The Auto-Transformer Rectifier Unit（ATRU） is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, t...The Auto-Transformer Rectifier Unit（ATRU） is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future.展开更多
Second-generation high-temperature superconducting(2G-HTS)magnets operating in persistent current mode(PCM)hold great promise for applications such as magnetic resonance imaging.The development of joint-less closed-lo...Second-generation high-temperature superconducting(2G-HTS)magnets operating in persistent current mode(PCM)hold great promise for applications such as magnetic resonance imaging.The development of joint-less closed-loop magnets has effectively tackled the challenges of fabricating joints for REBCO tape.However,certain closed-loop magnets cannot utilize conventional persistent current switches(PCS)and instead require multi-pulse magnetization techniques.This study explores the effects of multi-pulse magnetic field excitation on the flux trapping behavior of a four-pancake coil(FPC).A detailed comparison of the effects of different pulse types and periods on the FPC reveals that the background magnetic field exceeds the critical magnetic field of the coil,thereby creating resistance in the superconducting loop.The critical magnetic field of the FPC is determined experimentally,and a reasonable speculation on the multi-pulse field excitation mechanism is presented.展开更多
A monolithic integrated full-wave bridge rectifier consisted of horizontal Schottky-barrier diodes(SBD)is prepared based on 100 nm ultra-thin β-Ga_(2)O_(3)and demonstrated the solar-blind UV(SUV)light-modulated chara...A monolithic integrated full-wave bridge rectifier consisted of horizontal Schottky-barrier diodes(SBD)is prepared based on 100 nm ultra-thin β-Ga_(2)O_(3)and demonstrated the solar-blind UV(SUV)light-modulated characteristics.Under SUV light illumination,the rectifier has the excellent full-wave rectification characteristics for the AC input signals of 5,12,and 24 V with different frequencies.Further,experimental results confirmed the feasibility of continuously tuning the rectified output through SUV light-encoding.This work provides valuable insights for the development of optically programmable Ga_(2)O_(3)ACDC converters.展开更多
The face velocities of the high efficiency particulate air filters and the ultra low penetration airfilters in fan filter units (FFUs) have large relative standard deviation and turbulivity. It seriously affects the ...The face velocities of the high efficiency particulate air filters and the ultra low penetration airfilters in fan filter units (FFUs) have large relative standard deviation and turbulivity. It seriously affects the unidirectivity of the flow in the unidirectional flow clean zone and cleanroom. The cross contamination in this kind of unidirectional flow area is hardly controlled. It is significant to find optional method for keeping the face velocity uniformity of FFU and reducing the face velocity turbulivity of FFU, furthermore, to keep the cleanliness level under FFUs. The normal and easy method is to add flow rectifiers under filters. FFUs with various flow rectifiers have been tested. The uniformity and turbulivity of facevelocity under the FFU are presented in this paper. The influence of the facevelocity uniformity and turbulivity on the contamination boundary of the unidirectional flow is studiedas well.展开更多
In order to investigate the thermal shock and the heat conduction property of a target under multi-pulsed laser radiation,analytic expressions of both temperature and thermal stress fields in the target are deduced on...In order to investigate the thermal shock and the heat conduction property of a target under multi-pulsed laser radiation,analytic expressions of both temperature and thermal stress fields in the target are deduced on the basis of the non-Fourier conduction law and the thermo-elastic theory.Taking a stainless steel target as an example,we can solve the analytic expressions under appropriate boundary conditions by using the finite difference method and MATLAB software,and then reveal the evolution law of both surplus temperaturt,and thermal stress in the target.The results indicate that the temperature curves in the target irradiated by a multi-pulsed laser take on a delayed character in different sections away from the boundary,which is only affected by its relaxation time.The front of the stress wave is very steep in the non-Fourier numerical solutions,which presents an obvious thermal shock,so it is necessary to consider the non-Fourier effect of semi-infinite body under the high energy laser radiation.展开更多
This paper describes the successful fabrication of 4H-SiC junction barrier Schottky （JBS） rectifiers with a linearly graded field limiting ring （LG-FLR）. Linearly variable ring spacings for the FLR termination are...This paper describes the successful fabrication of 4H-SiC junction barrier Schottky （JBS） rectifiers with a linearly graded field limiting ring （LG-FLR）. Linearly variable ring spacings for the FLR termination are applied to improve the blocking voltage by reducing the peak surface electric field at the edge termination region, which acts like a variable lateral doping profile resulting in a gradual field distribution. The experimental results demonstrate a breakdown voltage of 5 kV at the reverse leakage current density of 2 mA/cm2 （about 80% of the theoretical value）. Detailed numerical simulations show that the proposed termination structure provides a uniform electric field profile compared to the conventional FLR termi- nation, which is responsible for 45% improvement in the reverse blocking voltage despite a 3.7% longer total termination length.展开更多
