零电流开关Buck变换器混沌现象的研究

鉴于软开关DC/DC变换器的应用越来越广泛,由于谐振元件的存在使得变换器的混沌现象变得复杂.本文以Buck ZCS PWM变换器为具体研究对象.借鉴采用模块化的思想,简化了电压反馈控制方式零电流开关 Buck变换器工作状态的分析,建立了变换器不连续导电模式下的系统离散混沌数学模型,为进一步的理论分析和模拟仿真打下基础.根据系统稳定性判据确定了稳定工作区域,得出主要元件参数的稳定工作范围,设计了电压反馈控制Buck变换器的仿真电路,仿真结果验证了理论分析的正确性.     

开关延迟对Buck变换器分岔的影响

研究了电流模式控制Buck变换器由于开关延迟带来的分岔和混沌现象的变化.首先给出Buck变换器的数学模型,然后针对理想开关和3种典型开关延迟参数的情况,以理想输入直流电压为变量,通过计算机仿真得到不同的分岔和混沌现象,并给出了庞加莱截面图、电流和电压波形图.根据实验分析可知,随着开关延迟时间的增加,系统分岔现象将加剧,甚至导致系统不稳定.     

基于整流源的Buck变换器混沌现象研究

在供电电源为带谐波的整流源而非理想直流电源的情况下,研究了电流模式控制Buck变换器的分岔和混沌现象.首先给出Buck变换器在连续导通模式下的数学模型,然后对理想直流电源供电和3种模拟的含不同电压幅值谐波分量的整流源供电的情况,在改变电压平均值的情况下,通过计算机仿真得到不同的分岔和混沌现象,并进行比较分析,最后给出典型的含10%直流电压幅值谐波的纹波电压对应的电流和电压波形图,并进行比较分析.     

不连续运行模式电流型Buck-Boost变换器中的分岔和混沌

在不连续运行模式条件下，建立了分析电流反馈型Buck—Boost变换器中的分岔行为和混沌过程的分段离散迭代映射方程，得到了以输入电压E为参数的分岔图和相图．数值结果表明，工作于不连续模式下的电流反馈型Buck—Boost变换器会出现特有的一些非光滑分岔现象．例如，与光滑系统中典型的倍周期分岔不同的是，在周期1到周期2的倍周期分岔点附近，周期2轨道分枝不垂直于周期1轨道分枝，并且直接经周期6到达混沌态．     

基于开关周期平均模型的仿真分析

采用PWM三端器件的开关周期平均化模型,建立了主要DC/DC变换器拓扑———Buck、Boost、Buck-Boost的统一的、适用于PSPICE软件的仿真模型.进行了上述变换器在CCM和DCM状态下仿真模型的推导,采用此模型进行仿真,具有速度快、实现简单且符合实际电路需求的特点.应用该模型,给出了Buck变换器的仿真实例.     

BOOST变换器不连续导通模式下的混沌现象分析

研究输出电压反馈型Boost DC/DC变换器,构建并推导了不连续导通方式下(即DCM方式)变换器的离散映射模型。基于此数学模型,以倍周期分岔理论分析了变换器的分岔特性。并利用Matlab软件搭建仿真模块,通过仿真验证了离散模型的正确性,并且详细给出了变换器从稳定逐步到混沌的全过程。该文的研究具有基础性,为更加深入研究Boost变换器工作时的混沌现象打下基础。     

基于ZVRT的零电压DC/AC变换器的研究

提出一种低频方波输出的零电压DC/AC变换器,它结合了Buck DC/DC变换器和半桥DC/AC变换器的特点,合二为一,负载侧输出为低频方波信号.在低频正负半波期间,电路工作在ZVRT-BUCK变换器模式,两个开关管互为主开关管和辅助开关管.详细分析了它的工作原理和软开关情况,由于采用了ZVRT技术,两个开关管均实现了零电压通断,提高了电路效率.实验结果验证了该方案是可行的.     

改进型本安Buck变换器的分析与设计

提出了一种输出具有LC滤波电路的本安Buck变换器,使得在特定的电气性能指标要求下,可不提高变换器工作频率,但能减小变换器内部的电感量及电容量,达到提升该变换器本质安全性能的目的。深入分析了该拓扑电路在电感电流连续模式(CCM)时的输出纹波电压,指出输出纹波电压最大值是在输入电压最大,负载电阻为CCM与DCM的临界电阻时取得。根据最大输出纹波电压指标要求,在给定的动态范围内,得出了本安Buck变换器电感、电容参数的设计方法。为了说明改进型Buck变换器相比于传统型Buck变换器的优势,在相同的输出纹波电压指标要求下,对传统型及改进型Buck变换器的电感、电容取值进行了比较分析,得出所提出的改进型Buck变换器采用较小的电感、电容即可满足电气性能指标要求,因而可提高其本安性能。因此,通过在Buck变换器的输出附加LC滤波电路,不仅能有效提高本安Buck变换器的输出功率,还能减小其体积。给出了设计实例,仿真与实验结果验证了改进电路拓扑理论分析的正确性及减小目标电感、电容量的可行性。     

两种控制模式的开关变换器的动力学行为研究

DC-DC变换器是开关电源的核心部分,在各个领域有着广泛的应用.电压模式控制Buck变换器和电流模式控制Boost变换器是电力电子的非线性研究中两种重要的研究对象,它们都有着非常广泛的应用.以这两种模式控制的开关变换器为研究对象,通过对它们进行建模、分析和实验等证实其中存在着丰富的动力学行为,如分岔和混沌等,为实际的电路系统的稳定设计提供了理论指导.     

