Sequence Impedance Modeling and Frequency Characteristic Analysis of MMC-based HVDC

Tong Huang,Xin Chen,Guanghui Li,Guoqing He 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Modular multilevel converter (MMC) has emerged as a preferred technology for high-voltage dc (HVDC) transmission, while many HVDC-MMC projects have been reported resonance problems. The existing researches show that stability of a HVDC-grid system is decided by both the sequence impedance characteristic of HVDC-MMC and power grid, and due to coupling effect, the power grid impedance will also impact the HVDCMMC impedance characteristic. Multi-harmonic linearization method will be adopted in this paper to develop a HVDC-MMC analytical sequence impedance model. Then the developed model is used to illustrate the effect of the power control loop as well as the bandwidth of other controllers on HVDC-MMC impedance characteristic. Finally, based on the sequence impedance model considering coupling effect, the influence of HVDC-MMC bandwidth on the system stability will be analyzed as well.

Characterization of intermediate wetting states on micro-grooves by water droplet contact line

Cheung Tong Cheng,Suet To,Guoqing Zhang 한국공업화학회 2020 Journal of Industrial and Engineering Chemistry Vol.91 No.-

The wetting state of a water droplet remarkably affecting its sliding behavior is characterized by thedroplet boundary contact line. This paper presents experimental studies of the apparent contact angleagainst droplet deposition time, as well as contact angle hysteresis, and compares the results with theWenzel and Cassie–Baxter models. Observations indicate that different intermediate wettingphenomena exist. The sliding performance of a droplet under intermediate wetting states is alsoinvestigated. It is found that the droplet does not slide under partial wetting but slides when the sidewalls of the grooves have been wetted by part of the droplet. Further, that droplets under differentwetting states on surfaces with varied groove spacing and widths, under the same groove spacing towidth ratio, present altered sliding performance before rolling off from the micro-grooves in a paralleldirection. This study broadens the characterization method of intermediate wetting states, whichdetermines the condition of anisotropic sliding on micro-grooves. Thefindings have great potential forapplication to artificial self-cleaning surfaces.

Frequency Characteristic and Impedance Analysis on Three-Phase Grid-Connected Inverters Based on DDSRF-PLL

Xiangqiang Wu,Tong Huang,Xin Chen,Haibing Hu,Guoqing He 전력전자학회 2019 ICPE(ISPE)논문집 Vol.2019 No.5

Decoupled double synchronous reference frame phase locked loop (DDSRF-PLL) can effectively eliminate negative-sequence fundamental frequency component, which means the PLL control loop will have an effect on the frequency characteristics and stability of gridconnected inverters. Based on the three-phase LCL-type grid-connected inverter, the positive- and negative-sequence output impedance model of the grid-connected inverter and the frequency characteristics of DDSRF-PLL were firstly derived. Meanwhile, the regulator parameters of DDSRFPLL were designed and its effect on impedance stability of inverter was analyzed. Then, the frequency characteristics of DDSRF-PLL and the output impedance model of the grid-connected inverter were verified by the simulation and experimental results. Finally, the stability of the gridconnected with different PLL bandwidths was analyzed and verified by experimental results.

Di-2-ethylhexyl phthalate induced oxidative damage involving FasL-associated apoptotic pathway in mouse spermatogenic GC-2spd cells

Xiao Tang,Kun Tong,Lishan Zhu,Guoqing Fu,Wei Chang,Ting Zhou,Zhibing Zhang,Ling Tong,Ling Zhang,Yuqin Shi,Ling Zhang,Yuqin Shi 대한독성 유전단백체 학회 2016 Molecular & cellular toxicology Vol.12 No.4

