Lp stability of networked control systems implemented on WirelessHART

International audienceThis paper provides results on input-output Lp stability of networked control systems (NCSs) implemented over WirelessHART (WH). WH is a communication protocol widely used in process instrumentation. It is mainly characterised by its multi-hop structure, slotted communication cycles, and the possibility to simultaneously transmit over different frequencies. We propose a non-linear hybrid model of WH-NCSs that is able to capture these network functionalities, and that it is more general than existing models in the literature. Particularly, the multi-hop nature of the network is translated into an interesting mathematical structure in our model. We then follow the emulation approach to stabilise the NCS. We first assume that we know a stabilising controller for the plant without the network. We subsequently 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. Specifically, we provide bounds on the maximum allowable transmission interval (MATI) under which all protocols that satisfy the property of being persistently exciting (PE) lead to Lp stable WH-NCSs. These bounds exploit the mathematical structure of our WH-NCS model, improving the existing bounds in the literature. Additionally, we explain how to schedule transmissions over the hops to satisfy the PE property. In particular, we show how simultaneous transmissions over different frequency channels can be exploited to further enlarge the MATI bound

Observer design for non-linear networked control systems with persistently exciting protocols

International audienceWe study the design of state observers for non-linear 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

Transmit power policies for stochastic stabilisation of multi-link wireless networked control systems

Transmit power control is one of the most important issues in wireless networks, where nodes typically operate on limited battery power. Reducing communicating power consumption is essential for both economic and ecologic reasons. In fact, transmitting at unnecessarily high power not only reduces node lifetime, but also introduces excessive interference and electromagnetic pollution. Existing work in the wireless community mostly focus on designing transmit power policies by taking into account communication aspects like quality of service or network capacity. Wireless networked control systems (WNCSs), on the other hand, have different and specific needs such as stability, which require transmit power policies adapted to the control context. Transmit power design in the control community has recently attracted much attention, and available works mostly consider linear systems or specific classes of non-linear systems with a single-link view of the system. In this paper, we propose a framework for the design of stabilising transmit power levels that applies to much larger classes of non-linear plants, controllers, and multi-link setting. By exploiting the fact that channel success probabilities are related to transmit power in a non-linear fashion, we first derive closed-loop stability conditions that relate channel probabilities with transmission rate. Next, we combine these results together with well-known and realistic interference models to provide a design methodology for stabilising transmit power in non-linear and multi-link WNCSs.Comment: 18 pages, 3 figure

Desenvolvimento de aplicações para monitorização de consumos de energia em instalações elétricas

As redes de energia inteligentes smart grids têm por objetivo melhorar a eficiência, fiabilidade e sustentabilidade da produção e consumo de energia elétrica, através de informação recolhida sobre a atividade dos produtores e consumidores. A sua implementação irá tornar possível a integração de fontes de energia renováveis, a redução das perdas de transporte e distribuição de energia e a implementação de tarifas dinâmicas de energia. Aliado a este conceito encontra-se a tecnologia de smart metering que permite a recolha de informação em tempo real, relativa ao consumo de energia o que vai influenciar os consumidores a mudarem os seus hábitos, tornando-os mais conscientes em relação ao seu perfil de consumo atual. A recolha dos dados referentes ao consumo energético dos consumidores, será efetuada por smart meters, que têm por função medir os consumos de energia elétrica de uma instalação, enviar as leituras efetuadas para uma unidade de armazenamento e processamento de dados, permitindo ao utilizador visualizar a informação recolhida, as estatísticas mais relevantes e os eventos detetados, em plataformas desenvolvidas para o efeito. O objetivo deste projeto compreendeu o desenvolvimento de um dispositivo eletrónico com a capacidade de adquirir, registar e armazenar valores relativos à energia consumida, a partir de um contador de energia digital. O dispositivo de aquisição foi desenvolvido utilizando um microcontrolador de baixo custo para estabelecer a comunicação com o contador de energia. Os dados adquiridos são guardados numa base de dados e numa memória volátil as quais servem de base às plataformas de ICT desenvolvidas: uma em ambiente web e uma aplicação Android, as quais permitem ao consumidor consultar os dados recolhidos referentes ao seu consumo de energia

Industrial Wireless Sensor Networks

Wireless sensor networks are penetrating our daily lives, and they are starting to be deployed even in an industrial environment. The research on such industrial wireless sensor networks (IWSNs) considers more stringent requirements of robustness, reliability, and timeliness in each network layer. This Special Issue presents the recent research result on industrial wireless sensor networks. Each paper in this Special Issue has unique contributions in the advancements of industrial wireless sensor network research and we expect each paper to promote the relevant research and the deployment of IWSNs

Emulation-based stabilisation of networked control systems over WirelessHART

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