环形驻波超声波电机定转子接触摩擦模型

超声波电机的接触摩擦模型对电机结构设计和性能优化具有重要作用。针对环形驻波超声波电机定转子接触摩擦问题,采用库伦摩擦+黏性摩擦定律建立了定转子接触摩擦模型。采用所建立的模型分析了一个振动周期内接触界面的摩擦力变化情况,也研究了定子不同径向振幅以及结构参数对电机输出性能的影响。最后,测量了电机的转矩 转速特性,并将测量值与计算值进行对比,二者吻合度较好。另外,对比了基于库伦摩擦定律所建立模型的转矩 转速特性计算值,对比结果表明,与基于库伦摩擦定律所建立的模型相比,基于库伦摩擦+黏性摩擦定律所建立的模型能更准确地描述定转子接触界面的摩擦传动特性。     

转子轴向碰摩非线性流固耦合动力学特性全自由度分析

基于Jeffcott转子模型,用六自由度方法研究了考虑涡轮非线性流固耦合力的转子轴向碰摩动力学特性。通过响应分叉图、波形图、频谱图、轴心轨迹和Poincare图分析了在涡轮非线性流固耦合力作用下转子轴向碰摩的动力学表现。分析表明,非线性涡轮叶尖间隙流体激励力对转子轴向碰摩的非线性特性影响不很明显,只是在低转速时轴向振动碰摩响应中会出现更高阶的偶数倍频的超谐波成分。在高转速情况下,碰摩响应的波形和频谱不能明显反映具有弱非线性的涡轮叶尖间隙流体激励力对轴向碰摩非线性动力学特性的影响,而轴心轨迹和Poincare图则能反映这种影响,反映出碰摩响应中出现的轻微混沌。     

不同涂层下的转子系统碰摩响应分析∗

文章基于当量线化法分别建立了硬涂层、软涂层和一般情况下的碰摩力模型;以含涂层的Jeffcott转子为研究对象,通过线性插值法和Runge-Kutta法相结合的方式研究了不同涂层情况下转子系统的动力学响应。数值仿真的结果表明:当转/静子部件表面喷涂硬涂层时,系统的动力学响应相对复杂,在较宽的转速区间内以拟周期运动为主;当转/静子部件表面喷涂软涂层时,转子系统的动力学响应相对简单,主要作周期运动。     

水轮发电机组转子不对中-碰摩耦合故障动力学分析

以水轮发电机组转子系统为研究对象,针对刚性联轴器综合不对中引起转子局部碰摩的问题,建立了机组转子不对中–碰摩耦合故障的动力学模型和微分方程,并利用数值积分方法研究该系统随不对中平行量和偏角参数变化的动力学行为。通过分岔图、Poincaré截面图、轴心轨迹图、时域波形图和幅值谱图系统地分析了发电机转子与水轮机转子在耦合故障下非线性动力学响应,发现机组转子系统随不对中平行量和偏角变化存在周期运动和复杂的拟周期,其碰摩过程非常复杂,机组故障特征频率除主要在1倍频外,还在0.3~0.4倍频处存在幅值较大的谐波分量。研究结果为水轮发电机组安全运行和准确识别转子不对中、碰摩故障提供有益的理论依据。     

考虑定子齿结构的行波超声波电机接触摩擦模型

本文分析了定子的振动、定转子的法向接触和切向摩擦,考虑了定子齿结构,采用解析法建立了环形行波超声波电机定转子接触摩擦模型。基于所建立的模型,分析了定子表面质点与转子间的接触时间和切向摩擦力以及电机的转矩-转速特性。此外,也对考虑定子齿结构和忽略定子齿结构的模型计算结果进行对比,结果显示,在相同的预压力下,考虑定子齿结构时,定子表面质点与转子的接触时间比忽略定子齿结构时要长,而且转矩-转速特性的计算结果要低于忽略定子齿结构时的计算结果。最后,将理论计算结果与实验结果进行了对比,考虑定子齿结构时的计算结果比忽略定子齿结构时更接近实验值,说明考虑定子齿结构的接触摩擦模型能准确地反映定转子间的接触和摩擦特性。     

