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This article proposes a current path tracking approach that uses a current path state to correlate device status and operating mode of an inverter under normal and abnormal conditions. Based on graph theory, a node-path modeling method is proposed and applied in the T-type inverter topologies. The model reflects system state transitions, given healthy or faulted transistors. Effective conduction paths and node potentials can be derived with the model to indicate circuit faults. In addition, a hierarchical diagnosis method is proposed for single-transistor open-circuit (OC) faults based on estimated output voltage vectors. The diagnosis involves two steps. First, an OC fault can be detected by following a residual between an actual voltage vector and its reference voltage vector calculated from duty ratios of intended current paths. Next, faulty transistors sharing similar features can be distinguished by adopting a current path state reconfiguration approach. Diagnosis variables can be obtained from the controller, and their errors, because of sampling, signal delay, and dead time, are taken into account to avoid misdiagnosis. Experimental results verify the robustness and effectiveness of the proposed method.

A redundant unit has been utilized in prior work for a T-type three-level inverter to handle multiple open-circuit faults, but the output was limited to two levels. In this article, equivalent switching state and improved virtual vector methods are proposed to complement switching states and provide better fault-tolerant performance. Under fault scenarios, equivalent replacement of unreachable switching states can be used to generate the target line-to-line voltages. If the replacement cannot be achieved by equivalent switching states, a virtual vector with redundant capability is employed to support two- and three-level modulations at the output. The rearranged switching sequences can be formed by employing virtual vectors and existing vectors. In addition, by reconstructing the virtual vectors, a balancing method is adopted to eliminate neutral point voltage offset in cases of multiple faults. Experimental tests verify the effectiveness and feasibility of the proposed method.

© 1986-2012 IEEE. This article considers fault detection in the case of a three-phase three-wire (3P3W) inverter, when only two current sensors are used to save cost or due to a faulty current sensor. With two current sensors, there is no current method addressing the diagnosis of both IGBT open-circuit (OC) faults and current sensor faults. In order to solve this problem, this article proposes a method which innovatively combines two kinds of diagnosis variables, line voltage deviations and phase voltage deviations. The unique faulty characteristics of diagnosis variables for each fault are extracted and utilized to distinguish the fault. Using an average model, the method only needs the signals already available in the controller. Both IGBT OC faults and current sensor faults can be detected quickly in inverter mode and rectifier mode, so that the converter can be protected in a timely way to avoid further damages. In addition, error-adaptive thresholds are adopted to make the method robust. Effects such as system unbalance are analyzed to ensure that the method is robust and feasible. Simulation and experimental results are used to verify and validate the effectiveness of the method.

This paper presents a transistor open-circuit fault diagnosis method based on an average model and post-fault reconfiguration algorithms for a grid-tied single-phase inverter that transfers power bi-directionally. The transistor open-circuit fault occurrence is detected by comparing the average bridge arm pole-to-pole voltage deviation and threshold first. Then, the exact faulty transistor is identified by developed algorithms based on post-fault reconfiguration of control (PFRC) and of utilizing redundant leg (PFRUR). These two fault identification algorithms are suitable for different situations. Compared with the PFRUR, the PFRC can identify the faulty transistor without the help of redundant leg, but the identification time is longer. For inverters equipped with redundant leg already, the PFRUR can achieve faster identification speed so that inverters in reliability-oriented applications can return to normal operation after fault with short interruption. With average model, this method only requires existing signals sampled for control, thus it can be embedded in system easily without adding extra sensors and diagnosis circuits. The sampling frequency can be as low as switching frequency. Furthermore, this method is suitable for both inverters with L or LCL filters. Finally, experiments are carried out on a 550-W/10-kHz grid-tied single-phase inverter to verify the effectiveness.

