Fuzzy logic control

Introduction to Fuzzy logic control

In fuzzy logic control the experience of human process operator, is incorporated in design of the controller. This logic controller provides a means of converting a linguistic control strategy based on operates knowledge into an automatic control strategy, linguistic variables are quantities like high, medium, low, etc., fuzzy logic is multivalued logic which enhances man machine interaction. Fuzzy logic is implemented using fuzzy sets.

A set is a well defined collection of objects. A crisp set is one which identities whether the object is present in that collection or not.

The function A(x) is such that


That is the object x will either belong to set or not.

Fuzzy set is one that allows partial membership of object in that set here the degree to which a variable is member of a given set is indicated.

Let X be a set and x is an element of X. then fuzzy set A is given by

A = {A(x)/x} ; x E X

A(x) given degree of membership and has a range of 0 to 1. it indicates that the degree of membership of an element x in a fuzzy set A ranges from 0 to 1 where 0 indicates null membership. 1 indicates full membership, and intermediate values represent partial membership.

Advantages of Fuzzy logic control:


  1. Relates input to output in linguistics terms; easily understood.
  2. Cheaper because they are easier to design.
  3. Increased robustness.
  4. Can achieve less overshoot & oscillation.
  5. Can achieve steady state in a shorter time interval.
  6. Simplify knowledge acquisition & representation.


Disadvantages of fuzzy logic control


  1. Hard to develop a model from a fuzzy system.
  2. Require more fine tuning and simulation before operational.


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