As is well known, Smart Grid is a complex nonlinear system whose dynamical behavior has many complicated forms such as low frequency oscillation, subsynchronous oscillation and even chaos. Thus this ...paper focuses on the chaotic phenomenon of the widely concerned Smart Grid and presents its stabilization condition via establishing generalized fuzzy hyperbolic model. Firstly, the concept of Smart Grid and its characteristic is introduced. The fourth-order model of a typical Smart Grid is put forward in which the wind turbine generator is considered as the distributed generator. According to numerical method, the Lyapunov exponents of the system are calculated. Chaotic phenomenon, which is harmful in power grid is discovered when the system parameters are in a special state. This moment, there is one positive Lyapunov exponent and the sum of all Lyapunov exponents is negative which verifies Smart Grid is in chaotic state. Secondly, because of difficulty in controlling the strong nonlinear chaotic system and universal approximation of generalized fuzzy hyperbolic model, the chaotic Smart Grid system can be approximated by generalized fuzzy hyperbolic model in any precision. Hence, the generalized fuzzy hyperbolic model is established to represent the complex nonlinear system. Controller of the generalized fuzzy hyperbolic model can be designed according to intelligent control theory. Then the complex problem of controlling a strong nonlinear system is converted to a problem of solving a linear matrix inequality (LMI). Finally, numerical simulation is given to demonstrate the effectiveness of the proposed control strategy.
Conventional heterogeneous-traffic scheduling schemes utilize zero-delay constraint for real-time services, which aims to minimize the average packet delay among real-time users. However, in light or ...moderate load networks this strategy is unnecessary and leads to low data throughput for non-real-time users. In this paper, we propose a heuristic scheduling scheme to solve this problem. The scheme measures and assigns scheduling priorities to both real-time and non-real-time users, and schedules the radio resources for the two user classes simultaneously. Simulation results show that the proposed scheme efficiently handles the heterogeneous-traffic scheduling with diverse QoS requirements and alleviates the unfairness between real-time and non-real-time services under various traffic loads.
The far-reaching impacts of central Pacific El Nino events on global climate differ appreciably from those associated with eastern Pacific El Nino events. Central Pacific El Nino events may become ...more frequent in coming decades as atmospheric greenhouse gas concentrations rise, but the instrumental record of central Pacific sea-surface temperatures is too short to detect potential trends. Here we present an annually resolved reconstruction of NINO4 sea-surface temperature, located in the central equatorial Pacific, based on oxygen isotopic time series from Taiwan tree cellulose that span from 1190 AD to 2007 AD. Our reconstruction indicates that relatively warm Nino4 sea-surface temperature values over the late twentieth century are accompanied by higher levels of interannual variability than observed in other intervals of the 818-year-long reconstruction. Our results imply that anthropogenic greenhouse forcing may be driving an increase in central Pacific El Nino-Southern Oscillation variability and/or its hydrological impacts, consistent with recent modelling studies.
