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Zhou, Shuhan,Zhou, Guohua,Zeng, Shaohuan,Xu, Shungang,Cao, Taiqiang The Korean Institute of Power Electronics 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1
The flyback converter, which can be regarded as a nonlinear time-varying system, has complex dynamics and nonlinear behaviors. These phenomena can affect the stability of the converter. To simplify the modeling process and retain the information of the output capacitor branch, a special sampled-data model of a peak current-mode (PCM) controlled flyback converter is established in this paper. Based on this, its dynamic behaviors are analyzed, which provides guidance for designing the circuit parameters of the converter. With the critical stability boundary equation derived by a Jacobian matrix, the stable operation range with a varied output capacitor, proportional coefficient of error the amplifier, input voltage, reference voltage and slope of the compensation ramp of a PCM controlled flyback converter are investigated in detail. Research results show that the duty ratio should be less than 0.5 for a PCM controlled flyback converter without ramp compensation to operate in a stable state. The stability regions in the parameter space between the output capacitor and the proportional coefficient of the error amplifier are enlarged by increasing the input voltage or by decreasing the reference voltage. Furthermore, the ramp compensation also can extend to the stable region. Finally, time-domain simulations and experimental results are presented to verify the theoretical analysis results.
Valley V² Control Technique for Switching Converters with Fast Transient Response
Guohua Zhou,Jianping Xu,Jin Sha,Yanyan Jin 전력전자학회 2011 ICPE(ISPE)논문집 Vol.2011 No.5
Valley V² control technique for switching converters is proposed in this paper. By utilizing output voltage ripple as pulse-width modulation ramp and valley voltage of output voltage ripple as additional control variable, valley V² control technique provides faster load transient response than conventional current-mode control techniques. Steady-state and transient performances of switching converters with valley V² control, peak V² control, and current-mode control are compared and verified by experimental results.
Shuhan Zhou,Guohua Zhou,Shaohuan Zeng,Shungang Xu,Taiqiang Cao 전력전자학회 2019 JOURNAL OF POWER ELECTRONICS Vol.19 No.1
The flyback converter, which can be regarded as a nonlinear time-varying system, has complex dynamics and nonlinearbehaviors. These phenomena can affect the stability of the converter. To simplify the modeling process and retain theinformation of the output capacitor branch, a special sampled-data model of a peak current-mode (PCM) controlled flybackconverter is established in this paper. Based on this, its dynamic behaviors are analyzed, which provides guidance for designingthe circuit parameters of the converter. With the critical stability boundary equation derived by a Jacobian matrix, the stableoperation range with a varied output capacitor, proportional coefficient of error the amplifier, input voltage, reference voltageand slope of the compensation ramp of a PCM controlled flyback converter are investigated in detail. Research results show thatthe duty ratio should be less than 0.5 for a PCM controlled flyback converter without ramp compensation to operate in a stablestate. The stability regions in the parameter space between the output capacitor and the proportional coefficient of the erroramplifier are enlarged by increasing the input voltage or by decreasing the reference voltage. Furthermore, the rampcompensation also can extend to the stable region. Finally, time-domain simulations and experimental results are presented toverify the theoretical analysis results.
Modeling and Optimization Method of Laser Cladding Based on GA-ACO-RFR and GNSGA-II
Guohua He,Yanbin Du,Qiang Liang,Zhijie Zhou,Linsen Shu 한국정밀공학회 2023 International Journal of Precision Engineering and Vol.10 No.5
Laser cladding is an environmentally friendly and reliable surface modification technology. The quality characteristics of the coating are directly affected by the process parameters of laser cladding. The reasonable selection of process parameters is essential to obtain high-quality coating. In this study, the single-track 15-5PH alloy coating was fabricated on the surface of 12Cr13 stainless steel. In view of the hybrid Genetic Algorithm and Ant Colony Optimization (GA-ACO) can effectively improve the prediction ability and robustness of Random Forest Regression (RFR), a prediction method of cladding layer quality characteristics based on GA-ACO-RFR was proposed. The fast non-dominated ranking genetic algorithm with elite strategy by introducing the Gaussian distribution crossover operator (GNSGA-II) was used to optimize the process parameters of laser cladding. The results showed that the multi-objective optimization method of laser cladding process parameters proposed in this paper can obtain high-quality laser cladding coating. This work demonstrated the potential of the proposed method in laser cladding process prediction and optimization.
