Performance Analysis and Comparison of Post-Fault PWM Rectifiers Using Various Space Vector Modulation Methods

Zhu, Chong,Zeng, Zhiyong,Zhao, Rongxiang The Korean Institute of Power Electronics 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.6

In this paper, some crucial performance characteristics related to the operational reliability of the post-fault Pulse Width Modulated (PWM) rectifiers, such as line current harmonic distortion, Common Mode Voltage (CMV), and current stress on the capacitors, are fully investigated. The aforementioned performance characteristics of post-fault rectifiers are highly dependent on the utilized space vector modulation (SVM) schemes, which are also examined. Detailed analyses of the three most commonly used SVM schemes for post-fault PWM rectifiers are provided, revealing the major differences in terms of the zero vector synthesis approaches. To compare the performances of the three SVM schemes, the operating principles of a post-fault rectifier are presented with various SVM schemes. Using analytical and numerical methods in the time domain, the performances of the line current distortion, common mode voltage and capacitor current are evaluated and compared for each SVM scheme. The proposed analysis demonstrates that the zero vector synthesis approaches of the considered methods have significant impacts on the performance characteristics of rectifiers. In addition, the advantages and disadvantages of the proposed SVM schemes are discussed. The experimental results verify the effectiveness and validity of the proposed analysis.

Performance Analysis and Comparison of Post-Fault PWM Rectifiers Using Various Space Vector Modulation Methods

Chong Zhu,Zhiyong Zeng,Rongxiang Zhao 전력전자학회 2016 JOURNAL OF POWER ELECTRONICS Vol.16 No.6

In this paper, some crucial performance characteristics related to the operational reliability of the post-fault Pulse Width Modulated (PWM) rectifiers, such as line current harmonic distortion, Common Mode Voltage (CMV), and current stress on the capacitors, are fully investigated. The aforementioned performance characteristics of post-fault rectifiers are highly dependent on the utilized space vector modulation (SVM) schemes, which are also examined. Detailed analyses of the three most commonly used SVM schemes for post-fault PWM rectifiers are provided, revealing the major differences in terms of the zero vector synthesis approaches. To compare the performances of the three SVM schemes, the operating principles of a post-fault rectifier are presented with various SVM schemes. Using analytical and numerical methods in the time domain, the performances of the line current distortion, common mode voltage and capacitor current are evaluated and compared for each SVM scheme. The proposed analysis demonstrates that the zero vector synthesis approaches of the considered methods have significant impacts on the performance characteristics of rectifiers. In addition, the advantages and disadvantages of the proposed SVM schemes are discussed. The experimental results verify the effectiveness and validity of the proposed analysis.

Numerical study on the moment capacity of zed-section purlins under uplift loading

Zhu, Jue,Chen, Jian-Kang,Ren, Chong Techno-Press 2014 Structural Engineering and Mechanics, An Int'l Jou Vol.49 No.2

In this paper a nonlinear finite element analysis model is established for cold-formed steel zed-section purlins subjected to uplift loading. In the model, the lateral and rotational restraints provided by the sheeting to the purlin are simplified as a lateral rigid restraint imposed at the upper flange-web junction and a rotational spring restraint applied at the mid of the upper flange where the sheeting is fixed. The analyses are performed by considering both geometrical and material nonlinearities. The influences of the rotational spring stiffness and initial geometrical imperfections on the uplift loading capacity of the purlin are investigated numerically. It is found that the rotational spring stiffness has significant influence on the purlin performance. However, the influence of the initial geometric imperfections on the purlin performance is found only in purlins of medium or long length with no or low rotational spring stiffness.

Experimental Study and Numerical Simulation of Precast Shear Wall with Rabbet-Unbonded Horizontal Connection

Chong-fang Sun,Shu-ting Liang,Xiao-jun Zhu,Hu Li,Jian-min Guo,Gang Li,Ya-min Song,Dong-yue Wu 한국콘크리트학회 2020 International Journal of Concrete Structures and M Vol.14 No.1

This paper reports the results of a seismic performance study of a precast shear wall with a new horizontal connection. The new connection is the rabbet-unbonded horizontal connection, which is composed of rabbets and unbonded rebar segments. The rabbets are used to improve the shear capacity and prevent slippage of the connection, and the unbonded rebar segments are used to improve the ductility and energy dissipation. Three specimens were tested with different parameters under cyclic quasi-static loading. The test results showed that the specimen with a larger unbonded level had a richer hysteresis curve, larger ductility, larger energy dissipation, and slightly smaller bearing capacity. Moreover, in relation to the stiffness degradation, in the initial stage, the specimen with a larger unbonded level had a smaller stiffness, whereas in the last stage, the stiffnesses were similar regardless of the unbonded level. A parameter analysis using a finite element model proved that the ductility and energy dissipation of a shear wall with the rabbet-unbonded horizontal connection increased with the unbonded length and level. In addition, when the axial compression ratio increased, the bearing capacity increased, but the load-displacement curves decreased more rapidly. It was concluded that the unbonded length and unbonded level could effectively improve the ductility and energy dissipation of a shear wall. However, they should not be too large under high pressure, and the design suggestions for the new connection need further research considering other factors.

