Comprehensive salient-pole synchronous machine parametric designanalysis using time-step finite element-state space modeling techniques

This paper details the application of a time-stepping coupled finite element-state space (CFE-SS) model to predict a salient-pole synchronous generator's parameters and performance, including damper bar current profiles and bar losses as well as iron core (including pole face) losses, under various operating conditions. The CFE-SS modeling environment is based on the natural ABC flux linkage frame of reference, which is coupled to a time/rotor stepping FE magnetic field and machine winding inductance profile computation model. This allows one to rigorously include the synergism between the space harmonics generated by magnetic saturation and machine magnetic circuit as well as winding layout topologies, and the time harmonics generated by the nonsinusoidal phase currents, ripple rich field excitation and damper bar currents. The impact of such synergism between these space and time harmonics on damper bar current profiles and losses, iron core losses, various machine winding current, voltage and torque profiles/waveforms is studied here for a 10-pole, 44.9 kVA, 17,143 RPM, 1428.6 Hz, 82 V (L-N), wound-pole aircraft generator     

Comparison between characterization and diagnosis of brokenbars/end-ring connectors and airgap eccentricities of induction motorsin ASDs using a coupled finite element-state space method

This paper describes how a rigorous and comprehensive time-stepping coupled finite element-state space (TSCPE-SS) modeling technique can be utilized in diagnostics and differentiation between induction motor rotor (cage) abnormalities of broken bars/connectors and airgap eccentricities. The model is used for the computation of time-domain performance characteristics, such as the stator phase current waveforms and developed torque profiles including these abnormalities. This is followed by analysis of the current waveforms and torque profiles using fast Fourier transform to obtain their corresponding frequency spectra. Comparison between the TSCFE-SS model's simulation results, which correlate very well with theoretical results, clearly illustrate that rotor bar and/or end-ring connector breakages can be distinguished from static and dynamic airgap eccentricities. This paper also gives an interesting comparison between the effects and implications of these various rotor abnormalities on machine parameters and performance characteristics. Furthermore, the results indicate that frequency components reported earlier to be produced only by the combined effects of static and dynamic airgap eccentricity could be observed in case of either static or dynamic eccentricity. Finally, this paper demonstrates the possible opportunities that can be made use of in noninvasive detection of airgap eccentricities via TSCFE-SS and current signature techniques     

Calculation of unbalanced magnetic pull in small cage inductionmotors with skewed rotors and dynamic rotor eccentricity

This paper sets out a simple analytical model which is able to account for the damping effects of a cage rotor on the unbalanced magnetic pull (UMP) when the rotor is dynamically eccentric. The algorithm is implemented for a 4-pole cage induction motor with a variety of rotors with different rotor eccentricity and skew. The model is verified by the assessment of the UMP vibration when the different rotors are fitted in the stator. The characteristics are compared and it is found that the predicted and measured UMP characteristics compare well. It is observed that skewing the rotor cage increases the UMP when the motor is loaded     

Core loss in buried magnet permanent magnet synchronous motors

The steady-state core-loss characteristics of buried-magnet synchronous motors operating from a sinusoidal constant frequency voltage supply are investigated. Measured and calculated core loss, with constant shaft load, is shown to increase with decreasing terminal voltage due to an increase in armature reaction-induced stator flux-density time harmonics. Finite-element modeling is used to show that the additional loss due to the time-harmonic fields can increase core loss by a factor of six over the loss associated with only the fundamental component field at low motor flux levels. A simple air-gap model of motor flux components shows that this increased loss is due to localized rotor saturation. Thus, stator-core harmonic fields should be expected for all buried-magnet rotor synchronous motors (with or without a cage) operating at low flux levels. This factor becomes increasingly important when the motors are operated in the high-speed low-flux mode in conjunction with a variable-speed drive     

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.     

An artificial-neural-network method for the identification ofsaturated turbogenerator parameters based on a coupledfinite-element/state-space computational algorithm

An artificial neural network (ANN) is used in the identification of saturated synchronous machine parameters under diverse operating conditions. The training data base for the ANN is generated by a time-stepping coupled finite-element/state-space (CFE-SS) modeling technique which is used in the computation of the saturated parameters of a 20-kV, 733-MVA, 0.85 PF (lagging) turbogenerator at discrete load points in the P-Q capability plane for three different levels of terminal voltage. These computed parameters constitute a learning data base for a multilayer ANN structure which is successfully trained using the backpropagation algorithm. Results indicate that the trained ANN can identify saturated machine-reactances for arbitrary load points in the P-Q plane with an error less than 2% of those values obtained directly from the CFE-SS algorithm. Thus, significant savings in computational time are obtained in such parameter computation tasks     