Di-2-ethylhexyl phthalate (DEHP) which belongs to phthalatic-acid esters, is a kind of harmful, global environmental pollutants. It is a known endocrine disrupting chemical and male reproductive toxicant. However, the mechanism by which DEHP exposure result in male reproductive toxicity is still unclear. To elucidate the productive toxicity mechanism of DEHP, we attemptted to investigate oxidative stress, apoptotic effects, mRNA and protein expression of apoptosis-associated genes including FasL, caspase-3, and caspase-8 in GC-2spd (mouse spermatogenic cells). The results showed that, with the increase of DEHP concentration, cell apoptosis rate increased; the activities of relation index of oxidative stress such as malondialdehyde (MDA), superoxide dismutase (SOD) and glutatione peroxidase (GSH-PX) changed significantly; the mRNA and protein expression levels of FasL, caspase-3, -8, altered obviously. These results suggested that DEHP could induce apoptosis of GC-2spd cells through oxidative stress and FasL-dependent pathway.

Strain rate dependent behaviors of a hot isotropically processed Ti-6Al-4V: Mechanisms and material model

Xiaohan Tang,Mingfa Ren,Fanzi Bu,Guoqing Chen,Gang Li,Tong Li 대한기계학회 2016 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.30 No.2

Split-Hopkinson pressure bar (SHPB) was adopted to study the dynamic response of a specifically designed Hot isotropically processed (HIP) Casting Titanium alloy (Ti-6Al-4V). The strain-stress curves were obtained in a range of strain rate (10 -3 ~2.6×10 3 /s) to study the constitutive relationships and the Johnson-Cook model is developed to describe this dynamic constitutive law. It can be found that the static microstructure of this specific HIP casting Ti-6Al-4V is lamellar structure. When the loading increases (strain rate higher than 10 3 /s), this lamellar structure changes to basket weave structure, which further changes the mechanical strength and plasticity.

A helix slope deviation compensation model for milling small modulus copper electrode gears

Zhipeng Feng,Zhao-Yao Shi,Shoujin Lin,Aijun Tong,Peng Wang,Guoqing Wu 대한기계학회 2022 JOURNAL OF MECHANICAL SCIENCE AND TECHNOLOGY Vol.36 No.7

When a milling tool is used to mill small modulus copper electrode gears (SMCEG), the deformation is inevitable, thus leading to the helix slope deviation (HSD) of copper electrode gears (CEG). To compensate the influence of milling tool deflection (MTD) on the HSD, a universal HSD compensation model was established for different sizes of milling tools. First, using the principle of orthogonal experiment, a linear regression model of milling parameters and milling tool radius is established. Secondly, the average value of the HSD obtained by the gear measuring instrument is converted into the maximum of MTD according to the principle of helix line formation. The maximum deflections of the milling tools are used as the response value of the regression analysis to fit the maximum deflection curve of the milling tool. Through the reverse adjustment of the rotation angle of the rotating motor, the HSD compensation is realized. Finally, the model was verified by the milling tests. The results showed that the helix deviation reached the requirements of level 4 to 5 in GB/T 38192-2019, and proved the correctness of the established MTD model. The model is significant for milling SMCEG.

Hybrid Perovskite Photoconductivity Visible Region Detector with High Speed and Stability

Baoliang Mi,Huanlin Zhou,Zihang Song,Guiqing Zhao,Guoqing Tong,YANG JIANG 성균관대학교(자연과학캠퍼스) 성균나노과학기술원 2017 NANO Vol.12 No.12

Hybird perovskite materials have been regarded as an outstanding candidate in the optoelectronic devices. In this work, a high speed perovskite photodetector (PD) based on the gas–solid reaction process was proposed and a high responsivity and detectivity of 5.87A W -1, 10 12 Jones were obtained after annealing at 120℃ for 30 min. Compared to traditional solution process, the gas–solid reaction provided a full coverage film with high crystallization, which is beneficial to the electrons transportation and the capture of the incident light. The response time of device is up to 248 μs/207 μs under 700 Hz. More importantly, the device exhibits a good stability after storing in the air for two months. The perovskite PD shows a high performance upon the light illumination, revealing that the hybrid perovskite is a promising candidate for optoelectronic applications.