2D FEM Based Fast Approach to Predict Electromagnetic Performances of a Variable-Speed FMaSynRM Considering Skewing Effects

Di Chong,Bao Xiaohua,Jiang Wei,Xie Bao 대한전기학회 2024 Journal of Electrical Engineering & Technology Vol.19 No.1

Skewing techniques have been widely used in the feld of the design of diferent types of electrical machines, because it can help to reduce the torque ripple, mitigate the electromagnetic noise and vibration, etc. To model the skewing efects in the electrical machine design accurately, the fnite element method is appreciated in both the academia and industry. To achieve a fast modelling of skewing efects, a novel 2D based approach to estimate the electromagnetic performances in the whole speed range for variable-speed electrical machines has been proposed in this paper, which is further improved from the traditional multi-slice method. Firstly, a series of simulations at diferent loads will be run to get the electromagnetic performances for the variable-speed machines. Secondly, based on the multi-slice method, the performance on diferent slices can be predicted from the results obtained from the existing simulations by coordinate transform and interpolation directly and no more extra simulations are needed. Thirdly, taking a ferrite magnet assisted synchronous reluctance machine (FMaSynRM) with skewing as an example, the electromagnetic performances including electromagnetic torque, stator current and voltage, efciency map are compared in detail by both the proposed method and experiments.

Effects of Ohmic Area Etching on Buffer Breakdown Voltage of AlGaN/GaN HEMT

Chong Wang,Xiao-Xiao Wel,Meng-Di Zhao,Yun-Long He,Xue-Feng Zheng,Wei Mao,Xiao-Hua Ma,Jin-Cheng Zhang,Yue Hao 한국전기전자재료학회 2017 Transactions on Electrical and Electronic Material Vol.18 No.3

This study is on how ohmic area etching affects the buffer breakdown voltage of AlGaN/GaN HEMT. The surfacemorphology of the ohmic metal can be improved by whole etching on the ohmic area. The buffer breakdown voltagesof the samples with whole etching on the ohmic area were improved by the suppression of the metal spikes formedunder the ohmic contact regions during high-temperature annealing. The samples with selective etching on theohmic area were investigated for comparison. In addition, the buffer leakage currents were measured on the differentradii of the wafer, and the uniformity of the buffer leakage currents on the wafer were investigated by PL mappingmeasurement.

Effects of Ohmic Area Etching on Buffer Breakdown Voltage of AlGaN/GaN HEMT

Wang, Chong,Wel, Xiao-Xiao,Zhao, Meng-Di,He, Yun-Long,Zheng, Xue-Feng,Mao, Wei,Ma, Xiao-Hua,Zhang, Jin-Cheng,Hao, Yue The Korean Institute of Electrical and Electronic 2017 Transactions on Electrical and Electronic Material Vol.18 No.3

This study is on how ohmic area etching affects the buffer breakdown voltage of AlGaN/GaN HEMT. The surface morphology of the ohmic metal can be improved by whole etching on the ohmic area. The buffer breakdown voltages of the samples with whole etching on the ohmic area were improved by the suppression of the metal spikes formed under the ohmic contact regions during high-temperature annealing. The samples with selective etching on the ohmic area were investigated for comparison. In addition, the buffer leakage currents were measured on the different radii of the wafer, and the uniformity of the buffer leakage currents on the wafer were investigated by PL mapping measurement.

Analysis of Slot Leakage Reactance of Submersible Motor with Closed Slots during Starting Transient Operation

Bao, Xiaohua,Di, Chong,Fang, Yong The Korean Institute of Electrical Engineers 2016 Journal of Electrical Engineering & Technology Vol.11 No.1

Generally, closed slots are adopted to reduce the water friction loss in both the stator and the rotor of water filling submersible motor due to the special environment of operation. One of the obvious differences between the traditional induction motors and water filling submersible motors is that the submersible motors only need relatively smaller starting torque. This paper aims to analyze the slot leakage reactance of water filling submersible motor during starting transient operation. An improved analytical method which considered the magnetic saturation of the slot bridge and the skin effect of rotor bars is proposed. The slot permeance factor which has a direct impact on the slot leakage reactance is calculated. Then finite element models with different stator slot types are constructed and search coils are introduced to measure the slot flux linkage. Moreover, the starting performances of the models with two typical stator slots are compared and the flux leakage characteristics are obtained. Finally, the results obtained by finite element method are very close to the results obtained by analytical method.

