新型软开关弧焊逆变器主电路的仿真与实验

利用UC3879移相控制集成电路,设计出了一种新型的全桥移相式软开关弧焊逆变器主电路,利用变压器次级饱和电感的磁开关作用,大大拓宽了主电路中滞后桥臂的软开关范围。     

升压式ZVT-PWM软开关变换器仿真研究

分析了零电压过渡脉宽调制型(ZVT-PWM)软开关变换器基本工作原理,利用PSPICE软件对升压式ZVT-PWM软开关变换器进行仿真,给出了仿真结果,并与一般的升压变换器进行了比较.仿真结果表明,ZVT-PWM软开关变换技术具有开关损耗小、电源电压和负载适应范围宽、恒频控制和变换效率高等优点.     

基于DSP的SPWM变频电源的设计

本文主要介绍了基于正弦脉宽调制(SPWM)变频电源的软硬件设计方法.主电路由不可控整流及智能功率模块( IPM)电路组成,使得变频电源具有较高的可靠性；控制部分采用TI公司的DSP实现了基于单极倍频的SPWM波形的数字化生成算法,该算法具有谐波失真小等优点,另外在软件设计中采用了双闭环数字PID控制方法,使得变频电源的输出稳定性得到了进一步的提升.     

高速无刷直流电机驱动用零电流转换电路

本文将一种新型的零电流转换降压斩波电路应用到大功率高速无刷直流电机控制系统中,详细分析了软开关电路的工作原理,并对该电路进行了实验验证,结果证明该变换器能实现所有开关和二极管的软开通和软关断,并且电路的EMI和开关损耗都有明显降低.     

5kW离子电推进大功率屏栅电源的设计研究

本文针对航天器用5kW离子电推力器核心供电模块屏栅电源的技术需求,采用移相全桥技术设计了低电压输入高电压输出的大功率屏栅电源模块。对比分析了ZVS和ZVZCS两种移相全桥方案后,得出ZVZCS更适合于电推进屏栅电源的设计。提出了ZVZCS移相全桥变换器CDD无损缓冲电路中辅助电容的设计方法,论述了屏栅电源功率级和控制电路的设计过程。通过实物产品验证表明：采用ZVZCS移相全桥技术设计的屏栅电源模块能在较宽的负载范围内实现超前桥臂和滞后桥臂的软开关,提高了变换器的效率;采用CDD无损缓冲电路能辅助实现滞后桥臂的零电流关断,降低原边电流的损耗,同时降低高压整流管的电压应力。在具备完善的输入滤波,浪涌抑制及母线开关等功能以后,最大功率下效率在95%以上。     

并联H桥DC/DC变换器软开关技术研究

与传统的Buck电路相比,基于H桥并联的DC/DC变换器可以实现电压的双极性输出和故障时的冗余控制,非常适合用于大功率电动机正反转控制的场合。分析了并联H桥型DC/DC变换器的结构组成和双脉宽调制(PWM)模式。为了降低双脉宽调制下H桥型DC/DC变换器的开通和关断损耗,对无源软开关技术进行了分析,重点探讨了RCD缓冲电路和最小应力缓冲电路之间的性能差异,指出最小应力软开关技术可以获得更好的软开关性能,并就将其用于双脉宽调制下的并联H桥DC/DC变换器进行了仿真研究。仿真结果表明:最小应力软开关技术用于双脉宽调制下并联H桥DC/DC变换器时,可以实现开关管的零电压开通和零电流关断。     

升压式ZVT—PWM软开关变换器仿真研究

分析了零电压过渡脉宽调制型(ZVT-PWM)软开关变换器基本工作原理，利用PSPICE软件对升压式ZVT-PWM软开关变换器进行仿真，给出了仿真结果，并与一般的升压变换器进行了比较。仿真结果表明，ZVT—PWM软开关变换技术具有开关损耗小、电源电压和负载适应范围宽、恒频控制和变换效率高等优点。     