The circulating current of modular multilevel converter (MMC) has a great impact on the power losses, the submodule (SM) capacitor voltage ripples, and the rating of power devices. Existing analysis of circulating current has considered the capacitor voltage and the modulation signal. In this paper, the effect of semiconductor devices on the circulating current is further presented. In order to realize the different circulating current injection targets under different conditions, a unified online calculation scheme by using the instantaneous information of MMC is proposed in this paper to generate the circulating current injection references. It avoids detecting the amplitude and phase of the output current or using an extensive lookup table. Besides, a mathematical analysis model is built and it reveals the impact on the capacitor voltage ripple and the rms value of arm current with different injection references, thus guide the determination of the injection ratio. Experimental results based on a three-phase MMC prototype with six SMs per arm are presented to demonstrate the analysis of circulating current and the proposed circulating current injection references generating method is verified by different circulating current control targets with different loads.

This paper presents a model-based method to diagnose single- and multiple-transistor open-circuit (OC) faults in grid-tied three-phase voltage-source inverters (VSIs). The method is based on calculated average bridge arm pole-to-pole (PTP) voltages and error-adaptive thresholds. Only existing signals for closed-loop control are needed; thus, this method can be easily embedded in the system without extra sampling and circuits. Average PTP voltage deviations are chosen as diagnosis variables, which show considerable distinction quickly after fault. Consequently, fast fault diagnosis speed can be achieved. The fault diagnosis time for single fault can be as short as two switching periods. Besides, diagnosis variables show the same faulty characteristics in inverter mode and rectifier mode; thus, this method is effective in both modes. Moreover, for the first time, the variation of inductance caused by conducted current is considered to obtain a more accurate variable-inductance model, and the thresholds are updated according to mathematically estimated diagnosis variable calculation errors from sampling error, inductance error, dead time, and delay time, which maintains high robustness as well as fast speed. Finally, the effectiveness of the proposed method is validated with experiments.

Convolutional neural network has been extensively used in image classification, video processing and semantic recognition. Generally speaking, convolutional neural network is accelerated by high power GPU, but this work uses the FPGA to speed up the convolutional neural network because of its configurability and low power consumption advantage over GPU. Especially, OpenCL-based high-level synthesis tools can provide fast verification and implementation flows. This work mainly uses the Winograd’s minimal filtering algorithm to accelerate VGG-16 network on Intel Arria 10 GX FPGA board and has a good effect on 3x3 convolution kernel. The peak performance of 227 GOP/S has been achieved with 544 DSP.

The modular multilevel converter (MMC) with nearest level modulation (NLM) is widely used in the high voltage applications for low switching frequency and easy implementation. Existing literature has not provided a complete submodule (SM) fault ride-through scheme for MMC with NLM. In this paper, a strategy including fault detection, localization, redundancy, and recovery is proposed to ensure continuous operation of MMC under IGBT open-circuit faults conditions. It only requires a few hardware and software resources. The features of MMC and SMs with three types of failures are studied, respectively. Based on these, the fault detection method is proposed by using a simple hardware circuit, thus high computation complexity is avoided. Since current fault localization schemes are limited to MMC with carrier phase shifted pulse width modulation, this paper further proposes a strategy for MMC with NLM to locate the faulty SM and identify the fault type. After this, the fault redundancy and the proposed fault recovery method are applied to eliminate the fault and then exit the failure state. Therefore, the ability of SM fault ride-through can be realized. Analysis of failure characteristics are verified in simulation. Experimental results based on a single-phase MMC prototype with 11 SMs per arm are presented to demonstrate the validity of the proposed fault ride-through strategy.

Inverters and loads can freely connect to any node in a meshed parallel inverters system, leading to variations of line impedance between two nodes and the structure of the electric network. More challenges exist for proportional load-sharing control in such a system. An improved proportional load-sharing strategy for a meshed parallel inverters system with complex impedances is proposed in this paper. The RL -type droop method is modified through injecting the power droop information of all other inverters, which can improve the load-sharing accuracy to some extent and completely compensate the voltage amplitude and frequency deviations caused by droop equations under accurate load-sharing conditions. Besides, an adaptive virtual resistance tuned by the integral of the linear combination of output active and reactive powers, is added to eliminate load-sharing errors. In addition, the central controller broadcasts the control variables to all inverters. This improves the simultaneity of control data and minimizes the mismatch of control delay. Three modified droop methods are compared with the small-signal analysis and simulation. Experimental results are presented to investigate the performance of the proposed control strategy.