Calculation of Electromagnetic Excitation Forces in Double Skewed Motors

Xiaohua Bao,Chong Di,Yang Zhou 대한전기학회 2018 Journal of Electrical Engineering & Technology Vol.13 No.2

An electromagnetic excitation force is caused by the air-gap flux density, which greatly influences the noise and vibration of the motor. In many real projects, skewed slot technology is widely used to reduce the harmonic components of the air-gap flux density to reduce the noise and vibration of the motor. However, a skewed slot has several side effects such as a transverse current and axial drifting. Thus, a double skewed slot rotor is selected with the aim of eliminating these side effects. This paper presents the exact structure of the double skewed slot rotor and the mechanism whereby the electromagnetic excitation force can be reduced. A multi-slice method is adopted to model the special structure. Finite element simulation is used to verify the theory.

Analysis of Slot Leakage Reactance of Submersible Motor with Closed Slots during Starting Transient Operation

Xiaohua Bao,Chong Di,Yong Fang 대한전기학회 2016 Journal of Electrical Engineering & Technology Vol.11 No.1

Generally, closed slots are adopted to reduce the water friction loss in both the stator and the rotor of water filling submersible motor due to the special environment of operation. One of the obvious differences between the traditional induction motors and water filling submersible motors is that the submersible motors only need relatively smaller starting torque. This paper aims to analyze the slot leakage reactance of water filling submersible motor during starting transient operation. An improved analytical method which considered the magnetic saturation of the slot bridge and the skin effect of rotor bars is proposed. The slot permeance factor which has a direct impact on the slot leakage reactance is calculated. Then finite element models with different stator slot types are constructed and search coils are introduced to measure the slot flux linkage. Moreover, the starting performances of the models with two typical stator slots are compared and the flux leakage characteristics are obtained. Finally, the results obtained by finite element method are very close to the results obtained by analytical method.

Calculation of Electromagnetic Excitation Forces in Double Skewed Motors

Bao, Xiaohua,Di, Chong,Zhou, Yang The Korean Institute of Electrical Engineers 2018 Journal of Electrical Engineering & Technology Vol.13 No.2

An electromagnetic excitation force is caused by the air-gap flux density, which greatly influences the noise and vibration of the motor. In many real projects, skewed slot technology is widely used to reduce the harmonic components of the air-gap flux density to reduce the noise and vibration of the motor. However, a skewed slot has several side effects such as a transverse current and axial drifting. Thus, a double skewed slot rotor is selected with the aim of eliminating these side effects. This paper presents the exact structure of the double skewed slot rotor and the mechanism whereby the electromagnetic excitation force can be reduced. A multi-slice method is adopted to model the special structure. Finite element simulation is used to verify the theory.

Detection of Eccentricity Fault Using Slot Leakage Flux Monitoring

Hanfeng Wang,Xiaohua Bao,Chong Di,Zhiheng Cheng 전력전자학회 2015 ICPE(ISPE)논문집 Vol.2015 No.6

Eccentricity is a common fault in the running of electrical machines. Aimed at the problem, a new approach to detect eccentricity fault is presented by monitoring the slot leakage flux of stator in this paper. In order to measure the slot leakage flux, two placements of search coil in the stator slot are applied. Firstly, the theoretical analysis shows the slot leakage flux contains more information about eccentricity fault than the stator current does. Then the submersible motor as a model, the induced voltages of search coil and the stator currents are obtained by finite element simulation under healthy motor, static, dynamic and mixed eccentricity, respectively. And various analysis and comparisons of simulations are made. The results show that monitoring the slot leakage flux is effective and has more advantages than the motor current signature analysis.

