AdvancedTopic 70 of 101Signals, Control & Comms
Robust control
Maintains performance despite uncertainty in the model.
In depth
Robust control ensures stability and performance despite model uncertainty and disturbances: H∞ synthesis, μ-synthesis, sensitivity shaping (S and T limits), loop shaping. Uncertainty modelled as additive, multiplicative or parametric. Trade-offs enforced by the Bode sensitivity integral.
Key points
- Small gain theorem
- Weighting functions
- Robust stability and performance
ExampleA flight controller stays stable as aircraft mass and speed change.
What is Robust control?
Maintains performance despite uncertainty in the model.
Why is it important to understand robust control?
Robust control keeps performance acceptable when the real plant differs from the model, which is essential in real systems that change.
What is model uncertainty?
The difference between the real plant and the model, which can come from parameter variation, unmodelled dynamics or nonlinearity.
What does a robust design guarantee?
Stability and acceptable performance for all plants within a defined uncertainty set, rather than only for the nominal model.
How is Robust control used in practice?
Typical applications include designing a flight controller that works across different payloads, keeping a robot stable when its mass varies by twenty percent and specifying an H-infinity controller for a plant with uncertain gain.
What should I learn before Robust control?
Study "Model predictive control" first (topic 69 of 101 in Signals, Control & Comms). It covers the groundwork this topic builds on.
What are the key points of Robust control?
Small gain theorem. Weighting functions. Robust stability and performance.
Can you give an example of Robust control?
A flight controller stays stable as aircraft mass and speed change.
What comes after Robust control?
The next topic is "Adaptive control", which builds directly on this one.
How difficult is Robust control?
It is classed as Advanced in Signals, Control & Comms (topic 70 of 101). It is an advanced topic. It assumes you are comfortable with the intermediate topics in Signals, Control & Comms.