The effect of the mesa configuration on the reverse breakdown characteristic of a SiC PiN rectifier for high-voltage applications is analyzed in this study.Three geometrical parameters,i.e.,mesa height,mesa angle and ...The effect of the mesa configuration on the reverse breakdown characteristic of a SiC PiN rectifier for high-voltage applications is analyzed in this study.Three geometrical parameters,i.e.,mesa height,mesa angle and mesa bottom corner,are investigated by numerical simulation.The simulation results show that a deep mesa height,a small mesa angle and a smooth mesa bottom（without sub-trench） could contribute to a high breakdown voltage due to a smooth and uniform surface electric field distribution.Moreover,an optimized mesa structure without sub-trench（mesa height of 2.2 μm and mesa angle of 20°） is experimentally demonstrated.A maximum reverse blocking voltage of 4 kV and a forward voltage drop of 3.7 V at 100 A/cm^2 are obtained from the fabricated diode with a 30-μm thick N^- epi-layer,corresponding to 85% of the ideal parallel-plane value.The blocking characteristic as a function of the JTE dose is also discussed for the PiN rectifiers with and without interface charge.展开更多
This paper proposes a double epi-layers 4H-SiC junction barrier Schottky rectifier （JBSR） with embedded P layer （EPL） in the drift region. The structure is characterized by the P-type layer formed in the n-type dr...This paper proposes a double epi-layers 4H-SiC junction barrier Schottky rectifier （JBSR） with embedded P layer （EPL） in the drift region. The structure is characterized by the P-type layer formed in the n-type drift layer by epitaxial overgrowth process. The electric field and potential distribution are changed due to the buried P-layer, resulting in a high breakdown voltage （BV） and low specific on-resistance （Ron,sp）. The influences of device parameters, such as the depth of the embedded P＋ regions, the space between them and the doping concentration of the drift region, etc., on BV and Ron,sp are investigated by simulations, which provides a particularly useful guideline for the optimal design of the device. The results indicate that BV is increased by 48.5% and Baliga＇s figure of merit （BFOM） is increased by 67.9% compared to a conventional 4H-SiC JBSR.展开更多
We report on a novel architecture to suppress the multi-pulse formation in an all-polarization-maintaining figure-9 erbium-doped fiber laser under high pump power. A 2×2 fiber coupler is introduced into the phase...We report on a novel architecture to suppress the multi-pulse formation in an all-polarization-maintaining figure-9 erbium-doped fiber laser under high pump power. A 2×2 fiber coupler is introduced into the phase-biased nonlinear amplifying loop mirror to extract part of intracavity laser power as a laser output, and the dependence of output couple ratio of fiber coupler on the mode-locking state is experimentally investigated. The intracavity nonlinear effect is mitigated by lowering the intracavity laser power, which is conducive to avoiding the multi-pulse formation. In the meantime, the loss-imbalance induced by fiber coupler is helpful in improving the self-starting ability. With the proposed laser structure,the multiple pulse formation can be suppressed and high power single pulse train can be obtained. The laser emits three pulse trains which is convenient for some applications. Finally, the output power values of three ports are 5.3 m W, 51.3 m W,and 13.2 m W, respectively. The total single pulse output power is 69.8 m W, which is more than 10 times the result without OC2. The total slope efficiency is about 10.1%. The repetition rate of three pulse trains is 21.17 MHz, and the pulse widths are 2.8 ps, 2.63 ps, and 6.66 ps, respectively.展开更多
This paper presents a cascode configuration synchronous rectifier device based on silicon MOSFET and Schottky diode,which can replace traditional power diode directly.This structure has self-driven ability with simple...This paper presents a cascode configuration synchronous rectifier device based on silicon MOSFET and Schottky diode,which can replace traditional power diode directly.This structure has self-driven ability with simple external circuit,and the conduction characteristic is preferable to a power diode.Static characterization and switching behavior analysis of proposed structure are conducted in this paper.The switching process is illustrated in detail using real model which considers the parasitic inductances and the nonlinearity of junction capacitors.The real time internal voltage and current value during switching transition are deduced with the equivalent circuit.To validate the analysis,two voltage specification rectifiers are built.Finally,double-pulse test results and the practical design example verify the performance advantages of proposed structure.展开更多
This paper investigates the behaviours of 4H--SiC merged PiN Schottky （MPS） rectifiers with junction termination extension （JTE） by extensive numerical simulations. The simulated results show that the present mode...This paper investigates the behaviours of 4H--SiC merged PiN Schottky （MPS） rectifiers with junction termination extension （JTE） by extensive numerical simulations. The simulated results show that the present model matches the experimental data very well. The influences of the JTE design parameters such as the doping concentration and length of the JTE on the breakdown characteristics are discussed in detail. Then the temperature sensitivity of the forward behaviour is studied in terms of the different designs of 4H--SiC MPS with JTE, which provides a particularly useful guideline for the optimal design of MPS rectifiers with JTE.展开更多
