Topology and start-up strategy for DC-DC transformers based on voltage balancing unit

Zhang, Jialin,Zha, Kunpeng,Tang, Xiaojun,Yang, Yuefeng,Yan, Hui,Wen, Fuyue,Shi, Mingming The Korean Institute of Power Electronics 2021 JOURNAL OF POWER ELECTRONICS Vol.21 No.7

As a core piece of equipment in DC distribution networks, DC solid-state transformers (DCSSTs) are attracting more and more attention in academia and industry. Due to the limitations in terms of the electrical stress of the switches, the input series output parallel (ISOP) structure is adopted in DCSSTs. This paper proposed an improved DCSST topology based on a voltage balancing unit (VBU). This topology has the advantages of higher power density, reduced weight, and cascaded number without compromising efficiency, cost, or reliability. The working modes, mathematical models, and control strategy are analyzed. In addition, a start-up strategy and a parameter design method are proposed in this paper. Simulation and experimental results verify the correctness and effectiveness of the proposed solution. The proposed DCSST is a practical scheme for the application of DC distribution networks.

Effect of proton irradiation on interfacial and electrical performance of N+Np+ InP/InGaAs hetero-junction

Zhang Chen,Su Yongbo,Mei Bo,Yang Feng,Zhang Jialin,Yun Huanqing,Liu Bo,Sun Yi,Zhang Haiming,Jin Zhi,Zhong Yinghui 한국물리학회 2023 Current Applied Physics Vol.48 No.-

InP-based hetero-junction bipolar transistors (HBTs) are attractive for various millimeter-wave and terahertz electronics due to their ultrahigh frequency performance. Therefore, the study of their irradiation reliability is extremely urgent. In this work, 2 MeV proton irradiation experiment has been carried out on self-fabricated N+Np+ InP/InGaAs hetero-junction. The degradation mechanisms have systematically been studied after exposure to protons of 5 × 1013 H+/cm2. The voltage range of recombination current at low forward bias has been largely expanded from 0-0.2 V to 0–0.6 V. Furthermore, the interface states properties have been characterized by utilizing the frequency-dependent conductance technique, the interface states density (Dit) has increased from approximately 9.02 × 1012 cm-2 eV-1–1.99 × 1013 cm-2 eV-1 to 9.51 × 1012 cm-2 eV-1–2.00 × 1013 cm-2 eV-1 after irradiation. The study would be great significance for understanding the evolution of proton irradiation on relative devices.

Model Predictive Power Control of a PWM Rectifier for Electromagnetic Transmitters

Jialin Zhang,Yiming Zhang,Bing Guo,Junxia Gao 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

Model predictive direct power control (MPDPC) is a widely recognized high-performance control strategy for a three-phase grid-connected pulse width modulation (PWM) rectifier. Unlike those of conventional grid-connected PWM rectifiers, the active and reactive powers of permanent magnet synchronous generator (PMSG)-connected PWM rectifiers, which are used in electromagnetic transmitters, cannot be calculated as the product of voltage and current because the back electromotive force (EMF) of the generator cannot be measured directly. In this study, the predictive power model of the rectifier is obtained by analyzing the relationship among flux, back EMF, active/reactive power, converter voltage, and stator current of the generator. The concept of duty cycle control in the proposed MPDPC is introduced by allocating a fraction of the control period for a nonzero vector and rest time for a zero vector. When nonzero vectors and their duration in the predefined cost function are simultaneously evaluated, the global power ripple minimization is obtained. Simulation and experimental results prove that the proposed MPDPC strategy with duty cycle control for the PMSG-connected PWM rectifier can achieve better control performance than the conventional MPDPC-SVM with grid-connected PWM rectifier.

Evaluation of the YOLO models for discrimination of the alfalfa pollinating bee species

Zhang Chuan-Jie,Liu Teng,Wang Jinxu,Zhai Danlan,Zhang Youxin,Gao Yang,Wu Hui-Zhen,Yu Jialin,Chen Min 한국응용곤충학회 2024 Journal of Asia-Pacific Entomology Vol.27 No.1

