磁悬浮制冷与传统压缩制冷技术比较

磁悬浮轴承是高技术含量产品,由于其价格昂贵,过去只被用于航天工程。在传统的制冷压缩机中,机械轴承是必须的部件,并且要有润滑油循环系统来保证机械轴承工作。据统计,在所有烧毁的压缩机中,90%是润滑失效引起的。而机械轴承不仅会产生摩擦损失,润滑油也会随制冷循环而进入到热交换器中,在传热表面形成的油膜成为热阻,影响热交换器的效率,系统中润滑油过多会对制冷效率带来很大的影响。但是,轴承在压缩机中是不可或缺的部件。磁悬浮轴承是一种利用磁场,使转子悬浮于空中,在旋转时不会产生机械接触和机械摩擦,因此磁悬浮轴承不再需要机械轴承以及机械轴承所必须的润滑系统。在制冷压缩机中使用磁悬浮轴承,可有效避免由于使用机械轴承而产生的一系列故障。当今新型的制冷压缩机正是应用了磁悬浮轴承技术。     

超声波轴承悬浮性能及承载能力的实验研究

超声波悬浮及减摩技术是一种新型的科学技术。在超声减摩方面我们已经做了大量的研究。文章在此基础上，首次提出超声波振动悬浮轴承的概念。分析对比了普通动压润滑滑动轴承与超声波悬浮轴承；模拟简单的静载推力轴承，并对其悬浮性能和承载能力进行了初步的研究。     

导航定位技术（自主式导航系统与组合导航）（续12）

electrostatically supported gyro一种双自由度自由转子陀螺，其角动量是由高速旋转的刚体转子产生的。转子被一个球形支承悬浮着。静电陀螺的主要特点就在于这个球形支承。与一般的滚珠轴承和宝石轴承不同，它是用静电场的力使陀螺球转子悬浮在一个超真空的球腔中心，故可称为静电轴承。由于球转子与外部没有任何机械连接和接触，     

关于讲解"无轴承电机径向悬浮力"

本文在回顾电机中的洛伦兹力和麦克斯韦力基础上,通过介绍无轴承电机基本结构,径向悬浮力产生机理和悬浮力系统的运动方程等来讲解无轴承电机的径向悬浮力,并且介绍了教学过程中的实践经验。通过采用本文的讲解方法,学生易于理解和掌握无轴承电机的结构和径向悬浮力产生原理。     

无轴承异步电机无速度传感器控制

为解决无轴承异步电机运行中转速辨识问题,提出了一种可以同时在线估计转子电阻和转速的方法。该方法首先通过电压型转子磁链模型估计出转子磁链,然后根据静止坐标系下的无轴承异步电机模型和电压型转子磁链模型推出包含转子电阻和转速的表达式,再将这两个表达式看作一个二元一次方程组并求解,最终得到转子电阻跟转速的解析表达式。最后应用这种转速估计方法构建无轴承异步电机无速度传感器控制系统,并开展仿真研究。仿真结果表明:所提方法能够实现无轴承异步电机转子电阻和转速的准确估计,并保证无轴承异步电机的稳定悬浮运行。     

基于STM32的磁悬浮轴承数字控制器设计

针对传统磁悬浮轴承转子系统开环不稳定、非线性和强耦合等特性,需要对电磁力施加主动控制才能使转子稳定悬浮的缺陷,本文设计了一种基于STM32的磁悬浮轴承数字控制器方案。该控制器以ARM STM32F407ZGT6微处理器为核心,设计了电源转换、电涡流位移传感器、功率放大器控制、实时时钟以及声光报警等硬件电路;同时编写了基于国产嵌入式实时操作系统RT-Thread的多线程软件框架,实现了数据采集、PID算法等功能。实验结果表明,该数字控制器下的磁悬浮轴承转子系统可以在200ms内达到稳定悬浮状态,运行可靠、实时性好、速度快、抗干扰能力强。     

基于轴向支撑超声波悬浮高速电机的研究

设计了一种轴向支承电机转子的超声波悬浮支撑结构。采用圆锥型轴承超声悬浮支撑结构,并对承载能力进行了分析和测试,获得了悬浮力与悬浮间隙间的关系,在振动过程中形成稳定的承载气膜;从理论上分析了在超声悬浮支承条件下,悬浮间隙变化对于电机转子临界转速与振动模态的影响情况,对转子最高转速与悬浮间隙的关系进行了实验研究。结果表明,通过减小悬浮间隙,能增强间隙气膜的刚度支承效果,并提高转子的最高转速。     

