Advanced Process Control: Fuzzy Logic and Expert Systems

摘要

Applying fuzzy logic to control the reactor using only the three existing process measurements—output flow, composition, and temperature—imposes a severe performance limit on the system. Without a mathematical derivative capability in the rule syntax the system can react to the current values of the measurements, but not to how fast they are changing. However, derivative action is very helpful in controlling variables that respond with a dominant capacity lag. For this application, product temperature is a lag dominant variable. For this reason, the design needs a fourth controlled variable—incremental temperature change. This allows the design to include logic that reacts more strongly when the temperature is changing than when it is steady. The setpoint for this variable is 0, meaning that the system should seek to keep temperature constant at its absolute setpoint.