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Microstructure and dielectric properties of La2O3 doped Ti-rich barium strontium titanate ceramics for capacitor applications

Zhang C., Chen F., Ling Z., Jian G., Li Y.

Materials Science Poland

2017

Vol. 35, No. 4

806--815

Microstructure and dielectric properties of La2O3 doped Ti-rich barium strontium titanate ceramics, prepared by solid state method, were investigated with non-stoichiometric level and various La2O3 content, using XRD, SEM and LCR measuring system. With an increase of non-stoichiometric level, the unit cell volumes of perovskite lattices for the single phase Ti-rich barium strontium titanate ceramics increased due to the decreasing A site vacancy concentration V″A. The unit cell volume increased and then decreased slightly with the increasing La2O3 content. Relatively high non-stoichiometric level and high La2O3 content in Ti-rich barium strontium titanate ceramics contributed to the decreased average grain size as well as fine grain size distribution, which correspondingly improved the temperature stability of the relative dielectric constant. The relative dielectric constant єrRT, dielectric loss tanδRT and the maximum relative dielectric constant єrmax decreased and then increased with the increasing non-stoichiometric level. With the increase of La2O3 doping content, the relative dielectric constant єrRT increased initially and then decreased. The maximum relative dielectric constant єrmax can be increased by applying low doping content of La2O3 in Ti-rich barium strontium titanate ceramics due to the increased spontaneous polarization.

Individual pitch control for torque fluctuation reduction in large-scale wind turbine generator systems

Dou Z., Wang H., Ling Z., Cai X.

Przegląd Elektrotechniczny

2013

R. 89, nr 3b

29--31

In order to capture maximum wind energy, smooth the wind turbine torque fluctuation and eliminate the unbalanced loads on the wind turbine, the individual pitch control strategy which directly controls the edgewise moment is proposed based on the multi-stage dynamic weight coefficient distribution of the pitch angle according to the blade azimuth. In order to verify the effeteness of the proposed individual pitch control, the simulation experiment is carried out on a 2MW wind turbine generator system. And the results show, compared with collective pitch control, the proposed individual pitch control not only regulates and smoothes the wind turbine torque fluctuation, but also indirectly reduces the fluctuation of the blade flapwise moment, the yaw moment and the tilt moment, and greatly improves the power output as well.

W artykule opisano strategię sterowania kątem natarcia płatami wirnika turbiny wiatrowej w celu lepszej stabilizacji momentu turbiny i eliminacji niezbalansowania obciążenia. Metoda oparta została na wielostopniowej wadze dynamicznej współczynników podziału kąta natarcia, w zależności od azymutu płata. Przedstawiono wyniki badań symulacyjnych sterowania w systemie generatorów wiatrowych o mocy 2MW, potwierdzające jego wysoką skuteczność i zwiększenie generowanej energii elektrycznej.