Disturbance Observer-Based Patient-Cooperative Control of a Lower Extremity Rehabilitation Exoskeleton

Chong Chen,Shimin Zhang,Xiaoxiao Zhu,Jingyu Shen,Zhiyao Xu 한국정밀공학회 2020 International Journal of Precision Engineering and Vol.21 No.5

Many patients with stroke are suff ering lower limb locomotor dysfunctions all over the world. Body weight supported treadmilltraining has proven to be an eff ective post-stroke rehabilitation training method for these people’s recovery. Nowadays,lower extremity rehabilitation exoskeleton composed of a pair of mechanical legs has been introduced into body weightsupported treadmill training, which can guide and assist the movements of the patient’s legs. However, active movementsof the patient are hardly to be achieved when the rehabilitation exoskeleton is controlled by a commonly utilized positionbasedpassive strategy. Considering the restriction above, a weight supported rehabilitation training exoskeleton device wasdesigned in this paper to ensure the stroke patient can participate in rehabilitation training voluntarily. To realize this goal,a patient-cooperative rehabilitation training strategy based on adaptive impedance control is adopted for the swing phase inthe training. Human–exoskeleton interaction torques are evaluated by a backpropagation neural network and a disturbanceobserver whose stability is proved by Lyapunov’s law. With no additional demand of interaction torque sensors, the complexityof this system is simplifi ed and the cost is reduced. In order to promote the involvement of patient during the rehabilitationtraining, fuzzy algorithm is used to adjust the impedance parameters according to the human–exoskeleton interaction torques. The eff ectiveness of the whole rehabilitation control strategy is demonstrated by experimental results.

웹캠을 이용한 골프공 인식 및 위치추정 시스템

Zhu Jiaqi,Jiang Chong,김강철 한국전자통신학회 2013 한국전자통신학회 논문지 Vol.8 No.12

A golf ball collecting robot in a golf ball driving range has been recently required because it is safer and more economic than a human being. In this paper, the golf ball recognition and distance estimation system based on a neural network and OpenCV is developed for the robot. The simulation results show that the recognition ratio is over 87% for the distance of less than 120cm and accurate rate for distance estimation is over 85% for golf balls in 30-180cm from a webcam. 골프 연습장에서 골프공 수거 시에 인간보다는 로봇이 사고의 염려가 없고 경제적이어서 골프공 수거 로봇과 골프공 인식 및 위치추적 시스템 개발의 요구가 증가되고 있다. 본 논문에서는 실내 골프 연습장에서 골프공을 수거하는 로봇이 골프공을 인식하고, 위치를 추정할 수 있는 영상처리 알고리즘과 시스템을 OpenCV 를 사용하여 개발하였다. 30-180cm 거리에 위치하는 골프공을 대상으로 실험을 수행하였으며, 120cm 이내에서는 87% 이상의 높은 인식률을 얻었으며, 골프공은 실제 거리의 85% 이내에 위치하였다.

Polarization Maintaining Dichroic Beam-splitter and Its Surface Shape Control by Back Side AR Coating

Chong Ma,Gang Chen,Dingquan Liu,Rong-Jun Zhang,Junbo He,Xudan Zhu,Daqi Li 한국광학회 2021 Current Optics and Photonics Vol.5 No.5

Dichroic beam-splitter (DBS) with polarization-maintaining took an important role in the free space quantum telecommunication tests on the Micius satellite of China. In this presentation, we designed and prepared a 50 layer polarization-maintaining DBS coating by a dual ion beam sputtering deposition (Dual-IBS) method. In order to solve a stress problem, an 18 layer special anti-reflection (AR) coating with similar physical thickness ratio was deposited on the backside. By stress compensation, the surface flatness RMS value of the DBS sample decreased from 0.341 λ (@632.8 nm) to 0.103 λ while beam splitting and polarization maintaining properties were almost kept unchanged. Further, we discussed the mechanism of film stress and stress compensation by equation deduction and found that total stress had a strong relationship with the total physical thickness and the ratio of layer materials.

A DoS Detection Method Based on Composition Self-Similarity

( Zhu Jian-qi ),( Fu Feng ),( Chong-kwon Kim ),( Yin Ke-xin ),( Liu Yan-heng ) 한국인터넷정보학회 2012 KSII Transactions on Internet and Information Syst Vol.6 No.5

Based on the theory of local-world network, the composition self-similarity (CSS) of network traffic is presented for the first time in this paper for the study of DoS detection. We propose the concept of composition distribution graph and design the relative operations. The (R/S)d algorithm is designed for calculating the Hurst parameter. Based on composition distribution graph and Kullback Leibler (KL) divergence, we propose the composition self-similarity anomaly detection (CSSD) method for the detection of DoS attacks. We evaluate the effectiveness of the proposed method. Compared to other entropy based anomaly detection methods, our method is more accurate and with higher sensitivity in the detection of DoS attacks.