Boost变换器软开关技术的研究

提出一种新型有源软开关技术,在辅助开关和谐振电路的作用下,可以实现开关电源中开关管的零电压开通和零电压关断,而且可以减小开关管的电压应力和电流应力。对电路工作原理和参数设置进行了分析,给出了关键参数的选取原则。利用实际电路,验证了有源软开关技术的有效性。     

脉冲等离子体推力器电源处理单元技术研究

为了进一步提高脉冲等离子体推力器点火的可靠性和使用寿命,采用理论计算和地面试验的方法,设计了一款可应用于立方体纳卫星脉冲等离子体推力器放电能量为2.6J的电源处理单元,其放电点火电路是基于LC振荡电路,且对放电点火电路的性能、开关管的电流应力和整个电源处理单元的稳定可靠性进行了研究。结果表明:LC振荡放电点火电路中,开关器件的电流应力较小,提高了整个电路的可靠性;该放电点火电路在输入电压800V时,点火电流的峰值可达到100A～150A,这种大电流放电有助于清除火花塞表面的积碳。     

PWM型半桥式开关稳压电源的设计

介绍了一款基于PWM技术的半桥式开关稳压电源.给出了高频变压器、PWM控制及驱动电路的详细设计方法.用该方法设计了一台功率为150 W、输出电压为 15 V的半桥式开关稳压电源,并给出了实验波形.     

极化滤波反射面隐身天线研究

介绍了一种极化滤波反射面天线,将天线工程中的周期结构反射面技术应用于解决飞行器天线的RCS问题,采用由金属丝栅网构成的周期结构作为天线主反射面,使其对正交极化的来波具有良好的透射性,从而降低了天线的RCS。给出了此天线辐射方向图和雷达散射截面(RCS)的实测结果,并与普通金属反射面天线的结果进行了比较。     

Electronic warfare. [A century of powered flight: 1903-2003]

Electronic warfare (EW) is a term that includes a number of different electronic technologies for intelligence gathering and/or interfering with enemy operations. Electronic intelligence (ELINT), or eavesdropping, has been going on since the invention of the telephone and telegraph. Electronic countermeasures (ECM) deprive an enemy of the electronic spectrum by creating interference (jamming) that obscures their information or generates false information (spoofing). Electronic counter countermeasures (ECCM) is an effort designed to mitigate and overcome enemy ECM operations. ECM objectives include: search for signals in frequency, azimuth, and elevation; detect and identify radar signals via characteristics; and establish signal importance; commence appropriate countermeasures. It is only recently that these technologies have traditionally been categorized as EW, and are also referred to as electronic combat (EC). This section will focus on EW as it relates only to aviation.     

Cathode design investigation based on iterative correction of predicted profile errors in electrochemical machining of compressor blades

Electrochemical machining (ECM) is an effective and economical manufacturing method for machining hard-to-cut metal materials that are often used in the aerospace field. Cathode design is very complicated in ECM and is a core problem influencing machining accuracy, especially for complex profiles such as compressor blades in aero engines. A new cathode design method based on iterative correction of predicted profile errors in blade ECM is proposed in this paper. A math-ematical model is first built according to the ECM shaping law, and a simulation is then carried out using ANSYS software. A dynamic forming process is obtained and machining gap distributions at different stages are analyzed. Additionally, the simulation deviation between the prediction profile and model is improved by the new method through correcting the initial cathode profile. Further-more, validation experiments are conducted using cathodes designed before and after the simulation correction. Machining accuracy for the optimal cathode is improved markedly compared with that for the initial cathode. The experimental results illustrate the suitability of the new method and that it can also be applied to other complex engine components such as diffusers.     

