2. INTRODUCTION
Designing a controller for non-linear systems is difficult. For
conventional controller design we require mathematical model and
higher order differential equations. Some times we linearize
mathematical model and design controller for system by applying
well developed techniques for solving linear equations. But, as we
know that real life problems are non-linear in nature and their
models are not easy to handle mathematically.
We solve daily life problems by if-else rules. For example, if the ball
is coming fast then swing the bat early. So, fuzzy rules logic
is heuristic based which takes if-else conditions to solve daily life
problems. It is linguistic based technique to design controller. It takes
conditions from experience and intuition. Fuzzy logic is imitations of
control laws that humans use.
3. CRUISE CONTROL:
Cruise Control is for maintaining fixed sped
of object (car, for example). This is a
feedback closed loop control system. A
reference input at which speed is to be
maintained is fed to the controller
as reference input and actual speed of
system is taken as feedback. The difference
between these two is termed as error
velocity. This error velocity is one input to
the controller.
The objective is to eliminate this error. If
there is some error, controller must act
accordingly.
4. CRUISE CONTROLLER USING FUZZY:
BLOCK DIAGRAM:
Following is block diagram of complete system with controller, plant
(to be controlled), input to the plant (control signal from fuzzy
controller) and inputs to the fuzzy controller.
5. INPUT MEMBERSHIP FUNCTIONS:
Using Fuzzy tool in MATLB we can input membership function of desire
shape. In this example we have velocity error and derivative of velocity error
i.e. acceleration. The membership function of both are given below in
triangular shape. we are considering three membership functions for each
inputs.
For Error Velocity:
NE: Negative error
ZE: Zero Error
PE: Positive Error
For Acceleration:
NA: Negative Acceleration
ZA: Zero Acceleration
PA: Positive Acceleration
6.
7. Base rule for controller is designed in such way that:
if the actual speed of car is less than desired/set speed, error will be
positive which means car needs to be speed up.
if the actual speed of car is greater, error will be negative and there
is need to slow down it.
Further, if speed is slow and acceleration is negative, which means
that its speed is constantly decreasing and vice versa for increasing
acceleration with negative error.
