- Electrical and Electronic Engineering - Research Publications
Electrical and Electronic Engineering - Research Publications
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ItemOptimization Methods on Riemannian Manifolds via Extremum Seeking AlgorithmsTARINGOO, F ; Dower, PM ; Nesic, D ; Tan, Y (Society for Industrial and Applied Mathematics, 2018)This paper formulates the problem of extremum seeking for optimization of cost function defined on Riemannian manifolds. We extend the conventional extremum seeking algorithms for optimization problems in Euclidean spaces to optimization of cost functions defined on smooth Riemannian manifolds. This problem falls within the category of online optimization methods. We introduce the notion of geodesic dithers, which is a perturbation of the optimizing trajectory in the tangent bundle of the ambient state manifolds, and obtain the extremum seeking closed loop as a perturbation of the averaged gradient system. The main results are obtained by applying closeness of solutions and averaging theory on Riemannian manifolds. The main results are further extended for optimization on Lie groups. Numerical examples on the Stiefel manifold V3;2 and the Lie group SEp3q are presented at the end of the paper.
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ItemA hybrid model of networked control systems implemented on WirelessHART networks under source routing configurationMaass, AI ; Nesic, D ; Dower, PM (IEEE, 2016)A Network control system (NCS) is a control system in which communication between subsystems takes place over a digital network. Numerous results exist in the literature on modelling, analysis and design of NCSs in the presence of specific communication constraints such as packet dropouts, delays, data rates, quantization, etc. However, when analysing NCSs implemented on real physical networks, the existing results are based on restrictive assumptions. We consider NCSs over WirelessHART, the first international standard for industrial process control. With the goal of closing the gap between theory and practice, we propose for the first time a hybrid control-oriented model of WirelessHART NCSs under source routing configuration. Moreover, asymptotic and exponential stability results are presented under reasonable conditions.
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ItemA max-plus primal space fundamental solution for a class of differential Riccati equationsDower, PM ; Zhang, H (SPRINGER LONDON LTD, 2017-09)
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ItemNo Preview AvailableConversion of Certain Stochastic Control Problems into Deterministic Control ProblemsMcEneaney, WM ; Dower, PM (ELSEVIER, 2020)
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ItemNo Preview AvailableStrong Solution Existence for a Class of Degenerate Stochastic Differential EquationsMcEneaney, WM ; Kaise, H ; Dower, PM ; Zhao, R (ELSEVIER, 2020)
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ItemNo Preview AvailableNewton's method: sufficient conditions for practical and input-to-state stabilityColabufo, GG ; Dower, PM ; Shames, I (ELSEVIER, 2020)
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ItemReaching Agreement in Quantum Hybrid NetworksShi, G ; Li, B ; Miao, Z ; Dower, PM ; James, MR (Nature Publishing Group, 2017-07-20)We consider a basic quantum hybrid network model consisting of a number of nodes each holding a qubit, for which the aim is to drive the network to a consensus in the sense that all qubits reach a common state. Projective measurements are applied serving as control means, and the measurement results are exchanged among the nodes via classical communication channels. In this way the quantum-opeartion/classical-communication nature of hybrid quantum networks is captured, although coherent states and joint operations are not taken into consideration in order to facilitate a clear and explicit analysis. We show how to carry out centralized optimal path planning for this network with all-to-all classical communications, in which case the problem becomes a stochastic optimal control problem with a continuous action space. To overcome the computation and communication obstacles facing the centralized solutions, we also develop a distributed Pairwise Qubit Projection (PQP) algorithm, where pairs of nodes meet at a given time and respectively perform measurements at their geometric average. We show that the qubit states are driven to a consensus almost surely along the proposed PQP algorithm, and that the expected qubit density operators converge to the average of the network’s initial values.
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ItemObserver design for networked control systems implemented over WirelessHARTMaass, AI ; Nesic, D ; Postoyan, R ; Dower, PM (IEEE, 2018)We study the design of state observers for nonlinear networked control systems (NCSs) that are implemented over WirelessHART (WH). WH is a wireless communication protocol for process automation applications. It is characterised by its multi-hop structure, slotted communication cycles, and simultaneous transmission over different frequencies. We present a solution based on the emulation approach. That is, given an observer designed with a specific stability property in the absence of communication constraints, we implement it over a WH 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 maximum allowable transmission interval. We assume that the plant dynamics and measurements are affected by noise and we guarantee an inputto- state stability property for the corresponding estimation error system.
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ItemEmulation-based stabilisation of networked control systems over WirelessHARTMaass, AI ; Nesic, D ; Postoyan, R ; Dower, PM ; S Varma, V (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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ItemObserver design for non-linear networked control systems with persistently exciting protocolsMaass, AI ; Nesic, D ; Postoyan, R ; Dower, PM (IEEE, 2020-07)We study the design of state observers for nonlinear networked control systems (NCSs) affected by disturbances and measurement noise, via an emulation-like approach. That is, given an observer designed with a specific stability property in the absence of communication constraints, we implement it over a network and we provide sufficient conditions on the latter to preserve the stability property of the observer. In particular, we provide a bound on the maximum allowable transmission interval (MATI) that guarantees an input-to-state stability (ISS) property for the corresponding estimation error system. The stability analysis is trajectory-based, utilises small-gain arguments, and exploits a persistently exciting (PE) property of the scheduling protocols. This property is key in our analysis and allows us to obtain significantly larger MATI bounds in comparison to the ones found in the literature. Our results hold for a general class of NCSs, however, we show that these results are also applicable to NCSs implemented over a specific physical network called WirelessHART (WH). The latter is mainly characterised by its multi-hop structure, slotted communication cycles, and the possibility to simultaneously transmit over different frequencies. We show that our results can be further improved by taking into account the intrinsic structure of the WH-NCS model. That is, we explicitly exploit the model structure in our analysis to obtain an even tighter MATI bound that guarantees the same ISS property for the estimation error system. Finally, to illustrate our results, we present analysis and numerical simulations for a class of Lipschitz non-linear systems and high-gain observers.