Publications
197 results found
Jerez JL, Kerrigan EC, Constantinides GA, 2011, A Condensed and Sparse QP Formulation for Predictive Control, IEEE Control and Decision Conference
Longo S, Kerrigan EC, Ling KV, et al., 2011, A parallel formulation for predictive control with nonuniform hold constraints, Annual Reviews in Control, Vol: 35, Pages: 207-214, ISSN: 1872-9088
This paper investigates the use of parallel computing architectures (multi-core, FPGA, GPU) to solve, at each sampling instant, a constrained optimal control problem. A set of approximated (hence smaller) problems are solved simultaneously and the solution of the one with lower open-loop cost is implemented. The approximation consists of the inclusion of additional hold constraints, which effectively reduce the number of steps in the prediction. Since smaller problems are solved, and these are solved in parallel, the computational delay is reduced and faster sampling becomes an option. The proposed method can outperform, in terms of closed-loop cost, a standard receding horizon control formulation because higher sampling rates can improve performance, even if suboptimal solutions are considered. Feasibility and stability can be guaranteed by an appropriate selection of the hold constraints.
Mayne DQ, Kerrigan EC, van Wyk EJ, et al., 2011, Tube-based robust nonlinear model predictive control, International Journal of Robust and Nonlinear Control, Vol: 21, Pages: 1341-1353, ISSN: 1099-1239
This paper extends tube-based model predictive control of linear systems to achieve robust control of nonlinear systems subject to additive disturbances. A central or reference trajectory is determined by solving a nominal optimal control problem. The local linear controller, employed in tube-based robust control of linear systems, is replaced by an ancillary model predictive controller that forces the trajectories of the disturbed system to lie in a tube whose center is the reference trajectory thereby enabling robust control of uncertain nonlinear systems to be achieved.
Jones BL, Kerrigan EC, Morrison JF, et al., 2011, Flow estimation of boundary layers using DNS-based wall shear information, International Journal of Control, Vol: 84, Pages: 1310-1325, ISSN: 1366-5820
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.
Norman AK, Kerrigan EC, McKeon BJ, 2011, The effect of small-amplitude time-dependent changes to the surface morphology of a sphere, JOURNAL OF FLUID MECHANICS, Vol: 675, Pages: 268-296, ISSN: 0022-1120
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- Citations: 17
Couchman IJ, Kerrigan EC, Boehm C, 2011, Model reduction of homogeneous-in-the-state bilinear systems with input constraints, AUTOMATICA, Vol: 47, Pages: 761-768, ISSN: 0005-1098
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- Citations: 9
Jerez J, Constantinides GA, Kerrigan EC, 2011, An FPGA Implementation of a Sparse Quadratic Programming Solver for Constrained Predictive Control, ACM International Symposium on Field Programmable Gate Arrays, Publisher: ACM
Jones BL, Kerrigan EC, Morrison JF, et al., 2011, Flow estimation of boundary layers using wall shear information, IFAC Proceedings Volumes (IFAC-PapersOnline), Vol: 44, Pages: 13813-13818, ISSN: 1474-6670
This paper investigates the problem of obtaining a state-space model of the disturbance evolution that precedes turbulent flow and the associated increase in skin-friction drag on aircraft surfaces. This problem is highly challenging since the flow system is governed by nonlinear, partial differential-algebraic equations (the Navier-Stokes equations) for which there currently exists no efficient controller/estimator synthesis techniques. In this paper it is shown how a sequence of model approximations can be employed to yield a linear, low-order state-space model, to which the standard tools of control theory can be applied. One of the novelties of this paper is the application of a numerical routine 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 (shear) measurements obtained from a high-fidelity nonlinear simulation. © 2011 IFAC.
