混沌调制抑制开关变换器EMI的实验研究

基于MCU和CPLD实现了开关变换器的4种混沌调制模式:混沌脉冲宽度调制(CPWM)、混沌脉冲位置调制(CPPM)、变占空比混沌载频调制(CCFM-VD)和定占空比混沌载频调制(CCFMFD)。实验结果表明定占空比混沌载频调制能够有效抑制开关变换器的电磁干扰(EM I),同时对输出电压的纹波影响较小,是一种较理想的混沌调制模式。     

固体推进剂燃烧微观诊断技术述评

对近年来用于固体推进剂燃烧的微观诊断技术的原理、结果进行了综述,分析了用扫描电镜、热分析、Ｘ－ｒａｙ电子能谱仪、红外傅里叶光谱技术,微热电偶测温技术,ＬＩＦ,ＣＡＲＳ测试固体推进剂燃烧现象的结果,提出了存在的问题和努力的方向。     

敬告读者

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Control System in Missiles for Whole-Trajectory-Controlled Trajectory Correction Projectile Based on DSP

A control system for correction mechanisms through the whole trajectory is proposed based on the principle of one-dimensional trajectory correction projectile. Digital signal processing （DSP） is utilized as the core controller and gobal positioning system （GPS） is used to measure trajectory parameters to meet the requirements of calculating ballistics and system functions. Firstly, the hardware, mainly including communication module, ballistic calculation module, boosting ＆ detonating module and data storage module, is designed. Secondly, the supporting software is developed based on the communication protocols of GPS and the workflow of control system. Finally, the feasibility and the reliability of the control system are verified through dynamic tests in a car and live firing experiments. The system lays a foundation for the research on trajectory correction projectile for the whole trajectory.     

Development and Prospectives of Ultra-High-Speed Grinding Technology

Ultra-high-speed grinding(UHSG)is a significant and powerful machining method in view of the enhanced productivity and precision demands.Previous researches regarding formation mechanisms and crucial technologies are comprehensively and thoroughly summarized to highlight state-of-art technology of UHSG.On the basis of the interdependence between process and machine innovations,theoretically,grinding mechanisms in strain hardening,strain rate strengthening,thermal softening,size effect and process characteristics need more in-depth studies to clarify the dominance of UHSG.Technically,CFRP wheel integrating with the brazed bonding has a prominent advantage in bonding strength and grit′s configuration over vitrified bonding,which would be superior in UHSG.Furthermore,external high pressure cooling combining with inner jet cooling methods,accompanied by scraper plates to alleviate the effect of air boundary,are crucial and practical measures for realizing effective cooling in UHSG.Grinding processes,especially those being related to grinding parameters and precise in-process measuring approaches,are also prerequisite for fitting and investigation of UHSG.     

Threshold Selection Method Based on Reciprocal Gray Entropy and Artificial Bee Colony Optimization

Since the logarithmic form of Shannon entropy has the drawback of undefined value at zero points,and most existing threshold selection methods only depend on the probability information,ignoring the within-class uniformity of gray level,a method of reciprocal gray entropy threshold selection is proposed based on two-dimensional（2-D）histogram region oblique division and artificial bee colony（ABC）optimization.Firstly,the definition of reciprocal gray entropy is introduced.Then on the basis of one-dimensional（1-D）method,2-D threshold selection criterion function based on reciprocal gray entropy with histogram oblique division is derived.To accelerate the progress of searching the optimal threshold,the recently proposed ABC optimization algorithm is adopted.The proposed method not only avoids the undefined value points in Shannon entropy,but also achieves high accuracy and anti-noise performance due to reasonable 2-D histogram region division and the consideration of within-class uniformity of gray level.A large number of experimental results show that,compared with the maximum Shannon entropy method with 2-D histogram oblique division and the reciprocal entropy method with 2-D histogram oblique division based on niche chaotic mutation particle swarm optimization（NCPSO）,the proposed method can achieve better segmentation results and can satisfy the requirement of real-time processing.     

Optimal Control Strategy for Buck Converter Under Successive Load Current Change

A new control algorithm is presented for digitally controlled dc-dc converters to achieve a fast response under a successive load-change. Under the steady-state condition, the tight voltage regulation is processed by the conventional digital PID compensator. If the load disturbance is significant, the controller switches to an optimal control scheme. With the integration of the capacitor current, the proposed algorithm predicts the optimal switch over time based on the charge balance control, and the minimal voltage derivation and recovery time are thus achieved when the load current has a successive load-change. The method for calculating the optimal switch over time is described, and the implementation of the proposed algorithm with a digital controller is treated in detail. Furthermore, the simulation and experiment results are provided to validate the effectiveness of the approaches.     

散射参数建模及其在传导电磁兼容中的应用

针对频谱仪法分析传导电磁干扰(Electromagnetic interference,EMI)的精度低、存在相位缺损且需使用功分器、信号源等辅助器件等问题,提出一种散射参数建模方法,并讨论了该方法在传导电磁兼容中的应用.散射参数建模方法不仅能够精确测定EMI噪声源内阻抗,EMI分离网络特性和EMI滤波器特性的幅值大小,而且能够提取相位信息,此外,测量过程无需借助辅助器件,降低了由辅助器件引起的测量误差.实验结果表明散射参数建模方法能够简单、快速地解决电力电子实际应用中存在的阻抗匹配问题,提高EMI分离网络和EMI滤波器特性参数测量精度,并为传导EMI噪声滤波器设计提供理论依据.     

基于双谐振棋盘式超表面的宽带RCS缩减技术

为实现宽频带的雷达散射截面（RCS）缩减效果,提出一种基于棋盘式超表面的RCS缩减技术,可达到宽带RCS缩减且极化不敏感的效果。介绍了提高RCS缩减带宽的原则,设计了X波段的棋盘式超表面,通过电磁散射对消技术,电磁波经超表面反射后分散向不同的方向,实现了异常反射从而降低RCS。与普通棋盘式超表面不同,为了克服一般超表面都有的相位收敛问题,提出了双谐振棋盘式超表面,即用两种谐振频率不同的结构组成双谐振单元结构,使单元具有均匀相位差的频段得以拓宽,从而扩展了超表面的缩减带宽,实现了10 dB缩减带宽达到8 GHz~14.5 GHz且极化不敏感的效果,通过仿真证明双谐振棋盘式超表面可以实现宽频率范围的RCS缩减效果,且极化不敏感。     

图像三要素与MTF的分析研究

中低分辨率在轨运行卫星遥感器的调制传递函数（Modulation Transfer Function，MTF）的监测一直是研究的难题。现提出的方法解决了中低分辨率在轨运行卫星遥感器MTF监测的关键技术。考虑到卫星遥感器的最终产物是遥感图像，从图像信息理解的三要素出发，即灰度、纹理和边缘，分析图像三要素与遥感器MTF的关系。在分析过程中，应用主成分分析方法，不仅对多组原始数据进行了简化，而且对图像参数进行了降维。通过与其它方法的比较，进一步验证了使用主成分分析方法降维的有效性；同时实验结果亦表明了主成分分析方法的可靠性。最后建立了图像单个综合参数与MTF的关系模型，拟合结果说明，此模型能较好地表达图像参数与MTF之间的关系，这将为在轨运行条件下的建模提供十分重要的技术支持。