The velvet electron emission characteristics and beams＇ brightness are investigated with a multi-pulsed mode. The results indicate that in the multi-pulsed mode the velvet emission is not uniform and the periphery em...The velvet electron emission characteristics and beams＇ brightness are investigated with a multi-pulsed mode. The results indicate that in the multi-pulsed mode the velvet emission is not uniform and the periphery emission is much stronger than that from the centre. The periphery emission contributes much more to the formation of the cathode plasma than the centre emission, which leads to diode impendence breakdown. The relationship between the cathode plasma expansion and the initial emittance of the cathode is deduced to describe the characteristics of the multi-pulsed vacuum diode. The emittance of the multi-pulsed beams is measured to be less than 1000mm·mrad. The brightness of the electron beams is better than 1× 10^8A/（m·rad）2.展开更多
TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetiti...TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetition rate, set up for operating in both single-pulse and multi-pulse regimes. A comparison of the deposition rate, the optical and morphological properties of the layers obtained from both ablation regimes was made, which showed that the multi-pulsed ablation produced layers with a higher surface quality and better optical properties.展开更多
In this paper, a one-dimensional discharge model is employed to study multi-pulse phenomena in Ar dielectric barrier discharge （DBD） under atmospheric pressure. The finiteelement method is employed to solve the mode...In this paper, a one-dimensional discharge model is employed to study multi-pulse phenomena in Ar dielectric barrier discharge （DBD） under atmospheric pressure. The finiteelement method is employed to solve the model. The influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of multi discharge pulses are investigated and discussed. The simulation results show that, both the intensity of discharge current and the number of discharge pulses increase with the amplitude of applied voltage, and narrower gas gap is more favorable for the formation of multi pulses. It is revealed that Ar DBDs behave in glow discharge mode when the applied voltage and gas gap distance vary from 2 kV to 6 kV and from 1 mm to 3 mm, respectively. With the frequency decreasing from 250 Hz to 125 Hz, the intensity of discharge current weakens and the number of discharge pulses increases, and the discharges behave in the typical Townsend discharge mode.展开更多
This paper presents an analysis on the nonlinear dynamics and multi-pulse chaotic motions of a simply-supported symmetric cross-ply composite laminated rectangular thin plate with the parametric and forcing excitation...This paper presents an analysis on the nonlinear dynamics and multi-pulse chaotic motions of a simply-supported symmetric cross-ply composite laminated rectangular thin plate with the parametric and forcing excitations. Firstly, based on the Reddy＇s third-order shear deformation plate theory and the model of the yon Karman type geometric nonlinearity, the nonlinear governing partial differential equations of motion for the composite laminated rectangular thin plate are derived by using the Hamilton＇s principle. Then, using the second-order Galerkin dis- cretization, the partial differential governing equations of motion are transformed to nonlinear ordinary differential equations. The case of the primary parametric resonance and 1：1 internal resonance is considered. Four-dimensional averaged equation is obtained by using the method of multiple scales. From the averaged equation obtained here, the theory of normal form is used to give the explicit expressions of normal form. Based on normal form, the energy phase method is utilized to analyze the global bifurcations and multi-pulse chaotic dynamics of the composite laminated rectangular thin plate. The theoretic results obtained above illustrate the existence of the chaos for the Smale horseshoe sense in a parametrical and forcing excited composite laminated thin plate. The chaotic motions of the composite laminated rectangular thin plate are also found by using numerical simulation, which also indicate that there exist different shapes of the multi-pulse chaotic motions for the composite laminated rectangular thin plate.展开更多
The aim of this paper is to contribute to the dynamic modeling of multi-pulse voltage sourced converter based static synchronous series compensator and static synchronous compensator. Details about the internal functi...The aim of this paper is to contribute to the dynamic modeling of multi-pulse voltage sourced converter based static synchronous series compensator and static synchronous compensator. Details about the internal functioning and topology connections are given in order to understand the multi-pulse converter. Using the 24 and 48-pulse topologies switching functions models are presented. The models correctly represent commutations of semiconductor devices in multi-pulse converters, which consequently allows a precise representation of harmonic components. Additionally, time domain models that represent harmonic components are derived based on the switching functions models. Switching functions, as well as time domain models are carried out in the original abc power system coordinates. Effectiveness and precision of the models are validated against simulations performed in Matlab/Simulink?. Additionally, in order to accomplish a more realistic comparison, a laboratory prototype set up is used to assess simulated waveforms.展开更多
