Override Control (超驰控制) and Selective Control (选择控制) Lei Xie Institute of Industrial Control, Zhejiang University, Hangzhou, P. R. China 2018/3/16
Contents n n Override/Constraint Control Problem Design of Constrain Control Systems Reset Windup and Its Prevention in Constrain Control Selective Control Schemes
Example 1: Tank and Flow Control Loop Problems To avoid the liquid level drops below hmin ?
Problem of Override Control There are one MV and more-than-one CVs in a override / constraint control (超驰控制, 也称 为约束控制) system, which includes: n A normal CV, which is desired to maintain at its setpoint; n Some assistant CVs, which are required to be maintained within limits, to ensure the safety.
Control Scheme #1 Introduce AUTOMATIC SW ? (＋ ) (－ ) Please analyze the controller action & compare the output of both controllers in NORMAL condition
Control Scheme #2 LS: Low Selector（低选器） u(t) = min(u 1, u 2) LS (＋ ) (－ ) Smooth Switch problem between two loops ?
Override Control Scheme LS: Low Selector（低选器） u(t) = min(u 1, u 2) RFB: (external) reset feedback（外部积分反馈）
Reset Windup Prevention in Constraint Control Discuss: ONLY the controller in closed-loop condition has integral action, and the output of inactive controller will follow the output of active controller.
Example 2: Simple Control System for an Ammonia Cooler Problems: How to prevent the liquid level exceeding its high limit ?
Override Control Scheme for the Ammonia Cooler Discuss: (1) Control diagram (2) Selection of controller action (3) Reset windup prevention
Cascade Control System for the Ammonia Cooler Note: Output limit must be applied in TC 31
Selective Control Example
Exercise 6. 3 Problem 5 -18 (p. 124) in Automated Continuous Process Control.
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