Table of Content

25 October 2020, Volume 48 Issue 10

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Energy, Power & Electrical Engineering

Analysis and Design of Bidirectional CLLC Resonant Converter Based on GaN Devices



DU Guiping, ZHENG Yanbin, LIU Yuanjun, et al

2020, 48(10):  1-10.  doi:10.12141/j.issn.1000-565X.190866

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GaN device has the advantages of fast switching speed，low on-off resistance，small parasitic parameters and low reverse recovery loss． As compared with other devices，it is more conducive to realizing the high frequency and high efficiency of bidirectional CLLC resonant converter． In this study，based on the characteristics of GaN de-vices，the resonance frequency of the bidirectional CLLC resonant converter was analyzed and calculated by using Thevenin equivalent theorem，and the condition to realize the soft switch was improved according to the charging and discharging characteristics of parasitic capacitance of switch tube． Finally，a bidirectional CLLC resonant con-verter based on GaN device was developed． An experimental prototype of bidirectional CLLC resonant converter with a rated power of 400W was built to achieve zero-voltage turn-on (ZVS) on the inverter side in all load range and zero-current turn-off (ZCS) on the rectifier side in a specific load range． Its maximum efficiency can reach to 97. 02% in the forward mode and 95. 96% in the reverse mode，and its maximum operating frequency is 548kHz．With features of high frequency and high efficiency，it verifies the correctness and effectiveness of the analyzed and designed converter．


Passivity-Based Control of Primary-Side and Secondary-Side Rectifier Bridge in Wireless Power Transfer System for Electric Vehicle



YANG Jinming SUN Jieshan LIU Runpeng

2020, 48(10):  11-18,47.  doi:10.12141/j.issn.1000-565X.190847

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A passivity-based control method for primary-side and secondary-side rectifier bridges of dynamic wire-less power transfer system for electric vehicle (EV) was proposed in this paper． It can realize power factor correc-tion and constant voltage control on both sides under the fluctuation of mutual inductance and load． Firstly，the control target was proposed，and the Euler-Lagrange (EL) model of the bridge was established． Then，based on the characteristics of dynamic wireless power transfer system，the passivity-based control law based on PI correction was designed． The control algorithm was verified by simulation in SIMULINK and the feasibility of the control me-thod was proved in the experimental platform．


Multi-Step Forecasting for Lighting and Equipment Energy Consumption in Office Building Based on Deep Learning



ZHOU Xuan LEI Shangpeng YAN Junwei

2020, 48(10):  19-29.  doi:10.12141/j.issn.1000-565X.190546

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Multi-step forecasting for lighting and equipment energy consumption is important for fine management of building energy，regulation of power load and other areas related to building energy saving． However，due to the uncertainty，randomness and nonlinearity caused by multiple factors，such as indoor human behavior，external en-vironment and relative humidity，it is difficult to make accurate prediction of lighting and equipment energy con-sumption． In this paper，the distribution tendency of time series of sub-item energy consumption in large-scale of-fice building was analyzed，and a multi-step forecasting method for lighting and equipment energy consumption was put forward based on long-short term model． Moreover，parameter selection issues concerning the deep learning model，such as the number of hidden layer，the number of hidden layer neurons and the times of iterations depth were discussed，and the influence of sample size on the model accuracy was investigated． Simulation results show that the average accuracy of the 24h multi-step forecasting model based on deep learning is improved by 13. 25% and 4. 23% respectively compared with that of the BP neural network and least squares support vector machine．


Decentralized Reactive Power Control for Distribution Systems Considering Voltage Maintain and Loss Reduction



ZHONG Lingshu GUAN Lin

2020, 48(10):  30-39.  doi:10.12141/j.issn.1000-565X.200124

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The increase of system loss and voltage out-off-limit caused by the massive access of distributed power sources such as photovoltaic and wind turbine bring new challenges to the secure and economical operation of distri-bution networks． This study put forward a decentralized reactive power control strategy for distribution systems to address this problem．According to the strategy，each distributed generator only regulate the reactive power accord-ing to the local synchronous phasor measurement data and the low-voltage alarm broadcasted by the surrounding load buses to minimize the total active power loss and maintain nodal voltages in the system． The proposed strategy estimates the sensitivity of the system loss with aspect to local reactive injection according to the linearized distribu-tion network model using the local voltage phasor measurement． Then it minimizes the total active loss with local re-active power control． The optimal voltage support strategy for load buses by distributed generators is presented to re-pair the low-voltage of load buses with the minimum power loss cost． As compared with the existing distributed re-active power regulation strategy based on feedback control，the proposed strategy can minimize the system loss with local reactive power control，so there is no communication requirement between distributed generators． After receiv-ing the low-voltage alarm of the load buses，the low-voltage can be maintained by only one regulation，so there is no need to monitor the load node's voltage for a long time．