A transient induction motor model including saturation and deep bareffect

Transient cage induction motor models for use in inverter-fed drives and controllers are reviewed. A simple transient model is presented that includes rotor deep bar effect and magnetic saturation of the magnetising and rotor leakage flux paths. The improved model requires motor details in the form of simple impedance versus frequency characteristics which can be obtained from a variety of external sources. These can range typically from detailed steady-state finite-element solutions to simple experimental measurements. The model is verified experimentally using a 75 kW, 4 pole vector controlled AC motor drive     

A new miniaturized engine based on thermomagnetic effect of magnetic fluids

A new engine system, essentially consisting of a permanent NdFeB magnet, a kerosene-based magnetic fluid and a rotor, is proposed based on the thermomagnetic effect of a temperature-sensitive magnetic fluid. The rotor was driven by the thermal convection of the magnetic fluid in the presence of a homogeneous external magnetic field. A digital camera was used to record the rotation speed of the rotor to investigate the performance of the engine system under varying conditions such as heat load, heat sink temperature, and magnetic field distribution. The peak angle velocity obtained for the rotor was about 2.1 rad/min. The results illustrate that the rotation speed of the rotor increases as the input heat load increases, or as the heat sink temperature decreases. The performance of the motor is considerably influenced by the magnetic field imposed. Therefore, the performance of such an engine can be controlled conveniently by changing the external magnetic field and/or the temperature distribution in the fluid.     

Three dimensional magnetic field computation by a coupledvector-scalar potential method in brushless DC motors with skewedpermanent magnet mounts-the formulation and FE grids

A three dimensional finite element (3D-FE) method for the computation of global distributions of 3D magnetic fields in electric machines containing permanent magnets is presented. The formulation of this 3D-FE method including 3D permanent magnet modeling, which is based on a coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) approach, is given. The development of the necessary 3D-FE grids and algorithms for the application of the method to an example brushless DC motor, whose field is three dimensional due to the skewed permanent magnet mounts on its rotor, is also given here. A complete set of results of application of the method to the computation of the global 3D field distributions and associated motor parameters under no-load and load conditions are detailed in a companion paper     

Effects of broken bars/end-ring connectors and airgapeccentricities on ohmic and core losses of induction motors in ASDsusing a coupled finite element-state space method

In this paper, effects of rotor abnormalities such as broken squirrel-cage bars, broken cage connectors and airgap eccentricity on ohmic and core losses of induction motors are presented. In this investigation, a comprehensive time-stepping coupled finite element-state space (TSCFE-SS) model was fully utilized to compute the time-domain elemental flux density waveforms and various time-domain waveforms of motor winding currents useful for core loss and ohmic loss computations. Such investigation is feasible by use of the TSCFE-SS model due to its intrinsic nature and characteristics. The results obtained from the simulations of an example 1.2-hp induction motor clearly indicate that faults due to broken squirrel-cage bars/end-connectors can increase motor core losses in comparison to the healthy case. The results also give the effect of saturation on the core loss distributions within the cross-section of the motor, and indicate the potential for possible excessive loss concentrations and consequent hot spots near zones of bar and connector breakages in the rotor     

A novel detection method of motor broken rotor bars based on wavelet ridge

Detection of cage motor broken rotor bars has long been an important but difficult job in the detection area of motor faults. The characteristic frequency component of faulted rotor (CFCFR) is very close to the power frequency component but by far less in amplitude, which brings about great difficulty for accurate detection. A new detection method based on wavelet ridge is presented in this paper. Aiming at the motor's starting period during which the motor accelerates progressively and CFCFR approaches the power frequency gradually in frequency spectrum, the wavelet ridge-based method is adopted to analyze this transient procedure and the CFCFR is extracted. The influence of power frequency can be effectively eliminated, and detection accuracy can be greatly improved by using the approach presented in this paper. Also, this is indeed a novel but excellent approach for the detection domain of cage induction motor broken rotor bars.     

Damper cages in genset alternators: FE simulation and measurement

This paper describes an investigation of the function and effectiveness of the damper cage in small salient pole genset alternators. A time-stepping finite-element (FE) simulation is described and its application to the damper circuit is validated through the use of a specially manufactured rotor with wound damper coils. Further validation is provided by comparison of measured and predicted stator and main field quantities in a standard machine when subjected to sudden application of load. The simulation is then used to predict the performance of the alternator with and without the dampers for balanced and unbalanced load conditions. The effect of the damper circuit is also investigated when a nonlinear, rectifier load is applied to the machine with the modified rotor.     