In some cases, only two current sensors are available in three-phase three-wire (3P3W) inverters. This occurs when one of three sensors is faulty, or the inverter is equipped with only two sensors to save cost. There has been no method addressing the diagnosis of both IGBT open-circuit faults and current sensor faults in the 3P3W inverter with only two current sensors. In order to solve this problem, a nonintrusive method based on average output voltage deviations is proposed. The deviations between the measured and estimated output line and phase voltages are utilized to detect and locate the fault. With average model, this method can diagnose the fault fast with only signals available in the controller. Therefore, no extra sampling or diagnosing circuits are needed. Besides, the error-adaptive thresholds are adopted to ensure the robustness. Finally, experimental results verified the effectiveness.

This paper aims at improving transient performance of LCL-filter-based grid-connected inverters with active damping. Transient performance of inverters controlled by capacitor current feedback active damping (C2FAD) is analyzed, revealing that grid-currents of the inverters may have overshoot and long settling time when loads fluctuate. To improve transient response better than C2FAD do, a dual current feedback active damping (DCFAD) is proposed. The proposed DCFAD could realize virtual resistor connected in parallel with capacitor and virtual resistor connected in series with grid-side inductor, consequently, adding a control parameter to the algorithm to configure the poles effectively without adding sensors. Experimental results based on a single-phase grid-connected inverter prototype with LCL filter are presented to demonstrate that DCFAD could eliminate overshoot and reduce settling time, when comparing with C2FAD.

Dynamic currents and voltages in power electronic converters often exceed rating when changing load. In this way, this paper researches on optimizing transient performance of LCL-type gird-connected inverter systems. Resistor connected in series with capacitor as passive damping (RCSCPD), which is widely used to damp resonance of LCL filter, needs to choose an appropriate resistor to acquire accurate and fast transient performance. To meet this requirement, an approach is proposed for analyzing and improving transient performance. It shows that passive resistor could damp resonance and stable system. Limitation of RCSCPD, which could not optimize dominant transient response, is exhibited as well. Hence, mix damping (MD) is proposed to achieve the goal. It could eliminate overshoot and decrease settling time efficiently when comparing with RCSCPD. MD could configure the poles effectively without adding precision sensors because it uses grid current, which used in control loop, to realize active damping resistor. Experimental results based on single-phase LCL-type gird-connected inverter prototype are given to show optimizing effects of transient performance.

Modular multilevel converter (MMC) is one of the most potential converter structures for medium/high power/voltage applications. Since the electrical energy is stored in the capacitances of its sub-modules during the operation of the MMC, the output power quality is directly related to the capacitor voltage. Therefore, capacitor voltage balance is of great importance. In this paper, a capacitor voltage balancing strategy for the carrier phase-shifted modulation strategy is presented for MMC by rotating the carriers, which not only solves the problem of capacitor voltage balance, but also avoids complex closed-loop modulation and voltage sequencing. Considering the potential additional switching process during carrier rotation, the algorithm is further improved to find the best rotation period. The experiment verifies the propositions.

This paper proposes a fast multiple semiconductor open-circuit fault diagnosis method for a T-type three-level inverter. In this method, appropriate Boolean operations are selected to represent the relationship between voltages across the upper half-bridge switches and switching signals. Based on this, the current path in the circuit can be tracked under normal and abnormal conditions. Logical relationships are linked to corresponding switch states, so this method is applicable even under multiple open circuit faults. Diagnosis results can be obtained rapidly, with simple hardware. Misdiagnosis caused by delays in power devices and sampling circuits can be avoided if switching signal dead time is longer than the total delay. This diagnostic scheme is immune to load disturbances and dead times. Experimental results obtained under various conditions demonstrate the applicability and performance of the approach.

