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

Decentralized event-triggered estimation of nonlinear systems

We investigate the scenario where a perturbed nonlinear system transmits its output measurements to a remote observer via a packet-based communication network. The sensors are grouped into N nodes and each of these nodes decides when its measured data is transmitted over the network independently. The objective is to design both the observer and the local transmission policies in order to obtain accurate state estimates, while only sporadically using the communication network. In particular, given a general nonlinear observer designed in continuous-time satisfying an input-to-state stability property, we explain how to systematically design a dynamic event-triggering rule for each sensor node that avoids the use of a copy of the observer, thereby keeping local calculation simple. We prove the practical convergence property of the estimation error to the origin and we show that there exists a uniform strictly positive minimum inter-event time for each local triggering rule under mild conditions on the plant. The efficiency of the proposed techniques is illustrated on a numerical case study of a flexible robotic arm

Interdisciplinary design methodology for systems of mechatronic systems focus on highly dynamic environmental applications

This paper discusses a series of research challenges in the design of systems of mechatronic systems. A focus is given to environmental mechatronic applications within the chain “Renewable energy production - Smart grids - Electric vehicles”. For the considered mechatronic systems, the main design targets are formulated, the relations to state and parameter estimation, disturbance observation and rejection as well as control algorithms are highlighted. Finally, the study introduces an interdisciplinary design approach based on the intersectoral transfer of knowledge and collaborative experimental activities

Compensation of distributed delays in integrated communication and control systems

The concept, analysis, implementation, and verification of a method for compensating delays that are distributed between the sensors, controller, and actuators within a control loop are discussed. With the objective of mitigating the detrimental effects of these network induced delays, a predictor-controller algorithm was formulated and analyzed. Robustness of the delay compensation algorithm was investigated relative to parametric uncertainties in plant modeling. The delay compensator was experimentally verified on an IEEE 802.4 network testbed for velocity control of a DC servomotor

Event-Based Control and Estimation with Stochastic Disturbances

This thesis deals with event-based control and estimation strategies, motivated by certain bottlenecks in the control loop. Two kinds of implementation constraints are considered: closing one or several control loops over a data network, and sensors that report measurements only as intervals (e.g. with quantization). The proposed strategies depend critically on _events_, when a data packet is sent or when a change in the measurement signal is received. The value of events is that they communicate new information about stochastic process disturbances. A data network in the control loop imposes constraints on the event timing, modelled as a minimum time between packets. A thresholdbased control strategy is suggested and shown to be optimal for firstorder systems with impulse control. Different ways to find the optimal threshold are investigated for single and multiple control loops sharing one network. The major gain compared to linear time invariant (LTI) control is with a single loop a greatly reduced communication rate, which with multiple loops can be traded for a similarly reduced regulation error. With the bottleneck that sensors report only intervals, both the theoretical and practical control problems become more complex. We focus on the estimation problem, where the optimal solution is known but untractable. Two simplifications are explored to find a realistic state estimator: reformulation to a mixed stochastic/worst case scenario and joint maximum a posteriori estimation. The latter approach is simplified and evaluated experimentally on a moving cart with quantized position measurements controlled by a low-end microcontroller. The examples considered demonstrate that event-based control considerably outperforms LTI control, when the bottleneck addressed is a genuine performance constraint on the latter

Active truncation of slender marine structures: Influence of thecontrol system on Fidelity

Performing hydrodynamic model testing of ultra-deep water floating systems at a reasonable scale ischallenging, due to the limited space available in existing laboratories and to the large spatial extent ofthe slender marine structures that connect the floater to the seabed. In this paper, we consider a methodbased on real-time hybrid model testing, namely the active truncation of the slender marine structures:while their upper part is modelled physically in an ocean basin, their lower part is simulated by anadequate numerical model. The control system connecting the two substructures inevitably introducesartefacts, such as noise, biases and time delays, whose probabilistic description is assumed to be known.We investigate specifically how these artefacts influence the fidelity of the active truncation setup, thatis its capability to reproduce correctly the dynamic behaviour of the system under study. We propose asystematic numerical method to rank the artefacts according to their influence on the fidelity of the test.The method is demonstrated on the active truncation of a taut polyester mooring line.acceptedVersio

