在分析了五电平NPC/H桥逆变器拓扑结构和工作原理的基础上,设计了载波层叠脉冲宽度调制(pulse w idth modulation,PWM)和三段式空间矢量脉冲宽度调制(space vector pulse w idth modulation,SVPWM)的策略,并介绍了这2种调制策略的原理...在分析了五电平NPC/H桥逆变器拓扑结构和工作原理的基础上,设计了载波层叠脉冲宽度调制(pulse w idth modulation,PWM)和三段式空间矢量脉冲宽度调制(space vector pulse w idth modulation,SVPWM)的策略,并介绍了这2种调制策略的原理。通过Simulink软件搭建仿真模型,对比了不同调制度和不同载波频率下逆变器的输出特性,得出结论:输出电压波形的电平数与调制度有关;提高载波频率可使主要高次谐波频率增大,减小谐波含量。以DSP+FPGA工控开发板为控制器搭建实验平台,实验结果表明调整策略有效。展开更多
USB卫星测控体制是现行航天测控领域的通用体制之一,对卫星的状态监测、姿态控制和轨道修正等需要通过调制载波实现遥测、遥控、测量信息的传递和交互,当副载波信号处于大调制度的情况下,容易造成载波错锁或假锁。本文在工程实践的基础...USB卫星测控体制是现行航天测控领域的通用体制之一,对卫星的状态监测、姿态控制和轨道修正等需要通过调制载波实现遥测、遥控、测量信息的传递和交互,当副载波信号处于大调制度的情况下,容易造成载波错锁或假锁。本文在工程实践的基础上,总结了载波错锁产生的原因,基于Matlab/Simulink建立了高斯白噪声影响下的中频接收载波环模型,仿真分析了不同调制度下的载波时频特性,提出奇异值分解(Singular Value Decomposition,SVD)降噪实现特征信号提取。通过仿真验证,副载波解调与频谱分析能有效抑制调制度较大的副载波分量,实现载波信号捕获,克服了大调制度下的载波错锁问题。展开更多
KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement ...KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries （e.g., width, morphology, and depth of defects） are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 p-m. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μm for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.展开更多
The KH2PO4 crystal is a key component in optical systems of inertial confinement fusion （ICF）. The microwaviness on a KH2PO4 crystal surface is strongly related to its damage threshold which is a key parameter for a...The KH2PO4 crystal is a key component in optical systems of inertial confinement fusion （ICF）. The microwaviness on a KH2PO4 crystal surface is strongly related to its damage threshold which is a key parameter for application. To study the laser induced damage mechanism caused by microwaviness, in this paper the near-field modulation properties of microwaviness to the incident wave are discussed by the Fourier modal method. Research results indicate that the microwaviness on the machined surface will distort the incident wave and thus lead to non-uniform distribution of the light intensity inside the crystal; in a common range of microwaviness amplitude, the light intensity modulation degree increases about 0.03 whenever the microwaviness amplitude increases 10 nm; 1 order diffraction efficiencies are the key factors responsible for light intensity modulation inside the crystal; the light intensity modulation is just around the microwaviness in the form of an evanescent wave, not inside the crystal when the microwaviness period is below 0.712μm; light intensity modulation degree has two extreme points in microwaviness periods of 1.064μm and 1.6μm, remains unchanged between periods of 3μm and 150μm, and descends above the period of 150μm to 920μm.展开更多
分析了 L i Nb O3 电光强度调制器的非线性调制特征 ,论述在主动谐波锁模掺铒光纤环形激光器 (AHML- EDFL)中利用该调制器的非线性来获取高阶锁模脉冲的物理机理和调制方法。在实验上 ,通过多种非线性调制手段 ,从 AHML- EDFL中获取了分...分析了 L i Nb O3 电光强度调制器的非线性调制特征 ,论述在主动谐波锁模掺铒光纤环形激光器 (AHML- EDFL)中利用该调制器的非线性来获取高阶锁模脉冲的物理机理和调制方法。在实验上 ,通过多种非线性调制手段 ,从 AHML- EDFL中获取了分频 ,2阶 ,3阶等高阶锁模脉冲序列。展开更多
文摘在分析了五电平NPC/H桥逆变器拓扑结构和工作原理的基础上,设计了载波层叠脉冲宽度调制(pulse w idth modulation,PWM)和三段式空间矢量脉冲宽度调制(space vector pulse w idth modulation,SVPWM)的策略,并介绍了这2种调制策略的原理。通过Simulink软件搭建仿真模型,对比了不同调制度和不同载波频率下逆变器的输出特性,得出结论:输出电压波形的电平数与调制度有关;提高载波频率可使主要高次谐波频率增大,减小谐波含量。以DSP+FPGA工控开发板为控制器搭建实验平台,实验结果表明调整策略有效。
