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Regions of Stability for Limit Cycles of Piecewise Linear Systems Goncalves, Jorge in Proceedings of the 42th IEEE Conference on Decision and Control (2003) This paper starts by presenting local stability conditions for limit cycles of piecewise linear systems (PLS), based on analyzing the linear part of Poincare maps. Local stability guarantees the existence ... [more ▼] This paper starts by presenting local stability conditions for limit cycles of piecewise linear systems (PLS), based on analyzing the linear part of Poincare maps. Local stability guarantees the existence of an asymptotically stable neighborhood around the limit cycle. However, tools to characterize such neighborhood do not exist. This work gives conditions in the form of LMIs that guarantee asymptotic stability of PLS in a reasonably large region around a limit cycle, based on recent results on impact maps and surface Lyapunov functions (SuLF). These are exemplified with a biological application: a 4th-order neural oscillator, also used in many robotics applications like, for example, juggling and locomotion. [less ▲] Detailed reference viewed: 77 (0 UL)L2-gain of double integrators with saturation nonlinearity Goncalves, Jorge in IEEE Transactions on Automatic Control (2002), 47(12), 2063-2068 This note uses quadratic surface Lyapunov functions (SuLFs) to efficiently check if a double integrator in feedback with a saturation nonlinearity has L -gain less than > 0. We show that for many such ... [more ▼] This note uses quadratic surface Lyapunov functions (SuLFs) to efficiently check if a double integrator in feedback with a saturation nonlinearity has L -gain less than > 0. We show that for many such systems, the L -gain is nonconservative in the sense that this is approximately equal to the lower bound obtained by replacing the saturation with a constant gain of 1. These results allow the use of classical analysis tools like -analysis or integral quadratic constraints to analyze systems with double integrators and saturations, including servo systems like some mechanical systems, satellites, hard disks, compact disk players, etc. [less ▲] Detailed reference viewed: 101 (0 UL)Quadratic Surface Lyapunov Functions in the Analysis of Feedback Systems with Double Integrators and Saturations Goncalves, Jorge in Proceedings of the 10th IEEE Mediterranean Conference on Control and Automation (2002) Many systems like servo systems, satellites, harddisks, and CD players, can be modeled as linear systems with a single integrator and a saturation. Many times, such systems are controlled with a PI ... [more ▼] Many systems like servo systems, satellites, harddisks, and CD players, can be modeled as linear systems with a single integrator and a saturation. Many times, such systems are controlled with a PI controller resulting in a feedback interconnection with a double integrator and a saturation. In this paper, we propose a loop transformation that results in bounded operators so that classical analysis tools like mu-analysis or IQCs can be applied. In order to show boundedness of all operators, we use quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2 -gain less than gamma > 0 . We show that for many of such systems, the L2 -gain is non-conservative in the sense that this is approximately equal to the lower bound obtained by replacing the saturation with a constant gain of . [less ▲] Detailed reference viewed: 56 (0 UL)L2-gain of double integrators with saturation nonlinearity Goncalves, Jorge in Proceedings of the 15th IFAC World Congress (2002) This paper uses quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2-gain less than gamma > 0. We show that for many of such ... [more ▼] This paper uses quadratic surface Lyapunov functions to efficiently check if a double integrator in feedback with a saturation nonlinearity has L2-gain less than gamma > 0. We show that for many of such systems, the L2-gain is non-conservative in the sense that they are approximately equal to the low erbound obtained by replacing the saturation with a constant gain of 1. These results allow the use of classical analysis tools like mu -analysis or IQCs to analyze systems with double integrators and saturations, including servo systems like some mechanical systems, satellites, hard-disks, CD players, etc. [less ▲] Detailed reference viewed: 74 (1 UL)Global stability of relay feedback systems Goncalves, Jorge ; ; in IEEE Transactions on Automatic Control (2001), 46(4), 550--562 For a large class of relay feedback systems (RFS) there will be limit cycle oscillations. Conditions to check existence and local stability of limit cycles for these systems are well known. Global ... [more ▼] For a large class of relay feedback systems (RFS) there will be limit cycle oscillations. Conditions to check existence and local stability of limit cycles for these systems are well known. Global stability conditions, however, are practically nonexistent. This paper presents conditions in the form of linear matrix inequalities (LMIs) that, when satisfied, guarantee global asymptotic stability of limit cycles induced by relays with hysteresis in feedback with linear time-invariant (LTI) stable systems. The analysis consists in finding quadratic surface Lyapunov functions for Poincaré maps associated with RFS. These results are based on the discovery that a typical Poincaré map induced by an LTI flow between two hyperplanes can be represented as a linear transformation analytically parametrized by a scalar function of the state. Moreover, level sets of this function are convex subsets of linear manifolds. The search for quadratic Lyapunov functions on switching surfaces is done by solving a set of LMIs. Although this analysis methodology yields only a sufficient criterion of stability, it has proved very successful in globally analyzing a large number of examples with a unique locally stable symmetric unimodal limit cycle. In fact, it is still an open problem whether there exists an example with a globally stable symmetric unimodal limit cycle that could not be successfully analyzed with this new methodology. Examples analyzed include minimum-phase systems, systems of relative degree larger than one, and of high dimension. Such results lead us to believe that globally stable limit cycles of RFS frequently have quadratic surface Lyapunov functions. [less ▲] Detailed reference viewed: 101 (0 UL)Global analysis of piecewise linear systems using impact maps and quadratic surface Lyapunov functions Goncalves, Jorge ; ; in Proceedings of the European Control Conference (ECC) 2001 (2001) In this paper we develop an entirely new constructive global analysis methodology for a class of hybrid systems known as Piecewise Linear Systems (PLS). This methodology consists in inferring global ... [more ▼] In this paper we develop an entirely new constructive global analysis methodology for a class of hybrid systems known as Piecewise Linear Systems (PLS). This methodology consists in inferring global properties of PLS solely by studying their behavior at switching surfaces associated with PLS. The main idea is to analyze impact maps, i.e., maps from one switching surface to the next switching surface, by constructing quadratic Lyapunov functions on switching surfaces. We found that an impact map induced by an LTI flow between two switching surfaces can be represented as a linear transformation analytically parameterized by a scalar function of the state. This representation of impact maps allows the search for quadratic surface Lyapunov functions to be done by simply solving a set of LMIs. Global asymptotic stability, robustness, and performance of limit cycles and equilibrium points of PLS can this way be efficiently checked. These new results were successfully applied to certain classes of PLS. Although this analysis methodology yields only sufficient criteria of stability, it has shown to be very successful in globally analyzing a large number of examples with a locally stable limit cycle or equilibrium point. In fact, it is still an open problem whether there exists an example with a globally stable limit cycle or equilibrium point that cannot be successfully analyzed with this new methodology. Examples analyzed include systems of relative degree larger than one and of high dimension, for which no other analysis methodology could be applied. [less ▲] Detailed reference viewed: 84 (0 UL)Quadratic Surface Lyapunov Functions in Global Stability Analysis of Saturation Systems Goncalves, Jorge in Proceedings of the American Control Conference (2001) Detailed reference viewed: 88 (0 UL)Global stability analysis of on/off systems Goncalves, Jorge in Proceedings of the 39th IEEE Conference on Decision and Control (2000) This paper considers quadratic surface Lyapunov functions in the study of global stability analysis of on/off systems (OFS), including those OFS with unstable nonlinearity sectors. In previous work ... [more ▼] This paper considers quadratic surface Lyapunov functions in the study of global stability analysis of on/off systems (OFS), including those OFS with unstable nonlinearity sectors. In previous work, quadratic surface Lyapunov functions were successfully applied to prove global asymptotic stability of limit cycles of relay feedback systems. In this work, we show that these ideas can be used to prove global asymptotic stability of equilibrium points of piecewise linear systems (PLS). We present conditions in the form of LMI that, when satisfied, guarantee global asymptotic stability of an equilibrium point. A large number of examples was successfully proven globally stable. These include systems with an unstable affine linear subsystem, systems of relative degree larger than one and of high dimension, and systems with unstable nonlinearity sectors, for which all classical fail to analyze. In fact, existence of an example with a globally stable equilibrium point that could not be successfully analyzed with this new methodology is still an open problem. This work opens the door to the possibility that more general PLS can be systematically globally