Architecture & Civil Engineering

Vertical Temperature Gradient Model of Concrete Box Girders Based on Ｒeal-Time Shadow Technology



SHENG Xingwang, ZHENG Yanhuang, ZHENG Weiqi, et al

2020, 48(10):  40-47.  doi:10.12141/j.issn.1000-565X.190279

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Ambient temperature，sunshine duration，and solar radiation intensity are three important parameters af-fecting the vertical temperature gradient of the concrete box girder． However，the current code temperature gradient model does not consider the significant differences in environmental and thermodynamic parameters between re-gions． In order to accurately reflect the differences in temperature patterns across regions in China，the representa-tive cities of typical climate regions were selected． Based on real-time shadow technology，the thermodynamic ana-lysis model of concrete pavement and asphalt concrete pavement concrete box girder was established by ANSYS，and the real-time temperature field and vertical temperature gradient of the concrete box girder were studied． The study shows that the maximum vertical temperature gradient value of the concrete box girder appears in Xi'an，and its vertical temperature gradient curve can be fitted by exponential function and straight line． The distribution of vertical temperature gradient in China's current highway code differs from that of actual temperature gradient to some extent． In the code，the temperature gradient at the top of box beams using concrete paving is too large，and the temperature gradient at the top of box beams using asphalt concrete paving is too small． As compared with the con-crete pavement，the 9 cm-thickness asphalt concrete pavement can reduce the upper limit value of the maximum vertical positive temperature gradient of the box girder by 4 ℃，the lower limit value by 3 ℃ and the occurrence time by two hours．


Application of Improved Particle Swarm Mutation Algorithm to Building Energy-Saving Optimization



LIU Gang, WANG Mo, DONG Weixing, et al

2020, 48(10):  48-55.  doi:10.12141/j.issn.1000-565X.190824

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When particle swarm optimization algorithm is used in the building energy-saving optimization，it is easy to converge untimely in the local optima due to the multi-peak characteristic of the building energy model． The combination of the distributed mutation operator and particle swarm algorithm can provide a solution to this pro-blem． In this paper，4 existing particle swarm mutation algorithms were studied． Aiming at the problem of low effects of optimization，the specific operations of the mutations were improved，and the effectiveness of 4 improved algo-rithms was verified by test functions． Then，they were applied to a building energy-saving optimization case． Experi-mental results show that，as compared with the existing particle swarm mutation algorithms，the improved algorithm can decrease the average value of object function by 1. 3% at least and increase the convergence rate by over 3 times，which means that the optimization effect is obviously improved． Thus，it is concluded that the improved al-gorithms is effective and applicable in general building energy-saving optimization．


Experimental Study on Mechanical Behavior of RC Beams Based on Compressive Force Path Method



XIONG Ergang, ZU Kun, ZHANG Qian, et al

2020, 48(10):  56-66,87.  doi:10.12141/j.issn.1000-565X.190919

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In order to study the mechanical behavior of reinforced concrete beams based on compressive force path method，six groups of specimens with shear-to-span ratios of 4. 0，3. 0，2. 5，2. 0，1. 5 and 1. 0，with two beams in each group，were designed． Through the monotonic loading test，the influence of different shear-to-span ratios on the mechanical behavior of reinforced concrete beams based on compressive force path method was investigated． By comparing the results with those of reinforced concrete beams under the Chinese code for design of concrete struc-tures，the mechanical properties such as failure process and failure mode，ultimate load，load-deflection curves and load-strain curves were analyzed． The results show that the stress transmitted along the compressive force path is the main factor affecting the shear capacity of the test beams． Under the six different shear-to-span ratios in the test，the shear capacity of the beam reinforced by the compressive force path method can be well guaranteed，and the ul-timate loads are not significantly different from those of the beams designed by the current code in China，but the amount of shear stirrup according to the compressive force path method can be desirably reduced． In addition，more stirrups can be saved with smaller shear-to-span ratio． The effectiveness and rationality of the compressive force path method was finally verified by experiments．


Optimization of Force State of Stiffened Long Cantilever Concrete Box Girder During Construction



SONG Xuming, LI Mengran, LAI Mingyuan, et al

2020, 48(10):  67-75.  doi:10.12141/j.issn.1000-565X.190854

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The prestressed concrete box girder bridge with long cantilever plates often has lateral and oblique cracks at the segmental junction during the construction process． In order to formulate reasonable measures to improve the cracks，the mechanism of crack development was studied． The bridge segment model was established by MIDAS FEA software and the shear lag effect under self-weight and pre-stress was analyzed． The finite element model was verified by comparing the finite element results with the measured values． By changing the tension sequence of the prestressed tendons，the stress state of the sections under different working conditions was studies． The results show that the insufficient compressive stress caused by shear lag effect at the end of the cantilever plate is one of the fac-tors contributed to the cracks at the cantilever end，and this can be improved by adding reinforcement at the canti-lever end． By reasonably changing the tension sequence of the prestressed tendons，the structural pretreatment and stress state can be effectively improved and the cracks during construction process can be reduced．