Guohua Wu,He Zhou,Tonggang Zhao,Hongzhan Liu,Zhengda Li,Xin Zhao 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.6
A model for electromagnetic multi-Gaussian Schell-model beams is introduced. An analyticalexpression for the cross-spectral density matrix of electromagnetic multi-Gausssian Schell-model(EMGSM) beams propagating through non-Kolmogorov turbulence is derived based on the extendedHuygens-Fresnel principle. With help of this expression, the average intensity, degree of coherence(DOC) and degree of polarization (DOP) of EMGSM beams are investigated in detail. Our resultsshow that by suitable choices of the source parameters, the distance that preserve a flat profile canbe prolonged. The effects of M and exponent value on DOC and DOP of EMGSM beams arestudied in detail.
Structure and electrical properties of Bi0.5(Na, K)0.5TiO3-BiGaO3 lead-free piezoelectric ceramics
Changrong Zhou,Xinyu Liu,Weizhou Li,Changlai Yuan,Guohua Chen 한국물리학회 2010 Current Applied Physics Vol.10 No.1
Lead-free piezoelectric ceramics (1 - x - y)Bi0.5Na0.5TiO3-xBi0.5K0.5TiO3- yBiGaO3 have been fabricated by an ordinary sintering technique, and their structure and electrical properties and depolarization temperature have been studied. The results of X-ray diffraction reveal that Bi0.5K0.5TiO3 and BiGaO3 diffuse into the Bi0.5Na0.5TiO3 lattices to form a new solid solution with a pure perovskite structure. An obvious change in microstructure with increasing concentration of Bi0.5K0.5TiO3 and BiGaO3 was observed. The piezoelectric constant d33 and the electromechanical coupling factor kp of the ceramics attain maximum values of 165 pC/N and 0.346 at y = 0.01(x = 0.18) and x = 0.21(y = 0.01), respectively. The temperature dependence of dielectric constant indicates an obvious relaxor characteristic with strong frequency dependence of dielectric constant. The depolarization temperature decreased with increasing content of BiGaO3 and first decreases and then increases with increasing amount of Bi0.5K0.5TiO3.
Ye Zhou,Zhan Fengjiang,Xu Guohua 한국항공우주학회 2020 International Journal of Aeronautical and Space Sc Vol.21 No.4
A high-resolution numerical method is developed to simulate the generation and evolution progress of the blade tip vortex for helicopter rotor in forward flight. In the current method, the Navier–Stokes equation is adopted as the governing equation. Along with fifth order WENO scheme, the upwind Roe scheme is employed for the calculation of convective flux. A dual time-stepping scheme is utilized for time discretization, and the LU-SGS scheme is used for every pseudo time step. The Spalart–Allmaras model is selected as the turbulence model. To trim the rotor in forward flight, a high-efficiency trim method is introduced to the current solver. Results for cases in different forward flight conditions show that trimming process has a great influence on the evolution characteristics of the rotor tip vortex. Compared with the cases with different Mach numbers, the evolution characteristics of rotor tip vortex have larger difference for cases with different advance ratios.
Xie Guohua,Dong ping,Chen Hui,Xu Ling,Liu Yi,Ma Yanhui,Zheng Yingxia,Yang Junyao,Zhou Yunlan,Chen Lei,Shen Lisong 생화학분자생물학회 2021 Experimental and molecular medicine Vol.53 No.-
ATF3 has been reported to be dysregulated in various cancers and involved in various steps of tumorigenesis. However, the mechanisms underlying the abnormal expression of ATF3 and its biological function in gastric cancer (GC) have not been well investigated. Here, we report ATF3 as one of the key regulators of GC development and progression. Patients with low ATF3 expression had shorter survival and a poorer prognosis. In vitro and in vivo assays investigating ATF3 alterations revealed a complex integrated phenotype that affects cell growth and migration. Strikingly, high-throughput sequencing and microarray analysis of cells with ATF3 silencing or of ATF3-low GC tissues indicated alterations in the Wnt signaling pathway, focal adhesions and adherens junctions. Mechanistically, the expression of β-catenin and cell migration inducing hyaluronidase 1 (CEMIP) was significantly upregulated in GC cells with downregulated ATF3, which was synergistically repressed by the β-catenin/TCF3 signaling axis and noncoding RNA miR-17-5p and HOXA11-AS. In addition, we found that WDR5 expression was promoted by TCF3 and is involved in miR-17-5p and HOXA11-AS activation in GC cells. Taken together, our findings revealed the mechanism of ATF3 downregulation and its biological role in regulating the expression of Wnt signaling-related genes during GC progression, suggesting new informative biomarkers of malignancy and therapeutic directions for GC patients.