Identifying insect pollinators and their roles in mediating pollen flow is critical to understand the potential gene flow risks of insect pollination-dependent crop species, such as alfalfa. This study was conducted to evaluate and compare the feasibility of You Only Look Once (YOLO) version 3 (YOLOv3), YOLOv5, YOLOv7, and YOLO Representation (YOLOR) to discriminate the three most common alfalfa pollinating bee species, including honeybee, bumblebee, and leafcutting bee. The metrics comparison results showed YOLOv3 and YOLOv5 out performed YOLOv7 and YOLOR regarding model precision, recall, F 1 score, and mAP50 values. YOLOv3 and YOLOv5 could successfully discriminate the three different bee species with an accuracy of almost 100% (99.9%, 99.8%, and 100% accuracy for honeybee, bumblebee, and leafcutting bee for the two models, respectively). Comparatively, YOLOv7 could discriminate honeybee with an accuracy of 95% but was more likely to mistakenly discriminate bumblebee and leafcutting bee due to the relatively lower discriminating accuracy (87.3% and 66.2%, respectively). While the values of determined parameters for YOLOR were lower than YOLOv3 and YOLOv5, the higher precision (0.99680) along with recall (0.98721), F 1 (0.99198), mAP50 (0.99323), and mAP50-100 (0.89076) values indicate that this model could be able to obtain a favorable performance in discriminating the three bee species. In summary, the proposed method in this study has the potential for identifying the alfalfa pollinating bee species, studying the bees’ flower-visiting behaviors, evaluating the risks of insect-mediated pollen flow, and thus contributing to the management of genetically engineered (GE) alfalfa transgene flow.

Model Predictive Power Control of a PWM Rectifier for Electromagnetic Transmitters

Zhang, Jialin,Zhang, Yiming,Guo, Bing,Gao, Junxia The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

Model predictive direct power control (MPDPC) is a widely recognized high-performance control strategy for a three-phase grid-connected pulse width modulation (PWM) rectifier. Unlike those of conventional grid-connected PWM rectifiers, the active and reactive powers of permanent magnet synchronous generator (PMSG)-connected PWM rectifiers, which are used in electromagnetic transmitters, cannot be calculated as the product of voltage and current because the back electromotive force (EMF) of the generator cannot be measured directly. In this study, the predictive power model of the rectifier is obtained by analyzing the relationship among flux, back EMF, active/reactive power, converter voltage, and stator current of the generator. The concept of duty cycle control in the proposed MPDPC is introduced by allocating a fraction of the control period for a nonzero vector and rest time for a zero vector. When nonzero vectors and their duration in the predefined cost function are simultaneously evaluated, the global power ripple minimization is obtained. Simulation and experimental results prove that the proposed MPDPC strategy with duty cycle control for the PMSG-connected PWM rectifier can achieve better control performance than the conventional MPDPC-SVM with grid-connected PWM rectifier.

A randomized controlled trial to compare the efficacy of regenerated and non-regenerated oxidized cellulose gauze for the secondary treatment of local bleeding in patients undergoing hepatic resection

Chengshuo Zhang,Dazhi Fu,Fengshan Wang,Xinping Zhong,Lei Yang,Gang Wu,Baifeng Li,Jialin Zhang 대한외과학회 2021 Annals of Surgical Treatment and Research(ASRT) Vol.100 No.4

Purpose: Oxidized cellulose is available in many forms, but manufactured using either a regenerated or non-regenerated process. In this study, we evaluated the effects of 2 different hemostatic agents for the treatment of local bleeding in patients undergoing hepatic resection. Methods: This was a monocentric, parallel-group, randomized, and controlled clinical trial to compare oxidized regenerated cellulose gauze (ORCG) with oxidized non-regenerated cellulose gauze (ONRCG) in patients undergoing hepatectomy. The primary endpoint was the time to hemostasis at the target bleeding site. The secondary endpoints were the postoperative drainage volume on the first 2 days after surgery and the hospital stay. Results: There was no significant difference between the ORCG and ONRCG groups in time to hemostasis from column analysis (238.8 ± 121.6 seconds vs. 193.7 ± 85.3 seconds, P = 0.068), and there were no differences in the rates of hemostatic success between the 2 groups at 120 seconds (18.4% vs. 24.3%; odds ratio [OR], 0.703; 95% confidence interval [CI], 0.231–2.136) and 300 seconds (71.1% vs. 89.2%; OR, 0.298; 95% CI, 0.085–1.041). However, the ONRCG group was superior to the ORCG group in hemostasis according to the survival analysis (log-rank test, P = 0.044). Moreover, there were also no significant differences between the 2 groups in postoperative drainage volume on the first 2 days (P = 0.436, P = 0.381) and hospital stay (P = 0.537, P = 0.200). Conclusion: ONRCG was not inferior to ORCG as a hemostatic agent in patients undergoing liver resection.

