State feedback policies for robust receding horizon control: uniqueness, continuity, and stability

Published versio

Offset-free control of constrained linear discrete-time systems subject to persistent unmeasured disturbances

This paper addresses the design of a dynamic, nonlinear, time-invariant, state feedback controller that guarantees constraint satisfaction and offset-free control in the presence of unmeasured, persistent, non-stationary, additive disturbances. First, this objective is obtained by designing a dynamic, linear, time-invariant, offset-free controller, and an appropriate domain of attraction for this linear controller is denned. Following this, the linear (unconstrained) control input is modified by adding a perturbation term that is computed by a robust receding horizon controller. It is shown that the domain of attraction of the receding horizon controller contains that of the linear controller, and an efficient implementation of the receding horizon controller is proposed.Published versio

Move blocking strategies in receding horizon control

Abstract — In order to deal with the computational burden of optimal control, it is common practice to reduce the degrees of freedom by fixing the input or its derivatives to be constant over several time-steps. This policy is referred to as “move blocking”. This paper will address two issues. First, a survey of various move blocking strategies is presented and the shortcomings of these blocking policies, such as the lack of stability and constraint satisfaction guarantees, will be illustrated. Second, a novel move blocking scheme, “Moving Window Blocking” (MWB), will be presented. In MWB, the blocking strategy is time-dependent such that the scheme yields stability and feasibility guarantees for the closed-loop system. Finally, the results of a large case-study are presented that illustrate the advantages and drawbacks of the various control strategies discussed in this paper

Optimal control of constrained, piecewise affine systems with bounded disturbances

Published versio

Designing model predictive controllers with prioritised constraints and objectives

Published versio

Numerical comparison of collocation vs quadrature penalty methods

Direct transcription with collocation-type methods (CTM) is a popular approach for solving dynamic optimization problems. It is known that these types of methods can fail to converge for problems that feature singular-arc solutions, high-index differential-algebraic equations and over-determined constraints. Recently, we proposed the use of quadrature penalty methods (QPM) as an alternative numerical approach to collocation-type methods. In contrast to the concept of collocation, which requires constraint-residuals to equal zero at individual points (e.g. at collocation points), the main idea of QPM is to simply oversample this number of points and use their respective quadrature weights in a quadratic penalty term, coining the name of quadrature penalty. In this paper, we provide numerical case studies and a broad numerical comparison on a wide range of problems, highlighting the benefits of QPM over CTM not only in difficult problems, but also in solving problems competitively to CTM. These results show that QPM can be considered an attractive first go-to method when solving general dynamic optimization problem

A power measure analysis of Amendment 36 in Colorado

Colorado’s Amendment 36 proposed to switch Colorado’s representation in the Electoral College from winner-takes-all to proportionality. We evaluate unilateral and uniform switches to proportionality both from Colorado’s perspective and from an impartial perspective on the basis of a priori and a posteriori voting power measures. The present system is to be preferred to a unilateral switch from any perspective on any measure. A uniform switch is to be preferred to the present system from Colorado’s perspective on an a priori measure, and from an impartial perspective on an a posteriori measure. The present system is to be preferred to a uniform switch from Colorado’s perspective on an a posteriori measure (with some qualifications), and from an impartial perspective on an a priori measure. We conclude with a discussion of the appropriateness of these measures

Flow estimation of boundary layers using DNS-based wall shear information

This article investigates the problem of obtaining a state-space model of the disturbance evolution that precedes turbulent flow across aerodynamic surfaces. This problem is challenging since the flow is governed by nonlinear, partial differential-algebraic equations for which there currently exists no efficient controller/estimator synthesis techniques. A sequence of model approximations is employed to yield a linear, low-order state-space model, to which standard tools of control theory can be applied. One of the novelties of this article is the application of an algorithm that converts a system of differential-algebraic equations into one of ordinary differential equations. This enables straightforward satisfaction of boundary conditions whilst dispensing with the need for parallel flow approximations and velocity–vorticity transformations. The efficacy of the model is demonstrated by the synthesis of a Kalman filter that clearly reconstructs the characteristic features of the flow, using only wall velocity gradient information obtained from a high-fidelity nonlinear simulation