optimal controller settings
TRANSCRIPT
OPTIMAL CONTROLLER SETTINGS
IN 604 PROCESS CONTROL
Submitted By,
Muhammed Raees PCMunawar CKNikitha AgarwalNitheesh Jeevan Bose
OPTIMIZING THE OPERATION OF A PLANT Desirable condition for operation of a plant
Minimum Production Cost Maximum Profit
Achieved by Optimizing Control Strategy, which Identifies when the plant must be moved to a
new operating point in order to reduce the operating cost
Makes the appropriate set point changes to bring the plant to the new optimum operating point
DESIGNING SYSTEM
The Steady State input-output relationships
d1,d2 –two disturbances m1,m2 – two manipulated variables y1,y2 - two output variables
Let Operating cost = cost = F(y1,y2)
SIMPLE PROCESS WITH ITS CONTROL LOOPS
When disturbances have the values the minimum operating cost is achieved for
Where,
The Values are the current set point values for the two control loops.
But, when the disturbance change, say
The values of y1 and y2 that minimize the cost function also change.
SUPERVISORY IMPLEMENTATION OF OPTIMIZING CONTROL STRATEGY
Let new optimum values be Again they satisfy the following conditions for
optimality:
THE OPTIMIZING CONTROL SYSTEM MUST BE ABLE TO :- Identify that the current set points no
longer correspond to optimum operating conditions.
Find the new optimum operating conditions (i.e. the values )
Bring the process to the new optimum operation by changing the set point values of the two control loops.
IMPLEMENTATION OF DIGITAL COMPUTERS FOR PROCESS CONTROL:- Allowed the implementation of optimizing
control strategies in plants. Usual mode of implementation – Supervisory
Control. Computer calculates new optimum set point
values and communicates them to the two control loops.
Optimizing control- extensive use Beneficial for large plants – significant
economic savings.
SIMPLE PERFORMANCE CRITERIA Overshoot Rise time Settling time Decay ratio Frequency of Oscillation of the transient
DECAY RATIO Most popular C/A = ¼ One-Quarter Decay Ratio Criterion The ratio of the amounts above the ultimate
value of two successive peaks. Related to Damping factor
CHARACTERISTICS OF AN UNDER DAMPED SYSTEM
TIME INTEGRAL PERFORMANCE CRITERIA Integral of the Square Error – ISE
Integral of the absolute value of the error – IAE
Integral of the time-weighed absolute error – ITAE
Where
GENERAL GUIDELINES FOR DESIGNING BEST CONTROLLER Select the type of controller and the values of
its adjusted parameters in such a way as to minimize the IAE,ISE,ITAE of the system’s response. To Strongly suppress large errors – ISE For Suppression of small errors – IAE To suppress errors that persists for long times -
ITSE
When we tune the controller parameters using IAE,ISE, ITAE performance criteria- Remember the following points
1. Different criteria lead to different controller designs
2.For the same time integral criterion, different input changes lead to different designs
CLOSED LOOP RESPONSE USING VARIOUS TIME INTEGRAL CRITERIA
REFERENCES Chemical Process Control – George
Stephanopoulos Handbook of Instrumentation Engineers (Process Measurement and Analysis) - Liptak