Electrical and Electronic Engineering - Research Publications
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ItemOn emulation-based observer design for networked control systems(IEEE, 2010)We extend our recent framework developed for the emulation-based observer design for networked control systems (NCS) to larger classes of systems and scheduling protocols. Consider a continuous-time observer that satisfies some input-to-state / input-to-output stability properties with respect to measurement errors, we prove that the observation error converges semiglobally and practically with the maximum allowable transmission interval (MATI) as parameter, when it is implemented via a network governed by a Lyapunov uniformly globally asymptotically stable (UGAS) protocol. We show that our results can be used to build various observers for NCS such as circle criterion observers. The stability analyses rely on trajectory based small gain theorems for parametrized systems.
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ItemA nonlinear estimator for the activity of neuronal populations in the hippocampus(IFAC - International Federation of Automatic Control, 2011-01-01)We present an estimator design to reconstruct the mean membrane potential of individual neuronal populations from a single channel simulated electroencephalographic signal based on a model of the hippocampus. The robustness of the estimator against variations in the synaptic gains of the neuronal populations and disturbances in the input and measurement is studied. Our results are further illustrated in simulations.
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ItemStability Analysis of Discrete-Time Infinite-Horizon Optimal Control With Discounted Cost(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2017-06)We analyze the stability of general nonlinear discrete-Time systems controlled by an optimal sequence of inputs that minimizes an infinite-horizon discounted cost. First, assumptions related to the controllability of the system and its detectability with respect to the stage cost are made. Uniform semiglobal and practical stability of the closed-loop system is then established, where the adjustable parameter is the discount factor. Stronger stability properties are thereupon guaranteed by gradually strengthening the assumptions. Next, we show that the Lyapunov function used to prove stability is continuous under additional conditions, implying that stability has a certain amount of nominal robustness. The presented approach is flexible and we show that robust stability can still be guaranteed when the sequence of inputs applied to the system is no longer optimal but near-optimal. We also analyze stability for cost functions in which the importance of the stage cost increases with time, opposite to discounting. Finally, we exploit stability to derive new relationships between the optimal value functions of the discounted and undiscounted problems, when the latter is well-defined.
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ItemObserver design for networked control systems with FlexRay(PERGAMON-ELSEVIER SCIENCE LTD, 2017-08)We design state observers for nonlinear networked control systems (NCS) implemented over FlexRay. FlexRay is a communication protocol used in the automotive industry, which has the feature to switch between two scheduling rules during its communication cycles. These switches induce technical difficulties when modeling, designing and analyzing observers for such systems compared to standard NCS. We present a solution based on the emulation approach. Given an observer in the absence of communication constraints, we implement it over the network and we provide sufficient conditions on the latter, to preserve the stability property of the observer. In particular, we provide explicit bounds on the maximal allowable transmission intervals, which adapt to the lengths of the segment associated to each scheduling rule. We assume that the plant dynamics and measurements are affected by noise and we guarantee an input-to-state stability property for the corresponding estimation error system. The overall system is modeled as a hybrid system and the analysis relies on the use of a novel hybrid Lyapunov function.
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ItemRobust event-triggered output feedback controllers for nonlinear systems(Elsevier, 2017-01-01)We address the robust stabilization of nonlinear systems subject to exogenous inputs using event-triggered output feedback laws. The plant dynamics is affected by external disturbances, while the output measurement and the control input are corrupted by noises. The communication between the plant and the controller is ensured by a digital channel. The feedback law is constructed in continuous-time, meaning that we ignore the communication network at this step. We then design the sampling rule to preserve stability. Two implementation scenarios are investigated. We first consider the case where the sampling of the plant measurements and of the control input is generated by the same rule, which leads to synchronous transmissions. We then study the scenario where two different laws are used to sample the measurements on the one hand, and the control input on the other hand, thus leading to asynchronous transmissions. In both cases, the transmission conditions consist in waiting a fixed amount of time after each sampling instant and then in checking a state-dependent criterion: when the latter is violated, a transmission occurs. In that way, Zeno phenomenon is a fortiori excluded. The proposed hybrid controllers are shown to ensure either an input-to-state stability property or an Lp stability property, depending on the assumptions. The results are applied to linear time-invariant systems as a particular case, for which the assumptions are formulated as linear matrix inequalities. The proposed strategy encompasses time-driven (and so periodic) sampling as a particular case, for which the results are new. The effectiveness of the approach is illustrated on simulations for a physical system.
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ItemEmulation-based stabilisation of networked control systems over WirelessHART(IEEE Press, 2017)We study the emulation-based stabilisation of nonlinear networked control systems (NCSs) implemented over WirelessHART (WH). WH is a communication protocol widely used in process instrumentation. It is characterised by its multi-hop structure, slotted communication cycles, and simultaneous transmission over different frequencies. To capture most functionalities of WH, faithful models are needed. We propose a hybrid control-oriented model of WH-NCSs that includes the key features of the network. We then follow an emulation approach to stabilise the NCS. We show that, under reasonable assumptions on the scheduling protocol, stability is preserved when the controller is implemented over the network with sufficiently frequent data transmission. We then explain how to schedule transmissions over the hops to satisfy those assumptions.
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ItemA Framework for the Observer Design for Networked Control Systems(IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC, 2012-05)
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