07-07-2012, 12:41 PM
OPTIMIZATION OF PID CONTROLLER FOR LIQUID LEVEL TANK SYSTEM
[attachment=27091]
Introduction
The liquid level control system automatically maintains the desired level of water in a
tank, i.e., it switches on the pump when the water level in the tank goes below a predetermined
minimum level and switches it off as soon as the water level reaches the predetermined
maximum level in the tank to prevent it from overflowing, thus maintains the
water level at a fixed level always .The user has the flexibility to decide by himself the water
level set-points for operations of pump. It ensures no overflows there by saves electricity and
water. Moreover the system consumes very little energy and hence is ideal for continuous
operation.
Due to the requirement of industrial manufacturing processes, the liquid tank level
control system is applied to many processing fields. For example, the raw materials stock of
chemical works, the mixture raw materials of nitrification process, the mould casting process,
and the steam generator of nuclear power plants…etc., involve liquid level control to a
certain extent. Conventionally, the linear PID control schemes are employed to have control
of the liquid level for a number of liquid tank systems. However, as regards the highprecision
control, it is insufficient to use linear PID controllers.
Objective of Dissertation Work
In this dissertation work, The GA and PSO programs are used to determine the
optimal values of the PID controller parameters to improve the transient response of the
system at time. This work demonstrated in detail how to employ the PSO and GA method to
search efficiently the optimal PID controller parameters. The liquid-level tank system has
limitations and it is difficult to control optimally using only PID controller as the parameters of
the system are changing constantly. We take the liquid level of three water tanks for object,
and use MATLAB to design Particle Swarm Optimization (PSO) and Genetic Algorithm (GA).
Then we analyze the control effect and compare it with the effect of PID controller. As a
result of comparing, it is found that PSO converges with less number of functional
evaluations, consistent for simple systems and in general ITSE,ISE & IAE is preferable for
quick settling time than GA. Transient response also improves.
LITERATURE REVIEWS
Introduction
The ‘Literature Reviews’ is the very important part of every research works as without
it, the problem cannot be evolved and structured properly. To this end, approximately more
than fifteen relevant research paper have been studied and discussed in this chapter. The
considerations of the benefits and limitations of each technique facilitate us in choosing the
most suitable one the respective sub-tasks. This chapter present an elaborate literature
review in the direction of tank liquid level control system.
Literature survey
Mohammed Obaid Ali, S. P. Koh, K. H. Chong, S.K.Tiong and Zeyad Assi Obaid [1].
This paper presents a design of PID controller for liquid-level tank system. The controller is
tuned online by Genetic Algorithm (GA). The liquid-level tank system has limitations and is
difficult to control optimally using only PID controller as the parameters of the system are
changing constantly. For this reason the strategy of online GA tuning is used in this work.
Genetic algorithm has been shown to be capable of locating high performance areas in
complex domains without experiencing the difficulties associated with high dimensionality or
false optima as may occur with gradient decent techniques.
CONCEPT AND THEORY OF THE PROBLEM
In this chapter, the focus is on the brief introduction to the techniques that are used
for liquid level tank system. The knowledge of these techniques serves as a background
material for this work of dissertation.
Introduction to PID
The PID controller is the most common form of feedback controllers. It was an
essential element of early governors and it became the standard tool when process control
emerged in the 1940s. In process control today, more than 95% of the control loops are of
PID type, most loops are actually PI control. PID controllers are today found in all areas
where control is used.
A proportional–integral–derivative controller (PID controller) is a generic control
loop feedback mechanism widely used in industrial control systems. A PID controller
attempts to correct the error between a measured process variable and a desired set point
by calculating and then outputting a corrective action that can adjust the process
accordingly and rapidly, to keep the error minimal.
[attachment=27091]
Introduction
The liquid level control system automatically maintains the desired level of water in a
tank, i.e., it switches on the pump when the water level in the tank goes below a predetermined
minimum level and switches it off as soon as the water level reaches the predetermined
maximum level in the tank to prevent it from overflowing, thus maintains the
water level at a fixed level always .The user has the flexibility to decide by himself the water
level set-points for operations of pump. It ensures no overflows there by saves electricity and
water. Moreover the system consumes very little energy and hence is ideal for continuous
operation.
Due to the requirement of industrial manufacturing processes, the liquid tank level
control system is applied to many processing fields. For example, the raw materials stock of
chemical works, the mixture raw materials of nitrification process, the mould casting process,
and the steam generator of nuclear power plants…etc., involve liquid level control to a
certain extent. Conventionally, the linear PID control schemes are employed to have control
of the liquid level for a number of liquid tank systems. However, as regards the highprecision
control, it is insufficient to use linear PID controllers.
Objective of Dissertation Work
In this dissertation work, The GA and PSO programs are used to determine the
optimal values of the PID controller parameters to improve the transient response of the
system at time. This work demonstrated in detail how to employ the PSO and GA method to
search efficiently the optimal PID controller parameters. The liquid-level tank system has
limitations and it is difficult to control optimally using only PID controller as the parameters of
the system are changing constantly. We take the liquid level of three water tanks for object,
and use MATLAB to design Particle Swarm Optimization (PSO) and Genetic Algorithm (GA).
Then we analyze the control effect and compare it with the effect of PID controller. As a
result of comparing, it is found that PSO converges with less number of functional
evaluations, consistent for simple systems and in general ITSE,ISE & IAE is preferable for
quick settling time than GA. Transient response also improves.
LITERATURE REVIEWS
Introduction
The ‘Literature Reviews’ is the very important part of every research works as without
it, the problem cannot be evolved and structured properly. To this end, approximately more
than fifteen relevant research paper have been studied and discussed in this chapter. The
considerations of the benefits and limitations of each technique facilitate us in choosing the
most suitable one the respective sub-tasks. This chapter present an elaborate literature
review in the direction of tank liquid level control system.
Literature survey
Mohammed Obaid Ali, S. P. Koh, K. H. Chong, S.K.Tiong and Zeyad Assi Obaid [1].
This paper presents a design of PID controller for liquid-level tank system. The controller is
tuned online by Genetic Algorithm (GA). The liquid-level tank system has limitations and is
difficult to control optimally using only PID controller as the parameters of the system are
changing constantly. For this reason the strategy of online GA tuning is used in this work.
Genetic algorithm has been shown to be capable of locating high performance areas in
complex domains without experiencing the difficulties associated with high dimensionality or
false optima as may occur with gradient decent techniques.
CONCEPT AND THEORY OF THE PROBLEM
In this chapter, the focus is on the brief introduction to the techniques that are used
for liquid level tank system. The knowledge of these techniques serves as a background
material for this work of dissertation.
Introduction to PID
The PID controller is the most common form of feedback controllers. It was an
essential element of early governors and it became the standard tool when process control
emerged in the 1940s. In process control today, more than 95% of the control loops are of
PID type, most loops are actually PI control. PID controllers are today found in all areas
where control is used.
A proportional–integral–derivative controller (PID controller) is a generic control
loop feedback mechanism widely used in industrial control systems. A PID controller
attempts to correct the error between a measured process variable and a desired set point
by calculating and then outputting a corrective action that can adjust the process
accordingly and rapidly, to keep the error minimal.