L11: Cascade Control

Prerequisites: L10 | Effort: 60 min | Seborg: Chapter 16

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Learning Objectives

1. ✅ Understand cascade control (inner + outer loops)
2. ✅ Implement fast inner loop + slow outer loop
3. ✅ Compare cascade vs single-loop performance
4. ✅ Apply to reactor temperature control (jacket temp as inner loop)

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Theory Recap: Cascade Control (Seborg Ch. 16)

Cascade Structure: - Outer (Primary) Loop: Slow process (reactor temp) - Inner (Secondary) Loop: Fast actuator (jacket temp)

Benefits: - Inner loop rejects disturbances before affecting outer - Faster response to setpoint changes - Handles actuator nonlinearities

Tuning Rule: - Tune inner loop first (10× faster than outer) - Then tune outer loop

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Odibi Hands-On

Example 1: Reactor Cascade Control

# reactor_cascade.yaml
# Outer: Reactor temperature (SP=80°C, τ=20 min)
# Inner: Jacket temperature (SP from outer, τ=2 min)

Working example: /examples/cheme_course/L11_cascade/reactor_cascade.yaml

Example 2: Cascade vs Single-Loop

Compare performance against single-loop control.

Working example: /examples/cheme_course/L11_cascade/cascade_vs_single.yaml

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Summary

• ✅ Cascade improves disturbance rejection
• ✅ Inner loop must be 5-10× faster than outer
• ✅ Tune inner first, then outer

Next: L12: Feedforward Control

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