A circuit configuration and a circuit topologic family of the novel forward mode AC/AC converters with high frequency link are presented. The circuit configuration is constituted of input cycloconverter, high frequenc...A circuit configuration and a circuit topologic family of the novel forward mode AC/AC converters with high frequency link are presented. The circuit configuration is constituted of input cycloconverter, high frequency transformer, output cycloconverter, input and output filters. The circuit topologic family includes eight circuit topologies, such as full-bridge-full-wave mode, etc. The bi-polarity phase-shifted control strategy and steady principles are thoroughly investigated. The output characteristics are obtained. By using the bi-polarity phase-shifted control strategy with phase-shifted control between the output cycloconveter and the input cycloconverter, commutation overlap period of the output cycloconverter, and polarity selection of the output filtering inductance current and the input voltage, the leakage inductance energy and the output filtering inductance current are naturally commutated, and surge voltage and surge current of the cycloconverters are overcome. The converters have such advantages as simple topology, two-stage power conversions(LFAC/HFAC/LFAC), bi-directional power flow, high frequency electrical isolation, good output waveforms, and strong ability to stabilize voltage. The converters lay key technical foundation on a new-type of regulated sinusoidal AC power supplies and electronic transformers. The correction and advancement of the converters are well verified by a principle test.展开更多
The longitudinal dynamic flight stability of a bumblebee in forward flight is studied. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eig...The longitudinal dynamic flight stability of a bumblebee in forward flight is studied. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are employed for solving the equations of motion. The primary findings are as the following. The forward flight of the bumblebee is not dynamically stable due to the existence of one （or two） unstable or approximately neutrally stable natural modes of motion. At hovering to medium flight speed [flight speed Ue = （0-3.5）m s^-1; advance ratio J = 0-0.44], the flight is weakly unstable or approximately neutrally stable; at high speed （Ue = 4.5 m s^-1; J = 0.57）, the flight becomes strongly unstable （initial disturbance double its value in only 3.5 wingbeats）.展开更多
We present a differentiation framework for plane-wave density-functional theory(DFT)that combines the strengths of forward-mode algorithmic differentiation(AD)and density-functional perturbation theory(DFPT).In the re...We present a differentiation framework for plane-wave density-functional theory(DFT)that combines the strengths of forward-mode algorithmic differentiation(AD)and density-functional perturbation theory(DFPT).In the resulting AD-DFPT framework derivatives of any DFT output quantity with respect to any input parameter(e.g.,geometry,density functional or pseudopotential)can be computed accurately without deriving gradient expressions by hand.We implement AD-DFPT into the Density-Functional ToolKit(DFTK)and show its broad applicability.Amongst others we consider the inverse design of a semiconductor band gap,the learning of exchange-correlation functional parameters,or the propagation of DFT parameter uncertainties to relaxed structures.These examples demonstrate a number of promising research avenues opened by gradient-driven workflows in first-principles materials modeling.展开更多
文摘A circuit configuration and a circuit topologic family of the novel forward mode AC/AC converters with high frequency link are presented. The circuit configuration is constituted of input cycloconverter, high frequency transformer, output cycloconverter, input and output filters. The circuit topologic family includes eight circuit topologies, such as full-bridge-full-wave mode, etc. The bi-polarity phase-shifted control strategy and steady principles are thoroughly investigated. The output characteristics are obtained. By using the bi-polarity phase-shifted control strategy with phase-shifted control between the output cycloconveter and the input cycloconverter, commutation overlap period of the output cycloconverter, and polarity selection of the output filtering inductance current and the input voltage, the leakage inductance energy and the output filtering inductance current are naturally commutated, and surge voltage and surge current of the cycloconverters are overcome. The converters have such advantages as simple topology, two-stage power conversions(LFAC/HFAC/LFAC), bi-directional power flow, high frequency electrical isolation, good output waveforms, and strong ability to stabilize voltage. The converters lay key technical foundation on a new-type of regulated sinusoidal AC power supplies and electronic transformers. The correction and advancement of the converters are well verified by a principle test.
基金the National Natural Science Foundation of China (10732030)
文摘The longitudinal dynamic flight stability of a bumblebee in forward flight is studied. The method of computational fluid dynamics is used to compute the aerodynamic derivatives and the techniques of eigenvalue and eigenvector analysis are employed for solving the equations of motion. The primary findings are as the following. The forward flight of the bumblebee is not dynamically stable due to the existence of one （or two） unstable or approximately neutrally stable natural modes of motion. At hovering to medium flight speed [flight speed Ue = （0-3.5）m s^-1; advance ratio J = 0-0.44], the flight is weakly unstable or approximately neutrally stable; at high speed （Ue = 4.5 m s^-1; J = 0.57）, the flight becomes strongly unstable （initial disturbance double its value in only 3.5 wingbeats）.
基金supported by the Swiss National Science Foundation (SNSF, Grant No. 221186)the NCCR MARVEL, a National Centre of Competence in Research, funded by the SNSF (Grant No. 205602). The funder played no role in study design, data collection, analysis and interpretation of data, or the writing of this manuscript. Fruitful discussions with Andrea Azzali, Gaspard Kemlin, Antoine Levitt, Uwe Naumann, Étienne Polack, and Markus Towara on the technical aspects of our AD-DFPT implementation and with Giovanni Pizzi regarding the pseudopotential training example are gratefully acknowledged.
文摘We present a differentiation framework for plane-wave density-functional theory(DFT)that combines the strengths of forward-mode algorithmic differentiation(AD)and density-functional perturbation theory(DFPT).In the resulting AD-DFPT framework derivatives of any DFT output quantity with respect to any input parameter(e.g.,geometry,density functional or pseudopotential)can be computed accurately without deriving gradient expressions by hand.We implement AD-DFPT into the Density-Functional ToolKit(DFTK)and show its broad applicability.Amongst others we consider the inverse design of a semiconductor band gap,the learning of exchange-correlation functional parameters,or the propagation of DFT parameter uncertainties to relaxed structures.These examples demonstrate a number of promising research avenues opened by gradient-driven workflows in first-principles materials modeling.