Global bifurcations and multi-pulse chaotic dynamics for a simply supported rectangular thin plate are studied by the extended Melnikov method. The rectangular thin plate is subject to transversal and in-plane excitat...Global bifurcations and multi-pulse chaotic dynamics for a simply supported rectangular thin plate are studied by the extended Melnikov method. The rectangular thin plate is subject to transversal and in-plane excitation. A two-degree-of-freedom nonlinear nonautonomous system governing equations of motion for the rectangular thin plate is derived by the von Karman type equation and the Galerkin approach. A one-to- one internal resonance is considered. An averaged equation is obtained with a multi-scale method. After transforming the averaged equation into a standard form, the extended Melnikov method is used to show the existence of multi-pulse chaotic dynamics, which can be used to explain the mechanism of modal interactions of thin plates. A method for calculating the Melnikov function is given without an explicit analytical expression of homoclinic orbits. Furthermore, restrictions on the damping, excitation, and detuning parameters are obtained, under which the multi-pulse chaotic dynamics is expected. The results of numerical simulations are also given to indicate the existence of small amplitude multi-pulse chaotic responses for the rectangular thin plate.展开更多
The acceleration grid power supply(AGPS) is a crucial part of the Negative-ion Neutral Beam Injection system in the China Fusion Engineering Test Reactor,which includes a 3-phase passive(diode) rectifier.To diagnose a...The acceleration grid power supply(AGPS) is a crucial part of the Negative-ion Neutral Beam Injection system in the China Fusion Engineering Test Reactor,which includes a 3-phase passive(diode) rectifier.To diagnose and localize faults in the rectifier,this paper proposes a frequencydomain analysis-based fault diagnosis algorithm for the rectifier in AGPS.First,time-domain expressions and spectral characteristics of the output voltage of the TPTL-NPC inverter-based power supply are analyzed.Then,frequency-domain analysis-based fault diagnosis and frequency-domain analysis-based sub-fault diagnosis algorithms are proposed to diagnose open circuit(OC) faults of diode(s),which benefit from the analysis of harmonics magnitude and phase-angle of the output voltage.Only a fundamental period is needed to diagnose and localize exact faults,and a strong Variable-duration Fault Detection Method is proposed to identify acceptable ripple from OC faults.Detailed simulations and experimental results demonstrate the effectiveness,quickness,and robustness of the proposed algorithms,and the diagnosis algorithms proposed in this article provide a significant method for the fault diagnosis of other rectifiers and converters.展开更多
The Vienna rectifier is a widely adopted solution for high-power rectification due to its efficiency and straightforward design.However,its performance can degrade under unbalanced three phase voltage conditions,leadi...The Vienna rectifier is a widely adopted solution for high-power rectification due to its efficiency and straightforward design.However,its performance can degrade under unbalanced three phase voltage conditions,leading to current zero-crossing distortion and compromised dynamic response.This paper investigates the causes of these distortions,identifying a phase shift between the input current and the grid voltage as a primary factor,and proposes an effective distortion phase identification strategy.Furthermore,the dynamic performance is enhanced through improved current reference calculations and a refined power feedforward strategy.This approach optimizes the system's response to load changes and maintains output voltage stability under unbalanced conditions.Simulation results validate the effectiveness of the proposed methods in reducing current distortion and improving overall performance.展开更多
In this study,Computational Fluid Dynamics(CFD)together with a component transport model are exploited to investigate the influence of dimensionless parameters,involving the height of the rectifier grid and the instal...In this study,Computational Fluid Dynamics(CFD)together with a component transport model are exploited to investigate the influence of dimensionless parameters,involving the height of the rectifier grid and the installation height of the first catalyst layer,on the flow field and the overall denitration efficiency of a cement kiln’s SCR(Selective catalytic reduction)denitrification reactor.It is shown that accurate numerical results can be obtained by fitting the particle size distribution function to the actual cement kiln fly ash and implementing a non-uniform particle inlet boundary condition.The relative error between denitration efficiency derived from experimental data,numerical simulation,and real-time system pressure drop ranges from 4%to 9%.Optimization of the SCR reactor is achieved when the rectifier grid thickness ratio k/H≥0.030,the rectifier grid height ratio h/H=0.04,and the spacing between the rectifier grid and the first catalyst layer l/H=0.10.Under these conditions,airflow distribution and particle dispersion upstream of the catalyst result in increased denitration efficiencies of 3.21%,3.43%,and 3.27%,respectively,compared to the least favorable operating conditions.展开更多
文摘The Auto-Transformer Rectifier Unit（ATRU） is one preferred solution for high-power AC/DC power conversion in aircraft. This is mainly due to its simple structure, high reliability and reduced k VA ratings. Indeed, the ATRU has become a preferred AC/DC solution to supply power to the electric environment control system on-board future aircraft. In this paper, a general modelling method for ATRUs is introduced. The developed model is based on the fact that the DC voltage and current are strongly related to the voltage and current vectors at the AC terminals of ATRUs. In this paper, we carry on our research in modelling symmetric 18-pulse ATRUs and develop a generic modelling technique. The developed generic model can study not only symmetric but also asymmetric ATRUs. An 18-pulse asymmetric ATRU is used to demonstrate the accuracy and efficiency of the developed model by comparing with corresponding detailed switching SABER models provided by our industrial partner. The functional models also allow accelerated and accurate simulations and thus enable whole-scale more-electric aircraft electrical power system studies in the future.
