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