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1887

access icon free MV bound and MV controller for convex-non-linear systems with input constraints

© The Institution of Engineering and Technology
Received 12/07/2017, Accepted 08/01/2018, Revised 23/11/2017, Published 09/01/2018

To assess the performance of a control loop based on the minimum variance (MV) benchmark, we need to calculate MV lower bound (MVLB). Even though there is a plethora of literature available for calculating MVLB for the linear systems, these methods are not suitable for non-linear systems. Furthermore, almost all of the real-world applications have been encountered with input variance constraints. These constraints limit controllers' abilities in decreasing the output variability. Therefore, existing MVLB computation methods, which do not account for input constraints, are not realistic when applied to constrained systems. The authors propose a novel approach to estimate MVLB by employing properties of dual Lagrangian functions to address these issues simultaneously in this study. Furthermore, to design the constrained non-linear MV controller (MVC), they propose to use the recurrent neural network for accommodating non-linearities and the input constraints. Then, control loop stability, optimality with respect to MVLB as well as the global convergence of the proposed controller are analytically proved for convex-non-linear systems with input constraints. The proposed control strategy is verified through simulations performed on a non-linear quadruple-tank system. The results indicate that the proposed design provides satisfactory results in decreasing output variance while satisfying the constraints.

Inspec keywords: nonlinear control systems; stochastic systems; recurrent neural nets; neurocontrollers; linear systems; convergence; stability; control system synthesis

Other keywords: linear systems; stochastic disturbance; controller performance assessment methods; control loop stability; control loop performance; recurrent neural network; constrained nonlinear MV controller design; saturation function; MV lower bound controller; output variance constraint; convex-nonlinear systems; global convergence; optimal performance quantification; MVLB computation methods; minimum variance MV benchmark; nonlinear quadruple-tank system; dual Lagrangian functions; input variance constraints

Subjects: Nonlinear control systems; Time-varying control systems; Control system analysis and synthesis methods; Stability in control theory; Linear control systems; Neurocontrol

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