Analysis and control of inter-electrode gap during leveling process in counter-rotating electrochemical machining

The inter-electrode gap (IEG) is an essential parameter for the anode shaping process in electrochemical machining (ECM) and directly affects the machining accuracy. In this paper, the IEG during the leveling process of an oval anode workpiece in counter-rotating ECM (CRECM) is investigated. The variation of the minimum IEG is analyzed theoretically, and the results indicate that rather than reaching equilibrium, the minimum IEG in CRECM expands constantly when a constant feed speed is used for the cathode tool. This IEG expansion leads to a poor localization effect and has an adverse influence on the roundness of the machined workpiece. To maintain a small constant IEG in CRECM, a variable feed speed is used for the cathode based on a fitted equation. The theoretical results show that the minimum IEG can be controlled at a small value by using an accelerated feed speed. Experiments have been conducted using a specific experimental apparatus in which the cathode tool is designed as a combined structure of two sectors and a thin sheet. By detecting the machining currents flowing through the minimum IEG, how the latter varies is obtained indirectly. The results indicate that using an accelerated feed speed is effective for controlling the IEG, thereby improving the roundness of the machined workpiece.     

Simulation and experimental investigation on a dynamic lateral flow mode in trepanning electrochemical machining

An appropriate flow mode of electrolyte has a positive effect on process efficiency, surface roughness, and machining accuracy in the electrochemical machining(ECM) process. In this study, a new dynamic lateral flow mode, in which the electrolyte flows from the leading edge to the trailing edge, was proposed in trepanning ECM of a diffuser. Then a numerical model of the channel was set up and simulated by using computational fluid dynamics software. The result showed that the distribution of the flow field was comparatively uniform in the inter-electrode gap. Furthermore, a fixture was designed to realize this new flow mode and then corresponding experiments were carried out. The experimental results illustrated that the feeding rate of the cathode reached 2 mm/min, the best taper angle was about 0.4°, and the best surface roughness was up to Ra= 0.115 lm. It reflects that this flow mode is suitable and effective, and can also be applied to machining other complex structures in trepanning ECM.     

边界扫描技术在电子控制器测试中的应用

航空发动机电子控制器向更高性能和更高集成度的方向发展,使得传统测试方法难以满足需要.提出了通过边界扫描技术来解决电子控制器核心电路的测试问题.设计了边界扫描测试技术验证平台,主要包括边界扫描测试适配器和被测电路.对被测电路开展了基于边界扫描的测试试验,完成了主要指令的测试.同时通过扫描链实现了对被测电路的故障注入,通过这种方法注入故障可对航空发动机电子控制器的机内测试(BIT)能力进行验证.      

一种基于反激变换器新型掉电保持电路的设计与分析

本文通过对民用机载设备小功率电源的需求分析和标准解析，总结了传统设备内单独设计掉电保持 电路的优缺点，设计一种基于反激变换器的掉电保持电路，通过分析与测试，验证了该方案的有效性，满足机 载设备的应用场景。     

基于JTAG的板级可测试性设计

阐述了JTAG技术的采用给电路板的可测试性带来的改善,从设计方法、优化策略以及实现技术等几个方面,讨论了利用边界扫描技术进行电路板的可测试性设计。     

边界扫描技术在电子控制器测试中的应用研究

航空发动机电子控制器向更高性能和更高集成度的方向发展,使得传统测试方法难以满足需要。本文提出了通过边界扫描技术来解决电子控制器核心电路的测试问题。为了论证这一方案的可行性,设计了边界扫描测试技术验证平台,主要包括边界扫描测试适配器和被测电路。对被测电路开展了基于边界扫描的测试试验,完成了主要指令的测试。同时通过扫描链实现了对被测电路的故障注入,通过这种方法注入故障可对航空发动机电子控制器的机内测试（BIT）能力进行验证。本文探索了边界扫描测试技术在航空发动机电子控制器中的应用     

Radar ECCM: A European Approach

The radar designer must optimize parameters for performance in electronic countermeasures (ECM) and avoid any constraints which could be exploited by ECM. ECM/electronic counter-counter measures (ECCM) strategy must take into account electromagnetic compatibility (EMC) including enemy EMC. Electronic scanning improves search performance, but also reduces ECCM performance in other ways. While electronic scanning avoids some constraints, it imposes others, particularly in the frequency domain. It is argued that simple radars of good performance may be as cost effective in ECM as more complex systems. Some examples of recent developments are given.