A delay-dependent dual-rate PID controller over an ethernet network

n this paper, a methodology to design controllers able to cope with different load conditions on an Ethernet network is introduced. Load conditions induce time-varying delays between measurements and control. To face these variations an interpolated, delay-dependent gain scheduling law is used. The lack of synchronization is solved by adopting an event-based control approach. The dual-rate control action computation is carried out at a remote controller, whereas control actions and measurements are taken out locally at the controlled process site. Stability is proved in terms of probabilistic linear matrix inequalities. TrueTime simulations in an Ethernet case show the benefit of the proposal, which is later validated on an experimental test-bed Ethernet environment.Manuscript received June 07, 2010; revised September 05, 2010; accepted September 15, 2010. Date of publication October 18, 2010; date of current version February 04, 2011. The authors A. Cuenca, J. Salt, and R. Piza are grateful to Grant PAID06-08 by the Universidad Politecnica de Valencia, Grant dpi2009-14744-c03-03 from the Spanish Ministry of Education, and Grant gv/2010/018 by Generalitat Valenciana. In addition, A. Cuenca is grateful to Grant dpi2008-06737-c02-01 by the Spanish Ministry of Education, and A. Sala is grateful to the financial support of the Spanish Ministry of Education Research Grant dpi2008-06731-c02-01, and Generalitat Valenciana Grant prometeo/2008/088. Paper no. TII-10-06-0127.Cuenca Lacruz, ÁM.; Salt Llobregat, JJ.; Sala Piqueras, A.; Pizá Fernández, R. (2011). A delay-dependent dual-rate PID controller over an ethernet network. IEEE Transactions on Industrial Informatics. 7(1):18-29. doi:10.1109/TII.2010.2085007S18297

Networked Digital Predictive Control for Modular DC-DC Converters

The concept of power electronics building blocks (PEBB) has driven advancements in highly modularized converter systems with many identical subsystems. PEBBs are distributed subsets of converter systems and thus require communication with a control system for their coordination. For this type of system, the communication latency with hard deterministic deadlines is the driving attribute of communication system requirements. However, inherent communication requirements for PEBB-based converter systems also provide opportunities for coordination of energy flow. Leveraging developments in Gigabit serial communication channels, a control and communication platform architecture for distributed control schemes based on the 2D-Torus communication network topology was developed for building-block-based power converter systems. The control platform architecture allows integrated control actions between PEBB control nodes to support energy coordinating operations. In addition to the platform architecture, a control method was developed that takes advantage of its communication speed. Predictive control methods utilize an internal model of the system to provide very fast regulation, which is suitable in this work since each PEBB is well defined. A distributed control architecture utilizing a predictive control scheme was developed to maintain fast regulation of voltage and current in a distributed manner within a time frame that can take advantage of the low latency provided by the 2-D Torus communication network. Distributed control requires state information from other control nodes for overall coordination. A strategy to minimize data communication was developed to scale the distributed predictive control across the most extensive PEBB-based system. Direct communication of low-level sensor measurements and control data between PEBBs in the network would increase data communication, resulting in data bottlenecks as system sizes are scaled up. Thus, a partitioning method was developed to reduce data transmission as much as possible by developing a real-time model-informed framework requiring only partial or limited knowledge of the system parameters. The proposed design relies on a multi-loop predictive controller that uses an observer\u27s estimated current and voltage states as the feedback values. The observer is based on a real-time model distributed utilizing a co-simulation method to partition the model such that each PEBB has a minimum sub-set consisting of that PEBB’s circuit elements. The PEBB control platform architecture and distributed predictive control framework developed in this dissertation allows distributed PEBB control nodes to rapidly coordinate and respond to multiple energy flow requirements with data exchanges as the core