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Quach, Huu Luong,Kim, Ho Min The Korea Institute of Applied Superconductivity a 2020 한국초전도저온공학회논문지 Vol.22 No.3
This study presents the experiment and simulation results on the magnetic field response and electrical stability behaviors of no-insulation (NI) and metal insulation with stainless steel tape (MI-SS) which wound in form of racetrack type coils. First of all, the structural design of the racetrack type bobbin was shown along with its parameters. Then, the current-voltage tests were carried out to measure the critical current of both test coils. Also, the sudden discharging and charging tests were performed in the steady state to estimate the decay field time and magnetic field response, respectively. Finally, the overcurrent tests were conducted in the transient state to investigate the electrical stability of these test coils. Based on the experimental results, the contact surface resistances were calculated and applied to the field coils (FCs) of 10-MW-class second generation high temperature superconducting generator (2G HTSG) used in wind offshore environment. The charging delay time and electrical stability for NI and MI-SS HTS FCs of 10-MW-class 2G HTSG are analyzed by the equivalent circuit model and the key parameters which were obtained from the electromagnetic finite element analysis results.
Harmonic Analysis of a Modular Multilevel Converter Using Double Fourier Series
Quach, Ngoc-Thinh,Chae, Sang Heon,Ahn, Jin Hong,Kim, Eel-Hwan The Korean Institute of Electrical Engineers 2018 Journal of Electrical Engineering & Technology Vol.13 No.1
This paper presents a harmonic analysis of the modular multilevel converter (MMC) using a double Fourier series (DFS) algorithm. First, the application of DFS for harmonic calculation in the MMC is made by considering the effect of arm inductor. The analytical results are then confirmed by comparing with the simulation results of using the fast Fourier transform (FFT) algorithm. Finally, distribution of harmonics and total harmonic distortion (THD) in the MMC will be analyzed in three cases: harmonics versus number of levels of MMC, harmonics versus total switching frequency and harmonics versus modulation index. The simulation results are performed in the PSCAD/EMTDC simulation program in order to verify the analytical results obtained by Matlab programming.
Quach, Hung,Kim, Jin-Jae,Nguyen, Duc-Toan,Kim, Young-Suk Elsevier 2020 International journal of mechanical sciences Vol.169 No.-
<P><B>Abstract</B></P> <P>A new phenomenological ductile fracture criterion that is proposed. The proposed model is associated with the micro mechanisms of void nucleation, void growth, and evolution of void coalescence. The secondary voids band and rotation of voids effect are considered in the new ductile fracture criterion. A series of upsetting test results of aluminum 2024-T351 and TRIP RA-K40/70 steel are used to construct and compare the accuracy of fracture locus proposed by new ductile fracture criterion, Modified Mohr-Coulomb criterion and extend Lou-Huh criterion. The fracture locus constructed using the proposed criterion is close to the experimental data points over a wide stress state range from uniaxial compression to balanced biaxial tension. Then, a series of upsetting tests and square cup drawing tests are conducted with Al6014-T4 to evaluate the accuracy of the proposed criterion. All results indicate that the proposed ductile fracture criterion can be utilized for predicting initial fracture in sheet metal forming.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A new phenomenological ductile fracture criterion considering micro mechanisms of void nucleation, void growth, and evolution of void coalescence is presented in this paper. </LI> <LI> The secondary voids band and rotation of voids effect are considered in the new ductile fracture criterion. </LI> <LI> The new ductile fracture criterion can be utilized for predicting initial fracture in sheet metal forming with lager range of stress triaxiality. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>
Quach Ngoc Thinh,Ji-Han Ko,Dong-Wan Kim,Eel-Hwan Kim 한국조명·전기설비학회 2013 조명·전기설비학회논문지 Vol.27 No.2
The dynamic voltage restorer (DVR) is an effective protection device for wind turbine generators based on doubly-fed induction generator (DFIG) that is operated under unbalanced voltage dip conditions. The compensating voltages of the DVR depend on the voltage dips and on the influence of the zero sequence component. The zero sequence component results in high insulation costs and asymmetry in terminal voltages. This paper proposes the use of a proportional-resonant controller in stationary reference frames for controlling zero sequence components in the DVR to protect the DFIG during unbalanced voltage dips. To enhance the proposed control method, a comparison is carried out between two cases: with and without using the control of a zero sequence component. Simulation results are presented to verify the effectiveness of the proposed control method by using the Psim simulation program.
Quach, Huu Luong,Kim, Ji Hyung,Hyeon, Chang Ju,Chae, Yoon Seok,Moon, Jae Hyung,Kim, Ho Min The Korea Institute of Applied Superconductivity a 2018 한국초전도저온공학회논문지 Vol.20 No.1
The thermal and electrical properties of the conductor are critical parametersfor the design and optimization of the superconducting magnet. This paper presents simulation code to analyze electrical and thermal stability characteristics of the second generation (2G) high-temperature superconductor (HTS) by varying copper stabilizer thickness. Two types of commercial 2G HTS coated conductor tapes, YBCO and GdBCO were used in this study. These samples were cooled by Liquid Nitrogen ($LN_2$) having boiling at 77.3 K and an equivalent electrical circuit model for them is choosen and analysed in details. Also, an over-current pulse test in which a current exceeding a critical current was performed. From the simulation results, the influences of the copper stabilizer thickness on the stability characteristics of these samples are presented.
Analyzing Stability of Jeju Island Power System with Modular Multilevel Converter Based HVDC System
Quach, Ngoc-Thinh,Lee, Do Heon,Kim, Ho-Chan,Kim, Eel-Hwan The Korean Institute of Electrical Engineers 2015 Journal of Electrical Engineering & Technology Vol.10 No.1
This paper proposes the installation of a new modular multilevel converter based high-voltage direct current (MMC-HVDC) system to connect between mainland and Jeju island power systems in Korea in 2020. The purpose is to combine with two old line-commutated converters (LCC)-based HVDC system to achieve a stability of the Jeju island power system. The operation of the overall system will be analyzed in three cases: (i) wind speed is variable, (ii) either one of the LCC-HVDC systems is shutdown because of a fault or overhaul, (iii) a short circuit fault occurs at the mainland side. The effectiveness of the proposed control method is confirmed by the simulation results based on a PSCAD/EMTDC simulation program.
Quach, Quang Huy,Chung, Bong Hyun The Royal Society of Chemistry 2014 The Analyst Vol.139 No.11
<P>A simple, rapid, and signal-on fluorescent assay was developed for activity analysis of DNA methyltransferase and for screening of its inhibitors based on a methylation-resistant endonuclease and SYBR Green I.</P> <P>Graphic Abstract</P><P>We introduce a signal-on and simple fluorescent assay for the detection of DNA methyltransferase activity based on methylation-resistant endonuclease and intercalating activity of SYBR Green I. <IMG SRC='http://pubs.rsc.org/services/images/RSCpubs.ePlatform.Service.FreeContent.ImageService.svc/ImageService/image/GA?id=c3an02129g'> </P>