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Higher power applications require a multilevel converter to meet high power ratings. A multimodule current-source converter (CSC) can provide a multilevel current waveforms and at the same time eliminate the bulky transformer at the ac side. However, it is required for the multimodule CSC to use multiple dc-link inductors for the purpose of power balance among different modules. Thus, one key issue in the design of the multimodule CSC is to balance the current through different dc-link inductors. This paper focuses on studying the control strategy of the multimodule CSC and a generalized current balancing method is presented. As presented, zero vectors are distributed based on the deviation of the dc-link inductor currents and the comparison of the capacitor voltages. Therefore, the current imbalance problems, not only those among the upper inductors but also those among the lower inductors are solved. Moreover, since the current balancing algorithm is not dependent on module numbers, the presented control strategy is very suitable for modularization. Especially, with the feedback of the capacitor voltages, the resonance arising from the inductor-capacitor (LC) filter is damped. In addition, a design method of the dc-link inductors is also derived. Finally, simulation and experimental results show the validity of the propositions. [ABSTRACT FROM AUTHOR]

This paper aims to explore the pulsewidthmodulation (PWM) schemes for three-phase current source converter, and a generic six-step direct PWM (SS-DPWM) scheme is proposed. In the SS-DPWM, one line cycle is divided into six 60° intervals, so called as "six-step." During each interval, only two of the three references, referred to as the Master and Slave references, respectively, compare with the carriers to directly generate the required switching patterns instead of using the transformation from bilogic signals to trilogic ones, as used in the conventional sinusoidal PWM (SPWM). In this paper, the variety of the Slave reference for each interval is identified, and many sets of modulating waveforms are presented for the SS-DPWM, resulting in very flexible and expanded modulations. The mechanism of the SS-DPWM is also presented to develop itsmodulating characteristics, and it is shown that, comparing with the conventional SPWM, the SS-DPWM has lower switching frequency, higher dc current utilization ratio, and in-phase transfer between the line currents and their references. A prototype has been built in the lab and the validity of the theoretical analysis is verified by the experimental results. [ABSTRACT FROM AUTHOR]

This paper examines the representation of Bai ethnicity based on a video made by a local Bai cameraman for temple carers. Presenting this video as a case of identity construction, this article deals with how a locally made video functions as a constructive tool which allows the cameraman and the locals, to some extent, to reproduce Bai ethnicity. In this case, the camera in 'native' hands is not used to visualise anthropology. The commonality between an independent video-making agenda and one that is geared toward anthropological inquiry challenges us to ponder if it is essential to distinguish between films made by anthropologists or the 'natives' that represent who they/we are. [ABSTRACT FROM AUTHOR]

This paper examines the construction of Bai ethnicity and Bai identity on the tourist market in Dali, Dali Bai Autonomous Prefecture, Yunnan, China. Focusing on how the social landscape of Dali has changed in response to the development of tourism, this paper explores how Bai ethnicity is advocated as a product loaded with potential economic values. The author discovers that 'commerce of authenticity' (T. Oakes, Tourism and modernity in China. London, Routledge, 1998), and different forms of ethnicity and artefacts promoted in the tourist market have not drowned out the sense of being ethnically Bai. Instead, the tourist industry has become a daily reminder of ethnicity to both insiders and outsiders by making people more self-conscious and reflexive about the 'cultural stuff' that they may have previously taken for granted, or may have left unattended. This paper demonstrates how locals actively appropriate state-defined categories and reshape them into the repertoire they desire. [ABSTRACT FROM AUTHOR]

Crystals of a 2-Helix fusion-core construct of MHV spike protein (commonly referred to as E2) have been grown at 291 K using PEG 4000 as precipitant. The diffraction pattern of the crystal extends to 2.8 Å resolution at 100 K in-house. Furthermore, a selenomethionine (SeMet) derivative of MHV spike protein fusion core has been overexpressed and purified. The derivative crystals were obtained under similar conditions and three different wavelength data sets were collected to 2.4 Å resolution from a single derivative crystal at BSRF (Beijing Synchrotron Radiation Facility). The crystals have unit-cell parameters a = b = 48.3, c = 199.6 Å, α = β = 90, γ = 120° and belong to space group R3. Assuming the presence of two molecules in the asymmetric unit, the solvent content is calculated to be about 46%. [ABSTRACT FROM AUTHOR]

There exists a strong coupling between real and reactive power owing to the complex impedances in droop based islanded microgrids (MGs). The existing virtual impedance methods consider improvements of the impedance matching for sharing of the voltage controlled power (VCP) (reactive power for Q-V droop, and real power for P-V droop), which yields a 1-DOF (degree of freedom) tunable virtual impedance. However, a weak impedance matching for sharing of the frequency controlled power (FCP) (real power for P-co droop, and reactive power for Q-co droop) may result in FCP overshoots and even oscillations during load transients. This in turn results in VCP oscillations due to the strong coupling. In this paper, a 2-DOF tunable adaptive virtual impedance method considering impedance matching for both real and reactive power (IM-PQ) is proposed to improve the power sharing performance of MGs. The dynamic response is promoted by suppressing the coupled power oscillations and power overshoots while realizing accurate power sharing. In addition, the proposed power sharing controller has a better parametric adaptability. The stability and dynamic performances are analyzed with a small-signal state-space model. Simulation and experimental results are presented to investigate the validity of the proposed scheme. [ABSTRACT FROM AUTHOR]

