H-infinity synthesis with Scilab Part III : Cascade design

At the end of Part II in our H design trilogy, we addressed the disturbance attenuation problem when the torque disturbance input affected the plant output significantly. A straightforward way to deal with this problem is to push the sensitivity weight further down in low-frequency region. This is not easy to do for a non-minimumphase plant, especialy when a closed-loop bandwidth constraint is also imposed. In the discussion below we propose an already known scheme to tackle the tracking and disturbance attenuation problems separately.

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H-infinity synthesis with Scilab Part II : Single-loop Tracking Example

From the problem setup discussion in Part I, we proceed with an example on tracking problem using S/T mixed-sensitivityH synthesis. The plant used in this example is a mechanical revolute joint driven by brushless servomotor in Figure 1, consisiting of joint, drive, and motor dynamics, together with a joint resonance model. This is quite a complicated, non-minimum phase plant that results in a challenging control problem.

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