Analytical and experimental investigation on the magnetic field and torque of a permanent magnet spherical actuator

This paper presents the torque model of a ball-joint-like three-degree-of-freedom (3-DOF) permanent magnet (PM) spherical actuator. This actuator features a ball-shaped rotor with multiple PM poles and a spherical stator with circumferential air-core coils. An analytical expression of the magnetic field of the rotor is obtained based on Laplace's equation. Based on this expression and properties of air-core stator coils, Lorentz force law is employed for the study of the relationship between the rotor torque and coil input currents. By using linear superposition, the expression of the actuator torque in terms of current input to the stator coils can be obtained in a matrix form. The linear expression of the actuator torque will facilitate real-time motion control of the actuator as a servo system. Experimental works are carried out to measure the actual magnetic field distribution of the PM rotor in three-dimensional (3-D) space as well as to measure the actual 3-D motor torque generated by the actuator coils. The measurement results were coincident with analytical study on the rotor magnetic field distribution and actuator torque expressions. The linearity and superposition of the actuator torque were also verified through the experiments.     

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。     

基于解析模型的永磁同步电机优化设计

永磁同步电机的电磁转矩和涡流损耗是两个重要指标,在体积等限制条件下,有效提高电磁转矩并降低转子涡流损耗是电机设计的关键。针对这个问题,文中采用解析法,分别计算电磁转矩和涡流损耗,并采用粒子群优化算法,对电机尺寸参数进行优化设计。解析模型包括电枢反应磁场和空载磁场模型。在计算涡流损耗时考虑涡流反应、永磁体周向分段等,优化算法的目标函数并使用权值将多目标转换成单目标。通过解析解与时步有限元数值解的对比可看出,解析解的误差在2%左右。参数影响分析的响应面显示,在定子绕组节距为25°时,电磁转矩和涡流损耗相关性一致。优化迭代结果显示,优化设计降低了76%的平均涡流损耗、22%的平均电磁转矩和68%的电磁转矩波动。     

Performance of induction motor with free-rotating magnets insideits rotor

This paper presents a new induction motor that has free-rotating magnets inside a rotor. The magnets can revolve freely against the rotor with the shaft. In this motor, the airgap flux is provided by both rotating permanent magnets and the stator coil current. A prototype motor was fabricated by modifying the rotor of a conventional three-phase four-pole 400 W squirrel-cage induction motor. The experimental results of a prototype motor showed superior performance in comparison to conventional motors in terms of the power factor, efficiency and torque characteristics. The power factor can be controlled to be unity, leading or lagging by changing the supply frequency and/or source voltage. The efficiency of the motor, over a wide output power range, is remarkably higher than that of the same size conventional induction motor. A high torque can be obtained in a high speed area     

一种新型径向磁浮轴承结构设计与磁场计算

在传统径向电磁轴承中,由于各电磁铁之间磁路相通而使磁场存在相互耦合,这将影响转轴的控制精度和动态响应,为此,提出一种新型的磁铁结构,解决了磁路耦合问题,并缩短了磁路长度.此外,当转子旋转时,磁场极性变化将使转子中产生涡流,此涡流将改变电磁轴承气隙回路中的磁场.利用ANSYS有限元分析软件,以实验样机系统为例,进行了相应的分析和计算.结果表明,随着转速的增加,涡流场将向磁极的后缘和表面集中,电磁吸力减小,而磁阻力增加.实际应用中应尽量选择相对磁导率较大而电导率较小的转子材料.     

Design and control of a disk-type integrated motor-bearing system

A disk-type integrated motor-bearing system having axial magnetic flux is newly invented and its design, analysis, and control methods are presented. Sinusoidal motoring currents to four symmetrically placed winding groups produce a torque, whereas control currents of the same magnitude but opposite signs added to the opposite winding groups create radial forces. The control currents are intended to break force symmetry, resulting in unbalanced radial forces. The system employs two stators not only to effectively remove the rotational frequency modulation effect in the radial control forces, but also to reduce the torque ripple. It is shown that the prototype integrated motor-bearing system built in the laboratory succeeds in stable radial direction control and operation of the rotor     

A magnetic flux model based method for detecting multi-DOF motion of a permanent magnet spherical motor

This paper presents a new method, referred to here as back-EMF method, for sensing the multi-DOF motion of a permanent magnet spherical motor (PMSM). With an explicit model characterizing the magnetic flux in the PMSM, a relationship between the electromotive force (EMF) induced in the winding of electro-magnets and the motion of the rotor permanent magnets is derived; and closed-form solutions that solves for multi-DOF Euler angles and angular velocities of the rotor are presented. This method allows for simultaneous estimation of both quantities in real-time by only measuring the voltages across the electro-magnets. Requiring no installation of additional sensors or fixtures on the rotor, the back-EMF method retains the structural simplicity of the PMSM. This method has been experimentally investigated on a prototype PMSM; the estimated Euler angles and angular velocities compare favorably with measurements from a commercialized gyroscope. As an immediate application, the motion states acquired using the back-EMF method are used for parameter estimation of the PMSM.     