Coronal Three-Dimensional Magnetic Resonance Imaging for Improving Diagnostic Accuracy for Posterior Ligamentous Complex Disruption In a Goat Spine Injury Model

Xuee Zhu,Jichen Wang,Dan Zhou,Chong Feng,Zhiwen Dong,Hanxiao Yu 대한영상의학회 2019 Korean Journal of Radiology Vol.20 No.4

Objective: The purpose of this study was to investigate whether three-dimensional (3D) magnetic resonance imaging could improve diagnostic accuracy for suspected posterior ligamentous complex (PLC) disruption. Materials and Methods: We used 20 freshly harvested goat spine samples with 60 segments and intact surrounding soft tissue. The animals were aged 1–1.5 years and consisted of 8 males and 12 females, which were sexually mature but had not reached adult weights. We created a paraspinal contusion model by percutaneously injecting 10 mL saline into each side of the interspinous ligament (ISL). All segments underwent T2-weighted sagittal and coronal short inversion time inversion recovery (STIR) scans as well as coronal and sagittal 3D proton density-weighted spectrally selective inversion recovery (3D-PDW-SPIR) scans acquired at 1.5T. Following scanning, some ISLs were cut and then the segments were rescanned using the same magnetic resonance (MR) techniques. Two radiologists independently assessed the MR images, and the reliability of ISL tear interpretation was assessed using the kappa coefficient. The chi-square test was used to compare the diagnostic accuracy of images obtained using the different MR techniques. Results: The interobserver reliability for detecting ISL disruption was high for all imaging techniques (0.776–0.949). The sensitivity, specificity, and diagnostic accuracy of the coronal 3D-PDW-SPIR technique for detecting ISL tears were 100, 96.9, and 97.9%, respectively, which were significantly higher than those of the sagittal STIR (p = 0.000), coronal STIR (p = 0.000), and sagittal 3D-PDW-SPIR (p = 0.001) techniques. Conclusion: Compared to other MR methods, coronal 3D-PDW-SPIR provides a more accurate diagnosis of ISL disruption. Adding coronal 3D-PDW-SPIR to a routine MR protocol may help to identify PLC disruptions in cases with nearby contusion.

Carotid stiffening predicts cardiovascular risk stratification in mid-life: non-invasive quantification with ultrafast ultrasound imaging

Zhengqiu Zhu,Lingshan Chen,Wenjun Liu,Yiyun Wu,Chong Zou,Xinyi Zhang,Shanshan He,Yinping Wang,Bixiao Shen,Xuehui Ma,Hui Gao,Yun Luan,Hui Huang 대한초음파의학회 2022 ULTRASONOGRAPHY Vol.41 No.3

Purpose: The present study investigated the association between Systematic COronary Risk Evaluation (SCORE)-estimated cardiovascular risk and carotid stiffening in a middle-aged population using ultrafast pulse wave velocity (ufPWV).Methods: This study enrolled 683 participants without known cardiovascular disease or diabetes mellitus who underwent ufPWV measurements. Clinical interviews, physical examinations, laboratory findings, carotid intima-media thickness (cIMT), pulse wave velocity (PWV) at the beginning of systole (PWV-BS), and PWV at the end of systole (PWV-ES) were assessed. Each participant underwent an assessment of SCORE risk based on major cardiovascular risk factors (CVRFs), including age, sex, smoking, systolic blood pressure (SBP), and total cholesterol (TC). Crude and adjusted odds ratios (ORs) with 95% confidence intervals and ordinal logistic regression were used. Overall CVRFs were adjusted to assess ORs.Results: cIMT and carotid stiffening in PWV-BS and PWV-ES were significantly different between sex subgroups (all P<0.05), but only PWV-ES increased gradually in age and SCORE-estimated risk subgroups (all P<0.05). Compared with cIMT (r=0.388, P<0.001) and PWV-BS (r=0.159, P<0.001), PWV-ES was more strongly correlated with SCORE categories (r=0.405, P<0.001). Higher PWV-ES values were associated with SCORE categories independently of sex, SBP, TC, and smoking in moderate-risk and high-risk subgroups (OR, 1.63; P<0.001 and OR, 2.12; P=0.024, respectively), but were not independent of age in all risk subgroups (all P>0.05).Conclusion: Carotid stiffening quantified by ufPWV is linked to SCORE categories, and elevated PWV-ES may aid in cardiovascular risk stratification.