Coupled finite-element/state-space modeling of turbogenerators inthe abc frame of reference-the short-circuit and load cases includingsaturated parameters

In this paper, a coupled finite-element/state space modeling technique is applied in the determination of the steady-state parameters of a 733 MVA turbogenerator in the abc frame of reference. In this modeling environment, the forward rotor stepping-finite element procedure described in a companion paper is used to obtain the various machine self and mutual inductances under short-circuit and load conditions. A fourth-order state-space model of the armature and field winding flux linkages in the abc frame of reference is then used to obtain the next set of flux linkages and forcing function currents for the finite-element model. In this process, one iterates between the finite-element and state-space techniques until the terminal conditions converge to specified values. This method is applied to the determination of the short-circuit, and reduced- and rated-voltage load characteristics, and the corresponding machine inductances. The spatial harmonics of these inductances are analyzed via Fourier analysis to reveal the impact of machine geometry and stator-to-rotor relative motion, winding layout, magnetic saturation, and other effects. In the full-load infinite-bus case, it is found that, while the three-phase terminal voltages are pure sinusoidal waveforms, the steady-state armature phase currents are nonsinusoidal and contain a substantial amount of odd harmonics which cannot be obtained using the traditional two-axis analysis     

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     

机电复合作用下发电电动机磁极连接线建模及应力分析

针对抽水蓄能机组发电电动机转子磁极连接线现有设计校核往往仅考虑单一机械应力作用,提出计及机端短路故障的机电复合作用下发电电动机磁极连接线建模及应力分析方法。首先,基于有限元方法建立某抽水蓄能机组发电电动机转子结构有限元模型,得到磁极连接线不同工况下单一机械应力结果,然后建立机端三相短路故障下发电电动机电磁场有限元模型,得到计及故障下电磁力作用的机电复合应力结果。结果表明,磁极连接线飞逸工况下承受机械应力约为额定工况时的2倍,电磁力对磁极连接线不同区域影响不均,受力方向和大小的变化规律与机械应力不同,机电复合作用下会造成磁极连接线局部应力激增。     

Electric propulsion with the sensorless permanent magnet synchronous motor: model and approach

In this paper, a rotor position estimator for the sensorless permanent magnet synchronous motor (PMSM) is developed. The proposed approach exploits the time-scale separation between the electrical and mechanical time constant of the PMSM to formulate a linear observer. The observer produces accurate rotor angle estimates in steady-state and transient, and is attractive for electric propulsion applications due to its independence from mechanical parameters such as load torque, inertia, and friction. The sensorless strategy is well-suited to the nonsaturating slotless PMSM, but the demonstrated robustness of the observer to modeling uncertainties allows for application to slotted construction as well. Experiments are conducted to confirm the effectiveness of the proposed approach.     

Analysis of the characteristics of single phase shaded poleinduction motor with two short-circuited auxiliary phases

This work presents a method of general two-phase harmonic symmetrical components, for the analysis and calculation of single-phase induction motor characteristics with shaded poles and two short circuited auxiliary phases. The method is based on rotating field theory applying the harmonic symmetrical current components of direct and inverse order. Thus, it is possible to make a motor characteristic analysis by taking into consideration the action of all significant space harmonics of the magnetomotive forces (MMF) to the rotor cage winding. The advantage of the presented method in regard to other methods is that the shaded pole motor calculation (by enlarging with the higher space harmonics MMF) is united in such a way that it is possible to apply the same calculation program to all structural types with either one or both of the auxiliary phases short-circuited     

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.     

Multiple signature processing-based fault detection schemes for broken rotor bar in induction motors

The existence of broken rotor bars in induction motors can be detected by monitoring any abnormality of the spectrum amplitudes at certain frequencies in the motor current spectrum. It has been shown that these broken rotor bar-specific frequencies are settled around the fundamental stator current frequency and are termed lower and upper sideband components. Broken rotor bar fault detection schemes should depend on multiple signatures in order to overcome or reduce the effect of any misinterpretation of the signatures that are obscured by factors such as measurement noises and different load conditions. Multiple discriminant analysis (MDA) provides an appropriate environment to develop such fault detection schemes because of its multi-input processing capabilities. The focus of this paper is to provide a new fault detection methodology for broken rotor bar fault detection and diagnostics in terms of its multiple signature processing feature and the motor operation partitioning concept to improve the overall detection performance. This paper describes two fault detection schemes within this methodology, and demonstrates that multiple signature processing is more efficient than single signature processing. The first scheme, which will be named the "monolith scheme," is based on a single large-scale MDA unit representing the complete operating load torque region of the motor, while the second scheme, which will be named the "partition scheme," consists of many small-scale MDA units, each unit representing a particular load torque operating region.     

Circumventing the blocked rotor test when evaluating model elementsof three phase induction motors

The paper proposes a method that may be used in lieu of the traditional but awkward blocked rotor test to evaluate the AC resistances and the leakage reactances of a polyphase motor. The method provides the element values of the five-element-per-phase Steinmetz model and the six-element-per-phase model of IEEE Standard 112-84. The test procedure is conducted with a freely-rotating motor operated at rated voltage, normal power line frequency and at power levels that may be a fraction of rated load of the machine being tested. Model elements are evaluated from the circular impedance locus of the Steinmetz model or a variation thereof adapted for the six-element-model. Data points on the locus are obtained with the machine operating as a motor and as an asynchronous generator