stopped and we are applying power to the motor then due zero

back emf present in the motor current flowing in the armature will be maximum and torque

also will be maximum. But as back emf start raising current slowing down when speed

reaches to maximum then current became very less now when the input supply cut off

then due to the field present (sapraitly excited motor) motor will start behaving as a generator

and opposite current will start flowing in the armature.

The Four-Quadrant Chopper DC Drive (DC7) block-

we have pasted this 'dc7_example' command in the command section and pressed enter.

then we have to get a four-quadrant chopper dc drive block as shown below

after running this model we have gotten the duty cycle of IGBT 1,4 and IGBT 2,3 and armature voltage, armature

current and motor speed graph as shown below

after zooming the armature voltage we have got the below graph

we have used the below signal for the converter signal

below is the converter signal after zooming

C)

comparison between H-bridge using BJT vs DC7 four-quadrant chopper in speed control of DC motor

H-bridge based DC7 four-quadrant chopper based

1 In this time two-transistor or two thyristors Here also at a time two-thyristor will in conduction

are in conduction mode and two of them will be mode two of them will be in the off state

in off state

2 Two quadrant operations possible in this Four quadrant operations are possible in this

device

3. It is a closed-loop system means there It is an open-loop system no feedback path will be

will be one feedback path present in it present in it

4. continuous signal will be present in it Descreat signal will be present in it

5. Ripple content will be more in this device. Ripple content will be less in this device

6 More harmonics will be present in this Less Harmonics will be present in this

device

Ans 2-

2-Quadrant Chopper

Aim-

Build a two-quadrant chopper using Simulink & explain the working of the same chopper.

Software used-

Matlab Simulink

Blocks used to build the model-

MOSFET, Battery, inductor, goto block, from the block, current sensor, voltage sensor,

scope, solver configuration and electrical reference

Below Picture is the Matlab model for 2 quadrant chopper

Theory-

This chopper is 2 quadrant chopper because in this voltage is but the current is positive as well as negative

so it will cover two-quadrant because of that we will call it as 2 quadrant chopper

below is the operation quadrant of the chopper

Both MOSFETs cannot be turned on due to a short battery circuit, so we will

use 180 phase difference between two gate signals. below is the gate signal used to turn

on the MOSFET we can see from this figure that for the N-channel of MOSFET both the MOSFET

cannot turn at the same time due to the 180-degree phase difference of the gate signal

1) when MOSFET first is on, Then below is the current path

when MOSFET2 is on, then below is the current path

Output-

Below is the output of the 2- quadrant chopper

positive half-cycle current is due to 1 MOSFET and the negative cycle is due to the 2 MOSFET turn on.

Brushless DC motor-

Brushless DC motors are a little bit different than brushed motors because as the name implies brushless

DC motor does not have a brush. That means there is no coil present on the rotor side. In this motor

permanent magnets are used to produce the magnetic field, rotor only will have coils which are fed by a

dc supply, In this motor, we can control the speed and torque by varying the input voltage. For the reverse

direction motion, we need to change the voltage terminal from negative to positive

In this motor, all stationary parts only have flowing electricity and the rotor part is just having a permanent

magnet. So in this type of motor commutator is not required.

When we are giving input supply to the stator then stator currents will start producing a magnetic field and

this magnetic field will interact with the rotor permanent magnet which will cause the rotation of the motor