robust adaptive control in the presence of bounded disturbances the model reference adaptive control of a linear plant subjected to bounded disturbances is considered by analyzing a set of nonlinear differential equations it is shown that the global behavior of the adaptive system depends upon the persistent excitation of the reference input as well as the amplitude of the external disturbances the principal contribution of the paper is the derivation of sufficient conditions on the persistent excitation of the reference input given the maximum amplitude of disturbance for the signals in the adaptive system to be globally bounded

a differential algebraic approach to speed estimation in an induction motor this note considers a differential algebraic approach to estimating the speed of an induction motor from the measured terminal voltages and currents in particular it is shown that the induction motor speed spl omega satisfies both a second and a third order polynomial equation whose coefficients depend on the stator voltages stator currents and their derivatives it is shown that as long as the stator electrical frequency is nonzero the speed is uniquely determined by these polynomials the speed so determined is then used to stabilize a dynamic luenberger type observer to obtain a smoother speed estimate with full knowledge of the machine parameters and filtering of the sensor noise simulations indicate that this estimator has the potential to provide low speed including zero speed control of an induction motor under full rated load

differential algebraic systems as differential equations on manifolds based on the theory of differential equations on manifolds existence and uniqueness results are proved for a class of mixed systems of differential and algebraic equations as they occur in various applications both the autonomous and nonautonomous case are considered moreover a class of algebraically incomplete systems is introduced for which existence and uniqueness results only hold on certain lower dimensional manifolds this class includes systems for which the application of ode solvers is known to lead to difficulties finally some solution approach based on continuation techniques is outlined

maximal ideals in modular group algebras of the finitary symmetric and alternating groups the main result of the paper is a description of the maximal ideals in the modular group algebras of the finitary symmetric and alternating groups provided the characteristic p of the ground field is greater than 2 for the symmetric group there are exactly p 1 such ideals and for the alternating group there are p 1 2 of them the description is obtained in terms of the annihilators of certain systems of the completely splittable irreducible modular representations of the finite symmetric and alternating groups the main tools used in the proofs are the modular branching rules obtained earlier by the second author and the mullineux conjecture proved recently by fordkleshchev and bessenrodt olsson the results obtained are relevant to the theory of pi algebras they are used in a later paper by the authors and a e zalesskii on almost simple group algebras and asymptotic properties of modular representations of symmetric groups

adaptive interconnected observer for sensorless induction motor an adaptive interconnected observer for induction motor im drive without mechanical sensors speed sensor and load torque sensor is presented the observer estimates the fluxes the angular velocity the load torque and the stator resistance even under or near unobservable conditions practical stability based on lyapunov theory is proved to guarantee the strongly uniformly practical stability of the estimation error dynamics a contribution of this article is the experimental validation of the observer on reference trajectories of a sensorless im observer benchmark the trajectories of this benchmark are chosen to test the motor near and under conditions of unobservability robustness with respect to parameters variations is proved and experimentally verified

irreducible restrictions of representations of symmetric and alternating groups in small characteristics abstract building on reduction theorems and dimension bounds for symmetric groups obtained in our earlier work we classify the irreducible restrictions of representations of the symmetric and alternating groups to proper subgroups such a classification is known when the characteristic of the ground field is greater than 3 but the small characteristics cases require a substantially more delicate analysis and new ideas our results fit into the aschbacher scott program on maximal subgroups of finite classical groups

semiglobal uniform asymptotic stability of an easy to implement pll like sensorless observer for induction motors in this work stability properties of a novel and easy to implement sensorless observer for induction motors are investigated the considered solution is inspired by phase locked loop strategies and it takes advantage from the rotor flux derivatives to define a rotating vector to align with even if such variables are not directly measured input to state stability properties are proven for suitably defined electrical and magneto mechanical observation error subsystems time scale separation is then exploited to invoke singular perturbation arguments and guarantee boundedness of the observation errors trajectories finally the small gain theorem is adopted to prove semiglobal uniform asymptotic stability of the presented scheme some additional interesting properties are discussed beside the main stream of the proposed analysis simulations indicate the observer can be profitably exploited for induction machines speed sensorless control applications

