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Goal
Design the pre-filter (W) and controller (K) on the basis of a nominal model $LaTeX: P_0$ for the plant $LaTeX: P$ such that the feedback system exhibits the following properties:

1. Stability: if the system is perturbed then the system will return to equilibrium
2. Small tracking error
• Good low frequency command following
• Good low frequency disturbance attenuation
• Good high frequency noise attenuation

Note
The stated goals must be achieved in the presence of the following sources of uncertainty

• $LaTeX: P_0 \ne P$
• $LaTeX: H$ is not known exactly
• $LaTeX: d_i$ and $LaTeX: d_o$ are not known exactly
• $LaTeX: n$ is not known exactly