Shahzad A, Jones BL, Kerrigan EC, et al., 2011, An efficient algorithm for the solution of a coupled Sylvester equation appearing in descriptor systems, Automatica, Vol: 47, Pages: 244-248, ISSN: 1873-2836
Descriptor systems consisting of a large number of differential-algebraic equations (DAEs) usually arise from the discretization of partial differential-algebraic equations. This paper presents an efficient algorithm for solving the coupled Sylvester equation that arises in converting a system of linear DAEs to ordinary differential equations. A significant computational advantage is obtained by exploiting the structure of the involved matrices. The proposed algorithm removes the need to solve a standard Sylvester equation or to invert a matrix. The improved performance of this new method over existing techniques is demonstrated by comparing the number of floating-point operations and via numerical examples.
Jerez J, Constantinides GA, Kerrigan EC, et al., 2011, Parallel MPC for Real-Time FPGA-based Implementation, IFAC World Congress 2011
Ahmed S, Kerrigan EC, Jaimoukha IM, 2011, Semidefinite Relaxation of a Robust Static Attitude Determination Problem, 50th IEEE Conference of Decision and Control (CDC)/European Control Conference (ECC), Publisher: IEEE, Pages: 5337-5342, ISSN: 0743-1546
Jerez JL, Constantinides GA, Kerrigan EC, 2010, FPGA Implementation of an Interior Point Solver for Linear Model Predictive Control, IEEE International Conference on Field-Programmable Technology
Automatic control, the process of measuring, com- puting, and applying an input to control the behaviour of a physical system, is ubiquitous in engineering and industry. Model predictive control (MPC) is an advanced control technology that has been very successful in the chemical process industries due to its ability to handle large multiple input multiple output (MIMO) systems with physical constraints. It has recently been proposed to be applied to higher bandwidth systems, which add the requirement of greater sampling frequencies. The main hurdle is the need to solve a computationally intensive quadratic programming (QP) problem in real-time. In this paper we address the need for acceleration by proposing a highly efficient floating-point field-programmable gate array (FPGA) implementation that exploits the parallelism opportunities offered by interior-point optimization methods. The approach yields a 5x improvement in latency and a 40x improvement in throughput for large problems over a software implementation. This work builds on a previous FPGA implementation of an iterative linear solver, an operation at the heart of the interior-point method.
Frederick M, Kerrigan EC, Graham JMR, 2010, Gust alleviation using rapidly deployed trailing-edge flaps, JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS, Vol: 98, Pages: 712-723, ISSN: 0167-6105
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- Citations: 21
Couchman IJ, Kerrigan EC, 2010, Control of mixing in a Stokes' fluid flow, JOURNAL OF PROCESS CONTROL, Vol: 20, Pages: 1103-1115, ISSN: 0959-1524
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- Citations: 10
Hasan A, Kerrigan EC, Constantinides GA, 2010, Quantization in Control Systems and Forward Error Analysis of Iterative Numerical Algorithms, Control 2010, Publisher: Institution of Engineering and Technology ( IET ), Pages: 391-396
The use of control theory to study iterative algorithms, which can be considered as dynamicalsystems, opens many opportunities to find new tools for analysis of algorithms. In this paper weshow that results from the study of quantization effects in control systems can be used to findsystematic ways for forward error analysis of iterative algorithms. The proposed schemes areapplied to the classical iterative methods for solving a system of linear equations. The obtainedbounds are compared with bounds given in the numerical analysis literature.
Shahzad A, Kerrigan EC, Constantinides GA, 2010, A Warm-start Interior-point Method for Predictive Control, UKACC Control 2010, Publisher: Institution of Engineering and Technology ( IET ), Pages: 949-954
In predictive control, a quadratic program (QP) needs to be solved at each samplinginstant. We present a new warm-start strategy to solve a QP with an interior-point methodwhose data is slightly perturbed from the previous QP. In this strategy, an initial guess of theunknown variables in the perturbed problem is determined from the computed solution of theprevious problem. We demonstrate the effectiveness of our warm-start strategy to a number ofonline benchmark problems. Numerical results indicate that the proposed technique dependsupon the size of perturbation and it leads to a reduction of 30–74% in floating point operationscompared to a cold-start interior-point method.