Metallo-β-Lactamase Production by<i>Pseudomonas otitidis</i>: a Species-Related Trait

Thaller, Maria Cristina,Borgianni, Luisa,Di Lallo, Gustavo,Chong, Yunsop,Lee, Kyungwon,Dajcs, Joseph,Stroman, David,Rossolini, Gian Maria American Society for Microbiology 2011 Antimicrobial agents and chemotherapy Vol.55 No.1

<B>ABSTRACT</B><P>Susceptibility to several β-lactams and β-lactamase production was investigated in a collection of 20 strains of<I>Pseudomonas otitidis</I>, a new<I>Pseudomonas</I>species that has been recently recognized in association with otic infections in humans. All strains appeared to be susceptible to piperacillin, cefotaxime, ceftazidime, and aztreonam, while resistance or decreased susceptibility to carbapenems was occasionally observed. All strains were found to express metallo-β-lactamase (MBL) activity and to carry a new subclass B3 MBL gene, named<I>bla</I>POM, that appeared to be highly conserved in this species.<I>P. otitidis</I>, therefore, is the first example of a pathogenic<I>Pseudomonas</I>species endowed with a resident MBL. The POM-1 protein from<I>P. otitidis</I>type strain MCC10330 exhibits the closest similarity (60 to 64%) to the L1 MBL of<I>Stenotrophomonas maltophilia</I>. Expression in<I>Escherichia coli</I>and<I>Pseudomonas aeruginosa</I>revealed that, similar to L1 and other subclass B3 MBLs, POM-1 confers decreased susceptibility or resistance to carbapenems, penicillins, and cephalosporins but not to aztreonam. Expression of the POM MBL in<I>P. otitidis</I>is apparently constitutive and, in most strains, does not confer a carbapenem-resistant phenotype. However, a strong inoculum size effect was observed for carbapenem MICs, and carbapenem-resistant mutants could be readily selected upon exposure to imipenem, suggesting that carbapenem-based regimens should be considered with caution for<I>P. otitidis</I>infections.</P>

Alcoholic and Nonalcoholic Fatty Liver Disease and Incident Hospitalization for Liver and Cardiovascular Diseases

Chang, Yoosoo,Cho, Juhee,Cho, Yong Kyun,Cho, Ara,Hong, Yun Soo,Zhao, Di,Ahn, Jiin,Sohn, Chong Il,Shin, Hocheol,Guallar, Eliseo,Ryu, Seungho Elsevier 2020 Clinical gastroenterology and hepatology Vol.18 No.1

<P><B>Background & Aims</B></P> <P>We compared the associations of nonalcoholic fatty liver disease (NAFLD) and alcohol-associated fatty liver disease (AFLD) with risk of incident hospitalization for liver and cardiovascular diseases.</P> <P><B>Methods</B></P> <P>We collected data from the Kangbuk Samsung Health Study on 218,030 men and women in Korea who underwent a health examination from 2011 through 2016. Fatty liver disease (FLD) was detected by ultrasound during the initial examination. The Fibrosis-4 index was used to identify individuals with liver fibrosis. Participants were followed up for as long as 5.9 years and data on hospitalizations for liver and cardiovascular diseases were collected.</P> <P><B>Results</B></P> <P>The prevalence of NAFLD was 22.0% and the prevalence of AFLD was 6.4%. Over a median follow-up period of 4.2 years, we observed 51 and 1097 incident cases of liver disease– or cardiovascular disease–related hospitalizations, respectively. After adjustment for potential confounders, the multivariable-adjusted hazard ratios for liver disease–related hospitalization, comparing NAFLD and AFLD with the reference category (no excessive alcohol intake and no FLD), were 1.73 (95% CI, 0.76–3.96) and 5.00 (95% CI, 2.12–11.83), respectively. The corresponding hazard ratios for cardiovascular disease hospitalization were 1.20 (95% CI, 1.02–1.40) and 1.08 (95% CI, 0.86–1.34), respectively. Among participants with FLD, the risk of liver disease–related hospitalization increased with high Fibrosis-4 index scores, whereas the risk of incident cardiovascular disease did not.</P> <P><B>Conclusions</B></P> <P>In a large cohort study, we found an increased risk of liver disease–related hospitalizations for patients with NAFLD or AFLD, especially among those with Fibrosis-4 index scores. An increased risk of cardiovascular disease–associated hospitalization was observed in patients with NAFLD but not AFLD.</P>