Research On The Positive Effects Of Network-Induced Delays On Stability And Performance Of Several Classes Of Oscillator Systems

The developing and integrating of communication network,computer technolo-gy and automatic control spark the emerging of networked control systems where the system components are connected via wired or wireless communication.A number of applications have been widely promoted,for example,telemedicine,smart home,intel-ligent transportation,military systems and other fields.The introducing of network in the control loop will bring new challenges to the analysis and design of systems.Network-induced delays in feedback loops have destabilizing effects on the per-formance of systems from the general point of view.There has been numerous research on how to eliminate,compensate or suppress the negative effects of time delay.How-ever,there indeed exist some classes of oscillator systems that are not stable without input delay,but can be stabilized by a controller with appropriate delay.Up to now,the research of the positive effects of time delay on the stability of systems is far from suf-ficient and limited in constant delay by using methods in frequency domain.Network-induced delays are usually time-varying,on one hand,it should be verified wether the time-varying delay can play positive effects on the stability of oscillator systems;on the other hand,new methods need to be searched for the fact that most of the existing results are no longer effective for the case of time-varying delay.This thesis is concerned with the positive effects of network-induced delays on the stability and performance of several typical oscillator systems from a novel point of view,the main contents of this thesis are outlined as follows:·The positive effects of network-induced delays on the H? synchronization of coupled negative damping oscillators in a master-slave framework is investigat-ed,in which the oscillators cannot be stabilized by a nondelayed position-based controller,but can be stabilized by a position-based controller with delays re-stricted by nonzero lower bounds and upper bounds.First,a configuration of networked master-slave oscillators with a remote controller is constructed and a packet scheduling algorithm is proposed.The closed-loop system is modeled as a system with interval time-varying delays in determinate sampling and stochas-tic sampling.Then some criteria for H? performance and controller design that are dependent on the delay bounds and sampling periods are derived by using a complete-type Lyapunov-Krasovskii functional.Finally,the effectiveness of the proposed method is verified by a simulation example.In addition,it is shown that there is a tradeoff between the network-induced delays and the sampling periods to help the network-induced delay benefit the synchronization behavior.The position-based synchronization of networked harmonic oscillators is investi-gated.Note the synchronization is achieved by velocity information and cannot be achieved via current-position-based protocols.First,the harmonic oscillators are connected via a shared digital communication network.System measurements from oscillator nodes are sampled in an asynchronous way;and network-induced delays are assumed to be time varying and bounded,and they do not need to be synchronous with those from the other communication channels.The controller computes control signal with its own period.Then,the synchronization error sys-tem is modeled as linear system with multiple interval time-varying delays.By employing the complete-type Lyapunov-Krasovskii functional method,some suf-ficient conditions are derived to design suitable control protocols.Finally,a multi-robot platform is given to demonstrate the effectiveness of the proposed method.·The sampled-position states based consensus of networked multi-agent system-s with second-order dynamics is concerned with,where agents are connected through communication channels subject to time-varying communication delays.Note that consensus in such systems cannot be reached using only the curren-t sampled-position states.This paper investigates the positive effects of time-varying communication delays on the consensus.For two cases,where a directed graph has a fixed or switching topology,several sufficient conditions on consensus are derived using a complete-type Lyapunov-Krasovskii functional method.Based on the obtained conditions,suitable control protocols can be devised through an iterative algorithm.Finally,simulation show that consensus can be achieved us-ing sampled-position states if the time-varying communication delays are within a certain time interval with its lower bound strictly greater than zero.The networked active vibration control for a multi-degree-of-freedom structural system subject to modeling uncertainties,stochastic sensor faults,and earthquake excitations.By adopting a positive velocity feedback controller and introducing a communication network that produces proper network-induced delays and pack-et dropouts in the feedback control loop,the closed-loop system is modeled by an uncertain stochastic system with a non-small internal time-varying input de-lay.Then a delay-dependent criterion is derived by employing a complete-type Lyapunov-Krasovskii functional such that the system with the proper non-zero in-put delay is stochastically stable with L2-gain performance,but unstable without delay.An iterative algorithm is presented to design the corresponding controller.A three-story building model subject to El Centro 1940 earthquake is provided to show the effectiveness of the proposed approach.Furthermore,it is also shown through this example that the designed controller can allow a larger input delay for the prescribed performance,and the method is applicable to design a negative velocity feedback controller with small controller force and larger input delay.