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Experimental validation of the stability and performance analysis of Networked Control Systems with delays

The focus of this thesis is on Networked Control Systems (NCSs). An NCS consists of a continuoustime plant that is coupled over a communication network to a discrete-time controller. The advantages of NCSs are that the usage is relatively cheap and that the system diagnosis and maintenance of both the plants and the computing hardware are easier due to the reduced system wiring. The disadvantages of using a communication network in a control-loop are network-induced delays, packet dropouts and multiple packet transmissions. Network-induced delays occur while exchanging data among devices that are connected to the shared communication network and can be either constant or time-varying. Packet dropout is the effect that a data packet does not arrive at its destination. Multiple packet transmissions are needed if the amount of data is larger than the maximum packet size. In combination with packet dropouts, this may result in delivery of only part of the data. This research focusses on the analysis and experimental validation of a discrete-time, linear, timeinvariant NCS model with constant and periodic delays. It is also assumed that packet dropouts and multiple packet transmissions do not occur. The experimental validation is performed on the PATO set-up, which is a second-order system (a single actuated inertia) on which known time-delays can be implemented to represent an NCS with either constant or periodic delays. Based on an exact discretization at the sampling instants, a discrete-time model with a constant delay is derived that represents the PATO set-up in combination with either a state-feedback or an output-feedback controller. To predict the stability of the PATO set-up, an eigenvalue-based stability-analysis is performed. This results in a stability region that gives the range of stabilizing controllers for a given constant time-delay. The dependence of the size of the stability region on the type of controller used, the delay and the sampling-time is also studied. Additionally, the influence of the type of controller used, the different controller-gains, the constant time-delay and the sampling-time on the performance, in terms of the settling-time and the bandwidth, is investigated. The performance is analyzed by studying the eigenvalues, Bode plots of the open-loop frequency-response and simulations. To design a controller for the PATO set-up, several criteria on the stability robustness, settling-time and bandwidth are set. This results in a range of feedback-gains for a given constant time-delay that meet these criteria. To experimentally validate the stability and performance analysis, the PATO set-up is used. In the PATO set-up, we can only measure the position of the inertia, thus a velocity estimator is used to estimate the velocity of the inertia. Therefore, the PATO set-up with an output-feedback controller is considered for the experimental validation. It is shown that the experimental results and the results of the model-based analysis match. This shows that the derived NCS model gives an accurate description of the PATO set-up and that it can be used to predict the stability and performance of the PATO set-up. Besides the validation of the NCS model for constant time-delays, validation of an NCS for known periodic delays is performed. Therefore, the derived discrete-time model with a constant delay is extended to describe the output-feedback controlled PATO set-up with periodic delays with a known sequence. Using an eigenvalue-based stability analysis and simulations, it is shown that a