A Lyapunov Variable-Free KYP Lemma for SISO Continuous Systems

This technical note proposes a novel frequency-selective Kalman-Yakubovich-Popov (FS–KYP) lemma for analysis of single-input single-output (SISO) continuous systems. In contrast to existing approaches, the proposed method only uses a minimal number of variables due to the absence of Lyapunov variables in semidefinite programming (SDP) formulation. The SDP formulation is extended to polytopic uncertain systems also without any additional variable and yields an efficient method for computation of the $H_{infty} $ gain for polytopic systems. The viability of the proposed method are demonstrated through several numerical examples.      

Sum-of-Squares Decomposition via Generalized KYP Lemma

The Kalman–Yakubovich–Popov (KYP) lemma establishes the equivalence between a frequency domain inequality (FDI) of a proper rational function and a linear matrix inequality (LMI). A recent result generalized the KYP lemma to characterize an FDI of a possibly nonproper rational function on a portion of a curve on the complex plane. This note examines implications of the generalized KYP result to sum-of-squares (SOS) decompositions of matrix-valued nonnegative polynomials of a single complex variable on a curve in the complex plane. Our result generalizes and unifies some existing SOS results, and also establishes equivalences among FDI, LMI, and SOS.      

Integrated servo-mechanical design of high-performance mechatronics using generalized KYP Lemma

High-performance mechatronics have specifications which are difficult to achieve when the mechanical plant is non-minimum phase and a low-order controller is used. In this paper, an integrated servo-mechanical design algorithm is proposed for systematic finite frequency redesign of a mechanical plant using the generalized Kalman–Yakubovic–Popov Lemma. The synthesis of a minimum phase plant is carried out based on a predesigned low-order controller, positive realness constraints, and performance specifications of the overall control system. Our simulation results using the proposed algorithm achieve a high-bandwidth control system with disturbance attenuation capabilities at the phase-stabilized resonant modes of the plant with the low-order controller.     

A KYP lemma and invariance principle for systems with multiple hysteresis non-linearities

Absolute stability criteria for systems with multiple hysteresis non-linearities are given in this paper. It is shown that the stability guarantee is achieved with a simple two part test on the linear subsystem. If the linear subsystem satisfies a particular linear matrix inequality and a simple residue condition, then, as is proven, the non-linear system will be asymptotically stable. The main stability theorem is developed using a combination of passivity, Lyapunov and Popov stability theories to show that the state describing the linear system dynamics must converge to an equilibrium position of the non-linear closed loop system. The invariant sets that contain all such possible equilibrium points are described in detail for several common types of hystereses. The class of non-linearities covered by the analysis is very general and includes multiple slope-restricted memoryless non-linearities as a special case. Simple numerical examples are used to demonstrate the effectiveness of the new analysis in comparison to other recent results, and graphically illustrate state asymptotic stability.     

A generalized KYP lemma based approach for disturbance rejection in data storage systems

This paper is concerned with disturbance rejection for data storage systems which applies microactuator to expand its servo bandwidth. An approach based on the generalized Kalman–Yakubovic–Popov (KYP) lemma together with the Youla parameterization is proposed which allows us to suppress disturbances of particular frequencies within or beyond the servo bandwidth via convex optimization. The rejection of narrowband high-frequency disturbances is achieved by using this approach. Simulation together with implementation results demonstrate the simplicity and effectiveness of the design method as compared with the traditional frequency weighting method.     

A note on Reusken's Lemma

A modification of the Lemma of Reusken is given. It allows us to improve the estimate of the smoothing property in cases where the contraction number of the iteration is small. This is of importance for robust multi-grid methods. Moreover, we describe a simple semi-iterative smoother with better asymptotic behaviour than for the stationary iterative smoother.     

The Kalman-Yakubovich-Popov Lemma for Pritchard-Salamon systems

In this paper we generalize the Kalman-Yakubovich-Popov Lemma to the Pritchard-Salamon class of infinite-dimensional systems, i.e. systems determined by semigroups of operators on a Hilbert space with unbounded input and output operators. At the same time we prove a comparison theorem for Riccati equations of the same class.     

An anti-windup technique for LMI regions

The anti-windup problem seeks to minimize closed loop performance deterioration due to input nonlinearities, such as saturation, for a given linear time-invariant plant and controller. This paper presents a linear matrix inequality (LMI) based method that attempts to minimize performance deterioration while explicitly restricting the anti-windup closed loop dynamics. The restriction placed on the dynamics is described via LMI regions, which is a form of regional pole placement. Finally, the techniques discussed in this paper are demonstrated on an electro-hydraulic testbed.     

LMI tools for eventually periodic systems

This paper is focused on the concept of an eventually periodic linear discrete-time system. We derive a necessary and sufficient analysis condition for checking open-loop stability and performance of such systems, and use this to derive exact controller synthesis conditions given eventually periodic plants. All the conditions derived are provided in terms of semi-definite programming problems. The motivation for this work is controlling nonlinear systems along prespecified trajectories, notably those which eventually settle down into periodic orbits and those with uncertain initial states.     

LMI designmethod for networked-based PID control

In this paper, we propose a methodology for the design of networked PID controllers for second-order delayed processes using linear matrix inequalities. The proposed procedure takes into account time-varying delay on the plant, time-varying delays induced by the network and packed dropouts. The design is carried on entirely using a continuous-time model of the closed-loop system where time-varying delays are used to represent sampling and holding occurring in a discrete-time digital PID controller.     

