Determination of radial-forces in relation to noise and vibrationproblems of squirrel-cage induction motors

The radial electromagnetic forces in induction motors play an important role in the production of audible noise and vibrations. The magnetic flux pulsations at the iron surfaces produce these radial forces, which act on the stator and rotor structures. An analysis for the calculation of the various field harmonics and radial forces in squirrel cage induction motors is presented in this paper. To verify the validity of the analysis, a squirrel cage induction motor is analyzed. Theoretical and experimental results are presented with a view to determine the actual role played by the air-gap harmonic fields on the radial forces. Also, the effects of loading on the radial forces and the ensuing vibrations are closely examined     

Asynchronous Performance Prediction of AC Permanent Magnet Motor

many permanent magnet synchronous motors are run up from standstill by a sudden connection with an ac supply. The cage windings in rotor slots produce induction motor torque to run up the rotor, but two torque dips are produced in the torque-slip curve of the permanent magnet motor; one is caused by the rotating permanent magnet, and the other by the magnetic and the electric asymmetry between the direct and quadrature axes. Therefore, the prediction of the asynchronous performance is very important, as motors cannot be run up, unless the minimum values of the torque dips exceed the load torques at the slips. In this paper, ``harmonic permeance coefficient' is newly introduced, which is used to combine the finite element field solution with the calculation of air gap inductance, and equations for the calculation of asynchronous performance of permanent magnet motors are also expressed. The calculated value by these equations agreed well with the experimental results.     

A novel double-circuit-rotor balanced induction motor for improvedslip-energy recovery drive performance. I. Modeling and simulation

A new construction for the rotor windings of balanced wound-rotor induction motors employed in the slip energy recovery drives is proposed, in this paper, to reduce the time harmonics which are commonly generated in the machine. The proposed machine has a double-circuit in the rotor. One circuit is star connected while the other is delta connected. Each of these two circuits is connected to a diode-bridge rectifier to achieve a twelve-pulse operation characteristics. The main objective of this paper is to develop a new model which is capable of simulating the proposed machine, neglecting nonlinearities due to magnetic saturation, and its associated converters. Such a model is further complicated due to the presence of the two rotor circuits and their mutual interaction     

A nonconventional method for fast starting of three phasewound-rotor induction motors

This paper presents a nonconventional method for the fast starting of three-phase wound rotor induction motors. This is achieved through shunting the stator and rotor windings across the supply for a predetermined short period. By this connection, the motor produces an extremely high starting torque. The feasibility of this basic idea has been confirmed through investigating the starting transients corresponding to this mode of operation. For this purpose, a rigorous state-space mathematical model has been developed and simulated. The validity of the proposed method and the findings from the mathematical model have been confirmed experimentally     

Instantaneous Shaft Radial Force Control with Sinusoidal Excitations for Switched Reluctance Motors

Unbalanced radial forces acting on a rotor shaft exist in motor applications where the external load is not balanced or when the rotor is not centered causing a nonuniform air gap. These forces are undesirable as they cause motor vibrations. In view of its special structure, the shaft radial force and the torque of a three-phase 12/8 pole switched reluctance motor (SRM) can be separately controlled by proper pole current selection in the energized phase. Therefore, radial forces can be produced intentionally to cancel the existing radial force produced by rotor eccentricity and the unbalanced load inertia. The motor vibrations are thereby reduced. In this paper, a sinusoidal current excitation scheme is proposed for the torque and radial force control of a 12/8 pole SRM. When controlled with the selected sinusoidal currents, the SRM can simultaneously produce the desired shaft radial force in any rotational plane direction and the required rotational torque. As all pole currents are individually controlled, a more sophisticated phase commutation strategy is also proposed that provides smoother torques and radial force ripples.     

An improved control method of buried-type IPM bearingless motors considering magnetic saturation and magnetic pull variation

An improved control method of the buried-type interior permanent magnet (IPM) bearingless motors has been presented. It is shown that the conventional method is not applicable to this type of IPM bearingless motor for loaded conditions. In IPM bearingless motors, the armature reaction flux is present due to high magnetic permeance with thin permanent magnets and small airgap length. An increase in d-axis flux linkage is caused by armature reaction as a torque-component flux is increased. Thus, it is likely that magnetic saturation occurs in the stator teeth. In addition, a magnetic attractive force caused by the displacement force factor is dependent on the armature reaction flux. A new decoupling controller for the IPM bearingless motor considering magnetic saturation is proposed in this paper. It also considers the influence of magnetic attractive force variations. In addition, a new parameter identification method for the decoupling controller is also proposed. The new controller is found quite suitable to realize successful stable operation of the experimental IPM bearingless motor.     