电流反馈型Buck-Boost变换器的非线性动力学研究

首先建立了电流反馈型buck—boost变换器的精确离散化模型,然后研究了变换器在不连续模式下的非线性动力学行为．通过研究发现：电流反馈型Buck—Boost变换器在不连续模式下,出现了特有的分岔和混沌现象．     

Markedness and its Interpretation in Language Use

Language markedness is a common phenomenon in languages, and is reflected from hearing, vision and sense, i.e. the variation in the three aspects such as phonology, morphology and semantics. This paper focuses on the interpretation of markedness in language use following the three perspectives, i.e. pragmatic interpretation, psychological interpretation and cognitive interpretation, with an aim to define the function of markedness.     

低渗透非均质砂岩油藏启动压力梯度研究

理论推导与室内实验相结合,建立了低渗透非均质砂岩油藏启动压力梯度确定方法。首先借助油藏流场与电场相似的原理,推导了非均质砂岩油藏启动压力梯度计算公式。其次基于稳定流实验方法,建立了非均质砂岩油藏启动压力梯度测试方法。结果表明:低渗透非均质砂岩油藏的启动压力梯度确定遵循两个等效原则。平面非均质油藏的启动压力梯度等于各级渗透率段的启动压力梯度关于长度的加权平均;纵向非均质油藏的启动压力梯度等于各渗透率层的启动压力梯度关于渗透率与渗流面积乘积的加权平均。研究成果可用于有效指导低渗透非均质砂岩油藏的合理井距确定,促进该类油藏的高效开发。     

On Tragic Consciousness In The Works By Ernest Hemingway

As an American modern novelist who were famous in the literary world, Hemingway was not a person who always followed the trend but a sharp observer. At the same time, he was a tragedy maestro, he paid great attention on existence, fate and end-result. The dramatis personae's tragedy of his works was an extreme limit by all means tragedy on the meaning of fearless challenge that failed. The beauty of tragedy was not produced on the destruction of life, but now this kind of value was in the impact activity. They performed for the reader about the tragedy on challenging for the limit and the death.     

Achieving Unusual States of Matter Under High Pressure

正The periodicity of the elements and the non-reactivity of the inner-shell electrons are two related principles of chemistry,rooted in the atomic shell structure.Within compounds,Group I elements,for example,invariably assume the+1 oxidation state,and their chemical properties differ completely from those of the p-block elements.These general rules govern our understanding of chemical structures and reactions.Using first principles calcula-     

Exchange-Correlation and Electronic Excitation Energies from Pairing Matrix Fluctuations

We have developed an adiabatic connection to formulate the ground-state exchange-correlation energy in terms of pairing matrix linear fluctuations.This formulation of the exchange-correlation energy opens a new channel for density functional approximations based on the many-body perturbation theory.We illustrate the potential of such approaches with an approximation based on the particle-particle Random Phase Approximation(pp-RPA).This re-     

Density Functional Theory for the Response of Periodic Systems to Electric Fields Based on the Vector Potential Approach

正The electronic and nuclear(structural/vibrational)response of 1D-3D nanoscale systems to electric fields gives rise to a host of optical,mechanical,spectral,etc.properties that are of high theoretical and applied interest.Due to the computational difficulty of treating such large systems it is convenient to model them as infinite and periodic(at least,in first approximation).The fundamental theoretical/computational problem in doing so is that     

On the Thermodynamic Limit for Responses to Static Electromagnetic Fields

For molecular systems,the quantum-mechanical treatment of their responses to static electromagnetic fields usually employs a scalar-potential treatment of the electric field and a vector-potential treatment of the magnetic field.Although the potential for each field separately is associated with the choice of an(unphysical)origin,the precise choice of the origin for the electrostatic field has little consequences for the results.This is different for the     

An affordable accurate evaluation of the binding conformations predicted by molecular docking studies in bio-system

Franck-Condon factors bridge the gap between theoretical modeling and experimental observations for molecular electronic spectroscopy and electron transfer.Under the displaced harmonic oscillator approximation,multidimensional Franck-Condon factors are decomposed into a product of many one-dimensional(1D)Franck-Condon(FC)factors,and each 1D-FC factor is associated with one Huang-Rhys factor that determines the leading contribution of     

Call for Papers

<正>"The Journal of Shanghai Normal University:Mathematics"is published by Shanghai Normal University as regular issues of The Journal of Shanghai Normal University each year from 2014 in English.The editors-in-chief of the issues are professors Yuhao Cong and Maoan Han.The Journal of Shanghai Normal University was started in 1958 with     

Journal of Donghua University ( English Edition) Contents of Volume 31

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