Analytical solution of electromagnetic field generated by induction logging tool in a fan-ring slot of drill collar while drilling

Based on the structural characteristic of metal drill collar for induction logging while drilling, we have given the analytical formulae of lengthways fields E _z and H _z when the tool is located in a fan-ring shaped slot of drill collar by the boundary conditions of electromagnetic field, and derived the other components of electromagnetic field in and out the fan-ring slot from E _z and H _z . In the other intervals of formation, where the drill collar is a solid cylinder, the analytical formulae of field are educed through the method of variable coefficient. The total analytical solutions of field in whole space have been obtained. With the help of the analytical formulae, we have also given numerical examples and analyzed the distributive characteristic of electromagnetic field. From the computational results we find that the secondary scattering field H _z is in a linear relation with the conductivity of stratum. The characteristic of field is very useful for induction logging while drilling, which can be used to measure and analyze the logging responses of the stratum conductivity. This paper sets up a theoretical foundation for us to study the distrbutions of field and to direct the design of logging instruments. Supported by the National Natural Science Foundation of China (Grant No. 10705049), the Beijing Natural Science Foundation (Grant No.1083011) and Funding Project for Academic Human Resources Development in Institutions of Higher Learning [PHR(IHLB)]     

分时控制MOSFET固态高频感应加热电源研究

研究了一种采用分时控制方法的MOSFET固态高频感应加热电源,电源输出频率是功率器件工作频率的n倍(采用n个桥分时工作)。利用MATLAB/SIMULINK实现了分时控制的仿真,分析了分时控制的工作状态,对器件功耗进行了理论推导,并对如何实现分时控制进行了介绍,且根据仿真画出了并行控制和分时控制2种控制方式下MOSFET器件损耗的曲线图。仿真结果表明分时控制在实现固态感应加热电源的高频化方面优于并行控制。     

螺线管式磁感应钢丝绳断丝检测系统设计

针对现有钢丝绳损伤检测采用人工检查或定期换绳的方法,存在效率低、成本浪费严重及安全性差等问题,设计了螺线管式磁感应钢丝绳断丝检测系统。系统检测原理:当钢丝绳出现断丝时,磁导率会相应降低,磁阻变大,电感量减小,从而导致线圈磁场不平衡并产生感应电动势,根据该感应电动势的大小可判断出钢丝绳断丝的状况。试验结果表明,该系统克服了传统电磁检测技术不能精确检测钢丝绳内部出现断丝的缺陷,检测精度可达95%以上。     

一种改进的异步电动机直接转矩控制方法

针对传统异步电动机直接转矩控制方法转矩及磁链脉动大、开关频率不固定的缺点,提出了一种改进的异步电动机空间矢量调制直接转矩控制方法。该方法通过转矩角闭环控制实现定子磁链幅值和相角的解耦,从而获得参考电压空间矢量,实现对磁链误差和转矩误差的控制。仿真结果表明,该方法有效地克服了传统直接转矩控制方法的缺陷,获得了良好的动态响应性能。     

基于红外感应开关控制的建筑照明节能改造

介绍建筑公共照明控制现状和红外感应开关控制原理,并对照明控制节能改造进行经济分析.     

Specificity of Systemically Released Cotton Volatiles as Attractants for Specialist and Generalist Parasitic Wasps

Cotton plants under herbivore attack release volatile semiochemicals that attract natural enemies of the herbivores to the damaged plant. The volatiles released in response to herbivory are not only released from the damaged leaves but from the entire cotton plant. We found that cotton plants that released myrcene, (Z)-3-hexenyl acetate, (E)--ocimene, linalool, (E)-4,8-dimethyl-1,3,7-nonatriene, (E)--farnesene, and (E, E)-4,8,12-trimethyl-1,3,7,11-tridecatetraene systemically from undamaged leaves of caterpillar damaged plants were attractive to the generalist parasitoid Cotesia marginiventris and the specialist parasitoid Microplitis croceipes. Plants from which the caterpillar damaged leaves were removed and that released those compounds systemically were significantly preferred over undamaged control plants in two-choice experiments in a flight tunnel. Artificially damaged cotton plants that released green leafy volatiles and constitutive terpenoids were less attractive for M. croceipes and C. marginiventris. Only C. marginiventris preferred artificially damaged plants over undamaged control plants, whereas M. croceipes showed no preference. The apparent lack of specificity of systemically released compounds in response to different herbivores feeding on the lower leaves is discussed.     

一种割草机无刷电机高频注入启动策略研究

针对割草机电机在启动过程中转子定位精度低,加速阶段稳定性差等问题,提出了一种手推式割草机的无感无刷电机高频方波注入启动策略;采用将割草机电机的启动分为低速和高速两个阶段的方法,在不同采样点提取αβ轴系下的高频响应电流,用于转子位置估计,该方法无需滤波器,降低了位置估计误差;文章还在正负脉冲注入的基础上,提出了一种在电机首次启动时d轴极性的判断方法;利用STM32F302芯片搭建硬件实验平台,实验结果表明:改进的脉冲注入转子极性判别方法,能够准确判断转子极性,利用优化后的综合电流处理策略能有效地进行转子位置估计,提高精准度,符合割草机电机启动的要求.     

基于等效转子电压的双馈感应发电机灭磁控制

针对电网电压故障引起的双馈感应发电机磁链弱阻尼振荡问题,提出一种采用等效转子电压的双馈感应电机灭磁控制策略。分析电网电压故障激起的双馈感应电机定子磁链的暂态过渡过程,建立定子磁链状态方程;通过求解状态方程的特征根和定子磁链的振荡频率及阻尼比,在转子电压前馈补偿项的基础上引入定子磁链的微分反馈项,得到等效转子电压参考值,并研究了其改善磁链欠阻尼特性和加快暂态磁链衰减的机理。最后,双馈感应发电机的仿真结果表明,本文方法可以较好地抑制故障期间的磁链振荡冲击,有利于双馈风电机组故障穿越能力的提高。     

AT供电网络及电磁兼容问题分析

本文侧重于对牵引供电系统运行时引起干扰的因素进行分析,用电磁场的理论建立干扰模型,在定性分析的基础上提出相应的抗干扰的措施。     

基于双馈风机变桨与变速协调的频率控制

为了改善大规模风电并网给电网频率带来的不利影响,基于双馈风电机组的控制特性,结合转子动能与备用功率控制的特点,提出一种频率分段控制的备用功率与转子动能相协调的多层次、多周期、多环节的联合调频控制方法.电网频率发生偏移时,风机既能快速释放或吸收转子动能,又能调节桨距角,实现风电机组的频率控制.在电力系统仿真软件中搭建供电网络模型,并结合实际电网运行情况进行仿真,仿真结果表明,该方法使得风电机组对频率变化具有快速响应能力,可有效改善电网的频率特性,为双馈风电机组安全稳定并网提供了可借鉴的依据.