Analysis of a single-phase induction machine with a shiftedauxiliary winding

This paper extents the method of multiple reference frames to the analysis of asymmetrical induction motors with nonorthogonal stator windings, with particular emphasis on the permanent split capacitor (PSC) machine. The predictions of the method are verified by comparison to both experimental results and to results obtained using a machine variable computer simulation. Once verified, the method is used to derive the transfer function relating rotor speed to load torque disturbance, which is of particular interest when analyzing PSC machines driving compressor loads. It is shown that the transfer function exhibits a distinct resonant point, and that the magnitude of the resonant peak increases as the motor approaches synchronous speed. It is also shown that the magnitude of the resonant peak may be lowered by increasing rotational inertia or rotor resistance     

Induction Motor Squirrel Cage Rotor Winding Thermal Analysis

Induction motor squirrel cage rotor winding performance operating range and reliability are influenced by the temperature of these windings and the temperature differences which occur within the windings, and between the windings and other parts of the rotor structure. These temperature responses have formed a basis for protective devices commonly in use to protect the winding from damage. This paper describes an anaytical effort which models the thermal response of the squirrel cage winding. The temperatures calculated using this model are in general agreement with previously published data.     

Preliminary performance evaluation of switched reluctance motors with segmental rotors

This paper examines the performance of switched reluctance machines which employ a segmental rotor construction in preference to the usual toothed structure. Two three-phase designs are considered, one in which the windings span a number of teeth and one in which they span a single tooth. Two demonstrators have been built-one for each design type, and their performances are compared with both conventional switched reluctance motors (SRMs) and a rare earth permanent-magnet machine. It is shown how these machines can operate from a standard SRM converter: running test results are presented and there is a discussion of general operating experience, ranging from the measurement of mean torque, voltage, and current-controlled operation to general thermal performance.     

3-D electro-magnetic analyses of a cage induction motor with rotorskew

The paper studied the performance characteristics of a three-phase cage induction motor using a 3D finite element technique. Especially, the effects of rotor skew and the rotor end-rings and the distribution of the electromagnetic field toward the axial direction, which have not been able to be analyzed accurately by 2D analysis, were investigated. Since the 3D analysis enabled the analysis of the continuity of the air gap flux density at the core ends and to take into consideration the rotor end-ring impedance, the motor parameters were calculated with high accuracy, compared with 2D analysis. Firstly, the authors made the relation of the rotor end-ring current with the rotor bar current clear, by analyzing the harmonics of the rotor bar current and the rotor end-ring current in the cases of motors without rotor skew and with rotor skew. Secondly, the torque and the rotor axial force were calculated from the distribution of the electromagnetic field obtained by the 3D analysis in the case of rotor skew. They also calculated the axial forces on the both end-rings in the case of rotor skew. The results obtained in the paper show the importance of 3D analysis for the design of induction motors     

Characterization of coil faults in an axial flux variable reluctance PM motor

Variable-reluctance (VR) and switch-reluctance (SR) motors have been proposed for use in applications requiring a degree of fault tolerance. A range of topologies, of brushless SR and VR permanent-magnet (PM) motors are not susceptible to some types of faults, such as phase-to-phase shorts, and can often continue to function in the presence of other faults. In particular, coil-winding faults in a single stator coil may have relatively little effect on motor performance but may affect overall motor reliability, availability, and longevity. It is important to distinguish between and characterize various winding faults for maintenance and diagnostic purposes. These fault characterization and analysis results are a necessary first step in the process of motor fault detection and diagnosis for this motor topology. This paper examines rotor velocity damping due to stator winding turn-to-turn short faults in a fault-tolerant axial flux VR PM motor. In this type of motor, turn-to-turn shorts, due to insulation failures, have similar I-V characteristics as coil faults resulting from other problems, such as faulty maintenance or damage due to impact. In order to investigate the effects of these coil faults, a prototype axial flux VR PM motor was constructed. The motor was equipped with experimental fault simulation stator windings capable of simulating these and other types of stator winding faults. This paper focuses on two common types of winding faults and their effects on rotor velocity in this type of motor.     

小波分析法在汽轮发电机转子绕组匝间短路故障诊断中的应用

提出了基于小波变换的汽轮发电机转子绕组匝间短路故障检测的一种诊断方法。这种方法是在探测线圈法的基础上，把小波变换用于突变信号的检测，对气隙中感应电势信号的故障特征进行提取和信号的消噪，可实现对发电机转子绕组匝间短路故障的检测。仿真实例表明，小波分析方法适合于转子绕组匝间短路故障的检测。图3参5     

Comparison of the electromagnetical performance of simplex wave andlap windings

A main feature of modern DC machines should be little maintenance. Improved commutation with reduced brush wear is therefore necessary. A comparison of simplex wave and lap windings is carried out, concerning good commutation. Wave windings need lower numbers of turns per armature coil than lap windings for the same rated motor data, which enables motors to reach longer operating intervals between brush exchange. Thus wave windings should be preferred in spite of higher brush load due to equalizing currents, and preferably excited slot-frequent shaft bending vibrations     

A brushless self-exciting three-phase synchronous generatorutilizing the 5th-space harmonic component of magneto motive forcethrough armature currents