Modeling of permanent magnet motor drives

Research has indicated that the permanent magnet motor drives, which include the permanent magnet synchronous motor (PMSM) and the brushless DC motor (BDCM) could become serious competitors to the induction motor for servo applications. The PMSM has a sinusoidal back EMF and requires sinusoidal stator currents to produce constant torque while the BDCM has a trapezoidal back EMF and requires rectangular stator currents to produce constant torque. The PMSM is very similar to the wound rotor synchronous machine except that the PMSM that is used for servo applications tends not to have any damper windings and excitation is provided by a permanent magnet instead of a field winding. Hence the d, q model of the PMSM can be derived from the well-known model of the synchronous machine with the equations of the damper windings and field current dynamics removed. Because of the nonsinusoidal variation of the mutual inductances between the stator and rotor in the BDCM, it is also shown that no particular advantage exists in transforming the abc equations of the BCDM to the d, q frame. Hence the solution of the original abc equations is proposed for the BDCM     

Field oriented control of induction machines employing rotor endring current detection

The usual method of induction motor torque control uses the indirect field orientation principle in which the rotor speed is sensed and slip frequency is added to form the stator impressed frequency. Unfortunately, the rotor resistance varies as the motor heats up under load thereby changing the rotor time constant which has a deleterious effect on the torque response. In this paper two new field oriented control schemes are presented which employ rotor end ring current detection and thereby remove the dependence of the controller accuracy on temperature so that the controller is entirely independent of rotor time constant variations. The field orientation schemes do not require an incremental encoder for rotor position sensing. The motor torque can be accurately controlled even down to zero speed operation     

Implementation of a DSP based real-time estimator of inductionmotors rotor time constant

Implementation of ac drives insensitive to parameter variations is an important need in the field of high performance drives. For drives controlled by the indirect rotor flux oriented control method (IRFOC), the rotor time constant (τ_r = L_r/R_r) exerts a dominant role in the loss of dynamic performance and its variation results in an undesirable coupling between flux and torque of the machine. This paper presents a new scheme for on-line estimation of rotor time constant using dq representation of the model in the stationary reference frame and measurements of accessible motor variables only (voltages, currents and speed). The estimator is tested by simulation in the MATLAB/SIMULINK environment and validated experimentally on a 1/4 hp squirrel cage motor and a 1/4 hp wound rotor motor with implementation on a TMS320C31 digital signal processor     

异步电机矢量控制系统的仿真建模与实现

异步电机矢量控制是在交流电机的双轴理论、机电能量转换和坐标变换理论的基础上发展起来的。为了实现对异步电动机磁场和转矩的解耦控制的目的;采用交流电机的磁场定向控制(即矢量控制)的方法;建立了一种在转子坐标系下异步电机的矢量控制系统仿真模型;仿真结果表明,基于矢量控制的方法能够实现对异步电机的解耦,即通过控制励磁电流分量和转矩电流分量的大小直接控制异步电机磁场和转矩,使交流异步电机获得和直流电机相媲美的控制性能。     

微马达结构、气隙磁场和绕组层数对微马达输出力矩的影响

电磁型微马达以其输出力矩大、运行寿命长、易于实用化的优点成为微机电系统、微型机器人和微型可动部件理想的驱动器。从微马达结构1气隙磁场、转子厚度、转子写入磁极数和定子绕组的层数对微马达输出力矩的影响进行了分析和讨论。     

Characteristics and control of a bidirectional axial gap combinedmotor-bearing

Introduces the design characteristics of a bidirectional axial gap combined motor-bearing where the flat disc motor has both rotation and axial position control capability. This motor consists of a disc rotor with a stator on each side of the rotor. The axial motion of the rotor is actively controlled while the other axes are constrained by additional passive or active radial magnetic bearings. Each stator produces a rotating magnetic flux in the air gap, to generate the motor torque. The axial force is controlled by changing the amplitude of the rotating flux. Both permanent-magnet motor and induction motor versions were analyzed theoretically and tested experimentally. The results demonstrated the capability of providing both the functions of a motor and a magnetic bearing     

Speed-sensorless control system of a bearingless induction motor based on iterative central difference Kalman filter

ABSTRACT

In order to obtain speed self-detecting with low cost for a bearingless induction motor (BIM) a speed-sensorless control strategy based on the iterative central difference Kalman filter (ICDKF) is proposed. Firstly, on the basis of the BIM mathematical model, the nonlinear state equation is established and its order is reduced from fifth-order to fourth-order using the stator terminal voltage and current as input. Then, a sterling interpolation formulation is used in the filter to reduce the model error, and an iteration loop link is adopted to improve the filter accuracy. Finally, the online speed of the BIM is identified through the filter rotor speed estimation. Theoretical analysis, simulation and experimental results by UKF and CDKF method have been compared. The results show that the proposed speed-sensorless control system not only has good speed tracking performance and reduce the load disturbance but also improves the BIM suspension performance.     

