圆形电流误差边界限定形式的永磁同步电机预测控制

针对图形边界限定形式的感应电机预测控制存在简洁、直观等优点,进一步考虑将该控制策略应用于永磁同步电机.预测控制将电机和逆变器作为一个系统整体考虑,以空间电流矢量为控制对象,直接产生逆变器的开关控制信号.基于永磁同步电机在转子磁场坐标系下的数学模型,推导出电流矢量导数的估测模型,进而预测出电流矢量的轨迹,根据最优电压矢量选择判据选定开关状态,完成基于圆形电流误差边界限定形式的永磁同步电机的预测控制算法.通过MATLAB/SIMULINK进行仿真,仿真结果证明了提出方法的有效性.     

基于反电动势的多相感应电机MRAS控制策略优化

针对舰用多相电力推进系统无速度传感器控制的需求,将带输入滤波环节的基于电机反电动势的模型参考自适应(MRAS)方法用于多相感应电机无速度传感器矢量控制系统,推导了系统的小信号模型,分析了滤波截止频率和转速估算PI参数对系统性能的影响,并在此基础上设计了变滤波截止频率变PI参数优化的MRAS控制策略。仿真和实验结果表明:该优化方法具有更高的转速估算精度和静、动态控制性能。     

异步电机矢量控制中转子磁链的直接观测方法

以异步电机的等效电路为模型提出了在电机的外部构造转子磁链物理观测器的方法.理论上证明了在选取合适参数之后,用该物理观测器可以直接得到感应电机转子磁链的大小与相位,该方法用于异步电机的矢量控制系统,具有很好的实时性,且避免复杂的数字运算.     

一种新型的转矩控制方法——矢量转矩控制

参考磁场定向控制(FOC)、直接转矩控制(DTC)两种方法的特点,提出了一种矢量转矩控制(VTC)的方法,它解决了传统DTC的输出电压矢量与控制变化量之间没有定量关系的缺陷,建立了输出电压矢量与控制变化之间的函数关系,同时改进了磁链低速模型.实验结果表明,该方法能够有效改善电机的输出特性.     

基于随机脉宽调制技术的感应电机矢量控制系统研究

随机脉宽调制技术可以使逆变器输出电压的谐波成分均匀地分布在一个较宽的频率范围内,达到抑制噪声和机械振动的目的.把随机脉宽调制技术引入感应电机矢量控制系统中,保证了调速系统的高性能,同时也降低了电机的有色噪声和机械振动.     

高性能永磁交流伺服系统研究

重点介绍了永磁交流伺服系统的控制策略,位置检测和辨识、主电路和驱动技术等关键技术.在研究了其物理方程、转矩方程和等效电路的基础上,提出了永磁同步电机的数学模型.叙述了矢量控制的原理,构建了永磁同步电机交流伺服系统,并对上述电机模型,矢量控制方法及相关硬件设计进行了研究.     

基于矢量控制的永磁同步电机控制系统的仿真

介绍了三相永磁同步电机常用的坐标系以及不同坐标系下的数学模型,并通过采用矢量控制方法实现电机的转速控制。在MATLAB6.5中的Simulink环境下,通过建立PMSM本体、坐标变换、电源逆变器、PI调节器等模块,搭建了永磁同步电机控制系统的速度和电流双闭环仿真模型。仿真结果验证了永磁同步电机矢量控制的正确性与可行性,为永磁同步电机控制系统设计提供了理论基础。     

长初级短次级十二相直线感应电动机数学模型分析

基于大功率直线推进的要求,设计了一种新型十二相双边长定子直线感应电动机,介绍了十二相直线感应电动机的绕组结构。在此基础上,推导了十二相双边长定子直线感应电动机的ABC坐标系数学模型,分析了由电机各相端部绕组空间相对位置决定的十二相直线感应电动机端部漏感的不对称规律,并与多相旋转电机端部漏感的规律进行了对比分析;建立了仿真模型,对电机的电磁性能进行了计算。仿真实验证明了该数学模型的正确性。     

永磁直线同步电机矢量控制系统建模与实现

针对永磁直线同步电机(PMLSM)的特点,建立PMLSM在dq两相坐标系下的数学模型。介绍了永磁直线同步电机矢量控制系统并给出了硬件和软件的设计思想。通过对控制电流以及电机位置的实验分析,验证了所研究的基于矢量控制的永磁直线同步电机矢量控制方法的有效性。     

“电机统一理论”在电机控制中的作用

直流电机在恒速时其电压方程为常系数的线性微分方程,在电机控制中能进行快速的转矩和磁通控制。而异步电机是一个多变量、强耦合、非线性的时变参数系统,很难直接通过外加信号准确控制电磁转矩。但若以转子磁通这一旋转的空间矢量为参考坐标,应用"电机统一理论",利用从静止坐标系到旋转坐标系之间的变换,则可以把定子电流中的励磁电流分量与转矩电流分量变成标量独立开来,进行分别控制。这样,通过坐标变换重建的电机模型就可等效为一台直流电机,从而可像直流电机那样进行快速的转矩和磁通控制,给电机控制系统带来新的契机。     

磁流变液的摩擦与润滑

采用四球摩擦磨损试验机考察了羰基铁-矿物油体系磁流变液和基础油摩擦系数随时间的变化曲线、磨斑直径,用扫描电镜观察了磨痕表面形貌.结果表明,与基础油相比,磁流变液的摩擦加剧,润滑性能降低,磁性颗粒是导致其润滑性能下降的首要原因;摩擦磨损机理主要是磨粒磨损,表现为犁沟效应.     