基金Project supported by the National Key Research and Development Program of China(Grant No.2022YFE03150203)the National Natural Science Foundation of China(Grant Nos.U2032217,52072366,and 52477031)Shandong Provincial Natural Science Foundation(Grant No.ZR2024ME217)。
文摘Second-generation high-temperature superconducting(2G-HTS)magnets operating in persistent current mode(PCM)hold great promise for applications such as magnetic resonance imaging.The development of joint-less closed-loop magnets has effectively tackled the challenges of fabricating joints for REBCO tape.However,certain closed-loop magnets cannot utilize conventional persistent current switches(PCS)and instead require multi-pulse magnetization techniques.This study explores the effects of multi-pulse magnetic field excitation on the flux trapping behavior of a four-pancake coil(FPC).A detailed comparison of the effects of different pulse types and periods on the FPC reveals that the background magnetic field exceeds the critical magnetic field of the coil,thereby creating resistance in the superconducting loop.The critical magnetic field of the FPC is determined experimentally,and a reasonable speculation on the multi-pulse field excitation mechanism is presented.
基金supported by Natural Science Basic Research Program of Shaanxi Province of China(Grant No.2023JCYB574)National Natural Science Foundation of China(Grant No.62204203)。
文摘A monolithic integrated full-wave bridge rectifier consisted of horizontal Schottky-barrier diodes(SBD)is prepared based on 100 nm ultra-thin β-Ga_(2)O_(3)and demonstrated the solar-blind UV(SUV)light-modulated characteristics.Under SUV light illumination,the rectifier has the excellent full-wave rectification characteristics for the AC input signals of 5,12,and 24 V with different frequencies.Further,experimental results confirmed the feasibility of continuously tuning the rectified output through SUV light-encoding.This work provides valuable insights for the development of optically programmable Ga_(2)O_(3)ACDC converters.
文摘The face velocities of the high efficiency particulate air filters and the ultra low penetration airfilters in fan filter units (FFUs) have large relative standard deviation and turbulivity. It seriously affects the unidirectivity of the flow in the unidirectional flow clean zone and cleanroom. The cross contamination in this kind of unidirectional flow area is hardly controlled. It is significant to find optional method for keeping the face velocity uniformity of FFU and reducing the face velocity turbulivity of FFU, furthermore, to keep the cleanliness level under FFUs. The normal and easy method is to add flow rectifiers under filters. FFUs with various flow rectifiers have been tested. The uniformity and turbulivity of facevelocity under the FFU are presented in this paper. The influence of the facevelocity uniformity and turbulivity on the contamination boundary of the unidirectional flow is studiedas well.
基金supported by the Chinese Natural Science Fund(No.10572020)
文摘In order to investigate the thermal shock and the heat conduction property of a target under multi-pulsed laser radiation,analytic expressions of both temperature and thermal stress fields in the target are deduced on the basis of the non-Fourier conduction law and the thermo-elastic theory.Taking a stainless steel target as an example,we can solve the analytic expressions under appropriate boundary conditions by using the finite difference method and MATLAB software,and then reveal the evolution law of both surplus temperaturt,and thermal stress in the target.The results indicate that the temperature curves in the target irradiated by a multi-pulsed laser take on a delayed character in different sections away from the boundary,which is only affected by its relaxation time.The front of the stress wave is very steep in the non-Fourier numerical solutions,which presents an obvious thermal shock,so it is necessary to consider the non-Fourier effect of semi-infinite body under the high energy laser radiation.
