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In order to control the nonlinear high-speed train with high robustness, the fractional order control of nonlinear switching systems is studied. The fractional order controller is designed for a class of nonlinear switching systems by the fractional order backstepping method. In this paper, a simple and effective online updating scheme of model coefficients is proposed by using the flexibility of the model predictive control algorithm and its wide range of model accommodation. A stochastic discrete nonlinear state space model describing the mechanical behavior of a single particle in a high-speed train is constructed, and the maximum likelihood estimation of the parameters of a high-speed train is transformed into an optimization problem with great expectations. Finally, numerical comparison experiments of motion characters of two high-speed trains are given. The results show the effectiveness of the proposed identification method.

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This study intends to establish the correlation between charging current under stepwise increased electric field and space charge formation in low density polyethylene (LDPE) and LDPE/ZnO nanocomposites. By applying stepwise increased electric field, the charging current and space charge distribution were measured as a function of time under 10, 30 and 50 kV/mm, respectively. The results show that homopolar space charge formation induces increasing charging current with time, while heteropolar space charge formation induces decaying charging current and excellent space charge suppression is accompanied by constant charging current with time. The abundant deep trapping states introduced by nanofillers dominate both the lower steady charging current and space charge suppression in the nanocomposite. The results indicate that charging current behavior induced by stepwise increased electric field is extremely informative and is feasible to be a direct method for rough estimation of space charge formation and suppression in polymer dielectrics. Addition of ZnO nanofillers suppresses space charge accumulation in LDPE, indicating LDPE/ZnO nanocomposite is a potential insulation material for high voltage direction current cables.Index Termsstepwise increased electric field, charging current, space charge, nanodielectrics, LDPE/ZnO.

SUMMARY Designing an efficient and effective maximum power point tracking (MPPT) method is a vital yet challenging task for modern large‐scale variable speed wind power systems. In this paper, an improved control and extremum seeking strategy is proposed to construct a novel MPPT scheme, and the merit of this scheme is twofold. On the one hand, a nonlinear speed tracking controller is developed on the basis of the dynamic model of wind turbines, which cannot only track a desired rotor speed trajectory but also provide the extremum seeking module with estimation of the varying rotor torque. On the other hand, an extremum seeking module blended with lookup‐table module is designed on the basis of a novel hill climbing searching method, which is more efficient because of its online updating structure and independence of the measurement of wind speed and output power. For simulation validation, a 10‐MW direct driven wind turbine is used as a benchmark to test the proposed strategy. Copyright © 2013 John Wiley & Sons, Ltd.

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