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Aiming at the problem of wide-band oscillation caused by power grid with high proportion of direct drive wind turbine (DDWT), a transient model of DDWT for wide-band oscillation analysis is established in this paper. Firstly, the mechanism and key factors of wide-band oscillation occurred in large power grid with high proportion of DDWT was analyzed. Secondly, the model of DDWT was established by simplifying the full electromagnetic transient model of DDWT while the key factors of wide-band oscillation mode were retained and the secondary factors unrelated or weakly related to wide-band oscillation mode were ignored. Finally, the simulation result shows that the model can improve the convergence and computational efficiency of the simulation analysis and ensure the accuracy of the simulation result at the same time, and can be applied to the simulation analysis of wide-band oscillation occurred in large power grid with high proportion of DDWT.

Relaxed Ge0.5Si0.5/Si heterostructure was grown by the rapid radiant heating, very low pressure chemical vapor deposition (RRH-VLP/CVD). We report the anomalous temperature dependence of photoluminescence (PL) from porous GeSi layer at 77-300 K. The peak-emission energy of PL spectra from porous GeSi layer decreases with increasing temperature while its peak intensity rises, which is quite different from the temperature dependence of porous Si layer. Such dependencies are reversible and independent of temperature-change directions. No obvious 480 cm-1 peak was observed in Raman spectrum, indicating that no substantial amorphous phase contributes the intense light emission from the porous materials. We attribute such anomalous behavior of porous GeSi layer to phonon participation in the light-emission process of porous GeSi layer.

The magnetic anisotropy of ferromagnetic (FM) Ni, Co, and Fe polycrystalline thin films grown on antiferromagnetic (AF) FeF(2)(110) epitaxial layers was studied, as a function of temperature, using ferromagnetic resonance. In addition to an in-plane anisotropy in the FM induced by fluctuations in the AF short-range order, a perpendicular (biquadratic) magnetic anisotropy, with an out-of-plane component, was found which increased with decreasing temperature above the AF Neél temperature (T(N) = 78.4 K). This is a surprising result given that the AF's uniaxial anisotropy axis was in the plane of the sample, but is consistent with prior experimental and theoretical work. The resonance linewidth had a strong dependence on the direction of the external magnetic field with respect to in-plane FeF(2) crystallographic directions, consistent with interface magnon scattering due to defect-induced demagnetizing fields. Below T(N), the exchange bias field H(E) measured via FMR for the Ni sample was in good agreement with H(E) determined from magnetization measurements if the perpendicular out-of-plane anisotropy was taken into account. A low field resonance line normally observed at H ≈ 0, associated with domain formation during magnetization in ferromagnets, coincided with the exchange bias field for TT(N), indicating domain formation with the in-plane FM magnetization perpendicular to the AF easy axis. Thus, biquadratic FM-AF coupling is important at temperatures below and above T(N).