Armature Reaction Flux Research Articles

Analysis of low saliency ratio and torque characteristics of the fractional slot concentrated winding surface mounted motors

In recent years, fractional slot concentrated winding permanent magnet synchronous motors (FSCW PMSMs) have become a hotspot in the research field. Due to the unique inductance characteristics of the FSCW PMSM, a fast and accurate calculation of the d/q-axis inductance and saliency ratio is necessary. In this paper, a method is proposed to calculate the d/q-axis reactance of the FSCW SPMSM, which constructs the equivalent magnetic circuit model of the d/q-axis armature reaction flux separately, and the saliency ratio characteristics of the FSCW SPMSM were demonstrated. In addition, to meet the high requirements of the modern industries, especially in servo systems, accurate consideration of the effect of stator resistance on torque and electromagnetic performance is important and more applicable. According to the relationship between the vector parameter, the explicit expression of the d/q-axis currents that consider the stator resistance is obtained, and the prediction of load angle at maximum electromagnetic torque is achieved. Then, combined with the finite element method, the influence mechanism of stator resistance on the motor steady-state performance is revealed. Finally, the experimental data are compared with the calculation data, and the correctness of the models and analysis was verified.

Comprehensive Armature Reaction Modeling and Flux Weakening Optimization of a Surface Permanent Magnet Vernier Motor

Surface permanent magnet vernier motors (SPMVMs) possess the potential for direct-drive applications due to the feature of high torque density. This paper presents a deep investigation into the armature reaction modeling and a semi-analytical optimization framework considering the constant power speed range (CPSR) in the flux weakening region for the SPMVM. The new armature reaction model can identify the armature air gap flux density of each harmonic component and armature flux linkage accurately, by conducting harmonics analysis, slot leakage flux computation and slotting effect evaluation, permitting to calculate the inductance. Then, the results from the armature reaction model and those obtained from finite element analysis (FEA) at the rated operating point together are applied to a comprehensive semi-analytical motor optimization framework developed for SPMVMs. The optimization framework is able to reflect the motor performance metrics over the entire speed range, with torque density, power factor and CPSR as objectives. Finally, a prototype designed according to the trade-offs of the optimization objectives is fabricated to confirm the validity of the armature reaction model and optimization framework.

Research of a Stator PM Excitation Solid Rotor Machine for Flywheel Energy Storage System

A typical flywheel energy storage system (FESS) includes an electrical machine, a flywheel, and magnetic bearings, which are independent of each other. Therefore, the structure of FESS is complicated, which leads to the problems of high cost and low integration. This article presents a novel stator PM excitation solid rotor machine (SPE-SRM) for FESS, which integrates an electrical machine, flywheels, and a magnetic bearing. The design method of the SPE-SRM is presented specifically. First, the structure and operation principle of the SPE-SRM are illustrated. Second, the design and optimization of the flywheel-rotor are presented with considering of power, energy storage, and mechanical strength. Third, the magnetic equivalent circuit of the SPE-SRM is established to simplify the design. Besides, the armature reaction and leakage flux factor are investigated. Fourth, the performance indexes, including torque, suspension force, no-load back electromotive force (back-EMF), losses, and temperature rise are fully analyzed by the finite element analysis. Finally, a 22 kW prototype is manufactured and tested. The rationality of the concept and design is validated by experiments. The SPE-SRM has the merits of high integration, robust structure, and low cost, so it has the potential for wide application in FESS.

Analysis of Rotor Losses in Permanent Magnet Vernier Machines

This article investigates rotor losses in permanent magnet Vernier machines. By analyzing air-gap field, the harmonic distribution and frequency of modulated open-circuit flux density and armature reaction flux density are obtained. Then, rotor losses production principle is revealed and the influence of each harmonic on the loss is analyzed. Meanwhile, the influence of each harmonic on torque is also studied. It is found that some harmonics have no contribution to torque but produce additional losses. On this basis, a new rotor structure is proposed to suppress the rotor losses. Comparison results indicate that by suppressing nonworking harmonics, the rotor losses can be reduced effectively without affecting the effective torque. Finally, the theoretical and finite-element analysis results are verified by prototype tests.