This paper designs an LLC converter with super-wide output voltage. A variable-mode control strategy with three operating modes is adopted for the converter, and a novel optimal parameters design method based on this strategy is proposed. The designed converter can achieve a super-wide output voltage range at various load without increasing circuit’s complexity, expanding the operating frequency and phase-shifted range. The magnetizing inductance is maximized to decrease magnetizing and conduction losses on condition that the requirements of wide gain and primary MOSFETs’ soft-switching are met, so the converter can maintain a high efficiency within the entire output voltage range. Finally, a 2.5kW experimental prototype with output voltage ranging from 25V to 150V is set up, by which the effectiveness of the strategy and the design method are proved.

Modular multilevel converters (MMC) can be used in many applications such as medium voltage multimegawatt drives and HVDC power transmission. Modulation strategy plays an important role for the good performance of MMC. In this paper, a submodule (SM) regrouping method of MMC is presented and based on this, a sampling time staggered space vector pulse width modulation (STS-SVM) technique is proposed for MMC. Each group has three SMs, which is irrespectively from three phases. Thus, the SVM scheme for the two-level converter can be applied in each group. For an MMC with n-SMs per arm, the two-level SVM for each group is staggered evenly over the sampling time, so as to achieve an equivalent switching frequency at the output. Therefore, the STS-SVM can be very easily expanded with the increasing of the SMs number, and also, the off-line or on-line effort/tasks about generating the SVM switching sequences are simplified significantly. Besides, the capacitor voltages of SMs can be balanced by rotating the gate signals of different SMs even without any capacitor voltage detecting or sorting because the even power distribution among SMs is realized. A three-phase MMC is simulated at both steady and dynamic states in MATLAB/Simulink and validate the performance of the proposition.

Inductive power transfer (IPT) system for electric vehicle battery charging has many advantages over the traditional plug-in system. EV battery can be regarded as a wide range load according to the charging profile. The charging process requires constant current (CC) stage and constant voltage (CV) stage. The charging profile for IPT system is influenced by inductively coupled transformer, compensation structure and operating frequency. This paper proposes an IPT topology which naturally obtains CC and CV output functions simultaneously without increasing the complexity of control system. The system switches between the two charging modes in succession along with the change of load condition. It operates under the CC mode when the load resistance is small, which corresponds to the beginning of battery charging state. With the increase of load resistance, it switches to CV mode at a load turning point after which the battery is under the state of cutoff voltage. As the system is completely compensated, zero phase angle input is achieved during the entire charging process, which realizes soft switching for the entire load range. A fixed frequency control method is used to adjust the output accurately. The experimental IPT system is established to verify the theoretical analysis.

This paper presents an average model-based transistor open-circuit fault diagnosis method for grid-tied single-phase inverters which transfer power bi-directionally. It is easy to detect whereas tricky to identify the faulty transistor, for two different faults may show the same characteristics. In order to solve this problem, the inverter is changed to boost mode after fault is detected, so that the diagnosis variable can show distinguishable characteristics to locate the faulty transistor. The main advantage of this method is that the fault can be diagnosed fast without adding extra circuits. Additionally, it is featured with strong robustness against power change and sampling error. Finally, the effectiveness of the proposed method is verified by experiments.

This paper presents an average model-based diagnosis method for current sensor fault and IGBT open-circuit fault in grid-tied three-phase voltage-source inverters (VSIs). The diagnosis algorithm is based on observed inductor current sum deviation and bridge arm line voltage residuals with adaptive thresholds. The proposed method can guarantee fast diagnosis speed as well as strong robustness for both current sensor faults and IGBT faults, without extra hardware circuits. The fault diagnosis speed can be as fast as one switching period. No tuning effort is needed under different operating conditions since all the diagnosis calculation errors are covered in the thresholds. Finally, experiments are carried out to prove the effectiveness.

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.