转子碰摩波内调制特征提取及其故障诊断应用

为深入分析不同转静碰摩故障引起振动响应信号波内调制特征的变化规律,以Jeffcott转子模型为基础,采用基于变分模态分解的Hilbert变换方法对不同碰摩故障仿真信号进行波内调制特征的提取与分析,揭示了碰摩转子的动力学特性与其故障信号波内调制特性间的关联机理。仿真结果表明,周期-k碰摩故障将导致振动响应信号中低频段波内调频模态的瞬时频率以1/k倍频为中心振荡,且振荡频率依然为1/k倍频,进而造成了频谱中的1/k边频带;在概周期碰摩故障中,波内调制频率为靠近1/k倍频的无理数倍频和整数倍频,且造成振动信号频谱中的无理数边频带。离心泵转子故障诊断试验表明,波内调制特征能够有效地对转子碰摩故障进行有效的诊断。     

汽轮机组碰摩故障的数值仿真分析

对转子轴系进行了合理的模化，利用有限元算法，并采用库仑摩擦模型建立了多元盘转子轴承系统的碰摩运动方程，并对200MW高压转子的振动特征进行了仿真计算，得出转子轴承系统发生碰摩后的一些特征，如较小的不平衡。则不会产生碰摩；较大的不平衡，则会使转子汽封发生碰摩；在复速级加重引发碰摩时，对转子各点的影响最大等。     

径向驻波型超声波电机接触摩擦特性建模与分析

超声波电机的接触摩擦模型对电机输出性能优化、控制电路设计具有重要的作用。现有对超声波电机接触摩擦模型的研究,大多基于库伦摩擦模型,其计算结果的精度有待进一步提高。该文基于Dahl摩擦模型对一种径向驻波型超声波电机的接触摩擦特性进行建模和分析。首先介绍电机的结构,然后分析定子的振动、定转子间的接触摩擦以及转子的旋转运动,考虑定子振动的瞬态响应过程,基于Dahl摩擦模型建立径向驻波型超声波电机定转子接触摩擦传动模型。利用所建立的模型,研究接触界面的摩擦力、不同负载下电机的速度响应情况以及电机的转矩-转速特性。最后测试样机的转矩-转速特性,将理论计算值与实验值进行对比,二者基本吻合,证明所建立模型的有效性。此外,该文也对基于库伦摩擦模型的计算值进行对比分析,结果表明:相比于库伦摩擦模型的计算值,基于Dahl摩擦模型的计算值具有更高的精度。     

不同载荷下基座松动转子系统动力学特性分析

主要针对一个双盘单跨转子系统,采用分段线性弹簧/阻尼模型来模拟基座松动故障,并将其与转子系统有限元模型进行耦联,根据API617标准采用2种不同的载荷加载工况,利用三维谱图和轴心轨迹图,分析未松动螺栓刚度、松动间隙和转速对系统动力学特性的影响。结果表明在2种不同加载形式下,系统运动存在不同的分岔形式,出现了多种周期及拟周期运动形式,且在第2种加载形式下系统运动更为复杂。得出的结论为转子–轴承系统故障诊断、动态设计和安全运行提供了理论参考。     

大型汽轮发电机组碰摩引起的振动突变机理

研究大型汽轮发电机组运行过程中碰摩引起的振动突变现象及其机理.研究结果表明:转子与定子之间的碰摩使得转子系统的刚度由线性刚度演变成非线性刚度,导致转子系统的振动行为发生变化;动静碰摩,在转子上施加了一个热不平衡量,这个热不平衡分量与原始不平衡量合成后,产生一个旋转的综合不平衡;当综合不平衡量达到最大值时,在非线性转子系统上施加一个很大的作用力,从而使转子的振动发生突变.控制转子的原始不平衡量和碰摩引起的热不平衡量是控制转子振动突变的根本措施.     