A New Fine-grain SMS Corpus and Its Corresponding Classifier Using Probabilistic Topic Model

( Jialin Ma ),( Yongjun Zhang ),( Zhijian Wang ),( Bolun Chen ) 한국인터넷정보학회 2018 KSII Transactions on Internet and Information Syst Vol.12 No.2

Nowadays, SMS spam has been overflowing in many countries. In fact, the standards of filtering SMS spam are different from country to country. However, the current technologies and researches about SMS spam filtering all focus on dividing SMS message into two classes: legitimate and illegitimate. It does not conform to the actual situation and need. Furthermore, they are facing several difficulties, such as: (1) High quality and large-scale SMS spam corpus is very scarce, fine categorized SMS spam corpus is even none at all. This seriously handicaps the researchers’ studies. (2) The limited length of SMS messages lead to lack of enough features. These factors seriously degrade the performance of the traditional classifiers (such as SVM, K-NN, and Bayes). In this paper, we present a new fine categorized SMS spam corpus which is unique and the largest one as far as we know. In addition, we propose a classifier, which is based on the probability topic model. The classifier can alleviate feature sparse problem in the task of SMS spam filtering. Moreover, we compare the approach with three typical classifiers on the new SMS spam corpus. The experimental results show that the proposed approach is more effective for the task of SMS spam filtering.

Spatial and Temporal Variability of Drought and Precipitation Using Cluster Analysis in Xinjiang, Northwest China

Yuhu Zhang,Pei Xie,Xiao Pu,Fuqiang Xia,Jialin An,Peng Wang,Qiwen Mei 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.2

Analyses of drought and precipitation require long-term historical data and reasonable drought index to ensure reliable monitoring and prediction, especially for the Xinjiang Uygur Autonomous Region, where is sensitive and vulnerable to drought disasters. Drought characteristic was expressed using the observational precipitation data and calculated precipitation threshold at 105 meteorological stations from 1979 to 2014. The results showed that the variation of drought and precipitation was not spatially uniform. Analysis in sub-areas was conducted based on mutli-statistical methods. The historical drought and precipitation situation in Xinjiang is better characterized by three clusters. Cluster 1 is the driest, cluster 2 has a clear increasing trend of precipitation, while cluster 3 is the wettest with the mean annual precipitation approximates to 300 mm. In addition, the precipitation concentration and distribution is becoming uniform, there is a faster rate of increasing precipitation in coolseason rather than in warm-season. The results provide critical support for the drought disasters management and mitigation, it also provide a base for in-depth investigation on the possible mechanisms of regional drought.

Hybrid Control Strategy of Phase-Shifted Full-Bridge LLC Converter Based on Digital Direct Phase-Shift Control

Guo, Bing,Zhang, Yiming,Zhang, Jialin,Gao, Junxia The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

A digital direct phase-shift control (DDPSC) method based on the phase-shifted full-bridge LLC (PSFB-LLC) converter is presented. This work combines DDPSC with the conventional linear control to obtain a hybrid control strategy that has the advantages of linear control and DDPSC control. The strategy is easy to realize and has good dynamic responses. The PSFB-LLC circuit structure is simple and works in the fixed frequency mode, which is beneficial to magnetic component design; it can realize the ZVS of the switch and the ZCS of the rectifier diode in a wide load range. In this work, the PSFB-LLC converter resonator is analyzed in detail, and the concrete realization scheme of the hybrid control strategy is provided by analyzing the state-plane trajectory and the time-domain model. Finally, a 3 kW prototype is developed, and the feasibility and effectiveness of the DDPSC controller and the hybrid strategy are verified by experimental results.

Hybrid Control Strategy of Phase-Shifted Full-Bridge LLC Converter Based on Digital Direct Phase-Shift Control

Bing Guo,Yiming Zhang,Jialin Zhang,Junxia Gao 전력전자학회 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.3

A digital direct phase-shift control (DDPSC) method based on the phase-shifted full-bridge LLC (PSFB-LLC) converter is presented. This work combines DDPSC with the conventional linear control to obtain a hybrid control strategy that has the advantages of linear control and DDPSC control. The strategy is easy to realize and has good dynamic responses. The PSFB-LLC circuit structure is simple and works in the fixed frequency mode, which is beneficial to magnetic component design; it can realize the ZVS of the switch and the ZCS of the rectifier diode in a wide load range. In this work, the PSFB-LLC converter resonator is analyzed in detail, and the concrete realization scheme of the hybrid control strategy is provided by analyzing the state-plane trajectory and the time-domain model. Finally, a 3 kW prototype is developed, and the feasibility and effectiveness of the DDPSC controller and the hybrid strategy are verified by experimental results.