Due to the inductor-capacitor (LC) filter, a pulsewidth-modulation (PWM) current-source converter may experience LC resonance. The resonance can be excited by system harmonics either from the PWM process or from the grid voltage distortions and hence results in the line current distorted. In this paper, feedback controls using different variables in the LC filter are first investigated and comprehensively analyzed. It is shown that the inductor-voltage feedback or the capacitor-voltage feedback can damp the current oscillations by increasing the damping ratio, while the inductor-current feedback or the capacitor-current feedback is able to suppress low-order harmonics by raising the resonance frequency. On this basis, a group of combined variable feedback control methods is presented by combining the feedbacks of the inductor/capacitor current and the inductor/capacitor voltage. Thus, not only the current oscillations can be damped, but also the low-order harmonics can be suppressed. Therefore, the line current waveform is improved, and the system performance can be flexibly optimized. A practical design method for feedback gains is also presented in this paper. Finally, the simulation and experimental results verify the feasibility and validity of the proposition.

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.

A novel fast open-transistor diagnosis approach for voltage-source inverters (VSI) based on calculated bridge arm pole-to-pole (PTP) voltages is proposed in this paper. The theoretical PTP voltages can be calculated with duty cycle ratio and DC input, and the real PTP voltages can be calculated with output voltages and currents. When no fault occurs, there should be no difference between the theoretical and the real PTP voltages. Once fault happens, great deviations between these two calculated voltages will be incurred and can be utilized to detect and localize the fault. This method is able to achieve fast diagnosing speed, while no extra hardware circuits and complex calculation are needed, thus it can be embedded in the existing control system with little effort. Furthermore, strong robustness against operation variation makes this method feasible in diversified applications. Simulations and experiments have been carried out to validate the correctness and effectiveness of this method.

In this paper, a zero-current switching (ZCS) current source converter (CSC) topology is proposed by adding an auxiliary circuit between the dc side. During each commutating process, the auxiliary circuit is activated, so that the outgoing switches can be turned off with zero current switching. As a result, all active switches can reach ZCS operations. This feature makes it possible to increase the switching frequency to improve the line current quality where a small size of ac filter is required. That means the presented ZCS CSC topology is very suitable for some applications with high PWM frequency. Simulation gives the verification.

A current soft-commutation Space Vector Modulation (SVM) scheme for three-phase current source converter (CSC) is proposed in this paper. With the presented SVM, the incoming switch has a positive collector-to-emitter voltage while the outgoing switch has a negative collector-to-emitter voltage during current commutations. That is, natural soft-commutations for switching transitions are achieved with accelerated current-commutating processes and lessened durations. As a result, distortion of the line currents can be reduced. Besides, due to the lessened overlapping time, the switching frequency is expected to reach as high as possible to reduce the ac filter and improve the line current quality. Especially, since the presented SVM is based on a closed-loop strategy, soft commutations can be reached in CSC with any power factor operation. The experiment verifies the proposition.

BACKGROUND Chloramphenicol (CAP), an antimicrobial drug that is widely used in animal feed, would have a negative effect on human health due to its low elimination rate and relatively high residue in animal food. It is important to develop a rapid and economic method to determine CAP in animal food to ensure that human health is not affected. RESULTS A new fluorescence immunochromatography strip was developed and established for the detection of CAP residue in chicken muscles for the first time. A CAP–bovine serum albumin conjugate, monoclonal antibody and polyclonal antibody against CAP were applied to constitute a fluorescence immunochromatography strip. The fluorescence intensity was detected by a charge-coupled device scanner and transformed to a digital value. The CAP linearity working range was from 0.1 ng mL−1 to 20 ng mL−1 with a limit of detection of 0.1 ng mL−1 within 10 min. The performance of the strip assay was compared with a commercial ELISA kit and the correlation coefficient was 0.99, which indicated that the new strip assay had a good quantification ability for CAP. CONCLUSION The fluorescence immunochromatography strip was successfully applied to the detection of CAP residues in chicken samples. To our knowledge, it is the first report regarding the development of a fluorescence immunochromatography method for screening CAP in animal samples. © 2013 Society of Chemical Industry

This paper presents a current soft-commutation pulsewidth modulation (PWM) scheme for three-phase current source converter. With the presented PWM scheme, the incoming switch has a positive collector-to-emitter voltage while the outgoing switch has a negative collector-to-emitter voltage during current commutations. Therefore, natural soft commutations for switching transitions are achieved, while current-commutating durations are also lessened. Moreover, some particular advantages can also be obtained such as reduced switching frequency, high dc current utilization ratio, and in-phase transfer between line currents and their references. For more efficient control, this paper then designs logic equations for mapping out the assignments from references to gating signals, allowing a simple implementation using a digital signal processor or a programmable logic device. The theoretical analysis is verified by experimental results.

