The Hurst parameter captures the amount of long-range dependence (LRD) in a time series. There are severalmethods to estimate the Hurst parameter, being the most popular: the variance-time plot, the R/S plot, theperiodogram, and Whittle’s estimator. The first three are graphical methods, and the estimation accuracy depends onhow the plot is interpreted and calculated. In contrast, Whittle’s estimator is based on a maximum likelihood techniqueand does not depend on a graph reading; however, it is computationally expensive. A new method to estimate theHurst parameter is proposed. This new method is based on an artificial neural network. Experimental results showthat this method outperforms traditional approaches, and can be used on applications where a fast and accurateestimate of the Hurst parameter is required, i.e., computer network traffic control. Additionally, the Hurst parameterwas computed on series of different length using several methods. The simulation results show that the proposedmethod is at least ten times faster than traditional methods.
The custom power park (CPP) is a concept that has been developed for the purpose of dealing with power quality problems. The CPP is powered by two independent feeders and consists of different types of custom power devices for compensation (dynamic voltage restorer, DVR) and reconfiguration (static transfer switch, STS). Normally, the loads are fed by the preferred feeder (PF) through the STS. When a fault occurs in the PF, the STS performs a reconfiguration of the feeders and feeds the load with an alternate feeder. In this paper, a two-input DVR based on the matrix converter is proposed to provide stable voltage to the load. Each of the DVR inputs is connected to a different feeder, and the PF powers the load. Thus, the DVR has an operational behavior like the STS when reconfiguring the energy transfer of the two feeders and injects it into the PF to guarantee a stable voltage in the load. The control algorithm in the DVR is performed in the dq reference frame to have a unit power factor in feeders and load. The modulation schemes are based on space vector modulation and modified carrier based pulse width modulation. The efficiency and multifunctionality of the proposed DVR is corroborated by simulations on the MATLAB/Simulink.
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