2-DOF OPTIMAL CONTROLLER IMPROVEMENT AND AUGMENTATION TO 3-DOF WITH NONLINEAR TRANSPORT DECOUPLING THEOREM
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Robust, predictive control of objects that follow Newton and Euler’s equations has been demonstrated feasible by combining feedforward and feedback control. Such objects can be represented by controllable combinations of process and actuator. This type of controller is called a two-degree-of-freedom (2-DOF) controller to indicate the two control opportunities. The feedback control portion in the 2-DOF controller is modified in this work for performance improvement at a higher cost. Both implementations significantly reduce the state and rate errors when simulated using variable or fixed step sizes, compared to a 1D baseline open-loop controller, which is different from the 2-DOF controllers in that it has no feedback control. Additionally, to better simulate reality, an extra degree of freedom (DOF) is added to the 2-DOF controller to address motion expressed in coordinates of a rotating reference frame, using the nonlinear transport theorem, forming a three-degree-of-freedom (3-DOF) controller. Variations of the 3-DOF controller are simulated on a spacecraft inertia model and all achieve considerable error reduction when simulated using variable or fixed step sizes, compared to a 3D baseline controller that has no corrective feedback control. A summary table is included in this work for controller selection based on scenarios and a general set of control requirements.