System identification and robust control (MSc thesis)

My MSc research dealt with a highly nonlinear dynamical system involving the interaction of a translational oscillator and a rotational actuator. The system is a benchmark for assessing the effectiveness of a given control method in terms of stabilizing a translational oscillator (mass-spring) system using a rotational actuator and models what happens in a dual-spin spacecraft. I built a prototype of the system with two flexible beams used to implement both the spring and a suspension (for zero friction such that the mass-spring system acts as an undamped oscillator).

Rotational actuator to control a translational oscillator. 

I used a nonparametric parameter estimation method to model the nonlinear system as a perturbed linear system in order to provide the information required for linear robust H∞ control design. Results confirmed the effectiveness of the approach and that it could effectively condense the whole nonlinearities, uncertainties, and disturbances within the system into a favorable perturbation block.

Top: The frequency responses of the estimated and nominal systems. Bottom: The uncertainty profile and the uncertainty weighting function.

Top: Closed-loop system as a generalized regulator problem. Bottom: Responses of the open-loop (dotted) and the closed-loop (solid) systems.

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