Advanced Process Control and Cascade Control Techniques
Explore the benefits and implementation of cascade control in process systems for faster disturbance compensation. Learn about controller tuning and practical examples in this in-depth course by Finn Aakre Haugen.
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Course: Process Control, NMBU Dec 2017 - April 2018 Cascade control By Finn Aakre Haugen, PhD, TechTeach (finnhaugen@hotmail.com) F. Haugen. Process Control. NMBU. 2018. 1
Benefit of cascade control (comparing with ordinary single loop control): Faster (more effective) compensation of process disturbances. F. Haugen. Process Control. NMBU. 2018. 2
3 Review: Single-loop control system Actuator (typically) Disturbance d Process Controller Process output variable y y1SP e u C1 P2 P1 Setpoint ym F S Filter Sensor F. Haugen. Process Control. NMBU. 2018. 3
4 Improved structure with faster (more effective) disturbance compensation: Cascade control system Secondary (internal) process variable Actuator (typically) Disturbance Primary (or master) controller Secondary (or slave) controller d Process Primary process variable y2 y1 y1SP e u1 = y2SP u C1 C2 P2 P1 Setpoint y2m F2 S2 Secondary loop Filters Sensors y1m F1 S1 Primary loop F. Haugen. Process Control. NMBU. 2018. 4
Interpretation: With cascade control, the original actuator is substituted by a "new" well-behaving" actuator: Controlled ( c ) actuator Well-behaving actuator New actuator y2 y1 y1SP e u1 = y2SP = u C1 P2,c P1 y1m F1 S1 Primary loop F. Haugen. Process Control. NMBU. 2018. 5
Controller tuning: 1.First, tune the secondary controller (with the primary controller in Manual mode). 2.Then, tune the primary controller (with the secondary controller in Auto mode). F. Haugen. Process Control. NMBU. 2018. 6
Example 1: Cascade control of temperature in a vessel Simulator(unzip all the files, and then run the exefile). 7 F. Haugen. Process Control. NMBU. 2018. 7
Example 1 cont.: Comparing performance indexes IAE (Integral of Absolute value of control Error): Excitation Cascade Single-loop Their ratio (Sprang = step) (Forstyrrelse = disturbance) Which of the control structures is the best? F. Haugen. Process Control. NMBU. 2018. 8
Example 2: Cascade control of heat exchanger Simulator 9 F. Haugen. Process Control. NMBU. 2018.