基金Project supported by the State Key Program of the National Natural Science Foundation of China(Grant No.61234006)
文摘This paper describes the successful fabrication of 4H-SiC junction barrier Schottky （JBS） rectifiers with a linearly graded field limiting ring （LG-FLR）. Linearly variable ring spacings for the FLR termination are applied to improve the blocking voltage by reducing the peak surface electric field at the edge termination region, which acts like a variable lateral doping profile resulting in a gradual field distribution. The experimental results demonstrate a breakdown voltage of 5 kV at the reverse leakage current density of 2 mA/cm2 （about 80% of the theoretical value）. Detailed numerical simulations show that the proposed termination structure provides a uniform electric field profile compared to the conventional FLR termi- nation, which is responsible for 45% improvement in the reverse blocking voltage despite a 3.7% longer total termination length.
基金supported by the State Key Program of the National Natural Science Foundation of China(Grant No.61234006)the Open Foundation of the State Key Laboratory of Electronic Thin Films and Integrated Devices,China(Grant No.KFJJ201301)the National Science and Technology Major Project of the Ministry of Science and Technology,China(Grant No.2013ZX02305-003)
文摘The effect of the mesa configuration on the reverse breakdown characteristic of a SiC PiN rectifier for high-voltage applications is analyzed in this study.Three geometrical parameters,i.e.,mesa height,mesa angle and mesa bottom corner,are investigated by numerical simulation.The simulation results show that a deep mesa height,a small mesa angle and a smooth mesa bottom（without sub-trench） could contribute to a high breakdown voltage due to a smooth and uniform surface electric field distribution.Moreover,an optimized mesa structure without sub-trench（mesa height of 2.2 μm and mesa angle of 20°） is experimentally demonstrated.A maximum reverse blocking voltage of 4 kV and a forward voltage drop of 3.7 V at 100 A/cm^2 are obtained from the fabricated diode with a 30-μm thick N^- epi-layer,corresponding to 85% of the ideal parallel-plane value.The blocking characteristic as a function of the JTE dose is also discussed for the PiN rectifiers with and without interface charge.
基金Project supported by the 13115 Innovation Engineering of Shaanxi Province of China(Grant No.2008ZDKG-30)
文摘This paper proposes a double epi-layers 4H-SiC junction barrier Schottky rectifier （JBSR） with embedded P layer （EPL） in the drift region. The structure is characterized by the P-type layer formed in the n-type drift layer by epitaxial overgrowth process. The electric field and potential distribution are changed due to the buried P-layer, resulting in a high breakdown voltage （BV） and low specific on-resistance （Ron,sp）. The influences of device parameters, such as the depth of the embedded P＋ regions, the space between them and the doping concentration of the drift region, etc., on BV and Ron,sp are investigated by simulations, which provides a particularly useful guideline for the optimal design of the device. The results indicate that BV is increased by 48.5% and Baliga＇s figure of merit （BFOM） is increased by 67.9% compared to a conventional 4H-SiC JBSR.
基金Project supported by the National Natural Science Foundation of China(Grant No.51905528)the Key Research Project of Bureau of Frontier Sciences and Education+1 种基金Chinese Academy of Sciences(Grant No.QYZDY-SSW-JSC008)the National Key Research and Development Project,China(Grant Nos.2019YFB2005600 and 2018YFB2003403)。
文摘We report on a novel architecture to suppress the multi-pulse formation in an all-polarization-maintaining figure-9 erbium-doped fiber laser under high pump power. A 2×2 fiber coupler is introduced into the phase-biased nonlinear amplifying loop mirror to extract part of intracavity laser power as a laser output, and the dependence of output couple ratio of fiber coupler on the mode-locking state is experimentally investigated. The intracavity nonlinear effect is mitigated by lowering the intracavity laser power, which is conducive to avoiding the multi-pulse formation. In the meantime, the loss-imbalance induced by fiber coupler is helpful in improving the self-starting ability. With the proposed laser structure,the multiple pulse formation can be suppressed and high power single pulse train can be obtained. The laser emits three pulse trains which is convenient for some applications. Finally, the output power values of three ports are 5.3 m W, 51.3 m W,and 13.2 m W, respectively. The total single pulse output power is 69.8 m W, which is more than 10 times the result without OC2. The total slope efficiency is about 10.1%. The repetition rate of three pulse trains is 21.17 MHz, and the pulse widths are 2.8 ps, 2.63 ps, and 6.66 ps, respectively.
基金supported in part by the National Natural Science Foundation of China (No.51777093)
文摘This paper presents a cascode configuration synchronous rectifier device based on silicon MOSFET and Schottky diode,which can replace traditional power diode directly.This structure has self-driven ability with simple external circuit,and the conduction characteristic is preferable to a power diode.Static characterization and switching behavior analysis of proposed structure are conducted in this paper.The switching process is illustrated in detail using real model which considers the parasitic inductances and the nonlinearity of junction capacitors.The real time internal voltage and current value during switching transition are deduced with the equivalent circuit.To validate the analysis,two voltage specification rectifiers are built.Finally,double-pulse test results and the practical design example verify the performance advantages of proposed structure.
