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1,358 results on '"Zhao, Jianfeng"'

209. A multi-task transient stability assessment method adapted to topology changes using multi-graph sample and aggregate-attention network.

Author

Huang, Lingxiang, Dong, Kun, Zhao, Jianfeng, Liu, Kangli, Jin, Cheng, Guo, Xirui, Liu, Chao, and Shi, Fang

Subjects
MULTIGRAPH, TOPOLOGY, ELECTRIC power distribution grids, LOSS control
Abstract

Transient stability assessment (TSA) plays a pivotal role in guiding power grid risk control strategies. However, it faces challenges when dealing with complex multi-graph inputs generated by pre-fault, fault occurrence, and post-fault states. Meanwhile, most previous research studies neglected the assessment of the transient stability level. To address this, we propose a multi-task transient stability assessment (MTTSA) approach. In MTTSA, we introduce a multi-graph sample and aggregate-attention network (GraphSAGE-A) designed to capture stability features even amidst topology changes. A multi-head attention mechanism and local normalization method are adopted for a better extraction of the global and contextual information. Additionally, we introduce a quantified transient stability risk index considering the transient stability boundary and incorporate a multi-task dense structure to enhance MTTSA's performance. Empirical tests, under changing operating conditions, conducted on the IEEE 39-bus system showcase a significant performance improvement with the proposed MTTSA method. [ABSTRACT FROM AUTHOR]

Published
2024
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210. Multi‐Hydrogen Bonds Enhanced Anchoring Effect Enabling High‐Efficiency Blue Phosphorescence, Single‐Molecule White Light, and Tunable Colorful Emission with Quantitative Energy Transfer.

Author

Xie, Yingjie, Wang, Zepeng, Yu, Peng, Zhang, Lan, Geng, Yun, and Zhao, Jianfeng

Subjects
ANCHORING effect, PHOSPHORESCENCE, ENERGY transfer, POLYMER films, STRUCTURAL optimization
Abstract

Ultralong organic room‐temperature phosphorescence (RTP) materials, especially high‐energy blue emission materials, have attracted tremendous attention but remain difficult to achieve. Here, a strategy based on the multi‐hydrogen bonds enhanced anchoring effect is developed to activate single‐molecule blue phosphorescence emission with the highest efficiency of 29.79%. Specifically, the aromatic electrophilic directing (AED) effect provides a rational explanation for the structural spectral change. The construction of artificial light‐harvesting systems via physical blending achieves on‐demand modulation for afterglow color, including white afterglow. Furthermore, cold‐white emission is also achieved via a structural π‐extension optimization strategy. Moreover, the high transmittance and reversible water‐sensitivity render these polymer films with applicability as smart organic optoelectronic materials. [ABSTRACT FROM AUTHOR]

Published
2024
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211. Genome-Wide Analysis of the HD-Zip Gene Family in Chinese Cabbage (Brassica rapa subsp. pekinensis) and the Expression Pattern at High Temperatures and in Carotenoids Regulation

Author

Yin, Lian, primary, Sun, Yudong, additional, Chen, Xuehao, additional, Liu, Jiexia, additional, Feng, Kai, additional, Luo, Dexu, additional, Sun, Manyi, additional, Wang, Linchuang, additional, Xu, Wenzhao, additional, Liu, Lu, additional, and Zhao, Jianfeng, additional

Published
2023
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244. High-Reliability Rotor Position Detection Method for Sensorless Control of Synchronous Condenser.

