Unusually large low field magetoresistance (LFMR), ~ 10 %, at 300 K has been observed with the sample of mono-dispersed Fe 3 O 4 magnetite nanospheres, ~ 200 nm, compactly cold-pressed and sintered at 800 o C. A detailed analysis on the transport and magnetic measurements indicates that the electron conduction is dominated by the spin-dependent scattering or tunneling at the grain boundaries. At low temperature, 140 K and 100 K near the Verwey transition, ~ 115 K, the LFMR (below 2 kOe) does a e-mail : cpchen@pku.edu.cn, Phone : +86-10-62751751, Fax : 86-10-62751615 2 not show any sign of dependence on the transition, and does not follow the variation of magnetization to reach the saturation region either. On the other hand, at 300 K, the MR saturates fast with the magnetization below 2 kOe. This temperature dependent property in LFMR is very likely attributed to the scattering or tunneling of the conduction electron passing through the grain boundary layer with spin disordered state.3
An important issue in the single phase converter system is to deal with the pulsating power which is the twice of the fundamental frequency. The pulsating power may shorten the lifetime of the dc-link capacitor and affect the system control performance. This paper has presented some methods to reduce the dc-link voltage ripple caused by the pulsating power in a modular converter for a multi-coil direct-drive permanent magnet wind generator system. At the generator side, the generator coils with 90 degree phase shift are rectified through power factor correction (PFC) circuit and connected in parallel to counteract the pulsating power to achieve the stable dc-link power. At the grid side, the pulsating power frequency (100Hz or 120Hz) will be twice of the grid frequency, which can be compensated by adjusting the wind generator output power, thus reducing the required dc-link capacitor value. A proportional-integral-resonant (PIR) controller is introduced in the dc-link voltage control loop and generator coil current control loop to generator the required pulsating power to compensate the grid-side pulsating power. The corresponding impact of the current harmonics to the generator torque is analyzed in the paper. Meanwhile, the required dc-link capacitor value is also given in the paper. The simulation results validate the proposed control scheme.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
customersupport@researchsolutions.com
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.