Transient Stability Simulation Analysis of Multi Node Power Network with Variable Speed Pumped Storage Units

Zhao Chong,Wang Longze,Ma Yiyi,Xiang Pengfei,Jiang Siyu,Chen Weidong,Zhang Yan,Li Meicheng 대한전기학회 2023 Journal of Electrical Engineering & Technology Vol.18 No.4

The output characteristics of variable speed pumped storage are different from conventional hydropower and constant speed pumped storage units. The continuous increase of installed capacity of variable speed pumped storage, poses a severe challenge to the safe and stable operation of the local power grid. Proposed in this paper is a kind suitable for multi-node containing variable speed pump machine storage unit electric power network transient stability method, considering the variable speed pumped storage units by the end of the instantaneous failure prone to sudden drop transient power, the power network with more nodes each busbar voltage stable operation as the goal, according to the regional power grid data under typical operation modes, Based on the power system analysis software package, an electromechanical simulation model of the 7-node power grid with variable speed pumped storage unit was established. The influence on the transient stability of a 7-node power grid is analyzed by removing variable speed pumped-storage units and three-phase short-circuit faults. The transient stability of the power grid can be maintained under the conditions of removing variable speed pumped-storage units and three-phase short-circuit faults, but some bus voltages are higher than the specified voltage upper limit. The reactive power compensation device is installed to improve the voltage stability of the power grid system, which can prevent the overvoltage accident caused by the fault of the communication system, achieve the purpose of multi-node power network stability, and improve the safety and stability of the regional power system when the fault occurs.

Ultrasound elastography of the thyroid: principles and current status

Chong-Ke Zhao,Hui-Xiong Xu 대한초음파의학회 2019 ULTRASONOGRAPHY Vol.38 No.2

Ultrasound (US) elastography has been introduced as a non-invasive technique for evaluating thyroid diseases. This paper presents a detailed description of the technical principles, peculiarities, and limitations of US elastography techniques, including strain elastography and shear-wave elastography. This review was conducted from a clinical perspective, and aimed to assess the usefulness of US elastography for thyroid diseases in specific clinical scenarios. Although its main focus is on thyroid nodules, the applications of US elastography for other thyroid diseases, such as diffuse thyroid diseases and thyroiditis, are also presented. Furthermore, unresolved questions and directions for future research are also discussed.

Surface quality prediction model of nano-composite ceramics in ultrasonic vibration-assisted ELID mirror grinding

Bo Zhao,Fan Chen,Xiao-feng Jia,Chong-yang Zhao,Xiao-bo Wang 대한기계학회 2017 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.31 No.4

Ultrasonic vibration-assisted Electrolytic in-process dressing (ELID) grinding is a highly efficient and highly precise machining method. The surface quality prediction model in ultrasonic vibration-assisted ELID mirror grinding was studied. First, the interaction between grits and workpiece surface was analyzed according to kinematic mechanics, and the surface roughness model was developed. The variations in surface roughness under different parameters was subsequently calculated and analyzed by MATLAB. Results indicate that compared with the ordinary ELID grinding, ultrasonic vibration-assisted ELID grinding is superior, because it has more stable and better surface quality and has an improved range of ductile machining.

High-Velocity Impact of Carbon/Epoxy Composite Laminates

Zhao, Gui Ping,Wang, Zheng Hao,Zhang, Jian Xin,Cho, Chong Du Trans Tech Publications, Ltd. 2007 Key Engineering Materials Vol.334-335 No.1

<P>The response of Carbon/epoxy composites under high velocity impact was investigated experimentally. The strain rate dependent behavior of T300 Carbon/epoxy matrix composite in tension is studied experimentally by split Hopkinson bar technique. Dynamic stress-strain plot was obtained and compared with the quasi-static tensile test results. The results of the study indicate that Carbon/epoxy composites are strain rate dependent materials. Stacking sequence has a significant effect on the material response. Tensile strength of the composites all increased with increasing strain rate. And failure strain decreased when strain rate increased.</P>

Dynamic Response and Damage of Composite Shell Under Impact

Chong Du Cho,Guiping Zhao 대한기계학회 1999 KSME International Journal Vol.13 No.9

A Case Study of the Effects of a Synoptic Situation on the Motion and Development of Warm-Sector Mesoscale Convective Systems over South China

Zhao-Ming Liang,Ying Liu,Jin-Fang Yin,Chong-Jian Liu 한국기상학회 2019 Asia-Pacific Journal of Atmospheric Sciences Vol.55 No.2

