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229
Structured Semidefinite Programs and Semialgebraic Geometry Methods in Robustness and Optimization
, 2000
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Safety Verification of Hybrid Systems Using Barrier Certificates
 In Hybrid Systems: Computation and Control
, 2004
"... This paper presents a novel methodology for safety verification of hybrid systems. For proving that all trajectories of a hybrid system do not enter an unsafe region, the proposed method uses a function of state termed a barrier certificate. The zero level set of a barrier certificate separates ..."
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Cited by 89 (6 self)
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This paper presents a novel methodology for safety verification of hybrid systems. For proving that all trajectories of a hybrid system do not enter an unsafe region, the proposed method uses a function of state termed a barrier certificate. The zero level set of a barrier certificate separates the unsafe region from all possible trajectories starting from a given set of initial conditions, hence providing an exact proof of system safety. No explicit computation of reachable sets is required in the construction of barrier certificates, which makes nonlinearity, uncertainty, and constraints can be handled directly within this framework.
On the Construction of Lyapunov Functions using the Sum of Squares Decomposition
, 2002
"... A relaxation of Lyapunov's direct method has been proposed recently that allows for an algorithmic construction of Lyapunov functions to prove stability of equilibria in nonlinear systems, but the search is restricted to systems with polynomial vector fields. In this paper, the above technique ..."
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Cited by 85 (16 self)
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A relaxation of Lyapunov's direct method has been proposed recently that allows for an algorithmic construction of Lyapunov functions to prove stability of equilibria in nonlinear systems, but the search is restricted to systems with polynomial vector fields. In this paper, the above technique is extended to include systems with equality, inequality, and integral constraints. This allows certain nonpolynomial nonlinearities in the vector field to be handled exactly and the constructed Lyapunov functions to contain nonpolynomial terms. It also allows robustness analysis to be performed. Some examples are given to illustrate how this is done.
Control of Underactuated Mechanical Systems with two Degrees of Freedom and Symmetry
"... In this paper, we consider a special class of underactuated mechanical systems with two degrees of freedom and symmetry. By symmetry, we mean the inertia matrix of the system is independent of the unactuated degree of freedom. We show that there exists a natural global change of coordinates obtained ..."
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Cited by 65 (9 self)
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In this paper, we consider a special class of underactuated mechanical systems with two degrees of freedom and symmetry. By symmetry, we mean the inertia matrix of the system is independent of the unactuated degree of freedom. We show that there exists a natural global change of coordinates obtained from the Lagrangian of the system that transforms the system into a partially linear cascade nonlinear system that is strict feedback. The nonlinear part of this system is nona#ne in control and this highly complicates control design for the system. We provide conditions under which this nonlinear subsystem can be globally stabilized and give globally stabilizing control laws for it. The strict feedback structure of the system in new coordinates allows us to obtain a globally stabilizing control law for the composite system using standard backstepping. We apply our result to global asymptotic stabilization of the Acrobot.
Distributed Control Design for Systems Interconnected Over an Arbitrary Graph
 IEEE TRANS. AUTOMATIC CONTROL
, 2004
"... We consider the problem of synthesizing a distributed dynamic output feedback controller achieving performance for a system composed of different interconnected subunits, when the topology of the underlying graph is arbitrary. First, using tools inspired by dissipativity theory, we derive sufficie ..."
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Cited by 53 (0 self)
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We consider the problem of synthesizing a distributed dynamic output feedback controller achieving performance for a system composed of different interconnected subunits, when the topology of the underlying graph is arbitrary. First, using tools inspired by dissipativity theory, we derive sufficient conditions in the form of finitedimensional linear matrix inequalities when the interconnections are assumed to be ideal. These inequalities are coupled in a way that reflects the spatial structure of the problem and can be exploited to design distributed synthesis algorithms. We then investigate the case of lossy interconnection links and derive similar results for systems whose interconnection relations can be captured by a class of integral quadratic constraints that includes constant delays.
Analysis of interconnected oscillators by dissipativity theory
 ACCEPTED FOR PUBLICATION IN IEEE TRANSACTIONS ON AUTOMATIC CONTROL
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A framework for worstcase and stochastic safety verification using barrier certificates
 IEEE TRANSACTIONS ON AUTOMATIC CONTROL
, 2007
"... This paper presents a methodology for safety verification of continuous and hybrid systems in the worstcase and stochastic settings. In the worstcase setting, a function of state termed barrier certificate is used to certify that all trajectories of the system starting from a given initial set do ..."
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Cited by 50 (1 self)
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This paper presents a methodology for safety verification of continuous and hybrid systems in the worstcase and stochastic settings. In the worstcase setting, a function of state termed barrier certificate is used to certify that all trajectories of the system starting from a given initial set do not enter an unsafe region. No explicit computation of reachable sets is required in the construction of barrier certificates, which makes it possible to handle nonlinearity, uncertainty, and constraints directly within this framework. In the stochastic setting, our method computes an upper bound on the probability that a trajectory of the system reaches the unsafe set, a bound whose validity is proven by the existence of a barrier certificate. For polynomial systems, barrier certificates can be constructed using convex optimization, and hence the method is computationally tractable. Some examples are provided to illustrate the use of the method.
Control of Asynchronous Dynamical Systems with Rate Constraints on Events
 In Proc. 38th IEEE Conf. Decision Control
, 1999
"... Abstract — In this paper we consider dynamical systems which are driven by “events ” that occur asynchronously. It is assumed that the event rates are fixed, or at least they can be bounded on any time period of length T. Such systems are becoming increasingly important in control due to the very ra ..."
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Cited by 49 (0 self)
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Abstract — In this paper we consider dynamical systems which are driven by “events ” that occur asynchronously. It is assumed that the event rates are fixed, or at least they can be bounded on any time period of length T. Such systems are becoming increasingly important in control due to the very rapid advances in digital systems, communication systems, and data networks. Examples of such systems include, control systems in which signals are transmitted over an asynchronous network; distributed control systems in which each subsystem has its own objective, sensors, resources and level of decision making; parallelized numerical algorithms in which the algorithm is separated into several local algorithms operating concurrently at different processors; and queuing networks. We present a Lyapunovbased theory for asynchronous dynamical systems and show how Lyapunov functions and controllers can be constructed for such systems by solving linear matrix inequality (LMI) and bilinear matrix inequality (BMI) problems. Examples are also presented to demonstrate the effectiveness of the approach.
Robust Pole Placement in LMI Regions
 IEEE Transactions on Automatic Control
, 1999
"... This paper discusses analysis and synthesis techniques for robust pole placement in LMI regions, a class of convex regions of the complex plane that embraces most practically useful stability regions. The focus is on linear systems with static uncertainty on the state matrix. For this class of uncer ..."
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Cited by 46 (0 self)
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This paper discusses analysis and synthesis techniques for robust pole placement in LMI regions, a class of convex regions of the complex plane that embraces most practically useful stability regions. The focus is on linear systems with static uncertainty on the state matrix. For this class of uncertain systems, the notion of quadratic stability and the related robustness analysis tests are generalized to arbitrary LMI regions. The resulting tests for robust pole clustering are all numerically tractable since they involve solving linear matrix inequalities (LMIs), and cover both unstructured and parameter uncertainty. These analysis results are then applied to the synthesis of dynamic outputfeedback controllers that robustly assign the closedloop poles in a prescribed LMI region. With some conservatism, this problem is again tractable via LMI optimization. In addition, robust pole placement can be combined with other control objectives such as H 2 or H1 performance to capture realist...