铁粉焊条熔化过程中基本参数研究

通过试验研究了焊条直径和铁粉加入量对焊条熔化参数的影响.试验结果表明,焊条直径增加,焊条药皮重量系数、熔敷效率增加,熔化速度和熔敷速度降低;熔敷金属中合金元素Mn、Si含量增加,但Mn、Si的过渡系数减小.当增加药皮中铁粉加入量,药皮重量系数、熔敷效率和熔敷速度增加,熔化速度降低,由于铁粉的稀释作用使熔敷金属中合金元素Mn、Si含量及过渡系数降低.     

中性水中铸铁和铸铝的缓蚀行为研究

以合成的磷酸醇胺与钼酸盐为缓蚀剂的主要成分,并且分别复配羧酸、胺,设计出4种体系,采用失重法和电化学方法研究它们在中性水中对铸铁及铸铝的缓蚀作用.实验结果表明,浓度高的磷酸醇胺有着良好的缓蚀性能,添加羧酸对铸铝有很好的效果,添加胺对铸铁有很好的效果.并且初步探讨了缓蚀机理.     

一种新型CVD铁涂层吸波纤维

利用Fe(CO)5受热分解,以CVD方法在SiC纤维表面涂覆单质铁的涂层。研究表明,涂层的引入对SiC纤维力学性能基本没有损伤;纤维依靠涂层导电,其电阻率显著降低;改变工艺条件,可以在较大范围内调节涂层纤维的介电常数,同时也引入了磁损耗机制;采用较低的沉积温度和较高的载气流速,可以提高介电常数和磁导率,同时有好的频散效应。     

Helping hands: civil–military cooperation and Italy's military operation abroad

In the Post-Bipolar Era the growing complexity of the military operations requires a new approach for the resolution of international crises. Since the end of the Cold War, peace support operations (PSO) have become the mainstay and principal occupation of most Western armies. At the same time, Italy has been one of the most important actors in such an area. The article focuses on the cooperation between military and civil components (a process called CIMIC) as a key variable in the Italian PSOs. We will analyse in detail the main lessons learned from past military interventions as well as the general context in which new tendencies are taking place. The maintaining of a minimum security frame becomes essential to fulfil activities ‘collateral’ to the mission: reconstructing services and infrastructure, food distribution, water and medication, law and order, de-mining, training of local forces, and supporting local institutions. These are the main tasks to obtain thrust and support from the population.     

Terrorism,insurgency, kidnapping,and security in Africa's energy sector

Energy continues to serve as the bedrock of modern economies and the main driver of modern society. For Africa, the production and supply of energy resources such as crude oil, natural gas, uranium, coal, biomass, biofuels and other renewables are an important source of employment, rents, taxes, royalties and profits. This sector brings in several tens of billions of dollars of revenue annually. The production and delivery of such resources, however, depend on critical infrastructures such as pipelines, refineries, processing plants, terminals, rigs, electrical energy pylons, substations, pump stations, vessels, and tankers. These infrastructures have been attacked by terrorists, insurgents, vandals and saboteurs, all of whom see them as targets against which to register their grievances and extract concessions from the state. This paper is a chronological account of some of the documented incidents of terrorism, insurgency, kidnapping, destruction, sabotage, and human casualties suffered in the oil and gas sectors in Africa between 1999 and 2012. It is based on data extracted from the databases of the RAND Database of World Terrorism Incidents and the University of Maryland's Global Terrorism Database (GTD).     

Tacit support for terrorism: The rapprochement between the USSR and Palestinian guerrilla organizations following the 1967 war

This article demonstrates the inconsistent and wavering Soviet attitude towards national liberation movements in general and the Palestinian organizations in particular. Until the late 1960s, the Soviets viewed these organizations with suspicion, hesitating to engage in political dialogue with them. However, in the 1970s, political and military events in the region, as well as modifications in the Kremlin's Cold War strategies, led to a general shift towards the Middle East in Soviet foreign policy. Soviet leaders showed increased willingness to provide certain Palestinian organizations with arms with which to conduct terrorist activities against Israeli, pro-Israeli, Jewish and Western targets. The article explores the complex relations between Palestinian organizations and the USSR in the field of international terror. The study also exposes and analyzes the nature and content of Soviet–Palestinian arms dialogues and transactions. It provides clear evidence that Soviet policymakers and other luminaries were fully informed of, and sometimes directly involved in, these transactions and dialogues at the highest levels.     

A1 Qaeda and the radical Islamic challenge to western strategy

The September 11 global crisis prompted by the attacks on the World Trade Center and the Pentagon raises major questions concerning the nature and trajectory of terrorism in the post-Cold War global order. Hitherto, terrorism has been largely debated by analysts at the level of nation states. Terrorist and insurgent movements have also been largely anchored in nationalist and ethnic power bases even when they have sought to mobilise a transnational ideological appeal on religious or class grounds. There have been a few exceptions to this pattern such as the alliance between the German Baader-Meinhof group and the Japanese Red Army Faction, but even such international alliances as this did not, until at least the 1980s, presage anything like a global terrorist network necessitating a global strategic response. This study examines terrorism and global strategic responses.     

Helping hands: external support for the KNU insurgency in Burma

This article analyses to what extent the Burmese KNU insurgency made use of external support from states, refugees, and diasporas. Based on extensive fieldwork it is concluded that support from neighbouring states and refugees has for years kept the Karen rebellion alive. Western countries perceived forms of resistance to the illegitimate Burmese regime as just and have therefore played a crucial role in the continuation of conflict in Karen State. It is important that policymakers and donors as well as executing organizations continue to reflect critically on the way they exercise their work.