Even though lots of the modern control theories are developed, the PID control is the most widely used in real industrial field which is familiar to control engineer. It offers satisfactory control performance in most case of industrial applications.
However, traditional PID control has fixed gain for particular operating conditions, thus the conventional unique PID strategy would be unsatisfactory when the system parameters have changed due to the change of operating condition, aging, etc. of the controlled plants. The Fuzzy Gain Scheduling strategy, which changes the controller parameters for operating condition variation, could be a solution of these problems.
Water level control systems are applied to the many industrial plants like chemical reaction process, but it is known very difficult to control precisely the tank level without any overflow and shortage Because of its complicate dynamic characteristics, it's impossible to realize the accurate control using the mathematical model which can be applied to the various operation modes.
In this paper, the author designed the PID controller for the various operating conditions like different water level points and different magnitude of step change, and verified the performance of these controllers by experiments as well as simulations. It is noticed that the PID controller with fixed gains does not meet the requirements of control performance with large overshoot or late convergence, with varying the magnitude of step change. To improve this problem, three kinds of PID gain were scheduled under Fuzzy Gain Scheduling strategy and simulated and experimented under those operating conditions.
The Fuzzy gain scheduled PID controller made satisfactory performance which fixed gain PID controller couldn't make to the various magnitude of step change command.