Forces exciting generation roll at rotor vibrations when rotor-to-stator rubbing

The consequences of emergencies of turbosets for different application are revealed, the cause of forced shutdown and even catastrophic destructions of which many researchers consider the rotor-to-stator rubbing and development—to a greater or lesser extent—of the phenomena of the rotor generation roll over the stator. The synchronous or asynchronous generation roll is determined by the rotor precession direction, coinciding or not coinciding with the self-rotation direction of the rotor. Asynchronous generation roll is the most dangerous form of the rotor-stator contact interaction with the vibrations with rubbing. The basic equations of rotor vibrations are presented: symmetric rotor fixed on two supports and that fixed on several supports after abrupt imbalance with and without rotor coming in contact with a flexible stator. The vibration process is considered as the rotor motion in a backlash with subsequent contact with the stator, loss of contact, or development of generation roll. The latter essentially depends on the properties of the “rotor–support–stator” dynamic system. The stator stiffness characteristic is specified in “force–deformation” coordinates that make it possible to take into account damping in the supports and power loss in the stator. The diagram of elastic-damping device was presented, which makes it possible to ensure a certain level of power loss at the stator displacements. The exciting forces promoting development of self-exciting vibrations of the rotor in the form of asynchronous generation roll were compared with the exciting forces of oil film of sliding bearings and forces of aerodynamic excitation in the turbine flow path and sealings. For the rotor systems of high and medium pressure of a 300 MW capacity turboset, the simulation results of the process of development of asynchronous generation roll at the vibrations with rubbing were revealed, and the basic characteristics of development of generation roll in a span between supports and time variation of casual coefficients of contact stiffness defining the forces exciting the generation roll at the contact interaction of the rotor with the stator were presented. The dependence of coefficients of contact stiffness on the rotor displacements submits to the hyperbolic law. The increase of damping decreases the probability of occurrence of dangerous consequences of emergencies, which are defined by many factors, including the rotor imbalance level.     

基于定子合成磁势分析的火电机组振动机理研究

定子绕组流过暂态不平衡电流时,发电机内部磁场分布将发生变化,继而会影响定、转子之间的受力和振动。分析定子绕组合成磁势方位角变化,可提取三种不用的定子磁场模式:旋转磁场、步进磁场以及固定磁场,且固定磁场下汽轮机振动急剧增加。文中采用有限元仿真计算,以单相绕组通直流电来模拟固定定子磁场的方式,发现随着定转子磁势夹角的变化,转子在较短时间内承受较大的冲击力矩,且在故障期间循环往复,最终导致跳机。     

无刷双馈电机谐波铜耗与铁耗的分析与计算

针对无刷双馈电机谐波含量高、谐波损耗大的问题,提出考虑谐波磁场、谐波电流、集肤效应和旋转磁化影响的BDFM损耗计算模型.基于二维场路耦合时步有限元模型和谐波分析方法,分别建立两种转子铜耗计算模型和三种定转子铁耗计算模型,分析不同计算模型对转子铜耗和定转子铁耗的影响,得到定转子谐波铜耗和铁耗的变化规律.结果表明,转子铜耗模型2以及定转子铁耗模型3更精确;随着控制绕组电压的增加,定转子铜耗先减小后增加,定转子铁耗持续增加;随着负载转矩的增加,定转子铜耗和铁耗均随之增加.通过与一台相似异步电机铜耗和铁耗的电磁设计数据和实验数据的比较,验证了模型与计算结果的正确性.     

Studying the development of asynchronous rolling of the rotor over the stator with the turbine unit protection systems having different response times

The possibility to stabilize the developing asynchronous rolling of the rotor over the stator under the conditions of power unit protections coming in action with different response times is considered. Asynchronous rolling of the rotor over the stator may develop when the rotating rotor comes in contact with the stator at high amplitudes of vibration caused by an abrupt loss of rotor balancing, by forced or self-excited vibration of the rotor, and by other factors. The danger of asynchronous rolling is connected with almost instantaneous development of self-excited vibration of the rotor when it comes in contact with the stator and with the rotor vibration amplitudes and forces of interaction between the rotor and stator dangerous for the turbine unit integrity. It is assumed that the turbine unit protection systems come in action after the arrival of signal of exceeding the permissible vibration level and produce commands to disconnect the generator from the grid, and to stop the supply of working fluid into the flow path, due to which an accelerating torque ceases to act on the turbine unit shaft. The protection system response speed is determined by a certain time t = ABtime that is taken for its components to come in action from the commencement of the event (application of the signal) to closure of the stop valves. The time curves of the main rolling parameters as functions of the ABtime value are presented. It is shown that the response time of existing protection systems is not sufficient for efficiently damping the rolling phenomenon, although the use of an electrical protection system (with the response time equal to 0.40–0.45 s) may have a positive effect on stabilizing the vibration amplitudes to a certain extent during the rolling and on smoothing its dangerous consequences. The consequences of rotor rolling over the stator can be efficiently mitigated by increasing the energy losses in the rotor-stator system (especially in the stator) and by fulfilling the recommendations of the machinery unit catastrophe prevention system.     