Author

Shi, Xiangjian, Liu, Teng, Mu, Wei, and Zhao, Jianfeng

Subjects
SIGNAL sampling, SYNCHRONOUS capacitors, ROTORS, FREQUENCY changers, POWER capacitors
Abstract

Static frequency converters (SFCs) are very important for starting the connection of synchronous capacitors to the power grid, which is beneficial for ensuring the impact of electric vehicle connection on the inertia of the power grid. In the traditional sensorless initial rotor position detection method, the signal-to-noise ratio of the induced voltage at the machine terminal is small, making it difficult to accurately extract the rotor position. In this study, a reliable initial position detection method for a sensorless-controlled synchronous machine drive is proposed. A step excitation voltage was applied to the excitation circuit before the motor was started, and the three-phase induction voltage at the terminals was sampled in real time. The sampling signal was processed in two ways: digital filter processing and stator flux calculation. The accuracy of the initial rotor position is determined by comparing the differences between the two results. This algorithm does not depend on additional hardware circuits and has fewer setting parameters; therefore, it is easy to apply in engineering applications. Finally, a comparative experiment was conducted using a real-time digital system (RTDS) to verify the feasibility and effectiveness of the proposed method. The proposed rotor position detection method can effectively improve the detection reliability and ensure the start-up reliability of SFCS. [ABSTRACT FROM AUTHOR]

Published
2023
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245. Open-Circuit Fault Diagnosis and Analysis for Integrated Charging System Based on Bidirectional Gated Recurrent Unit and Attention Mechanism

Author

Zhou, Jingyang, Liu, Kangli, Zhao, Jianfeng, Wang, Qingsong, Jin, Cheng, Pan, Xiaogang, Zhang, Congyue, and Chen, Peng

Abstract

Due to the widespread adoption of electric vehicles, integrated charging stations have been increasingly applied. However, because of the extensive number of components, when a fault occurs, how to identify the faulty components is a great challenge. In this article, considering the power conversion system of integrated charging stations, the impact of internal open-circuit faults in IGBTs and capacitors, along with fault identification methods, is discussed. By combining signal processing and deep learning for fault localization, the neural network model based on the bidirectional gated recurrent unit (Bi-GRU) and attention mechanism is proposed, which can flexibly learn crucial information, enhance the perception of important segments in sequences, and achieve higher accuracy in open-circuit fault identification. Through comparative analysis of the validation set among different models, the effectiveness and advantages of the proposed model and analysis are proved. The proposed method has good versatility and can be used for fault identification and operation reliability improvement for other power electronics-based systems.

Published
2024
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246. Boundaries Extension of Stability Region and z-Domain Controller Implementation for Grid-Forming Converters

Author

Zhang, Sen, Liu, Kangli, Zhao, Jianfeng, Tian, Wei, Jin, Cheng, Kennel, Ralph, and Heldwein, Marcelo Lobo

Abstract

Grid-forming (GFM) converters can support system voltage and frequency, which promotes the integration between distributed generations and power grid. Due to the time delay of digital control, the virtual impedance exhibits opposite damping characteristics on both sides of 1/6 of the sampling frequency (fs/6). The stable operation of GFM converters can be achieved by setting a reasonable damping feedback coefficient in each separate frequency interval. However, the load or line impedance variation may cause the resonant frequency of LC filter to cross the frequency boundary, so GFM converters will not be stable when the resonant frequency is near the frequency boundary. In this article, an improved active damping control with a lead compensator is proposed to achieve positive damping from 0 to fs/4, which eliminates the instability resonant frequency region, and the stability of GFM converters is significantly improved. Then, the procedures of parameter tuning for obtaining the maximum system damping are presented. Furthermore, the discrete-time domain resonant controller is proposed to acquire a high-performance voltage control, which brings a fast transient response without overshoot for output voltage. Finally, experimental results verify the effectiveness of the analysis.

Published
2024
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247. Containment-Based Distributed Cooperative Control of Microgrid Clusters: Accurately Constraining the Bus States of Loads and Microgrids

Author

Zhang, Congyue, Zhao, Jianfeng, Dou, Xiaobo, Hu, Qinran, Leng, Jingwen, and Liu, Kangli