Jones BL, Kerrigan EC, 2010, When is the discretization of a spatially distributed system good enough for control?, AUTOMATICA, Vol: 46, Pages: 1462-1468, ISSN: 0005-1098
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- Citations: 22
Shahzad A, Kerrigan EC, Constantinides GA, 2010, A Fast Well-conditioned Interior Point Method for Predictive Control, IEEE Control and Decision Conference
Interior point methods (IPMs) have proven to be an efficient way of solving quadratic programming problems in predictive control. A linear system of equations needs to be solved in each iteration of an IPM. The ill-conditioning of this linear system in the later iterations of the IPM prevents the use of an iterative method in solving the linear system due to a very slow rate of convergence; in some cases the solution never reaches the desired accuracy. In this paper we propose the use of a well-conditioned, approximate linear system, which increases the rate of convergence of the iterative method. The computational advantage is obtained by the use of an inexact Newton method along with the use of novel preconditioners. Numerical results indicate that the computational complexity of our proposed method scales quadratically with the number of states and linearly with the horizon length.
Hasan A, Kerrigan EC, Constantinides GA, 2010, An ISS and l-stability Approach to Forward Error Analysis of Iterative Numerical Algorithms, IEEE Control and Decision Conference
Coetzee LC, Craig IK, Kerrigan EC, 2010, Robust Nonlinear Model Predictive Control of a Run-of-Mine Ore Milling Circuit, IEEE TRANSACTIONS ON CONTROL SYSTEMS TECHNOLOGY, Vol: 18, Pages: 222-229, ISSN: 1063-6536
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- Citations: 42
Couchman IJ, Kerrigan EC, 2010, Feedback solution to a bilinear fluid mixing control problem, 49th IEEE Conference on Decision and Control (CDC), Publisher: IEEE, Pages: 2966-2971, ISSN: 0743-1546
Kerrigan EC, Shahzad A, Constantinides GA, 2010, Preconditioners for Inexact Interior Point Methods for Predictive Control
Couchman IJ, Kerrigan EC, Boehm C, 2010, Model reduction of homogeneous-in-the-state bilinear systems with input constraints, American Control Conference, Publisher: IEEE, Pages: 2718-2723, ISSN: 0743-1619
Spjotvold J, Kerrigan EC, Mayne DQ, et al., 2009, Inf-sup control of discontinuous piecewise affine systems, INTERNATIONAL JOURNAL OF ROBUST AND NONLINEAR CONTROL, Vol: 19, Pages: 1471-1492, ISSN: 1049-8923
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- Citations: 1
Goulart PJ, Kerrigan EC, Alamo T, 2009, Control of Constrained Discrete-Time Systems With Bounded ℓ2 Gain, IEEE Transactions on Automatic Control
Lopes AR, Shahzad A, Constantinides GA, et al., 2009, More FLOPS or More Precision? Accuracy Parameterizable Linear Equations Solvers for Model-Predictive Control
Jones BL, Kerrigan EC, 2009, When is the discretization of a PDE good enough for control?, IEEE International Conference on Control and Automation, Publisher: IEEE, Pages: 133-+, ISSN: 1948-3449
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- Citations: 1
Jones CN, Kerrigan EC, Maciejowski JM, 2008, On polyhedral projection and parametric programming, JOURNAL OF OPTIMIZATION THEORY AND APPLICATIONS, Vol: 138, Pages: 207-220, ISSN: 0022-3239
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- Citations: 32
Goulart PJ, Kerrigan EC, 2008, Input-to-state stability of robust receding horizon control with an expected value cost, Automatica, Vol: 44, ISSN: 1873-2836
This paper is concerned with the stability of a class of receding horizon control (RHC) laws for constrained linear discrete-time systems subject to bounded state disturbances and convex state and input constraints. The paper considers the class of finite horizon feedback control policies parameterized as affine functions of the system state, calculation of which can be shown to be tractable via a convex reparameterization. When minimizing the expected value of a finite horizon quadratic cost, we show that the value function is convex. When solving this optimal control problem at each time step and implementing the result in a receding horizon fashion, we provide sufficient conditions under which the closed-loop system is input-to-state stable (ISS).
Lopes AR, Constantinides GA, Kerrigan EC, 2008, A Floating-Point Solver for Band Structured Linear Equations, Pages: 353-356
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