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Item type:Publication, Access status: without files , A decentralized asymmetric weighting approach for improved convergence of multi-agent systems with undirected interactionThis work considers the convergence rate of multi-agent systems with discrete-time single-integrator dynamics and undirected interaction topologies. In recent work it has been proven that in case of lattice interaction topologies the convergence rate can be bounded away from zero, independent of the network size, using asymmetric weightings that give the interaction graph a preferred communication direction. Approximation methods for more general graphs, based on relative angles between agents, are presented, which suggest that the convergence rate is bounded away from zero as well. This work proposes alternative approximation methods, that improve the convergence rate compared to previous approximation methods. Furthermore it is shown that the improvement of the approximation methods degrade in comparison to other weighting approaches, the more the considered topology differs from a lattice graph. Therefore an iterative algorithm is proposed, that extends the idea of a preferred communication direction to general graphs, which are not similar to lattices or where the relative angles are not known.Publicationtype: Conference Paper28 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Conservatism of analysis and controller synthesis of decomposable systemsRecently, distributed controller synthesis approaches for decomposable systems, a subclass of distributed systems with identical subsystems, where the interconnection can be described as LFT interconnection, have been proposed. In order to make these approaches tractable for systems containing a very large number of subsystems, constraints on the Lyapunov matrix and the multiplier matrices are introduced that render the complexity of analysis and controller synthesis smaller and in best case independent on the number of subsystems. Those assumptions have to be paid for with conservatism, which is investigated in this work. It is proven that the conservatism is not reduced if either only the Lyapunov or only the multiplier matrices are constrained, when compared with having constraints on both simultaneously.Publicationtype: Conference Paper20 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Nonlinear model predictive missile control with a stabilising terminal constraint(Elsevier, 2014); ; ; In this paper, an MPC scheme for a missile pitch axis autopilot is proposed. The scheme uses a nonlinear prediction model to give it an ability to push the controlled missile very close to its operating limits, and is stabilised through the use of an ellipsoidal terminal constraint. Tracking performance and computational load of the scheme are compared to that with a linear prediction model and other types of terminal constraint. Specifically, the choice of ellipsoidal, polytopic, or no terminal constraint is discussed. The terminally constrained nonlinear MPC scheme achieves comparable solution times to that with a linear prediction model, whilst being more aggressive to give a superior tracking performance.Publicationtype: Conference Paper16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Cooperative and consensus-based approaches to formation control of autonomous vehicles(2014); This paper presents a distributed robust control scheme for the formation flight of autonomous aerial vehicles, which is obtained from combining two existing approaches: cooperative and consensus-based formation control. These schemes are examined using a mixed H∞/ℓ1 design approach to provide robustness against arbitrary changes of the communication topology as well as any communication delays. The presented architectures mainly differ in the coupling of the agents, which influences performance and formation maintenance. Furthermore, these approaches are analyzed by means of a simulation study on a group of quad-rotor helicopters. The results indicate significant benefits from combining these existing schemes.Publicationtype: Conference Paper27 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Modeling of the master laser oscillator phase noise for the European XFEL using fractional order systemsThe European X-ray Free-Electron Laser will generate high energy light pulses in the femto-second range. A clock signal, which synchronizes all components, is distributed via laser pulses. The accuracy of these laser pulses is crucial to achieve precise measurements which are needed to control the Free-Electron Laser. In order to reach the maximum performance, advanced model-based control approaches are used to compensate external influences. This paper shows the modeling of the Master Laser Oscillator by fractional order systems, which improve known approaches to system modeling by providing a higher accuracy.Publicationtype: Conference Paper22 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Self-scheduled control of a gyroscopeA classical mixed sensitivity minimization approach and a model matching formulation are compared with the goal to design a linear parameter-varying augmented state feedback control law for a laboratory-scale control moment