Stability analysis of a controlled-current source-fed induction motor vector control system without a speed sensor

One of the representative vector-controlled induction motor drive systems without a speed sensor is composed of a rotor flux estimator, a PI torque current controller and a conventional vector-controlled current source. However, the stability analysis of this system has not been reported. In this paper, the flux estimator is interpreted as a flux observer. Then a linear model of the system is proposed by deriving the equations of the flux estimator in a synchronously rotating reference frame. By computing the trajectories of the poles and zeros and the transient responses, the following results are obtained. (1) If the rotor flux is estimated using only the stator equations (voltage model), the system becomes unstable when the actuator stator resistance is smaller than the value used by the controller. (2) By choosing a small time constant of the first-order lag element in the flux estimator (reciprocal number of observer gain), the poles and zeros on the imaginary axis move to the stable region. However, another pair of poles has reverse performance. (3) From the viewpoint of stability, the gain of the PI torque current controller should be chosen as large as possible and the stator and rotor resistances in the controller should be set to values smaller than their actual values.     

Specific features relating to the motion of a rotor with rubbing against the stator

Specific features relating to the motion of a rotor with rubbing against the stator and the rolling of a rotor over the stator are considered. Conditions under which rolling of the rotor over the stator occurs and the kinematic and force characteristics of this phenomenon are investigated. Simple analytical solutions are obtained for a model assuming that an absolutely rigid rotor and an absolutely rigid stator come in absolutely inelastic contact with each other, which allow one to get a clear idea about the roll-over phenomenon. An attempt is made on the basis of the proposed model to understand some striking features of the accident that occurred in the 300 MW power unit at the Kashira district power station in 2002.     

Observer-based direct field orientation: analysis and comparison ofalternative methods

This paper focuses on methods of achieving direct field orientation (DFO) of induction machines based on closed-loop, stator, and rotor flux observers which are well suited to both zero and very high-speed operation. Both observer topologies are dominated by a current model at zero and low speeds, and a voltage model at high speeds. Application of such rotor and stator flux observers to both stator and rotor direct field orientation is presented, including experimental results for three different methods. The influence which flux regulation has on parameter sensitivity of the complete DFO system is analyzed. A rotor-flux-regulated and -oriented system is shown to be sensitive to leakage inductance under high slip (i.e., field weakened) operation. Both a stator-flux-regulated and -oriented system and a stator-flux-regulated, rotor-flux-oriented system are shown to have reduced parameter sensitivity at high speeds. Unlike stator flux orientation using simple voltage integration stator flux models, excellent zero and low-speed operation of an observer-based stator-flux-oriented system is demonstrated     

圆管内对流换热的场协同理论分析

以空冷电机转子通道内的流动换热问题为背景,将场协同理论应用于旋转坐标系中。通过理论分析,指出了场协同理论应用于静止坐标与旋转坐标中的差异,说明了在旋转坐标系下对流换热问题的规律。采用数值模拟方法对旋转坐标下的三维轴向直圆管模型内部流动与换热进行了研究,验证了理论分析结果,并进一步对比了不同转速、不同入口条件下换热情况。理论分析与数值计算结果均证明在旋转坐标系下,高转速带预旋入口条件的轴向通道内固体壁面对流体做功量对总换热量的影响不可忽视。     

非接触式球形转子压电作动器的研究

提出了一种基于近声场悬浮的非接触式球形转子压电作动器,由压电陶瓷激发碗式定子产生两相B04驻波并合成一高声强行波,进而诱发高声强声场来同时悬浮和驱动球形转子。建立了非接触式球形转子压电作动器的有限元模型,对定子进行了动力学分析与优化设计,确定了结构方案,最后加工、制造了样机。通过试验得到了定子的振动参数,搭建了整个样机的测试系统,对其悬浮和驱动特性进行了分析,结果表明球形转子在近声场的作用下成功地实现了非接触式旋转。