IntermediateTopic 59 of 101Signals, Control & Comms
State-space models
Describe systems with first-order equations x'=Ax+Bu.
In depth
State-space: ẋ=Ax+Bu, y=Cx+Du models multi-input multi-output, time-varying and nonlinear (after linearisation) systems. Transfer function G(s)=C(sI-A)⁻¹B+D; eigenvalues of A are poles. Realisations are not unique (similarity transforms). Foundation for modern control.
Key points
- State variables
- Canonical forms
- Matrix exponential e^{At}
ExampleA two-mass system has four states: positions and velocities.
What is State-space models?
Describe systems with first-order equations x'=Ax+Bu.
Why is it important to understand state-space models?
State-space models describe multi-input multi-output systems in a compact form, which suits modern control design and simulation.
What is the state vector?
The set of variables that describe the internal condition of the system, so that the future depends only on the state and inputs.
What do matrices A, B, C and D mean?
A describes the internal dynamics, B the effect of inputs, C how states appear at the output, and D the direct input to output path.
How is State-space models used in practice?
Typical applications include modelling a drone with position, velocity and attitude states, writing the equations of a two-tank process for a controller and designing a controller for a robot with several joints.
What should I learn before State-space models?
Study "Lead and lag compensators" first (topic 58 of 101 in Signals, Control & Comms). It covers the groundwork this topic builds on.
What are the key points of State-space models?
State variables. Canonical forms. Matrix exponential e^{At}.
Can you give an example of State-space models?
A two-mass system has four states: positions and velocities.
What comes after State-space models?
The next topic is "Controllability and observability", which builds directly on this one.
How difficult is State-space models?
It is classed as Intermediate in Signals, Control & Comms (topic 59 of 101). It is an intermediate topic. Work through the beginner topics in Signals, Control & Comms first.