新型单绕组无轴承异步电机控制系统

研究了一种新型结构的单绕组无轴承异步电机,与传统的双绕组无轴承异步电机相比,采用一套绕组即可实现电机转子的悬浮和旋转。在分析单绕组无轴承异步电机新型结构和工作原理的基础上,推导出电机径向悬浮力和转矩部分的数学模型。针对单绕组无轴承异步电机的定子电流连接的复杂性,采用电流叠加控制方法,并设计基于气隙磁场定向控制的控制系统。在MATLAB/Simulink中建立控制系统的仿真模型进行仿真验证,并制作实验样机进行悬浮特性试验。结果表明,该方法控制的样机转速响应好、悬浮特性优良,从而验证了所提方法的正确性与有效性。     

红外窗口和整流罩材料的新领域（上）

化学汽相淀积的具有光学品质的金刚石,除了具有合成金刚石的低强度特性之外,其光学特性,热特性以及机械特性均与天然的Ⅱａ型金刚石相似,现已生产出直径达６０ｍ,厚度为０．７５ｍｍ的透明窗口,并用一种可将表面粗糙度减小到１μｍ的激光加工方法在外表面上生长和加工了直径为６０～７５ｍｍ,厚度为１ｍｍ的整流罩。金刚石窗口和整流罩面临的主要难题是：（１）增加机械强度;（２）提高生长速率,（３）提高抛光效率。论证了     

基于有限元分析的直流电机控制策略

无轴承无刷直流电机集成了直流和交流电机的优点,具有重要的实际应用价值,针对传统悬浮力控制方法存在工作复杂、逆变器通断频繁等缺陷,为了提高磁悬浮力的控制效果,提出了基于有限元分析的无轴承无刷直流电机悬浮力控制策略。首先对无轴承无刷直流电机的结构以及悬浮力产生的原理进行了分析,然后采用有限元分析法对电机转矩和悬浮力进行计算,从而实现无轴承无刷直流电机控制,最后采用Matlab/Simulink工具对其性能进行测试与验证。结果表明,本文策略可以提高转子悬浮的稳定性,能够保证无轴承无刷直流电机的正常运行。     

液悬浮转子微陀螺的磁场建模研究

液悬浮转子式微机械陀螺的高精度、双轴角速度和二轴加速度测量特性,相比传统陀螺有着独特的优势,在军事和民用领域均有一定应用,本文基于实现对液悬浮转子式微机械陀螺结构优化的目的,探求其磁场力随着结构的变化的规律,对该类机械陀螺结构进行建模,并对其磁场力进行数值仿真处理。结果表明,随着半径从7 mm增加至11 mm,陀螺受力及对应力矩呈指数增长。     

Design and analysis of a novel wound rotor for a bearingless induction motor

The traditional squirrel-type bearingless induction motor (BIM) suspension winding generates induced current in its squirrel-cage rotor and affects the phase and amplitude of the suspension force. Based on the analysis of the spatial distribution of torque winding magnetic field and suspension winding magnetic field, a new type of wound rotor BIM is designed. Different from the squirrel-cage rotor, the wound rotor uses a special method of embedding a set of coils at any symmetrical four rotor slot positions, so as to only induce the torque winding magnetic field. The induced current, air-gap magnetic density, magnetic field line distribution, suspension force as well as electromagnetic torque of the traditional squirrel-cage motor and the new wound motor are analysed by Maxwell finite element calculation. The results show that the designed new wound BIM can not only effectively suppress the induced current of suspension winding, eliminating its influence on the suspension force, but also has a better starting performance.     

Electrostatic suspension of dielectrics

This paper reports the successful electrostatic suspension of dielectric materials. In order to implement a stable suspension, the electrostatic forces exerted on a dielectric are actively controlled on the basis of the measured suspension gap lengths. The principle of electrostatic force generation for dielectrics is different from that for conductors. By utilizing a stator electrode pattern containing many boundaries over which potential differences exist, the suspension characteristics, such as dynamic stability, suspension initiation time and stiffness of lateral motion are greatly improved. The dynamic model of the suspension system and the influence of the resistivity of a dielectric on the closed-loop stability are described, followed by the experimental apparatus and stabilizing controller. As dielectric objects, glass plates have been suspended electrostatically at a gap length of about 0.3 mm. Apart from the structure of the stator electrode, the suspension initiation time is also influenced by air humidity, glass type, supplied voltage and gap length, which have been experimentally explored. Experimental results on the lateral dynamic characteristics are also presented     

