DC Voltage Sensorless Control Strategy of Grid-tied Two-stage Three-phase Photovoltaic System

Jianhua Yuan,Feng Gao,Houlei Gao 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

The variable dc voltage generated by photovoltaic (PV) array can be harnessed as much as possible through the well-known two-stage inversion in gridtied configuration, where the controlled dc-link voltage can be maintained stably to ensure the desired low harmonic ac output. Traditionally, the front-end dc Boost converter generally operates to track the maximum power point (MPP) of PV array by directly measuring the input current and voltage, meanwhile the rear-end inverter is controlled to generate sinusoidal output current and keep dc-link voltage unchanged. The PV voltage and dc-link voltage are measured to assist the accurate control of whole PV generation system. This paper proposes a novel control strategy to eliminate both dc voltage sensors assumed in traditional two-stage grid-tied PV system while not downgrade the system performance with regard to the MPPT accuracy and ac output quality. Matlab simulations verified the proposed control strategy with captured waveforms to illustrate its performance.

Theoretical Prediction of Heat Transport in Few-Layer Graphene/ Epoxy Composites

Jianhua Zeng,Jiao Li,Peng Yuan,Ping Zhang 한국고분자학회 2018 Macromolecular Research Vol.26 No.11

Graphene is widely employed to improve the overall thermal conductivity of polymer composites because of its remarkable thermal conductivity. However, the magnitude of its improvement of thermal conductivity is far below the values expected from the remarkably high thermal conductivity of graphene and is very much less than the production cost of graphene, greatly limiting its large-scale applications in the field of thermal management. Therefore, understanding heat transport behaviors within the polymer composites and studying the related influential factors are very important. Here, heat transport behaviors within few-layer graphene (FLG)/epoxy composites are studied using molecular dynamics (MD) simulations. The influences of interfacial thermal resistance, FLG volume fraction and FLG length on overall thermal conductivity of the composites are specifically analyzed, finding that there is a significant interfacial thermal resistance between FLG and epoxy because of the mismatch of the phonon vibration power spectrum (VPS). Furthermore, the interfacial thermal resistance, FLG volume fraction, and FLG length play important roles in improving the overall thermal conductivity of FLG/epoxy composites. Our findings provide a better understanding of the heat transport behaviors within polymer composites and should be useful for future development of various thermal management applications.

Effects of Heteroatom Substitutions on the Crystal Structure, Film Formation, and Optoelectronic Properties of Diketopyrrolopyrrole‐Based Materials

Liu, Jianhua,Walker, Bright,Tamayo, Arnold,Zhang, Yuan,Nguyen, Thuc‐,Quyen WILEY‐VCH Verlag 2013 Advanced functional materials Vol.23 No.1

<P><B>Abstract</B></P><P>Substitution of the heteroatoms in the aromatic end‐groups of three diketopyrrolopyrrole containing small molecules is investigated to evaluate how such substitutions affect various physical properties, charge transport, and the performance in bulk heterojunction solar cells. While the optical absorption and frontier orbital energy levels are insensitive to heteroatom substitution, the materials' solubility, thermal properties, film morphology, charge carrier mobility, and photovoltaic performance are altered significantly. Differences in material properties are found to arise from changes in intra‐ and intermolecular interactions in the solid state caused by heteroatom substitution, as revealed by the single crystal structures of three compounds. This study demonstrates a systematic investigation of structure–property relationships in conjugated small molecules.</P>

Significance of Vesicle-Associated Membrane Protein 8 Expression in Predicting Survival in Breast Cancer

Mengci Yuan,Jianhua Liao,Ji Luo,Mengyao Cui,Feng Jin 한국유방암학회 2018 Journal of breast cancer Vol.21 No.4

Purpose: Vesicle-associated membrane protein 8 (VAMP8) is a soluble N-ethylmaleimide-sensitive factor receptor protein that participates in autophagy by directly regulating autophagosome membrane fusion and has been reported to be involved in tumor progression. Nevertheless, the expression and prognostic value of VAMP8 in breast cancer (BC) remain unknown. This study aimed to evaluate the clinical significance and biological function of VAMP8 in BC. Methods: A total of 112 BC samples and 30 normal mammary gland samples were collected. The expression of VAMP8 was assessed in both BC tissues and normal mammary gland tissues via a two-step immunohistochemical detection method. Results: The expression of VAMP8 in BC tissues was significantly higher than that in normal breast tissues. Furthermore, increased VAMP8 expression was significantly correlated with tumor size (p=0.007), lymph node metastasis (p= 0.024) and recurrence (p=0.001). Patients with high VAMP8 expression had significantly lower cumulative recurrence-free survival and overall survival (p<0.001 for both) than patients with low VAMP8 expression. In multivariate logistic regression and Cox regression analyses, lymph node metastasis and VAMP8 expression were independent prognostic factors for BC. Conclusion: VAMP8 is significantly upregulated in human BC tissues and can thus be a practical and potentially effective surrogate marker for survival in BC patients.