gyroscope. Dynamic weighting filters are used to impose integral action and roll-off on the controller. Consequently, measurement noise is effectively suppressed and steady state accuracy is guaranteed even in the presence of input disturbances. Both designs are validated in real-time experiments and compared to a previous design that uses static weights. With the new designs, control effort is reduced while transient performance is maintained and tracking accuracy, as well as disturbance attenuation, is improved.Publicationtype: Conference Paper26 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , LPV formation control of non-holonomic multi-agent systemsThis paper studies a formation control problem for nonlinear multi-agent systems; specifically non-holonomic vehicles represented as linear parameter-varying (LPV) models are of interest here. The objective of this study is twofold. First, we demonstrate the applicability of a novel approach to distributed control for LPV decomposable systems (Hoffmann et al, 2013). Second, we investigate different LPV representations of non-holonomic vehicles. We consider a group of agents in a leader-follower configuration which communicate through a directed time-varying but diagonalizable interconnection topology, where follower vehicles must achieve a desired formation and track the path determined by the leader agent. In addition, the leader vehicle is equipped with an LPV flatness-based controller to track a reference trajectory. The problem is formulated in terms of linear fractional transformations (LFT) for LPV systems with the objective of minimizing the closed-loop induced C2 gain. Simulation results with a formation of non-holonomic discs illustrate the proposed approach.Publicationtype: Conference Paper32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Complexity of implementation and synthesis in linear parameter-varying control(2014); In this paper an analysis of the complexity involved in the implementation and synthesis of linear parameter-varying (LPV) controllers is presented. Its purpose is to provide guidance in the selection of a synthesis approach for practical LPV control problems and reveal directions for further research with respect to complexity issues in LPV control. Standard methods are classified into polytopic, linear fractional transformation and gridding-based techniques with an emphasis on output-feedback synthesis. Carried out as a convex optimization problem via finitely many linear matrix inequalities (LMIs) for both parameter-independent and parameter-dependent Lyapunov functions (PiDLF/PDLF), the complexity of LPV controller existence conditions is assessed in terms of the number of decision variables and total size of the LMI. The implementation complexity is assessed in terms of the number of arithmetic operations required to compute the parameter-varying state space matrices of the controller, as well as the memory requirements to store associated variables. The results are applied to the LPV controller synthesis for a three-degrees-of-freedom robotic manipulator and the charge control of a spark-ignited engine, for which multiple models, as well as associated synthesis results have been reported in the literature.Publicationtype: Conference Paper36 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Linear parameter-varying control of complex mechanical systems(2014); In standard linear fractional representation (LFR)-based linear parameter-varying (LPV) modeling the size of the (diagonal) scheduling block depends on the number of scheduling parameters and their repetitions, which in turn influences both the complexity of synthesis conditions and the computational load during online implementation of LPV controllers. A modeling framework motivated by, but not limited to, mechanical systems is proposed, where the size of the scheduling block depends on the system's physical degrees-of-freedom. The scheduling block then turns out block-diagonal and can be parameterized in an affine or rational manner. This parameterization yields less complex LFRs when considering the example of a three degrees-of-freedom robotic manipulator, for which then full-block multipliers are tractable and also necessary in synthesis. Synthesis and both simulation and experimental implementation results indicate that the novel rational LPV controller provides improved performance at both reduced implementation and synthesis complexity as compared to an affine LPV controller.Publicationtype: Conference Paper32 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , On the use of second-order modifiers for real-time optimizationWe consider the real-time optimization of static plants and propose a generalized version of the modifier-adaptation strategy that relies on second-order adaptation of the cost and constraint functions. We show that second-order adaptation allows checking whether a (local) plant optimum is reached upon convergence. A sufficient convergence condition that is applicable to first- and second-order modifier-adaptation schemes is proposed. We also discuss how second-order updates can lead to SQP-like model-free RTO schemes. The approach is illustrated via the simulated example of a continuous reactor.Publicationtype: Conference Paper6