Mechanical Engineering

Online Detection System of Bearing Roller's Surface Defects Based on Computational Vision



WEN Shengping, ZHOU Zhengjun, ZHANG Xiaoyan, et al

2020, 48(10):  76-87.  doi:10.12141/j.issn.1000-565X.190890

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A reasonable detection algorithm for surface defects in bearing rollers was designed based on the analysis of some most common surface defect types． It combines the traditional computer vision method with deep learning and adopts the improved ＲetinaNet model to realize the surface defect detection of bearing rollers． The experimental results show that the accuracy of this method is more than 95%． As compared with the traditional defect detection method，the proposed detection algorithm can make improvement in accuracy，recall rate and F1-score．


Coupling Among Filling Velocity，Layer Thickness and Nozzle Temperature in Fused Deposition Modeling Process



CHEN Songmao CHEN Yulin

2020, 48(10):  88-95.  doi:10.12141/j.issn.1000-565X.200093

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In the process of fused deposition modeling，the interactive coupling effects of filling velocity with layer thickness and nozzle temperature affects the forming accuracy of the parts． In this paper，a double-variate experi-ment on two types of PLA samples was conducted． Taking dimensional accuracy as the assessment index，ANOVA and multivariate nonlinear regression analysis were used to study the coupling mechanism among filling velocity，layer thickness and nozzle temperature．Results show that: (1) the interactive coupling effect of filling velocity with layer thickness and nozzle temperature has a significant impact on the dimensional accuracy of parts; (2) the di-mensional size and shape of parts could affect the coupling control function construction of filling velocity，layer thickness and nozzle temperature; and (3) by employing the coupling control method of filling velocity with layer thickness and nozzle temperature，dimensional deviation of FDM parts can be effectively improved and stabilized．


Wake Vortex Shedding Flow Analysis of Two-Dimension Airfoil with Different Reynolds Numbers



YANG Xiaopei, WANG Wei, JIANG Boyan, et al

2020, 48(10):  96-104,112.  doi:10.12141/j.issn.1000-565X.200021

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The wake vortex shedding flow mechanism of airfoils at different Reynolds numbers (Re =5 ×10⁴ ，1 ×
10⁵ ，2 ×10⁵ ，5 ×10⁵ ，respectively) was analyzed in this paper，by generating algebraic meshes with Hermite in-
terpolation function． The results show that，when periodic flow occurs，Strouhal number increases with the increase
of Re at the same angle of attack as the fluid viscosity decreases; and that，the variation of lift coefficient of airfoil
is consistent with that of wake vortex shedding． The peak lift coefficient appears just after the tail edge counter-
clockwise vortex sheds，while the valley lift coefficient appears when the tail edge counterclockwise vortex reaches
the maximum size． When the airfoil enters the periodic flow state，the development law of wake vortex shedding is
2S (Single) mode first，then 2P (Pair) mode，chaotic state，and finally quasi-periodic flow state，as the angle of
attack increases． The investigation into the aerodynamic characteristics and wake vortex shedding mechanism pro-
vides a basis for the design of flow control methods．


Inherent Characteristics Analysis and Optimization of Powertrain Mounting Systems Involving Fuzzy Uncertainty



Lü Hui, YANG Kun, HUANG Xiaoting, et al

2020, 48(10):  105-112.  doi:10.12141/j.issn.1000-565X.200026

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In engineering practice，various uncertainties inevitably exist in the powertrain mounting system (PMS) of vehicle． In this study，fuzzy variables were introduced to address the uncertain parameters of a PMS involving fuzziness． Firstly，the fuzzy Monte-Carlo method (FMCM) was developed to calculate the fuzzy responses of inhe-rent characteristics of PMS． Then，an efficient analysis method named as fuzzy perturbation-central difference me-thod (FPCDM) was derived to improve computational efficiency． Next，the reliability-based analysis and design optimization method of the PMS with fuzziness was proposed based on FPCDM． Finally，the effectiveness of the pro-posed method was verified by a numerical example，and the fuzzy reliability and optimal design of the PMS with fuzziness were also investigated．