文摘USB卫星测控体制是现行航天测控领域的通用体制之一,对卫星的状态监测、姿态控制和轨道修正等需要通过调制载波实现遥测、遥控、测量信息的传递和交互,当副载波信号处于大调制度的情况下,容易造成载波错锁或假锁。本文在工程实践的基础上,总结了载波错锁产生的原因,基于Matlab/Simulink建立了高斯白噪声影响下的中频接收载波环模型,仿真分析了不同调制度下的载波时频特性,提出奇异值分解(Singular Value Decomposition,SVD)降噪实现特征信号提取。通过仿真验证,副载波解调与频谱分析能有效抑制调制度较大的副载波分量,实现载波信号捕获,克服了大调制度下的载波错锁问题。
基金Project supported by the National Natural Science Foundation of China (Grant No. 50875066)
文摘KH2PO4 crystal is a crucial optical component of inertial confinement fusion. Modulation of an incident laser by surface micro-defects will induce the growth of surface damage, which largely restricts the enhancement of the laser induced damage threshold. The modulation of an incident laser by using different kinds of surface defects are simulated by employing the three-dimensional finite-difference time-domain method. The results indicate that after the modulation of surface defects, the light intensity distribution inside the crystal is badly distorted, with the light intensity enhanced symmetrically. The relations between modulation properties and defect geometries （e.g., width, morphology, and depth of defects） are quite different for different defects. The modulation action is most obvious when the width of surface defects reaches 1.064 p-m. For defects with smooth morphology, such as spherical pits, the degree of modulation is the smallest and the light intensity distribution seems relatively uniform. The degree of modulation increases rapidly with the increase of the depth of surface defects and becomes stable when the depth reaches a critical value. The critical depth is 1.064 μm for cuboid pits and radial cracks, while for ellipsoidal pits the value depends on both the width and the length of the defects.
基金Project supported by the National Natural Science Foundation of China (Grant No.50875066)the National High Technology Research and Development Program of China (Grant No.2009AA044305)
文摘The KH2PO4 crystal is a key component in optical systems of inertial confinement fusion （ICF）. The microwaviness on a KH2PO4 crystal surface is strongly related to its damage threshold which is a key parameter for application. To study the laser induced damage mechanism caused by microwaviness, in this paper the near-field modulation properties of microwaviness to the incident wave are discussed by the Fourier modal method. Research results indicate that the microwaviness on the machined surface will distort the incident wave and thus lead to non-uniform distribution of the light intensity inside the crystal; in a common range of microwaviness amplitude, the light intensity modulation degree increases about 0.03 whenever the microwaviness amplitude increases 10 nm; 1 order diffraction efficiencies are the key factors responsible for light intensity modulation inside the crystal; the light intensity modulation is just around the microwaviness in the form of an evanescent wave, not inside the crystal when the microwaviness period is below 0.712μm; light intensity modulation degree has two extreme points in microwaviness periods of 1.064μm and 1.6μm, remains unchanged between periods of 3μm and 150μm, and descends above the period of 150μm to 920μm.
