Modeling and control of a floating platform

A platform with a rotating crane resting on three adjustable floats in a tub has been built on laboratory scale. Controller design is studied to prevent the platform from leaning due to crane movements. The system dynamics can be described primarily by a simple sixth order linear model. Model errors are then due mainly to unmodeled effects of waves that are essentially linear transfers. It is precisely under these conditions that H_∞ design should perform well. Actual design and tests show that H_∞ controllers do not substantially outperform LQG designs combined with feedforward controllers, but the combination of both feedforward and feedback controllers can easily be obtained by H_∞ design techniques