Advertising plays a vital role in the development of society and economy. Its function can not be underestimated. Advertising language is a special applying language when it compares with others like literary and technological languages. It has become an indispensable part of daily life because of its particular characteristics. It makes a brief introduction into the definition, function of advertising at first in this paper. Then, it mainly summarizes and analyzes the linguistics characteristics of cosmetic advertisements at lexical, rhetorical levels and sentence structure. Through the analysis of cosmetic advertisements, the linguistic features of advertisements are summarized. It is important for people to understand the beauty of language in advertisements.

Vocabulary is one of the three elements of language, the building material and the basic of language. To communicate with others fluently, the first premise is that we must have a certain amount of vocabularies. Facing so many words to learn, it’s necessary to investigate the vocabulary leaning strategies. The paper mainly studies the strategies of English vocabulary learning. Firstly it introduces the importance of vocabulary learning. Secondly, it explains the significance and purpose of the study, and does the survey to the current problems of students’ vocabulary learning. Thirdly, it gives the definition and classification about the vocabulary learning strategies. Then, in the paper some factors which affect the strategies of vocabulary learning are listed. Finally, it points out the specific strategies of vocabulary learning and gets some opinion about it. It is hoped that this paper can offer some help for students’ English vocabulary learning, and expand students’ vocabulary. Also, it can improve students’ interest in vocabulary learning and make vocabulary learning easy.

This paper aims to explore the pulsewidth modulation (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 its modulating 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.

Movie titles are films’ eyes, having double effect of art appreciation and commercial advertisement, and directly playing the role of guidance and promotion. Good film names could convey the films' content as well as arouse audience's interest to get great box. With the continuous development of international cultural exchanges, film begins to get the attention of every nation increasingly as an important media in cultural exchange. With the opening of the Chinese market, we have more and more English movies. The Chinese audiences need to understand the movie titles before they enjoy the movies. But due to different cultural traditions, contexts, customs and thinking modes between the western and eastern world, the choices of their film names embodies distinctive cultural features. Movie titles convey the story to the audience to attract them. This requires the translation of movie titles to be accurate and embody the commercial values. This paper analyzes the translation strategies of English movie titles and explores a new strategy according to previous research results and research methods. This paper introduces the definition of translation strategies and some features of English movie titles and functions. Then it describes the principles of English movie titles translation and points out the translation strategies of English film titles. It is hoped that the context can help people to realize the necessity of proper translation of English movie titles, and accordingly promote the development of films in international market.

This paper explores the issue of constructing multilevel current source converter (MCSC) topologies using the duality principle. Three circuit cells for MCSCs are derived from the applications of the duality on the three common leg circuit cells of multilevel voltage source converters (MVSCs). Based on the presented three cells, three families of MCSC topologies, which are also corresponding to three families of MVSCs, are constructed. Analytical results show that these derived MCSCs and their corresponding MVSCs present analogous features such as the ac side currents/voltages and inductor/capacitor currents/voltages, though they are not direct dual structures. Some experimental results are given to verify the presented MCSC structures.

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.

Three-phase inverter has been widely applied in various applications, and lots of control schemes are investigated for the inverter powering nonlinear load, aiming to achieve favorable performance. However, the model currently proposed for inverter is based on linear load, which is not suitable for condition with nonlinear load. In this paper, a novel modeling method for three-phase inverter powering nonlinear load is proposed. Then, the mathematical derivation and performance analysis of the proposed model are presented in detail. Based on the proposed model, a control scheme is further presented, incorporating PI control and capacitor current feedback. In addtion, the second-order system damping theory and phase-plane analysis method are well developed to describe the steady-state and dynamic performance of the proposed model and control scheme. Compared with conventional dual-loop control, low THD of the ouput voltage could be acheived by means of the proposed scheme, which is perfectly validated by the simulation results.

