Question

Consider the controller design for a Central Air Condition System. Suppose you would like to have a steady room temp. Around 74 F degree. The outside temperature can be varied relative to the room temperature depending upon various seasons and weather conditions. The ranges of changes include "very cold", "cold", "medium", "hot" and "very hot" temperature (i)Design a Fuzzy Logic Controller (FLC) for this system (ii) Draw the major block diagrams for the process as well as FLC (iii) Show step by step your FLC design

Answer 1

(i)
Fuzzy Logic Controller Fan Power Supply Temparature Sensor Fan Driver Fuzzy Controller Keyboard Temperature Sensor Analog to Digital Converter Display and Indicators

(2)
Heat/ Cool/ Fuzzy Logic Controller Final target Command No Change Control Room Temperature Element Room Temperature

FUZZY LOGIC ARCHITECTURE RULE BASE OUTPUT INPUT DEFUZZIFIER FUZZIFIER INFERENCE ENGINE
(3) Step by Step process

Temperature Sensor : We use temperature sensor to sense the current room temperature and give it to the fuzzy controller.

Analog to Digital Controller : Analog to digital converter used to convert the Analog values to digital values and give it to fuzzy controller

Controller : Controller calculates error between set point value and current value and consider as Input
function of fuzzy logic.

De-fuzzification Process : It calculates actual value of PWM for Air conditioner which is output of the temperature control
system.

Explanation of Fuzzy Logic Architecture

RULE BASE: It contains the set of rules useful in decision making system

FUZZIFICATION: It is used to convert inputs i.e. crisp numbers into fuzzy sets. Crisp inputs are basically the exact inputs

INFERENCE ENGINE: It determines the matching degree of the current fuzzy input with respect to each rule and decides which rules are to be fired according to the input field. Next, the fired rules are combined to form the control actions.

DEFUZZIFICATION: It is used to convert the fuzzy sets obtained by inference engine into a crisp value. There are several defuzzification methods available and the best suited one is used with a specific expert system to reduce the error.

Fuzzy Rules

1	IF(temperature is cold OR very cold)AND(target is medium)THEN command is heat
2	IF(temperature is hot OR Very hot)AND(target is medium)THEN command is cool
3	IF(temperature is medium)AND(target is medium)THEN command is heat

Fuzzy Matrix Representation

Temperature/Target	Very cold	Cold	Medium	Hot	Very Hot
Very Cold	No Change	Hot	Hot	Hot	Hot
Cold	Cold	No Change	Hot	Hot	Hot
Medium	Cold	Cold	No Change	Hot	Hot
Hot	Cold	Cold	Cold	No Change	Hot
Very Hot	Cold	Cold	Cold	Cold	No Change