Electronics, Communication & Automation Technology

Triboelectric Nanogenerator Based on MoS 2 /Graphene Composite



GENG Kuiwei XU Zhiping LI Xu

2020, 48(10):  113-119,128.  doi:10.12141/j.issn.1000-565X.190642

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A triboelectric nanogenerator (TENG) based on MoS₂ /Graphene composite nanomaterial embedded in electron-receiving layer was prepared． The effects of different electron-receiving layers on the output voltage re-sponse，the frequency response and the load response of TENG were studied，and the related enhancement mecha-nism was also discussed． Under the working frequency of 5Hz，the output voltage of TENG embedded in the elec-tron-accepting layer is increased by 3 to 8 times，as compared with that of the TENG without the embedded elec-tron-accepting layer． At the optimum external load impedance，the maximum output power of the TENG (TENG-M/G) with the electron-receiving layer of MoS₂ /Graphene is 23 times that of the TENG (TENG-PI) with the elec-tron-receiving layer of polyimide film． By analyzing the total transfer quantity of electric charge，the causes of the difference in output among TENGs with different electron-accepting layers were discussed． In order to further prove the experimental results，metal-insulator-semiconductor (MIS) devices with different doped PI films as gate insula-ting layers were prepared． By analyzing its C-V characteristic curve at 1 kHz，the internal mechanism causing the difference of TENG output and the charge trapping effect of MoS₂ /Graphene composite in TENG were discussed．


Research on Energy Efficiency of Cloudlet-Enhanced Fiber-Wireless Access Network



YANG Jing, WU Xiaodang, ZHANG Ruoying, et al

2020, 48(10):  120-128.  doi:10.12141/j.issn.1000-565X.190828

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In order to solve the problem of high energy consumption of nodes in the cloudlet enhanced fiber-wireless access network，a resource management scheme for cooperative hibernation and scheduling was proposed． This study used signaling frame interaction in the optical domain to obtain a service request and a cloud server buffer backlog，and adopted a load level-aware bandwidth allocation manner to formulate a sleep time slot for ensuring service coexistence． At the same time，combining with bandwidth configuration and wireless node energy optimiza-tion，the wireless domain node power state was scheduled during the allocation of time slots of the optical domain node，thereby reducing network energy consumption． The simulation results show that the proposed method can ef-fectively improve the energy efficiency of the whole network．


Reading Ｒecognition Method of Pointer-Type Meter Based on Accurate Scale Localization



XIANG Youjun JIANG Wen RUAN Rongju

2020, 48(10):  129-135.  doi:10.12141/j.issn.1000-565X.200013

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In order to solve the problem that the reading recognition of pointer-type oil-level meter is easily affected by the change of shooting angle and illumination conditions，a new method for recognizing the readings based on ac-curate scale location was proposed by considering the characteristics of pointer in the industrial production． It only uses the scale and pointer to calculate the reading of meter． In this method，firstly the images of oil-level meter taken by the patrol robot was preprocessed; then all possible scale areas in the picture were recognized coarsely;and finally the scale was accurately located by fine recognition． In view of the problem that the traditional instru-ment recognition method is hard to solve the relationship between the center of the circle and the center line of the pointer is not certain to be established when the shooting angle is large，this paper adopted an improved method to select the center of the circle． This method is more suitable for the calculation under the influence of the shooting angle change，and can improve the reading accuracy． The experimental results show that the reading accuracy of the instrument obtained by this method is 99. 08% on average，and the algorithm is reliable and stable．


Identification of Rice Pests Based on Space Transformation by Elliptic Metric Learning



BAO Wenxia, QIU Xiang, HU Gensheng, et al

2020, 48(10):  136-144.  doi:10.12141/j.issn.1000-565X.200078

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To improve the accuracy of identification of rice pest，an algorithm was proposed in this study． Firstly，the U-Net network of deep semantic segmentation was used to remove the influence of complex background． Then，the sliding window method was used to extract the HSV color feature and the scale-invariant local ternary pattern (SILTP) texture feature of rice pest images． The feature vector was formed by gathering the maximum value of the features in the same horizontal sliding window． Then the discriminative features of the rice pest images were ob-tained by the Relief-F optimization algorithm． At the same time，an elliptic metric with good distinguishability for data was introduced in this study． The nonlinear transformation that reflects the space structure and semantic infor-mation of rice pest image features was determined via elliptic metric learning． Then the model for the potential rela-tionship among rice pest image features was built． This model reduced the distance between same-class features but increases the distance between different-class features． In elliptic metric learning，the regular term of the Frobenius norm was added to the triple constraint function to avoid overfitting and improve generalization ability． Finally，the elliptic metric matrix was used to transform the features of the rice pest images into a new feature space． Thereby，the identification performance of the SVM classifier was improved． The identification results of 13 kinds of common rice pests show that the proposed method can significantly promote the few-shot identification accuracy of rice pest images in complex background and can provide valuable reference for the intelligent recognition of crop pest in pre-cision agriculture．