The new three-phase 5-level current-source inverter (CSI) proposed in this paper was developed by connecting three separate single-phase 5-level CSIs in series, and its operational principle was analyzed. There are two major problems existing in current-source multilevel inverters, one is the complex PWM control method (2-logic to 3-logic conversion), and the other is the problem of current-unbalance between different levels. A simple current-balance control method via DC current feedback is applied in each single-phase 5-level CSI cell to implement the current-balance control between different levels. And to reduce the output current harmonics, POD PWM control technique was used. Simulation and experimental results showed that this new three-phase 5-level CSI topology operates correctly.

Quantitative Risk Assessment（QRA）, as a new technique, is widely applied in construction and operation for oil and gas pipelines. However QRA technology has usually been applied for land use or making maintenance plan during the construction or the pipeline operation respectively. Thus it has less been applied for station design of pipeline. This paper analyzes the risk of gas station in China by using QRA technology and provides suggestion for station design according to the assessment result.

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.

This paper intends to explore reproductive dynamics in a Yi village at a particular point in time (two decades after the two-child policy) by demonstrating how people respond to and deal with birth control policies an how micro-level fertility in individual households is affected. (excerpt)

In this paper, a novel hysteresis loss calculation approach named the double-envelope method is proposed. The method can clearly separate the low-frequency loss and the high-frequency loss. By recording the points where the inductor current reaches minimum or maximum in every switching period, the envelopes of magnetic field H and flux density B in the time domain are acquired, and then the double envelopes on the B-H plane can be obtained. A dynamic minor loop of amorphous core is modeled to calculate the high-frequency loss. With this method hysteresis loss of the AC filter inductor in PWM inverters can be calculated accurately and rapidly. Moreover only the width of the minor loop is needed to measure in experiments, while other parameters can be acquired at the design stage. In order to verify the proposed method, the total loss of an AC filter inductor in a three-level NPC inverter is measured in different switching frequencies and load conditions. The changing trends of the low-frequency loss and the high-frequency loss with currents and switching frequencies are discussed.

LCL filter presents a significant attenuation of switching harmonics, however its resonance peak influences the system stability. Passive damping reduces the switching current harmonics attenuation and increases the extra losses. Nevertheless, traditional active damping method often needs additional sensors or increases the complexity of algorithm. According the Nyquist stability criterion, a novel active damping method is proposed in this paper based on the grid current feedback compensation which adds no more sensors and easy to control. Two kinds of current compensation transfer function are presented. Moreover, the design principles and the range of stable system with active damping are derived step by step. Finally, it compares the damping effect of the different compensation methods through experiment and verifies the theoretical analysis at the same time.

An improved switching loss calculation method for IGBT switching on, switching off and the diode reverse recovery energy losses in neutral point clamped inverter is proposed in this paper. A model of linear instantaneous switching on and off waveforms is presented to approximate actual switching process. The IGBT switching on and off duration, the changing rates of current di/dt and collector-emitter voltage dv/dt all can be calculated at different load currents with the given IGBT parameters. Besides, the proposed method is apparently different from the linear waveform method used before which assuming switching time to be a constant value. In addition, compared with the traditional mathematical equation that uses measured data to fit a formula, the equation proposed here is based on physical model and it can indicate the relationship between gate drive resistor, the IGBT capacitance, trans-conductance and switching process. An inverter employing a switching pattern as sinusoidal PWM (SPWM) was designed and experiment was carried out to test the switching waveforms under different output currents. Switching loss under different currents was also measured and compared with calculated value using mathematical equation proposed in this paper.

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 A resolution at 100 K in-house. The crystals have unit-cell parameters a = 121.2, b = 66.3, c = 70.0 A, alpha = gamma = 90, beta = 107.4 degrees and belong to space group C2. Assuming the presence of six molecules per asymmetric unit, the solvent content is estimated to be about 28%.

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 A 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 A 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 A, alpha = beta = 90, gamma = 120 degrees 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%.