Distributed Consensus Of Multiple Euler-Lagrange Systems Based On Sampled-data Information Exchanges

In recent years, with the rapid development of computer technologies and communication networks, the researches on multi-agent systems have attracted tremendous attention, which have grown from academic studies into practical systems in the real world,such as coordination of distributed sensor networks, attitude alignment of spacecrafts,formation control of multiple unmanned aerial vehicles and autonomous underwater vehicles. As one of the important and fundamental issues of multi-agent systems, the consensus problem has been an active area of research. Generally speaking, the consensus objective is to achieve certain kind of agreement of group interest based on local information exchanges among the agents.In particular, since the Euler-Lagrange equation can describe many types of physical systems with complex nonlinearities and strong couplings, the consensus problems of multiple Euler-Lagrange systems have drawn increasing research interest and achieved some initial results. However, it is worth mentioning that most of the existing results on multiple Euler-Lagrange systems heavily rely on the assumption of continuous-time information exchanges. Unfortunately, fundamental di?culties still remain in establishing reliable continuous-time communication networks, especially for long-distance or wireless communications. Moreover, the energy consumption issues should be considered since the energy supplies are always limited for multi-agent systems. From the energy perspective, continuous-time information exchanges may be quite energy-consuming as the communication channels are always occupied continuously. Therefore, a more practical and energy-e?cient consensus protocol is of both theoretical and practical significance.With this background, a sampled-data information exchange strategy is proposed to solve the consensus problem of multiple Euler-Lagrange systems. Based on this strategy,the issues of stochastic sampling periods, time-varying transmission delays and probabilistic time-varying transmission delays are further studied respectively and the main researches of this dissertation can be summarized as follows.Based on the sampled-and-hold mechanism for sampled-data information exchanges,the consensus problem of multiple Euler-Lagrange systems is investigated under directed communication topology, which is an important theoretical foundation for subsequent analysis. Since discrete-time information exchanges are employed instead of continuoustime communications, the proposed scheme is more reliable and practical for real world networks. Distributed consensus protocols are designed to deal with the external bounded disturbances and parameter uncertainties. Su?cient conditions are further established to guarantee the consensus. Moreover, the maximum allowable sampling period is given by solving an optimization problem. Two illustrative application examples of distributed formation control of 6-DOF autonomous underwater vehicles and adaptive attitude synchronization for spacecraft formation flying under directed topology are provided to demonstrate the e?ectiveness and applicability of the proposed method. It is worth mentioning that the simulation results show that the proposed sampled-data strategy can e?ectively reduce the communication energy consumption for the consensus problem.Based on the above obtained results, the sampled-data information exchange strategy with stochastic sampling period is further studied by considering the time-varying sampling periods in real world applications. By introducing the stochastic variable describing the sampling period, the distributed consensus protocol is designed under directed communication topology. Su?cient conditions are derived to ensure that the consensus of the multiple Euler-Lagrange systems can be achieved. A synchronization example for manipulators is illustrated to verify the theoretical results. The simulation results have verified the e?ectiveness of the designed protocol. Moreover, the comparisons of communication energy consumption and time consumption are further provided between the proposed sampled-data and continuous-time information exchanges for the consensus problem.Since time delays may degrade the consensus performance or even destroy the consensus properties, the time-varying transmission delays are considered in the consensus problem of multiple Euler-Lagrange systems. The distributed sampled-data consensus protocol with time-varying transmission delays is developed under directed topology and delay-dependent su?cient conditions are established to guarantee the consensus of the multiple Euler-Lagrange systems. It is worth mentioning that the proposed scheme imposes no constrains on the derivatives of time-varying delays, which has a wide practical background. Based on the derived results, the designed consensus protocol is extended to deal with the switching communication topologies. An illustrative example is given to demonstrate the usefulness and expansibility of the proposed scheme.The probabilistic occurrence of time-varying delays in the information exchanges is discussed and a more realistic sampled-data communication strategy is proposed. In particular, the probabilistic e?ects of the time-varying delays are described by a stochastic variable and the sampling period is assumed to be time-varying. Based on the established model, distributed controllers are designed for the multiple Euler-Lagrange systems to achieve the consensus under directed topology and an optimization procedure is given to calculate the maximum allowable upper bound of time-varying delays. Finally, the synchronization example for manipulators is presented to show the applicability of the designed consensus protocol and the advantages on communication energy consumption.