Performances of bearingless and sensorless induction motor drive based on mutual inductances and rotor displacements estimation

A self-sensing bearingless motor is considered as an effective solution to reduce cost and shorten a shaft length. In this paper, a novel estimation method of a rotor displacement is proposed. The method is based on the detection of currents induced by mutual inductances, which vary as a function of the rotor displacements. A high-frequency carrier voltage is superimposed on a motor main terminal voltage. The induced carrier-frequency current component is distinguished from the suspension-winding current. The carrier signal is selected high enough to suspension-current components. However, the carrier current is disturbed in transient conditions. The disturbed current results in a vibration of the estimated rotor displacements. A suspension-current estimator is proposed to reduce this vibration and to obtain the difference between the detected current and the estimated current. As a result, the disturbance vibration is significantly reduced. It is shown that a successful magnetic suspension is realized with the proposed method.     

Electrostatic micromotor and its reliability

Research and development in microelectromechanical systems (MEMS) have made remarkable progress since the advent of the first electrostatic micromotor in 1987. Considerable efforts have been directed to the investigation of the failure mechanisms and reliability of electrostatic micromotors. This paper provides a brief overview of failure modes and mechanisms and solving methods in electrostatic micromotors that are commonly met. It focuses on the introduction of the failure modes and mechanisms with numerical and experimental methods as well as the recent methods for reducing the failures and the development in future. In addition, the paper illustrates our investigation on the contact dynamics between the rotor and bearing hub and the effects of gas-lubricated bearing which decrease the possibility of friction, contact, and wear in electrostatic micromotors.     

磁环在双馈风电变频器共模抑制中的应用

双馈风电变频器直接驱动转子,在转子轴上产生较高的共模电压。该电压是有害的,向前可以使齿轮箱发生电蚀,向后可以损坏编码器,还使双馈电机自身的轴承发生电蚀;而共模电流可以传导到控制系统和电源系统,产生电磁兼容问题;对于发电机自身,使转子局部损耗增大,破坏电机绝缘。为了保证系统可靠性和稳定性,需对共模电压/电流进行抑制,本文将就磁环在共模电压/电流抑制中的应用进行探讨。     

Electrostatic levitator for hard disk media

This paper discusses developments in contact-less electrostatic levitators for use in ultra-high-vacuum (UHV) and clean environments. Presented is the first demonstration of an electrostatic levitation technology which can suspend disk-shaped metals and alloys. A 3.5-in diameter aluminum hard disk media has been suspended successfully by actively controlling an electrostatic attractive force acting on it. This paper describes the basic principle of electrostatic suspension, the structure of an experimental levitator, electrode design, position feedback control method, a linear system model, and operational procedures. In addition, experimental data are given to confirm the suspension. The electrostatic levitation technology will be a key technique in the developments of contactless and friction-free manipulation and transportation equipments utilized in UHV and clean environments, both of which are necessary for the manufacture of the new generation of semiconductor devices     

Variable-capacitance micromotor with levitated diamagnetic rotor

A novel micromotor is described, in which the gear-shaped pyrolytic graphite rotor is levitated, rotated and constrained by the combination of static magnetic, electrostatic forces and torques. Two concentric ring-shaped permanent magnets are presented, which are used for realising the static magnetic field. By the microelectromechanical systems process, the metal electrodes, pads and SU-8 column post were fabricated on the silicon substrate above the magnets. The stator was assembled by the silicon and the magnets. The three-phase axial variable-capacitance motor principle was applied for driving the rotor. The rotor is stably levitated to a height of about 0.70 mm over the magnets. When a 30 V driving voltage was added, the rotor speed was over 10 rpm in atmosphere.     

State-feedback decoupling control of 5-DOF magnetic bearings based on α-order inverse system

In the face of magnetic bearing rotor system multivariable, nonlinear, strong coupling control problems, a novel control decoupling method based on inverse system state feedback decoupling theory for the five degree of freedom of active magnetic bearing is presented. It solved the problem of ignoring the limitation of control parameters in conventional control methods. In this paper, the rigid body dynamics model of magnetic suspension rotor is established and the linearization is carried out. In this study, a decoupling pseudo-linear system is constituted by cascading the α-order inverse system based on the state-feedback with the original system. Moreover, in order to improve the robustness of the whole system and reject the influence of the un-modeled dynamics, the internal model controller is designed to synthesize the whole system. Both simulations and experiments demonstrate the effectiveness in decoupling of magnetically-levitated rotor system, and the disturbance rejection of proposed control scheme can be enhanced compared with un-decoupled control schemes.