The effects of a synoptic situation on the motion and development of warm-sector mesoscale convective systems (MCSs) in a heavy rainfall event occurred in South China on 8 May 2014 are investigated using high-resolution observational data and ERA-Interim data. The results show that the blocking of an eastward moving low-level trough over southwestern China by a stable anticyclone over eastern China induced strong southerly winds ahead of the trough and an eastward vertical slant of the wind speed maximum. Consequently, a southeastward low-level wind shear formed in the region under the southerly jet, which caused a southeastward turning of the motion of a large inland MCS. Meanwhile, a northeastward/eastward low-level wind shear formed in the region under the east side of the southerly jet, leading to northeastward/eastward movement of some small MCSs in the coastal region. The continuous merging of the southeastward-moving MCS with the northeastward/eastward-moving MCSs resulted in heavy rainfall along the coastal region. On the other hand, the intensification and expansion of associated low and high mean-sea-level pressure (MSLP) centers caused southeastward migration of strong boundary-layer moisture flux convergence and high convective available potential energy zones, which promoted the persistent development of the large MCS and the later development of the small MCSs. Moreover, the strong boundary-layer southeasterly winds associated with the high MSLP center continuously enhanced the frontal ascent of the large MCS. These southeasterly winds also triggered the small MCSs through the convergence induced by differential surface friction between the land and sea or the convergence of them with the southwesterly winds from the South China Sea.

Effect of Template Removal on Synthesis of Organic-Inorganic Hybrid Mesoporous MCM-48

Zhao, Ya Nan,Li, San Xi,Han, Chong-Soo Korean Chemical Society 2012 Bulletin of the Korean Chemical Society Vol.33 No.10

Post-synthesis is used to synthesize organic hybrid inorganic mesoporous sieves. In this method, the activity and structure of the base sieve are crucial to obtain the definable hybrid materials. The chemical and physical properties of the base can be largely changed either by the final step of its synthesizing processes, by template removal which is accomplished with the oxidative thermal decomposition (burning) method or by solvent extraction method. In this paper we compared two methods for the post-synthesis of organic hybrid MCM-48. When the template was extracted with HCl/alcohol mixture, the final product showed larger pore size, larger pore volume and better crystallinity compared to the case of the thermal decomposition. The reactivity of the surface silanol group of template free MCM-48 was also checked with an alkylsilylation reagent $CH_2=CHSi(OC_2H_5)_3$. Raman and $^{29}Si$ NMR spectra of MCM-48 in the test reaction indicated that more of the organic group was grafted to the surface of the sample after the template was removed with the solvent extraction method. Direct synthesis of vinyl-MCM-48 was also investigated and its characteristics were compared with the case of post-synthesis. From the results, it was suggested that the structure and chemical reactivity can be maintained in the solvent extraction method and that organic grafting after the solvent extraction can be a good candidate to synthesize a definable hybrid porous material.

Simulation and Experimental Investigation of Impact Damage in Composite Shell

Zhao, Gui Ping,Cho, Chong Du,Kwon, Oh Yang Trans Tech Publications, Ltd. 2005 Key Engineering Materials Vol.297 No.-

<P>In this paper, the energy absorption characteristics on extruded aluminum box-section strengthened with carbon-fiber-reinforced plastics (CFRP) laminates and/or foam material were investigated under impact loading. Impact tests using a pneumatic impact tester were conducted with the specimens in three-point bending flexure with consideration given to the side-door impact beams in vehicles. The absorbed energy to the specimen during the impact was determined from the loaddisplacement curve, which was obtained from the strain gauge attached to the impactor and the laser displacement transducer. From the results, it was found that the strengthening by externally bonding with CFRP laminates improved the impact-induced energy absorption. Also, the effect of the improvement was clearly seen in the case of the use of filling form material in the aluminum extrusion together with attaching CFRP laminates.</P>

Synthesis, Cytotoxicity and Structure-Activity Relationship Study of Terpyridines

Zhao, Long-Xuan,Sherchan, Jyoti,Park, Jung-Ki,Jahng, Yurng-Dong,Jeong, Byeong-Seon,Jeong, Tae-Cheon,Lee, Chong-Soon,Lee, Eung-Seok The Pharmaceutical Society of Korea 2006 Archives of Pharmacal Research Vol.29 No.12

For the development of novel antitumor agents, we designed and synthesized terpyridines, and their biological activities were evaluated. Although most of the newly prepared terpyridines showed strong cytotoxicity against several human cancer cell lines, [2,2';6',2"]-terpyridine displayed the most significant cytotoxicity.

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.