基金Project supported by Shaanxi 13115 Innovation Engineering Foundation (Grant No. 2008ZDKG-30)Pre-research Project(Grant No. 51308040302)
文摘This paper investigates the behaviours of 4H--SiC merged PiN Schottky （MPS） rectifiers with junction termination extension （JTE） by extensive numerical simulations. The simulated results show that the present model matches the experimental data very well. The influences of the JTE design parameters such as the doping concentration and length of the JTE on the breakdown characteristics are discussed in detail. Then the temperature sensitivity of the forward behaviour is studied in terms of the different designs of 4H--SiC MPS with JTE, which provides a particularly useful guideline for the optimal design of MPS rectifiers with JTE.
文摘The velvet electron emission characteristics and beams＇ brightness are investigated with a multi-pulsed mode. The results indicate that in the multi-pulsed mode the velvet emission is not uniform and the periphery emission is much stronger than that from the centre. The periphery emission contributes much more to the formation of the cathode plasma than the centre emission, which leads to diode impendence breakdown. The relationship between the cathode plasma expansion and the initial emittance of the cathode is deduced to describe the characteristics of the multi-pulsed vacuum diode. The emittance of the multi-pulsed beams is measured to be less than 1000mm·mrad. The brightness of the electron beams is better than 1× 10^8A/（m·rad）2.
文摘TiO2 thin films were prepared on glass substrates using the PLD (Pulsed Laser Deposition) technique. In order to carry out the ablation process, a Nd:YAG laser was used emitting in 1064 nm wavelength at 10 Hz repetition rate, set up for operating in both single-pulse and multi-pulse regimes. A comparison of the deposition rate, the optical and morphological properties of the layers obtained from both ablation regimes was made, which showed that the multi-pulsed ablation produced layers with a higher surface quality and better optical properties.
基金supported in part by China Foundation for the Author of National Excellent Doctoral Dissertation(No.200338)Fundamental Research Funds for the Central Universities of China(No.xjj20100160)
文摘In this paper, a one-dimensional discharge model is employed to study multi-pulse phenomena in Ar dielectric barrier discharge （DBD） under atmospheric pressure. The finiteelement method is employed to solve the model. The influences of applied voltage amplitude and frequency as well as gas gap distance on the variation of multi discharge pulses are investigated and discussed. The simulation results show that, both the intensity of discharge current and the number of discharge pulses increase with the amplitude of applied voltage, and narrower gas gap is more favorable for the formation of multi pulses. It is revealed that Ar DBDs behave in glow discharge mode when the applied voltage and gas gap distance vary from 2 kV to 6 kV and from 1 mm to 3 mm, respectively. With the frequency decreasing from 250 Hz to 125 Hz, the intensity of discharge current weakens and the number of discharge pulses increases, and the discharges behave in the typical Townsend discharge mode.
基金supported by the National Natural Science Foundation of China (Nos. 10732020 and 11072008)the Funding Project for Academic Human Resources Development in Institutions of Higher Learning under the Jurisdiction of Beijing Municipality (PHRIHLB)
文摘This paper presents an analysis on the nonlinear dynamics and multi-pulse chaotic motions of a simply-supported symmetric cross-ply composite laminated rectangular thin plate with the parametric and forcing excitations. Firstly, based on the Reddy＇s third-order shear deformation plate theory and the model of the yon Karman type geometric nonlinearity, the nonlinear governing partial differential equations of motion for the composite laminated rectangular thin plate are derived by using the Hamilton＇s principle. Then, using the second-order Galerkin dis- cretization, the partial differential governing equations of motion are transformed to nonlinear ordinary differential equations. The case of the primary parametric resonance and 1：1 internal resonance is considered. Four-dimensional averaged equation is obtained by using the method of multiple scales. From the averaged equation obtained here, the theory of normal form is used to give the explicit expressions of normal form. Based on normal form, the energy phase method is utilized to analyze the global bifurcations and multi-pulse chaotic dynamics of the composite laminated rectangular thin plate. The theoretic results obtained above illustrate the existence of the chaos for the Smale horseshoe sense in a parametrical and forcing excited composite laminated thin plate. The chaotic motions of the composite laminated rectangular thin plate are also found by using numerical simulation, which also indicate that there exist different shapes of the multi-pulse chaotic motions for the composite laminated rectangular thin plate.
