Passivity based stabilization of non-minimum phase nonlinear systems

summary:A cascade scheme for passivity-based stabilization of a wide class of nonlinear systems is proposed in this paper. Starting from the definitions and basic concepts of passivity-based stabilization via feedback (which are applicable to minimum phase nonlinear systems expressed in their normal forms) a cascade stabilization scheme is proposed for minimum and non-minimum phase nonlinear systems where the constraint of stable zero dynamics imposed by previous stabilization approaches is abandoned. Simulation results of the proposed algorithm are presented to demonstrate its performance

Stability analysis of switched systems

Ph.DDOCTOR OF PHILOSOPH

Output Consensus Control for Heterogeneous Multi-Agent Systems

We study distributed output feedback control of a heterogeneous multi-agent system (MAS), consisting of N different continuous-time linear dynamical systems. For achieving output consensus, a virtual reference model is assumed to generate the desired trajectory for which the MAS is required to track and synchronize. A full information (FI) protocol is assumed for consensus control. This protocol includes information exchange with the feed-forward signals. In this dissertation we study two different kinds of consensus problems. First, we study the consensus control over the topology involving time delays and prove that consensus is independent of delay lengths. Second, we study the consensus under communication constraints. In contrast to the existing work, the reference trajectory is transmitted to only one or a few agents and no local reference models are employed in the feedback controllers thereby eliminating synchronization of the local reference models. Both significantly lower the communication overhead. In addition, our study is focused on the case when the available output measurements contain only relative information from the neighboring agents and reference signal. Conditions are derived for the existence of distributed output feedback control protocols, and solutions are proposed to synthesize the stabilizing and consensus control protocol over a given connected digraph. It is shown that the H-inf loop shaping and LQG/LTR techniques from robust control can be directly applied to design the consensus output feedback control protocol. The results in this dissertation complement the existing ones, and are illustrated by a numerical example. The MAS approach developed in this dissertation is then applied to the development of autonomous aircraft traffic control system. The development of such systems have already started to replace the current clearance-based operations to trajectory based operations. Such systems will help to reduce human errors, increase efficiency, provide safe flight path, and improve the performance of the future flight

Nonlinear control of feedforward systems with bounded signals

Published versio

Data-driven stabilization and safe control of nonlinear systems

The recent successes of machine learning solutions have inspired the research of new control algorithms derived directly from the available data without any intermediate step. Being able to design a stabilizing controller directly from data has the main advantage that, since it does not rely on a model of the system to control, the controller design is not influenced by any modeling error.Most of the time real systems are simplified with linear models to reduce the overall complexity in the controller design discarding all the complex nonlinear behaviors. A linear approximation could be an excessive simplification for complex system where the presence of nonlinear dynamics are important to understand those processes and nonlinearities can not be ignored. However, the analysis and control of a nonlinear model is often challenging. This thesis investigates data-based control methods for continuous and discrete-time nonlinear systems that do not require to model the system. In particular, we have developed a solution to obtain a stabilizing state feedback controller for the case of nonlinear systems. Stabilizing a closed-loop system is critical, but sometimes it is not enough. Safety is another important criteria considered in the design of a controller. We were able to formulate a new data-driven procedure to find a stabilizing controller that can also guarantee that the state of the system never violates the safety constraints.For all the solutions presented, we discussed how to handle real noisy measurements