20MJ补偿脉冲发电机的设计与仿真

由于补偿脉冲发电机集惯性储能、机电能量转换和脉冲成形的综合技术优势,研制了一台额定转速为12 000 r/min的20 MJ补偿脉冲发电机,并研究了其中关键材料包括屏蔽筒和转轴等的选择。在理论计算和仿真分析的基础上设计了电机励磁回路以及电枢绕组,提出了一种新的补偿绕组结构即定子上安放两套电枢绕组,在电机放电时,脉冲电流将会提高,绕组的温度会降低,磁场密度会增强。     

A new flux-barrier-type reluctance motor with a slit rotor

A reluctance motor, with a rotor which has many slits, is proposed. The slits are used to generate magnetic flux in the d-axis direction. In practice, the rotor, which has a fewer number of slits, is desired to increase productivity. With a fewer number of slits, torque ripple becomes large. Therefore, torque ripple reduction methods are also proposed. In simulations and experiments, rated torque of the proposed motor is 1.7× as much as that of the conventional brushless DC motor with ferrite permanent magnets. The peak-to-peak (p-p) torque ripple is 1.5% p-p of the rated torque at the rated torque. The efficiency is 91% and the power factor is 61%, at the rated torque and 1200 min^-1. The characteristics of the field weakening and the constant power control are also shown. The breakpoint frequency of speed controls is about 200 Hz. Therefore, the proposed reluctance motor is feasible for general applications     

Design and control of a permanent magnet spherical wheel motor

We present a permanent magnet–based spherical wheel motor that can be used in omnidirectional mobility applications. The proposed motor consists of a ball‐shaped rotor with a magnetic dipole and a hemispherical shell with circumferential air‐core coils attached to the outer surface acting as a stator. Based on the rotational symmetry of the rotor poles and stator coils, we are able to model the rotor poles and stator coils as dipoles. A simple physical model constructed based on a torque model enables fast numerical simulations of motor dynamics. Based on these numerical simulations, we test various control schemes that enable constant‐speed rotation along arbitrary axes with small rotational attitude error. Torque analysis reveals that the back electromotive force induced in the coils can be used to construct a control scheme that achieves the desired results. Numerical simulations of trajectories confirm that even without explicit methods for correcting the rotational attitude error, it is possible to drive the motor with a low attitude error (<5°) using the proposed control scheme.     

Corrosion Model of a Rotor-Bar-Under-Fault Progress in Induction Motors

A corrosion model of a rotor-bar-under-fault progress in induction motors is presented for simulations of induction machines with a rotor-bar fault. A rotor-bar model is derived from the electromagnetic theory. A leakage inductance of the corrosion model of a rotor bar is calculated from the relations of magnetic energy, inductance, current, and magnetic-field intensity by Ampere's law. The leakage inductance and resistance of a rotor bar varies when the rotor bar rusts. In addition, the skin effect is considered to establish the practical model of a rotor bar. Consequently, the variation of resistance and leakage inductance has an effect on the results of motor dynamic simulations and experiments, since a corrosive rotor bar is one model of a rotor bar in fault progress. The results of simulations and experiments are shown to be in good agreement with the spectral analysis of stator-current harmonics. From the proposed corrosion model, motor current signature analysis can detect the fault of a corrosive rotor bar as the progress of a rotor-bar fault. Computer simulations were achieved using the MATLAB Simulink with an electrical model of a 3.7-kW, three-phase, and squirrel-cage induction motor. Also, experimental results were obtained by real induction motors, which had the same specification as the electrical model used in the simulation     

A Novel Design of a Brushless DC Motor Integrated with an Embedded Planetary Gear Train

This paper presents a novel design by integrating a planetary gear train (PGT) within a brushless dc (BLDC) motor to be a compact structure assembly. It provides functional and structural integrations to overcome the inherent disadvantages of the traditional designs. The effects of the gear teeth on the magnetostatic field of the BLDC motor associated with the kinematics of the PGT are investigated. By designing the number of gear teeth integrated on the stator and magnet poles on the rotor, the cogging torque of the proposed motor configuration is effectively reduced. The magnetic field distribution and the output torque of the novel design with different standard gear modules are numerically calculated by two-dimensional finite-element analysis. Through the kinematic analysis that utilizes the fundamental circuits, feasible solutions for the number of gear teeth of the PGT are determined to meet the desired speed ratio.