A novel brushless self-exciting three-phase synchronous generator is proposed. It consists of three-phase armature windings on the stator, one field winding and one exciting winding with five times as many poles as that of the armature winding on the rotor, and a three-phase reactor connected to the terminal of the armature windings. By utilizing the 5th-space harmonic component of armature electromotive force, small voltage regulation for various loads and no oscillatory tension occurring at the rotor shaft were realized. The basic constitution, principle of operations, and exciting characteristics are described. The experimental results obtained from using a trial generator demonstrated its practical usefulness     

A novel multilayer switched reluctance motor

The switched reluctance motor is a simple and robust machine, which has found application over wide power and speed ranges in different shapes and geometries. This paper introduces a new configuration for a high starting torque switched reluctance motor (SRM). This configuration allows more space for coil windings in small size motors with a high number of stator and rotor poles. It also presents a centrifugal switch mounted on the motor shaft for a sudden advancement of current-pulses relative to rotor position after reaching a preset motor speed in order to develop higher torque at starting. To evaluate the motor performance, two types of analysis, namely numerical techniques and an experimental study have been utilized. In the numerical analysis, due to the highly nonlinear nature of the motor, a finite element analysis is employed, and for the experimental study, a prototype motor has been built and tested. Finally, the prototype motor is compared with a conventional SRM of the same size. The calculated results compare favorably with the test results. In comparison with the conventional SRM, the proposed motor in this paper seems to be very promising     

Analysis of electromagnetic and thermal fields for induction motorsduring starting

In order to improve the starting performance of squirrel-cage induction motors, the so-called “skin effect” becomes very serious, which causes a highly uneven distribution of rotor-bar currents. The corresponding conduction losses of the upper and lower portions of rotor bars create high thermal stress, which may damage the rotor bars, particularly at the junction of rotor bars and end-rings. Hence, it is important to predict the starting and operating characteristics of induction motors more accurately for the purpose of ensuring the reliability of motor operation. This paper employs a visual-aided finite-element method to analyze the electromagnetic and thermal fields of induction motors during starting. By using visual and interactive pre- and post-processing techniques, the analysis can be applied to squirrel-cage induction motors with any physical dimensions, material properties, and system parameters. The starting performance, including the distributions of magnetic flux density, current density, loss density and temperature rise, are presented dynamically by computer animation, which are convenient and powerful for the evaluation and design optimization of induction motors. The theoretical predictions are verified by direct comparison with experimental results     

What stator current processing-based technique to use for induction motor rotor faults diagnosis?

In recent years, marked improvement has been achieved in the design and manufacture of stator winding. However, motors driven by solid-state inverters undergo severe voltage stresses due to rapid switch-on and switch-off of semiconductor switches. Also, induction motors are required to operate in highly corrosive and dusty environments. Requirements such as these have spurred the development of vastly improved insulation material and treatment processes. But cage rotor design has undergone little change. As a result, rotor failures now account for a larger percentage of total induction motor failures. Broken cage bars and bearing deterioration are now the main cause of rotor failures. Moreover, with advances in digital technology over the last years, adequate data processing capability is now available on cost-effective hardware platforms, to monitor motors for a variety of abnormalities on a real time basis in addition to the normal motor protection functions. Such multifunction monitors are now starting to displace the multiplicity of electromechanical devices commonly applied for many years. For such reasons, this paper is devoted to a comparison of signal processing-based techniques for the detection of broken bars and bearing deterioration in induction motors. Features of these techniques which are relevant to fault detection are presented. These features are then analyzed and compared to deduce the most appropriate technique for induction motor rotor fault detection.     

Speed Control System for Brushless Cascade Induction Motors in Control Range of Slips s1>1 and S2>1

This paper describes principles together with analytical and experimental studies of a speed control system for brushless induction motors of cascade connection in the control range of the slips s1> 1 and s2>1 which was devised by one of the authors. Steady state analyses of the performances of the motor control system are discussed, and results of the tests are presented. It is found that the motor can be controlled widely and comparatively efficiently by controlling the converters which are connected electrically to one of the stator windings of the two motors.     

Permanent-magnet-excited AC servo motors in tooth-coil technology

Permanent-magnet-excited ac servo motors can be produced usefully with tooth-coil windings; they allow an increase of the torque density due to their compact construction. The winding systematics and the winding variants, interesting for ac servo motors, are introduced. The steady-state behavior of the ac servo drive is calculated analytically in dependence of the winding variant. The influence of the winding variant on the M(n)-characteristic is discussed in examples. A comparison between calculations and measurements verifies the represented modeling.     

Numerical investigation and optimization of the thermal performance of a brushless DC motor

A computational study of a brushless DC motor is presented to determine the thermo-flow characteristics in the windings and bearings under the effects of heat generation. The rotation of the rotor blades drives an influx of ambient air into the rotor inlet. The predicted inflow rates were higher at the front inlet than at the rear inlet due to non-uniform pressure distribution. A recirculation zone appeared in the tiny interfaces between windings. The poor cooling performance was caused by flow separation near the groove threshold by the inclination angle of the bearing groove and by a relatively slow velocity near the bearing and between windings. Based on these results, design parameters for the inlet location and geometry, and for the bearing groove geometry, were determined and optimized to enhance the cooling performance up to 24%.