analyzed using quadratic surface Lyapunov functions. [less ▲] Detailed reference viewed: 101 (1 UL)Global stability of relay feedback systems Goncalves, Jorge ; ; in Proceedings of the IEEE American Control Conference (2000 ACC) (2000) For a large class of relay feedback systems (RFS) there will be limit cycle oscillations. Conditions to check existence and local stability of limit cycles for these systems are well known. Global ... [more ▼] For a large class of relay feedback systems (RFS) there will be limit cycle oscillations. Conditions to check existence and local stability of limit cycles for these systems are well known. Global stability conditions, however, are practically non-existent. The paper presents conditions in the form of linear matrix inequalities (LMIs) that guarantee global asymptotic stability of a limit cycle induced by a relay with hysteresis in feedback with an LTI stable system. The analysis is based on finding global quadratic Lyapunov functions for a Poincare map associated with the RFS. We found that a typical Poincare map induced by an LTI flow between two hyperplanes can be represented as a linear transformation analytically parametrized by a scalar function of the state. Moreover, level sets of this function are convex. The search for globally quadratic Lyapunov functions is then done by solving a set of LMIs. Most examples of RFS analyzed by the authors were proven globally stable. Systems analyzed include minimum-phase systems, systems of relative degree larger than one, and of high dimension. This leads us to believe that quadratic stability of associated Poincare maps is common in RFS. [less ▲] Detailed reference viewed: 97 (0 UL)Semi-global analysis of relay feedback systems Goncalves, Jorge ; ; in Proceedings of the 37th IEEE Conference on Decision and Control (1998) This paper presents semi-global sufficient stability conditions of limit cycles for relay feedback systems. Local stability conditions exist. These are based on analyzing the linear part of the Poincare ... [more ▼] This paper presents semi-global sufficient stability conditions of limit cycles for relay feedback systems. Local stability conditions exist. These are based on analyzing the linear part of the Poincare map. We know that when a certain limit cycle satisfies those local conditions, a neighborhood around the limit cycle exists such that any trajectory starting in this neighborhood converges to the limit cycle as time goes to infinity. However, tools to characterize this neighborhood do not exist. In this work, we present conditions, in the form of linear matrix inequalities (LMI), that guarantee the stability of a limit cycle in a reasonably large set around it. These results differ from previous local results as they take into account the high order terms of the Poincare map. [less ▲] Detailed reference viewed: 102 (0 UL)Necessary conditions for robust stability of a class of nonlinear systems Goncalves, Jorge ; in Automatica (1998), 34(6), 705-714 Input-output stability results for feedback systems are developed. Robust stability conditions are presented for nonlinear systems with nonlinear uncertainty defined by some function (with argument equal ... [more ▼] Input-output stability results for feedback systems are developed. Robust stability conditions are presented for nonlinear systems with nonlinear uncertainty defined by some function (with argument equal to the norm of the input) that bounds its output norm. A sufficient small gain theorem for a class of these systems is known. Here, necessary conditions are presented for the vector space (L- infinity ll . ll infinity). These results capture the conservatism of the small gain theorem as it is applied to systems that do not have linear gain. The theory is also developed for the case of L2 signal norms, indicating some difficulties which make this case less natural than L-infinity. [less ▲] Detailed reference viewed: 68 (1 UL)Necessary and sufficient conditions for robust stability of a class of nonlinear systems Goncalves, Jorge ; in Proceedings of the 34th IEEE Conference on Decision and Control (1995) Input-output stability results for feedback systems are developed. Robust stability conditions are presented for nonlinear systems with nonlinear uncertainty defined by some function (with argument equal ... [more ▼] Input-output stability results for feedback systems are developed. Robust stability conditions are presented for nonlinear systems with nonlinear uncertainty defined by some function (with argument equal to the norm of the input) that bounds its output norm. A sufficient small gain theorem for a class of these systems is presented. Then it is also shown that, for the vector spaces (l∞, ||·||∞) and (l2, ||·||2), the sufficient conditions are also necessary with some additional assumptions on the systems. These results capture the conservatism of the small gain theorem as it is applied to systems that do not need to have linear gain. [less ▲] Detailed reference viewed: 116 (7 UL) |
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