convergence of optimal control problems with an h norm constraint this paper considers the problem of computing a stabilizing controller for a multivariable plant so that the performance objective defined on a closed loop transfer matrix is minimized while the h norm of possibly another transfer matrix is constrained in other words the problem is one of keeping the induced l2 to l2 norm from an input vector to an output vector below some pre specified level e g for guaranteeing robust stability against unstructured perturbations while achieving the best possible performance as measured by a function defined over a closed loop transfer matrix such a problem is referred to as a mixed optimization problem and includes h2 h l1 h and time domain constrained h control as special cases the approach in this paper is to approximate the mixed problem which is infinite dimensional by one involving a finite number of variables the performance achieved by a solution to the finite problem can be arbitrarily close to the optimal performance of the mixed problem moreover given a level of suboptimality the number of variables involved in the optimization can be bounded a priori in terms of the data the theory is illustrated by briefly discussing two examples

asymptotic results on modular representations of symmetric groups and almost simple modular group algebras in fact this is a question about infinite simple groups because it is easy for g finite and because a non trivial normal subgroup gives rise to a non trivial ideal different from the augmentation ideal also note that the problem reduces easily to the question on when the augmentation ideal is simple as a ring the first interesting class of groups with almost simple fg was discovered in 3 this class is rather exotic and contains groups like the universal hall group and algebraically closed groups for locally finite groups g a substantial progress was achieved recently by using representation theory of finite groups see 18 19 16 and others the representation theory approach transforms the problems on ideals to certain problems on asymptotic behavior of representations of finite groups which are often of independent interest the method is more effective over fields of characteristic zero as the theory of ordinary representations is much better elaborated than the modular theory this paper is devoted to the modular aspect of the theory one of our main results deals with the case where g is a direct limit of alternating groups and f is any field of characteristic p 2 we note that the case where charf 0 was considered in 18 let n be the set of natural numbers denote by alt and sym or simply an and n the alternating and symmetric groups respectively on a set with n let alt 1 alt 2 alt i 1

a proof of the mullineux conjecture a partition of a positive integer n is a sequence 1 2 m 0 of integers such that i n for a positive integer p a partition 1 2 m or its young diagram is called p regular if it does not have p or more equal parts i e if there does not exist t m p 1 with t t 1 t p 1 let f be a field of characteristic p 0 it is well known that irreducible representations of the symmetric group sn over f are naturally parametrized by pregular partitions of n cf for example 9 12 if is such a partition we denote the corresponding irreducible module by d let sgnn be the one dimensional sign representation of sn over f i e sgnn f as a vector space and g f sgn g f for any g sn f f here sgn g is just the sign of the permutation g it is clear that for any irreducible d the tensor product d sgnn is also irreducible the problem usually called the problem of mullineux is to find the p regular partition such that d sgnn d put d sgnn dn in this way a bijection bn on the set pn of p regular partitions of n is defined for each positive integer n and the problem is

on parameter convergence in adaptive control it is well known that the parameter error as well as the model plant mismatch error in a model reference adaptive scheme tends exponentially to zero iff a certain sufficient richness condition holds for signals inside the time varying plant control loop in this paper we give conditions on the reference signal the exogenous input to the adaptive loop namely that it have as many spectral lines as there are unknown parameters in order to guarantee parameter convergence

speed and rotor flux estimation of induction machines using a two stage extended kalman filter this paper presents an effective implementation of an extended kalman filter used for the estimation of both rotor flux and rotor velocity of an induction motor an algorithm proposed by hsieh and chen in hsieh c s chen f c 1999 optimal solution of the two stage kalman estimator ieee transactions on automatic control 44 1 194 199 for linear parameter estimation is extended to non linear estimation where parameters such as the velocity of an induction machine are present in the transition matrix and in the augmented state space compared to a straightforward implementation of an extended kalman filter our modified optimal two stage kalman estimator reduces the number of arithmetic operations by 25 allowing higher sampling rate or the use of a cheaper microcontroller