A new LMI condition for robust stability of discrete-time uncertain systems

In this paper, a new robust stability condition is derived for uncertain discrete-time linear systems with convex polytopic uncertainties. The condition is expressed in terms of a set of linear matrix inequalities (LMIs) involving only the vertices of the polytope domain. It enables us to determine robust stability of uncertain systems easily by solving some LMIs. A rigorous proof is given to show that an interesting result appeared recently is a special case of the proposed condition. Numerical examples also demonstrate the merit of the present condition in the aspect of conservativeness over other results in the literature.     

A Mechanized Proof of the Basic Perturbation Lemma

We present a complete mechanized proof of the result in homological algebra known as basic perturbation lemma. The proof has been carried out in the proof assistant Isabelle, more concretely, in the implementation of higher-order logic (HOL) available in the system. We report on the difficulties found when dealing with abstract algebra in HOL, and also on the ongoing stages of our project to give a certified version of some of the algorithms present in the Kenzo symbolic computation system. J. Aransay was partially supported by Ministerio de Educación y Ciencia, MTM2006/06513, and by Gobierno de La Rioja ANGI2005/19 and J. Rubio was partially supported by Ministerio de Educación y Ciencia, MTM2006/06513, and by Gobierno de La Rioja ANGI2005/19.     

A Structure Exploiting Preprocessor for Semidefinite Programs Derived From the Kalman-Yakubovich-Popov Lemma

Semidefinite programs derived from the Kalman-Yakubovich-Popov (KYP) lemma are quite common in control and signal processing applications. The programs are often of high dimension which makes them hard or impossible to solve with general-purpose solvers. Here we present a customized preprocessor, KYPD, that utilizes the inherent structure of this particular optimization problem. The key to an efficient implementation is to transform the optimization problem into an equivalent semidefinite program. This equivalent problem has much fewer variables and the matrices in the linear matrix inequality constraints are of low rank. KYPD can use any primal-dual solver for semidefinite programs as an underlying solver.     

Optimized ellipsoid algorithm for LMI feasibility problems

Ellipsoid algorithm with deepest-cut method is presented for LMI(Linear Matrix Inequality) feasibility problems. The proposed algorithm removes more than half of the previous step’s ellipsoid to obtain faster convergence than the original ellipsoid method. The cutting-direction is also optimized to maximize the volume reduction ratio at each step.     

Improved ellipsoid algorithm for LMI feasibility problems

An improved ellipsoid algorithm for solving general LMI feasibility problems is proposed. The proposed algorithm uses a deep-cut approach and introduces an affine transformation-based design to obtain the minimal-volume ellipsoid. It is shown that the proposed method improves the convergence rate of the ellipsoid algorithm dramatically. Faster convergence rate of the proposed algorithm is mathematically proved and then tested by simulation.     

A Barbalat-Like Lemma with Its Application to Learning Control

This paper presents the convergence property for a sequence of functions over a finite interval of time, which square integral has a zero limit. It is proven that if such a sequence of functions is equicontinuous, the sequence itself will converge uniformly to zero over the entire interval. For illustration purposes, this result is applied and its usefulness shown in learning control systems analysis.     

Lemma and cut strategies for propositional model elimination

This paper describes new “lemma” and “cut” strategies that are efficient to apply in the setting of propositional Model Elimination. Previous strategies for managing lemmas and C-literals in Model Elimination were oriented toward first-order theorem proving. The original “cumulative” strategy remembers lemmas forever, and was found to be too inefficient. The previously reported C-literal and unit-lemma strategies, such as “strong regularity”, forget them unnecessarily soon in the propositional domain. An intermediate strategy, called “quasi-persistent” lemmas, is introduced. Supplementing this strategy, methods for “eager” lemmas and two forms of controlled “cut” provide further efficiencies. The techniques have been incorporated into “Modoc”, which is an implementation of Model Elimination, extended with a new pruning method that is designed to eliminate certain refutation attempts that cannot succeed. Experimental data show that on random 3CNF formulas at the “hard” ratio of 4.27 clauses per variable, Modoc is not as effective as recently reported model-searching methods. However, on more structured formulas from applications, such as circuit-fault detection, it is superior. This revised version was published online in June 2006 with corrections to the Cover Date.     

A Characterisation of Multiply Recursive Functions with Higman's Lemma

We prove that string rewriting systems which reduce by Higman's lemma exhaust the multiply recursive functions. This result provides a full characterisation of the expressiveness of Higman's lemma when applied to rewriting theory. The underlying argument of our construction is to connect the order type and the derivation length via the Hardy hierarchy.     

Generalized KYP lemma: unified frequency domain inequalities with design applications

The celebrated Kalman-Yakubovic/spl caron/-Popov (KYP) lemma establishes the equivalence between a frequency domain inequality (FDI) and a linear matrix inequality, and has played one of the most fundamental roles in systems and control theory. This paper first develops a necessary and sufficient condition for an S-procedure to be lossless, and uses the result to generalize the KYP lemma in two aspects-the frequency range and the class of systems-and to unify various existing versions by a single theorem. In particular, our result covers FDIs in finite frequency intervals for both continuous/discrete-time settings as opposed to the standard infinite frequency range. The class of systems for which FDIs are considered is no longer constrained to be proper, and nonproper transfer functions including polynomials can also be treated. We study implications of this generalization, and develop a proper interface between the basic result and various engineering applications. Specifically, it is shown that our result allows us to solve a certain class of system design problems with multiple specifications on the gain/phase properties in several frequency ranges. The method is illustrated by numerical design examples of digital filters and proportional-integral-derivative controllers.