Abstract

Collaborative control of microgrid clusters is challenging due to their nested control structures and the integration of heterogeneous microgrids. Besides, the wide coverage also causes some remote and sensitive industrial loads to face degraded voltage levels in the cluster system. To tackle these challenges, this work develops a novel distributed control strategy for islanded microgrid clusters. The strategy introduces tracking differentiator technology to unify different inner dynamics in heterogeneous microgrids, making them able to be coordinated in the same distributed network. Additionally, to accurately maintain the voltage level of sensitive and remote loads during distributed coordination, a containment control scheme that designs the leaders based on the running bus states of selected loads is developed. This scheme can flexibly and accurately converge the bus states of selected loads and controlled microgrids into a predefined containment range. Furthermore, to prevent instability caused by extended buffer time, a prediction-based mechanism is proposed to compensate for asynchronous delays. Finally, the effectiveness of our strategy is validated through several simulation cases and an RTLAB-based experiment.

Published
2024
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248. BMI Modifies the Association Between Depression Symptoms and Serum Copper Levels

Author

Wu, Hongrong, Li, Qingqi, Gao, Rong, Tang, Shuangyang, Zhang, Kaifang, and Zhao, Jianfeng

Subjects
Inorganic Chemistry, Endocrinology, Diabetes and Metabolism, Biochemistry (medical), Clinical Biochemistry, General Medicine, Biochemistry
Abstract

Depression is one of the most common mental disorders which dramatically threatens public health and wellness. Copper has been known to be involved in many biological processes that could help explaining the occurrence of depression. However, studies focusing on its effect have yielded mixed results. The present study aims to evaluate the association between serum copper levels and depression symptoms. It also investigates the effect of modification of BMI (body mass index) on depression symptoms. A total of 5419 US adults aged 20 years or older from the National Health and Nutrition Examination Survey (NHANES) 2011-2016 participated in the cross-sectional study. Logistic regression models were applied using depression levels as the outcome and serum cooper/selenium/zinc categories as the main predictor, with the adjustments of gender, age, marital status, race, education, family income level, alcohol drinking, cigarette smoking, diabetes, pressure, stroke, and BMI. The interaction terms for copper levels and other covariates were further incorporated into the model to assess their roles in predicting depression symptoms. The prevalence of depression symptoms was significantly higher in samples with a high copper level. Among the levels of serum copper, selenium, and zinc, only the association between depression symptoms and serum copper levels was observed to be significant in the unadjusted model (P = 0.002). Individuals with a high copper level (114-134 μg/dL) and a very high copper level (≥ 134 μg/dL) had 1.85 (95% CI 1.24, 2.77)- and 1.72 (95% CI 1.21, 2.44)-fold higher odds ratio of depression symptoms, respectively, compared to those with a normal serum copper level. Although the association was not significant in the adjusted models, in which confounders were added, the interaction of copper level, including high and very high copper levels, and obesity (BMI ≥ 30 kg/m

Published
2022
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250. Minimum hydrogen consumption power allocation strategy for the multi-stack fuel cell (MFC) system based on a discrete approach

Author

Liang, YiFan, Liang, QianChao, Zhao, JianFeng, and He, JunNeng

Subjects
Economics and Econometrics, Fuel Technology, Renewable Energy, Sustainability and the Environment, Energy Engineering and Power Technology
Abstract

In high-powered application scenarios, a multi-stack fuel cell system (MFCS) could have advantages such as higher robustness, lifetime, and reliability than a single-stack fuel cell system. In particular, MFCS could maintain a high efficiency and increase system redundancy by power configuration between subsystems. In order to reduce the operational expenses for systems, a reasonable power management strategy is necessary to minimize the hydrogen consumption of MFCS. First, the power-hydrogen consumption curve of the single-stack fuel cell system is discretized from experimental measurements. Next, the discrete data are reassembled by the inverse derivation of the dynamic programming method to produce a minimum solution for the hydrogen consumption in the output power range. It is found that the strategy varies depending on activated state On or Off. Finally, two power allocation strategies are developed and modeled in a lookup-table block considering the activated state. The optimal stack output power strategy is analyzed with four stacks. The results indicate that the hydrogen consumption is smaller and more efficient than the other allocation strategies. It can respond to the load demand with a high efficiency sooner than the average strategy.

Published
2022
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