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Nonlinear Predictive Control for Fast Constrained Systems By Ahmed Youssef
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What’s MBPC Introduction CV: controlled variableMV: manipulated variable
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Introduction Shortcomings of current industrial nonlinear MBPC Computing the MBPC control law demands significant on-line computation effort Inability to deal explicitly with the plant model uncertainty. Objective of research work Reducing the computational complexity of nonlinear MBPC & adding the robustness property whilst preserving its good attributes to make it more effective practical tool for controlling systems of fast- constrained dynamics.
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Given the nonlinear dynamic model Reformulate into nonlinear state-dependent form This is not a linearisation Trivial example State Dependent State-Space Models
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Hamilton-Jacobi-Bellman
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The NLQGPC quadratic infinite horizon cost function: The optimal control vector in terms of the states of the system and reference model: NLQGPC Control Law
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The Coupled Algebraic Riccati Equations
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Control Lyapunov Function A C 1 function V(x): n is said to be a discrete CLF for the system: if V(x) is positive definite, unbounded, and if for all x 0 Dealing with Stability Issue
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Satisficing is based on a point-wise cost / benefit comparison of an action. The benefits are given by the “Selectability” function P s (u,x), while the costs are given by the “Rejectability” function P r (u,x). The “satisficing” set is those options for which selectability exceeds rejectability: Stability via Satisficing
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Satisficing generates the state dependent set of controls that render the closed-loop system stable with respect to a known CLF. CLF-Based Satisficing Technique
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Magnitude Saturation Rate-Limited Actuators Actuator Dead-Zone Therefore the common term is the Saturation function Dealing with Input Constraints Examples of Actuator Constraints
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the actuator range of operation is limited L imiting functions that map the interval (- , ) onto (0, 1) L imiting functions that map the interval (- , ) onto (-1, 1) Approximation of Magnitude Saturation
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Error function(Blue) Tanh function(Green) Sigmoid function(Red) Sigmoid function(Black) Approximation of Magnitude Saturation
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Case Studies F-8 fighter aircraft F-16 fighter aircraft Caltech Ducted Fan
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Controlling of F-8 Fighter
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CONCLUSIONS Properties of NLQGPC controller: 1. High performance 2. Less computational burden 3. Dealing with input constraints 4. Guaranteeing asymptotic stability to the closed-loop system. 5.Possesses both performance robustness & stability robustness
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