Motor eliminates the steady state error, but

Motor
can be controlled by many ways, but mostly it is controlled by PID controller.
PID controller consists of proportional, integral and derivative controls which
control the speed of the motor. Proportional control (Kp) will control the rise
time of the motor and it will reduce it, but it can’t eliminate the steady
state error of the motor. Integral control (Ki) eliminates the steady state
error, but it may make the transient response worse. Derivative control (Kd)
increases the stability of the system, reduces the overshoot and improves the
transient response of the system 1. All controls will
be used together to control the speed of the motor efficiently.

 

2.1    
Related
technologies

The
related technologies of the PID controller are following.

 

2.1.1   
Proportional
Control (Kp) Mode

Proportional
controller is most widely used method of control for many kinds of the systems.
In proportional controller, steady state error depends inversely upon the
proportional gain. The proportional controller can be regulated by multiplying
the error with a proportional constant (Kp).       

P
= Kp * error (t)

The
proportional control depends only upon the difference between two points, which
are the set point and process variable. The proportional gain (Kc) controls the
ratio of the output response to the error signal. Increasing the proportional
gain results in the increment of control system’s response speed. If the proportional
gain is huge, the process variable will commence to oscillate. If gain is
further increased, then those oscillations will increase a lot too, which in
turn shall unstable the
system. If proportional gain is very low, the control action may be too small
when responding to the system. Consequently, a proportional controller will
have the effect of reducing the rise time and will reduce, but never eliminate
the steady state 2.

2.1.2            
Integral Control
(Ki) mode

Integral controller sums the error term over
the passage of time. The result will be in such a way that a small error term will
be the cause for integral component slow increment. The integral response will
continually increase over time unless the error is zero, so the effect is to
drive the steady state error to zero. Steady state error is the final difference
between the set point and the process variable 1. An integral control
will have the effect of eliminating the steady state error, but it may make the
transient response worse.

I
= k ?error (t) dt

2.1.3         
Derivative Control (Kd) mode

The
derivative control mode decreases the output if the process variable increases
sharply. The response which is usually derivative is proportional to the degree
of variation of the process variable. Whenever the derivative time (Td)
parameter increases, it will be the basis for the control system to respond more
powerfully to the changes in the error term and then, the speed of overall
control system response will increase 1. Most practical
system use very small derivative time.

D = Kd. d error (t)/dt

2.2    
Related
projects

The
project related to PID controller is following.

2.3.1   
DC
motor speed control using ATMEGA controller

In
this project, the speed of the motor is controlled by using the microcontroller,
as the controller gets the speed set by the user. A sensor is used to measure
the current speed of the motor. After that user entered speed and current speed
of the motor is compared and the difference is calculated as error and in accordance
to that error the PWM signal given to the IC for driving motor through
microcontroller is varied 3.

2.4    
Limitations

·        
Proportional controller (Kp) affects the
rise time and overshoot.

·        
Integral controller (Ki) makes the
transient response worse.

·        
Derivative Controller (Kd) reduces the
over shoot.

·        
The project becomes inefficient and costly
by using the ATMEGA 4.

 

2.5    
Summary

The speed of the motor can be controlled by
many methods like by single controller or by ATMEGA. Using single controller
i.e. proportional, integral and derivative controllers is not very much
effective. If the speed of the motor is controlled by Atmega, it will become
costly. Using PID controller for controlling speed of the motor is one of the
effective methods. It is easy to implement and the motor is controlled
according to the requirements. In this project PID was used to control the
speed of the DC motor.

 

Chapter 3

PROJECT DESIGN
AND IMPLEMENTATION

This project is about using PID controller control the DC motor’s speed.
For that purpose, four circuits are used. These circuits are FVC (frequency to
voltage converter), Encoder (motor driver), Subtractor, and PID. Different
components like, resistors, capacitors, motor and IC’s are used in this
project.   

3.1          
Proposed Design Methodology

Figure 1:
Proposed Design

+ –
 –
 

   PID

MOTOR DRIVER

      FVC

Y(t)

 

 

 

 

 

 

 

The reference input was given to the summer which subtracts the
error amount which is coming from the output and then gives that signal to the PID controller as
input. PID controller generates the signal as input to the motor driver circuit.
Tachometer is used to measure the speed in rpm, then FVC was used which converts
frequency into voltage. LM2907
IC was used for conversion purpose, it gives output to summer which calculates the
error.

3.2          
Analysis Procedure

We have to figure out a way
to control the speed of the small dc motor using 555 timers. Using a small
permanent magnet DC motor
to build small projects like, cars, robots, or quads, requires a speed
controller to make their work easier.

Figure 2:
Analysis Procedure

 

 

 

 

 

 

 

3.3          
Design of the Project Hardware/ Software            

The project has three main components for designing. All three of
them will combine to control the motor’s speed.

PID
controller
Encoder
(motor driver)
Frequency
to voltage converter circuit

3.3.1   
PID controller
design