constrained h_infty optimal control over an infinite horizon it has been recently shown in automatica j ifac 29 1993 pp 969 983 ieee trans automat control 39 1994 pp 762 779 that time domain constraints can be incorporated explicitly into h infty optimal control problems over a finite horizon in this paper we construct a sequence of such finite horizon constrained h infty optimization problems and show that their solutions converge to the solution of the infinite horizon h infty optimization we prove that convergence is uniform in the h infty norm and that the optimal solution to the infinite horizon problem is unique

irreducible tensor products over alternating groups abstract we classify irreducible tensor products of modular representations of the alternating group over an algebraically closed field of characteristic p 5

global observability and detectability analysis of uncertain reaction systems and observer design observation issues are of fundamental importance for reaction systems due to the limited availability of on line sensors and the uncertainties related to the mathematical model the objective of this work is to propose a methodology to make a global analysis of observability and detectability of such systems with a particular concern about the design of robust observers for this the uncertainties of the reaction system are modelled as arbitrary unknown inputs these results include and generalize the standard asymptotic observers well known in the biotechnology moreover the observability properties required for the existence of such observers and for the assignability of their convergence dynamics are clarified

a game theory approach to constrained minimax state estimation this paper presents a game theory approach to the constrained state estimation of linear discrete time dynamic systems in the application of state estimators there is often known model or signal information that is either ignored or dealt with heuristically for example constraints on the state values which may be based on physical considerations are often neglected because they do not easily fit into the structure of the state estimator this paper develops a method for incorporating state equality constraints into a minimax state estimator the algorithm is demonstrated on a simple vehicle tracking simulation

global observability analysis of sensorless induction motors the current problems to successfully apply sensorless controllers for induction motors are the existence of operation regimes for which the performance is remarkably deteriorated due to the difficulties in estimating correctly motor speed and flux and the lack of a theoretical explanation for this kind of behavior in this paper a global observability analysis for these machines is carried out it is first shown that all indistinguishable trajectories of the system i e pairs of state trajectories with the same input output behavior can be described by a differential equation on a manifold named here the indistinguishable dynamics studying the stability properties of this latter system it can be shown that the induction motor is not completely observable nor detectable in a local or in a global sense and for every set of parameters this implies that it is impossible to construct a state observer for the motor that converges for every trajectory of the system moreover the indistinguishable dynamics provides a systematic method to study understand and explain particular operation regimes and this is illustrated by some case studies of practical relevant operating conditions

a speed sensorless indirect field oriented control for induction motors based on high gain speed estimation the authors design a new speed sensorless output feedback control for the full order model of induction motors with unknown constant load torque which guarantees local asymptotic tracking of smooth speed and rotor flux modulus reference signals and local asymptotic field orientation on the basis of stator current measurements only the proposed nonlinear controller exploits the concept of indirect field orientation no flux estimation is required in combination with a new high gain speed estimator based on the torque current tracking error the estimates of unknown load torque and time varying rotor speed converge to the corresponding true values under a persistency of excitation condition with a physically meaningful interpretation basically equivalent to non null synchronous frequency stability analysis of the overall dynamics has been performed exploiting the singular perturbation method the proposed control algorithm is a true industrial sensorless solution since no simplifying assumptions flux and load torque measurements are required simulation and experimental tests show that the proposed controller is suitable for medium and high performance applications

path following for linear systems with unstable zero dynamics a constructive solution to the path following problem for mimo linear systems with unstable zero dynamics is developed while the original control variable steers the system output along the path the path parameter q is used as an additional control to stabilize zero dynamics with a feedback law which is nonlinear due to the path constraint a sufficient condition for solvability of the path following problem is given in terms of the geometric properties of the path when this condition is satisfied an arbitrary small l 2 norm of path following error can be achieved thus avoiding performance limitations of the standard reference tracking problem imposed by unstable zero dynamics

semiprimitivity of group algebras of locally finite simple groups let g be a locally finite simple group which is not a linear group for any field k we prove that the group algebra k g is semiprimitive the argument is almost entirely group theoretic in nature and ultimately rests upon the classification of the finite simple groups