14,009 research outputs found
Universal Droop Control of Inverters With Different Types of Output Impedance
Droop control is a well-known strategy for the parallel operation of inverters. However, the droop control strategy changes its form for inverters with different types of output impedance, and so far, it is impossible to operate inverters with inductive and capacitive output impedances in parallel. In this paper, it is shown that there exists a universal droop control principle for inverters with output impedance having a phase angle between -(π/2) rad and (π/2) rad. It takes the form of the droop control for inverters with resistive output impedance (R-inverters). Hence, the robust droop controller recently proposed in the literature for R-inverters actually provides one way to implement such a universal droop controller that can be applied to all practical inverters without the need of knowing the impedance angle. The small-signal stability of an inverter equipped with the universal droop controller is analyzed, and it is shown to be stable when the phase angle of the output impedance changes from -(π/2) rad to (π/2) rad. Both real-time simulation results and experimental results from a test rig consisting of an R-inverter, an L-inverter, and a C-inverter operated in parallel are presented to validate the proposed strategy
Dr. Yang Zhong: an explorer on the road forever
On the morning of September 25th 2017, grievous news spread from the remote Ordos region of Inner Mongolia to Fudan University campus in Shanghai. Professor Yang Zhong, a famous botanist and the Dean of Fudan University’s graduate school, passed away in a tragic car accident while on a business trip
Celebrities-ReID: A Benchmark for Clothes Variation in Long-Term Person Re-Identification
© 2019 IEEE. This paper considers person re-identification (re-ID) in the case of long-time gap (i.e., long-term re-ID) that concentrates on the challenge of clothes variation of each person. We introduce a new dataset, named Celebrities-reID to handle that challenge. Compared with current datasets, the proposed Celebrities-reID dataset is featured in two aspects. First, it contains 590 persons with 10,842 images, and each person does not wear the same clothing twice, making it the largest clothes variation person re-ID dataset to date. Second, a comprehensive evaluation using state of the arts is carried out to verify the feasibility and new challenge exposed by this dataset. In addition, we propose a benchmark approach to the dataset where a two-step fine-tuning strategy on human body parts is introduced to tackle the challenge of clothes variation. In experiments, we evaluate the feasibility and quality of the proposed Celebrities-reID dataset. The experimental results demonstrate that the proposed benchmark approach is not only able to best tackle clothes variation shown in our dataset but also achieves competitive performance on a widely used person re-ID dataset Market1501, which further proves the reliability of the proposed benchmark approach
The curvature-induced gauge potential and the geometric momentum for a particle on a hypersphere
For a particle that is constrained to freely move on a hypersurface, the
curvature of the surface can induce a gauge potential; and for a particle on
the hypersphere, the gauge potential derived from the \textit{generalized
angular momentum algebra }on it has been known long before (J. Math. Phys.
\textbf{34}(1993)2827). We demonstrate that the momentum for the particle on
the hyperspherecan be the geometric one which obey commutation relations , in which is the
Planck's constant, and () symbolizes the th component
of the geometric momentum, and specifies the th component of the
angular momentum containing the spin-curvature coupling, and denotes the
radius of the dimensional hypersphere.Comment: 6 pages, no figur
Self-Synchronized Universal Droop Controller
In this paper, a self-synchronization mechanism is embedded into the universal droop controller
(UDC), which is applicable to inverters having an impedance angle between −π/2 rad and π/2 rad,
to form a self-synchronized UDC (SUDC). Both the voltage loop and the frequency loop of the UDC are
modified to facilitate the standalone and grid-connected operation of inverters. Importantly, the dedicated
phase-locked-loop that is often needed for grid-connected or parallel-operated converters is removed. The
inverter is able to achieve synchronization before and after connection without the need of a dedicated
synchronization unit. Since the original structure of the UDC is kept in the SUDC, the properties of the
UDC, such as accurate power sharing and tight output voltage regulation, are well maintained. Extensive
experimental results are presented to demonstrate the performance of the proposed SUDC for a gridconnected
single-phase inverter
In Situ Structure Characterization in Slot-Die-Printed All-Polymer Solar Cells with Efficiency Over 9%
Herein, high-performance printed all-polymer solar cells (all-PSCs) based on a bulk-heterojunction (BHJ) blend film are demonstrated using PTzBI as the donor and N2200 as the acceptor. A slot-die process is used to prepare the BHJ blend, which is a cost-effective, high-throughput approach to achieve large-area photovoltaic devices. The real-time crystallization of polymers in the film drying process is investigated by in situ grazing incidence wide-angle X-ray scattering characterization. Printing is found to significantly improve the crystallinity of the polymer blend in comparison with spin coating. Moreover, printing with 1,8-diiodooctane as the solvent additive enhances the polymer aggregation and crystallization during solvent evaporation, eventually leading to multi-length-scale phase separation, with PTzBI-rich domains in-between the N2200 crystalline fibers. This unique morphology achieved by printing fabrication results in an impressively high power conversion efficiency of 9.10%, which is the highest efficiency reported for printed all-PSCs. These findings provide important guidelines for controlling film drying dynamics for processing all-PSCs
The hyperon mean free paths in the relativistic mean field
The - and -hyperon mean free paths in nuclei are firstly
calculated in the relativistic mean field (RMF) theory. The real parts of the
optical potential are derived from the RMF approach, while the imaginary parts
are obtained from those of nucleons with the relations:
and . With the
assumption, the depth of the imaginary potential for is
3.5 MeV, and for is 7 MeV at
low incident energy. We find that, the hyperon mean free path decreases with
the increase of the hyperon incident energies, from 200 MeV to 800 MeV; and in
the interior of the nuclei, the mean free path is about fm for
, and about fm for , depending on the hyperon
incident energy.Comment: 5 figures, 6 page
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