In this paper, a hybrid modular multilevel converter (MMC) topology with an improved nearest level modulation method is proposed for medium-voltage high-power applications. The arm of the proposed topology contains N series connected half-bridge submodules (HBSMs), one full-bridge submodule (FBSM) and an inductor. By exploiting the FBSM, half-level voltages are obtained in the arm voltages. Therefore, an output voltage with a 2N+1 level number can be generated. Moreover, the total level number of the inserted submodules (SMs) is a constant. Thus, there is no pulse voltage across the arm inductors, and the SM capacitor voltage is rated. With the proposed voltage balancing method, the capacitor voltage of the HBSM is twice the voltage of the FBSM, and each IGBT of the FBSM has a relatively low switching frequency and an equalized conduction loss. The capacitor voltage balancing methods of the two kinds of SMs are implemented independently. As a result, the switching frequency of the HBSM is not increased compared to the conventional MMC. In addition, according to a theoretical calculation of the total harmonic distortion of the electromotive force (EMF), the voltage quality with the presented method can be significantly enhanced when the SM number is relatively small. Simulation and experimental results obtained with a MMC-based inverter verify the validity of the developed method. [ABSTRACT FROM AUTHOR]

Owing to mismatched feeder impedances in an islanded microgrid, the conventional droop control method typically results in errors in reactive power sharing among distributed generation (DG) units. In this study, an improved droop control strategy based on secondary voltage control is proposed to enhance the reactive power sharing accuracy in an islanded microgrid. In a DG local controller, an integral term is introduced into the voltage droop function, in which the voltage compensation signal from the secondary voltage control is utilized as the common reactive power reference for each DG unit. Therefore, accurate reactive power sharing can be realized without any power information exchange among DG units or between DG units and the central controller. Meanwhile, the voltage deviation in the microgrid common bus is removed. Communication in the proposed strategy is simple to implement because the information of the voltage compensation signal is broadcasted from the central controller to each DG unit. The reactive power sharing accuracy is also not sensitive to time-delay mismatch in the communication channels. Simulation and experimental results are provided to validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

The surface transmembrane glycoprotein is responsible for mediating virion attachment to cell and subsequent virus-cell membrane fusion. However, the molecular mechanisms for the viral entry of coronaviruses remain poorly understood. The crystal structure of the fusion core of mouse hepatitis virus S protein, which represents the first fusion core structure of any coronavirus, reveals a central hydrophobic coiled coil trimer surrounded by three helices in an oblique, antiparallel manner. This structure shares significant similarity with both the low pH-induced conformation of influenza hemagglutinin and fusion core of HIV gp41, indicating that the structure represents a fusion-active state formed after several conformational changes. Our results also indicate that the mechanisms for the viral fusion of coronaviruses are similar to those of influenza virus and HIV. The coiled coil structure has unique features, which are different from other viral fusion cores. Highly conserved heptad repeat 1 (HR1) and HR2 regions in coronavirus spike proteins indicate a similar three-dimensional structure among these fusion cores and common mechanisms for the viral fusion. We have proposed the binding regions of HR1 and HR2 of other coronaviruses and a structure model of their fusion core based on our mouse hepatitis virus fusion core structure and sequence alignment. Drug discovery strategies aimed at inhibiting viral entry by blocking hairpin formation may be applied to the inhibition of a number of emerging infectious diseases, including severe acute respiratory syndrome. [ABSTRACT FROM AUTHOR]

Highly conserved heptad-repeat (HR1 and HR2) regions in class I viral fusion (F) proteins, including the F protein from paramyxovirus, interact with each other post-fusion to form a six-helix bundle called a fusion core. Crystals of the fusion core of Nipah virus have been grown at 291 Kusing PEG 4000 as precipitant. The diffraction pattern of the crystal extends to 2.1 Å resolution at 100 K in-house. The crystals have unit-cell parameters a = 31.664, b = 31.725, c = 51.256 Å, α = 80.706, β = 86.343, γ = 65.812° and belong to space group P1. Crystals of the fusion core of Hendra virus have also been grown at 291 K using PEG 4000 as precipitant. The diffraction pattern of the crystal extends to 2.0 Å resolution at 100 K in-house. A selenomethionine (SeMet) derivative of the HeV fusion core was overexpressed using the same Escherichia coli expression system and purified. The derivative crystals were obtained under similar conditions and three different wavelength data sets were collected to 2.0 Å resolution from the derivative crystal at BSRF (Beijing Synchrotron Radiation Facility). The crystals have unit-cell parameters a = 31.997, b = 31.970, c = 53.865 Å, α = 85.990, β = 85.842, γ = 68.245° and belong to space group P1. [ABSTRACT FROM AUTHOR]

The aetiological agent of an emergent outbreak of atypical pneumonia, severe acute respiratory syndrome (SARS), is a positive-stranded RNA virus (SARS-CoV) belonging to the Coronaviridae family with a genome that differs substantially from those of other known coronaviruses. Highly conserved heptad-repeat (HR1 and HR2) regions in class I viral fusion proteins, including spike protein from SARS coronavirus, interact with each other to form a six-helix bundle, which is called a fusion core. The crystal structure of the fusion core is expected to greatly facilitate drug design. Crystals of the fusion core of SARS-CoV spike protein have been grown at 291 K using PEG 4000 as precipitant. The diffraction pattern of the crystal extends to 2.8 Å resolution at 100 K in-house. The crystals have unit-cell parameters a = 121.2, b = 66.3, c = 70.0 Å , α = γ = 90, β = 107.4° and belong to space group C2. Assuming the presence of six molecules per asymmetric unit, the solvent content is estimated to be about 28%. [ABSTRACT FROM AUTHOR]