The large PV medium-voltage (MV) DC power collection system is more efficient than the traditional AC collection system, which provides an alternative for future PV applications. As one of the core ...components of the PV MVDC power collection system, key techniques of DC transformer are presented here in detail, including the technical requirements, and fault operation analysis in the DC collection system. When part of the PV DC module in the low-voltage (LV) side of DC transformer fails and bypassed, the DC collection system continues working normally with only part of power lost. When the MV side of DC transformer is shorted, all the PV modules exist and the collection system splits without ride-through techniques. The fault operation principle of DC transformer in PV MVDC power collection system is verified by simulations.
Multi-label classification learning provides a multi-dimensional perspective for polysemic object, and becomes a new research hotspot in machine learning in recent years. In the big data environment, ...it is urgent to obtain a fast and efficient multi-label classification algorithm. Kernel extreme learning machine was applied to multi-label classification problem (ML-KELM) in this paper, so the iterative learning operations can be avoided. Meanwhile, a dynamic, self-adaptive threshold function was designed to solve the transformation from ML-KELM network’s real-value outputs to binary multi-label vector. ML-KELM has the least square optimal solution of ELM, and less parameters that needs adjustment, stable running, faster convergence speed and better generalization performance. Extensive multi-label classification experiments were conducted on data sets of different scale. Comparison results show that ML-KELM outperformance in large scale dataset with high dimension instance feature.
The power electronic transformer (PET) has recently emerged as a type of power converter. It features the basic functions of power conversion and isolation as well as additional functions related to ...power quality control. A novel PET for a distribution grid called a flexible power distribution unit is proposed in this paper, and the energy exchange mechanism between the network and the load is revealed. A 30 kW 600 VAC/220 VAC/110 VDC medium-frequency isolated prototype is developed and demonstrated. This paper also presents key control strategies of the PET for electrical distribution grid applications, especially under grid voltage disturbance conditions. Moreover, stability issues related to the grid-connected three-phase PET are discussed and verified with an impedance-based analysis. The PET prototype is tested, and it passes the voltage-disturbance ride-through function. The experimental results verify the power quality control abilities of the PET.
The redistribution of elements in a multicomponent oxyfluoride glass is induced by a 250 kHz femtosecond laser. Elemental distribution in the cross section of the modified region along the laser ...propagation axis is analyzed by an electron microprobe analyzer. The results indicate that the relative concentrations of network formers of the glass are higher in the central area of the modified region and lower in the periphery of the modified region compared with the unirradiated areas. However, the relative concentrations of network modifiers are as opposed to that of network formers. Fluorescence spectra confirm that the distribution of fluorescence intensity of Yb(3+) in the modified region is consistent with that of its concentration. The effects of spherical aberration of the incident beam on the elemental redistribution are also discussed.
People often concern the relationships between symptoms and diseases when seeking medical advices. In this paper, medical data are divided into three copies, records related to main disease ...categories, records related to subclass disease types, and records of specific diseases firstly; then two disease recognition methods only based on symptoms for the main disease category identification, subclass disease type identification, and specific disease identification are given. In the methods, a neural network and a support vector machine (SVM) algorithms are adopted, respectively. In the method validation part, accuracy of the two diagnosis methods is tested and compared. Results show that automatic disease prediction only based on symptoms is possible for intelligent medical triage and common disease diagnosis.
Controllable microstructures are formed on a glass surface after irradiation of a focused 800 nm, 250 KHz femtosecond laser beam. Field-emission scanning electron microscope and 3D measuring laser ...microscope images reveal that the induced structures are circular and linear protuberances and can be controlled from 10 microm to hundreds of micrometers in width, and from 1 microm to tens of micrometers in height. The protuberance structure is proposed to be formed as a consequence of the laser-induced high temperature and pressure owing to linear and nonlinear absorption near the laser focal point, and low softening and melting temperature of the glass sample.
With the irradiation by femtosecond (fs) laser with high repetition rate, GeS
2 micro/nano-crystalline formation and microstructural modification occurred in pseudo-binary GeS
2–In
2S
3 glass, while ...almost no similar change was observed in GeS
2 glass. The addition of In
2S
3 is beneficial for the precipitation of GeS
2 micro/nano-crystals. It is expected that functional micro/nano-crystals can be controllably prepared in chalcogenide glasses by fs laser irradiation through glass composition design.
The acoustic environment in an urban dwelling is a key factor in human health, especially in megacities, where there are high levels of traffic noise. This study investigated the effects of various ...socio-economic indicators (gender, age, roadside residence, average daily time at home) on the subjective evaluation of residential acoustic environments, employing a series of questionnaire surveys and in-depth interviews in two Chinese megacities (Chongqing and Guangzhou). The findings indicate that residents in Chongqing, a typical mountainous city, are less satisfied with their acoustic environment than those in Guangzhou, a city built on a plain. However, there were no significant differences between residents in the two Chinese megacities in terms of their perspectives on their thermal, humid or luminous environments or noise-related health symptoms. Regarding perceptions of acoustic environments, there were significant differences between residents in the mountainous city and the plain city, as well as those in roadside and non-roadside homes, but no significant differences were identified between the views of men and women or the young and the old, and time spent at home appeared to have no impact. Moreover, age and average daily time spent at home are likely to be associated with noise-related health symptoms.
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