Investigation of Cu Interlayer on Joint Formation of Ti/Mg Bimetal Fabricated by Liquid–Solid Compound Casting Process

Fulin Wen,Jianhua Zhao,Kaiqing Feng,Miaowang Yuan,Dengzhi Zheng,Cheng Gu,Bei Xu 대한금속·재료학회 2022 METALS AND MATERIALS International Vol.28 No.7

In this paper, TC4/AZ91D bimetallic composites has been prepared by liquid–solid compound casting process adaptingvarious thickness of Cu coating. The effects of Cu coating thickness on the evolution of interface microstructures and jointmechanical properties are investigated. The results indicate that metallurgical bonded joints are obtained with Cu coatingthickness ranging from 36.7 to 51.4 μm. With the increase of Cu coating thickness, the interface microstructure evolvesfrom δ-Mg + Mg2Cueutectic structure to Mg–Cu intermetallic compound (IMC) Cu2Mg+ Mg2Cuand Mg–Al–Cu ternaryintermetallic compound. The calculation results of formation enthalpy and chemical potential of Mg–Al–Cu system suggestthat Cu element prefers to react with Mg element and formed Mg–Cu IMC. In particular, when Cu coating thickness reaches36.7 μm, the average shear strength of the bimetal reaches a maximum of 65.3 MPa. Further increasing Cu coating thicknessleads to the generation of thick Mg2CuIMC layer and Mg2Cu+ Cu2Mgmixed IMC layer which are proved to be harmful tothe shear strength of TC4/AZ91D bimetals. All the fracture surfaces of the bimetallic composites exhibite to have a brittlefracture morphology. However, the fracture location is different with each other. For Cu coating thickness of 36.7 μm, theinterface fractures at the δ-Mg + Mg2Cueutectic structure, while the interface fractures at the Cu2Mg+ Mg–Al–Cu ternaryintermetallic layers when Cu coating thickness is 44.2 μm and 51.4 μm.

Dead-Time Elimination and Zero Common Mode Voltage Operation of Neutral-Point-Clamped Inverter

Feng Gao,Jianhua Yuan,Ding Li,Poh Chiang Loh,Houlei Gao 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5

This paper presents the dead-time elimination scheme for modulating neutral-point-clamped inverter. Unlike the dead-time compensation methods reported for mitigating negative effects induced by dead-time insertion, the proposed scheme simply separates each pair of switches by treating every switch independently and triggers the corresponding switches per phase according to the judged current direction. The removal of dead-time interval, together with the introduction of an appropriate modulation scheme, can then help mitigate switching common mode voltage, even without those narrow alternating spikes generated by common dead-time insertion in traditional pulsewidth modulation (PWM) techniques.

A Mutli-Agent Task Allocation Model in Open-Space Emergency Evacuation Management

Lei Du,Guixing Zheng,Yuan Kan,Bo Xu,Jianhua Kang 보안공학연구지원센터 2013 International Journal of Hybrid Information Techno Vol.6 No.5

Parallel Execution of Data-intensive Web Services Based on Data-flow Constructs and I/O Operation Ratio

Dongjin Yu,Qi Zhu,Jianhua Shao,Chang Li,Youwei Yuan,Wanqing Li 보안공학연구지원센터 2014 International Journal of Database Theory and Appli Vol.7 No.4

Constant Output Power Control Methods for Variable-Load Wireless Power Transfer Systems

Liu, Xu,Clare, Lindsay,Yuan, Xibo,Wang, Jun,Wang, Chonglin,Li, Jianhua The Korean Institute of Power Electronics 2018 JOURNAL OF POWER ELECTRONICS Vol.18 No.2

This study proposes a comprehensive mathematical model that includes coil-system circuit and loss models for power converters in wireless power transfer (WPT) systems. The proposed model helps in understanding the performance of WPT systems in terms of coil-to-coil efficiency, overall efficiency, and output power capacity and facilitates system performance optimization. Three methods to achieve constant output power for variable-load systems are presented based on system performance analysis. An optimal method can be selected for a specific WPT system by comparing the efficiencies of the three methods calculated with the proposed model. A two-coil 1 kW WPT system is built to verify the proposed mathematical model and constant output power control methods. Experimental results show that when the load resistance varies between 5 and $25{\Omega}$, the system output power can be maintained at 1 kW with a maximum error of 6.75% and an average error of 4%. Coil-to-coil and overall efficiencies can be maintained at above 90% and 85%, respectively, with the selected optimal control method.

Separation and Characterization of Organic Chlorides in a Chinese Crude Oil

Xiaohui Li,Rui Ma,Liang Ding,Huiying Yuan,Bencheng Wu,Jianhua Zhu 대한화학회 2018 Bulletin of the Korean Chemical Society Vol.39 No.4

A crude oil from Shengli oilfield of China was extracted with N,N‐dimethylformamide (DMF) for separation and enrichment of organic chlorides. The resulting extract with relatively higher chlorine concentration was analyzed with gas chromatography–mass spectrometry (GC/MS). Among the identified heteroatom compounds in the extract sample, nitrogen‐containing compounds were most abundant in the extract sample, followed by chlorine‐, sulfur‐, and oxygen‐containing compounds, respectively. Four organochlorines with an aromatic core structure, i.e., 5‐chloro‐2‐methylaniline, 2‐chloro‐6‐methylaniline, 4‐chloro‐2‐nitrotoluene, and 1‐(5‐chloro‐2‐hydroxyphenyl)ethanone, were identified from crude oil extract. The dominant abundant organic chloride is 5‐chloro‐2‐methylaniline with relative content of 65.1% in the total of identified organic chlorides, followed by 1‐(5‐chloro‐2‐hydroxyphenyl)ethanone of 16.3%, 2‐chloro‐6‐methylaniline of 14.5%, and 4‐chloro‐2‐nitrotoluene of 4.1%, respectively.