文摘The aim of this paper is to contribute to the dynamic modeling of multi-pulse voltage sourced converter based static synchronous series compensator and static synchronous compensator. Details about the internal functioning and topology connections are given in order to understand the multi-pulse converter. Using the 24 and 48-pulse topologies switching functions models are presented. The models correctly represent commutations of semiconductor devices in multi-pulse converters, which consequently allows a precise representation of harmonic components. Additionally, time domain models that represent harmonic components are derived based on the switching functions models. Switching functions, as well as time domain models are carried out in the original abc power system coordinates. Effectiveness and precision of the models are validated against simulations performed in Matlab/Simulink?. Additionally, in order to accomplish a more realistic comparison, a laboratory prototype set up is used to assess simulated waveforms.
基金Project supported the National Natural Science Foundation of China (Nos. 10732020,11072008,and 11102226)the Scientific Research Foundation of Civil Aviation University of China (No. 2010QD04X)the Fundamental Research Funds for the Central Universities of China (Nos. ZXH2011D006 and ZXH2012K004)
文摘Global bifurcations and multi-pulse chaotic dynamics for a simply supported rectangular thin plate are studied by the extended Melnikov method. The rectangular thin plate is subject to transversal and in-plane excitation. A two-degree-of-freedom nonlinear nonautonomous system governing equations of motion for the rectangular thin plate is derived by the von Karman type equation and the Galerkin approach. A one-to- one internal resonance is considered. An averaged equation is obtained with a multi-scale method. After transforming the averaged equation into a standard form, the extended Melnikov method is used to show the existence of multi-pulse chaotic dynamics, which can be used to explain the mechanism of modal interactions of thin plates. A method for calculating the Melnikov function is given without an explicit analytical expression of homoclinic orbits. Furthermore, restrictions on the damping, excitation, and detuning parameters are obtained, under which the multi-pulse chaotic dynamics is expected. The results of numerical simulations are also given to indicate the existence of small amplitude multi-pulse chaotic responses for the rectangular thin plate.
基金supported by the National Key R&D Program of China(No.2017YFE0300104)National Natural Science Foundation of China(No.51821005)
文摘The acceleration grid power supply(AGPS) is a crucial part of the Negative-ion Neutral Beam Injection system in the China Fusion Engineering Test Reactor,which includes a 3-phase passive(diode) rectifier.To diagnose and localize faults in the rectifier,this paper proposes a frequencydomain analysis-based fault diagnosis algorithm for the rectifier in AGPS.First,time-domain expressions and spectral characteristics of the output voltage of the TPTL-NPC inverter-based power supply are analyzed.Then,frequency-domain analysis-based fault diagnosis and frequency-domain analysis-based sub-fault diagnosis algorithms are proposed to diagnose open circuit(OC) faults of diode(s),which benefit from the analysis of harmonics magnitude and phase-angle of the output voltage.Only a fundamental period is needed to diagnose and localize exact faults,and a strong Variable-duration Fault Detection Method is proposed to identify acceptable ripple from OC faults.Detailed simulations and experimental results demonstrate the effectiveness,quickness,and robustness of the proposed algorithms,and the diagnosis algorithms proposed in this article provide a significant method for the fault diagnosis of other rectifiers and converters.
文摘The Vienna rectifier is a widely adopted solution for high-power rectification due to its efficiency and straightforward design.However,its performance can degrade under unbalanced three phase voltage conditions,leading to current zero-crossing distortion and compromised dynamic response.This paper investigates the causes of these distortions,identifying a phase shift between the input current and the grid voltage as a primary factor,and proposes an effective distortion phase identification strategy.Furthermore,the dynamic performance is enhanced through improved current reference calculations and a refined power feedforward strategy.This approach optimizes the system's response to load changes and maintains output voltage stability under unbalanced conditions.Simulation results validate the effectiveness of the proposed methods in reducing current distortion and improving overall performance.
基金Anhui Province Key Research and Development Plan of the Ecological Environment Project(No.202104i07020016).
文摘In this study,Computational Fluid Dynamics(CFD)together with a component transport model are exploited to investigate the influence of dimensionless parameters,involving the height of the rectifier grid and the installation height of the first catalyst layer,on the flow field and the overall denitration efficiency of a cement kiln’s SCR(Selective catalytic reduction)denitrification reactor.It is shown that accurate numerical results can be obtained by fitting the particle size distribution function to the actual cement kiln fly ash and implementing a non-uniform particle inlet boundary condition.The relative error between denitration efficiency derived from experimental data,numerical simulation,and real-time system pressure drop ranges from 4%to 9%.Optimization of the SCR reactor is achieved when the rectifier grid thickness ratio k/H≥0.030,the rectifier grid height ratio h/H=0.04,and the spacing between the rectifier grid and the first catalyst layer l/H=0.10.Under these conditions,airflow distribution and particle dispersion upstream of the catalyst result in increased denitration efficiencies of 3.21%,3.43%,and 3.27%,respectively,compared to the least favorable operating conditions.