Magnetic Circuit Modeling of Dual-Armature Flux-Switching Permanent Magnet Machine

Three lumped-parameter magnetic circuit (LMC) models of dual-armature flux-switching permanent magnet (DA-FSPM) machines are proposed and compared in this article. First, the characteristics of the magnetic flux fields produced by the PM, stator armature reaction, and rotor armature reaction flux sources are analyzed, with particular attention paid to the air-gap and slot leakage flux paths. Based on the former analyses, three LMC models are developed, which consider the air-gap and slot leakage permeances in different ways. The electromagnetic performances of the DA-FSPM machines are predicted by the three LMC models and validated by the finite-element method, including the flux linkage, average torque, inductance, and power factor. The model accuracy sensitivity to the geometric parameters, copper loss allocation, electric loading, stator pole/rotor tooth number combinations, power level, and conductor distributions are analyzed. It shows that appropriate consideration of slot leakage permeance is important to improve the model accuracy.

Study on Magnet Eddy Current Losses in Interior Permanent Magnet Machines for Aircraft Electric Green Taxiing Systems

The magnet eddy current of multi-layered interior permanent magnet (IPM) machines is studied in the paper for the aircraft electric green taxiing systems. The armature reaction flux density distribution, eddy current density and harmonic spectrum at the end of permanent magnet are analysed. A method to reduce the magnet eddy current of multi-layered IPM machines is presented. That is to increase the distance between outer permanent magnet and rotor surface and the distance between two layers of permanent magnet so as to provide a larger core path for armature reactive flux. This method can effectively reduce the magnet eddy-current loss of the multi-layered IPM machines and improve the operation efficiency.

Modeling of Airgap Fluxes and Performance Analysis of Five Phase Permanent Magnet Synchronous Generator for Wind Power Application

This paper proposes an Improved Magnetic Circuit (IMC) model for the optimal design and characteristics evaluation of the Five-Phase Permanent Magnet Synchronous Generator (FP-PMSG) for wind power application. Along with the Finite Element Method (FEM), the IMC model is also preferred for its faster result generation capabilities. The proposed model is used for optimal designing and performance evaluation of FP-PMSG by considering parameters such as leakage fluxes, properties of core material for rotor and stator, properties of rotor permanent magnet sleeve material, effect of saturation and armature reaction. To compute the armature reaction flux, the winding function approach has been opted. Furthermore, extensive analysis is done with respect to different sleeve and core materials along with improvising various dimensional parameters like magnet height, Magnet to Magnet (M-M) gap and sleeve length for high quality performance of FP-PMSG. To validate the results obtained from IMC model and FEM, an experimental prototype is developed and the electromagnetic performances such as generated voltage, Percentage Total Harmonic Distortion (THD) of generated voltage, terminal voltage vs load current, generated Electromotive Force (EMF) vs speed, rectified Direct Current (DC) Voltage vs DC current, output DC Power vs load resistance and percentage (%) efficiency vs current are evaluated. Through fabrication of the prototype of FP-PMSG in the laboratory, a substantial amount of engineering values have been acquired.

Line start permanent magnet motors with double‐barrier configuration for magnet conservation and performance improvement

This study proposes a new configuration for line start permanent magnet (PM) motors with low consumption of PM material, providing improved performance. The configuration is developed by analysing PM flux density distribution in the machine airgap and focusing on the d-axis armature reaction flux path and also different magnetisation types in the PM poles. It features double flux barriers for each rotor pole to facilitate near sinusoidal flux density distribution. Main characteristics of a motor with the proposed configuration are analysed by finite element method (FEM) and compared with the characteristics of a motor with the conventional configuration. Finally, the motor is built and tested. The FEM and experimental results verify the advantages of the proposed configuration. The results show that the required PM material reduces by one-third, while desirable performance is provided. The machine is capable of working with delta connection causing negligible circulating current and low torque ripples.

Analytical Calculation of Yoke Flux Patterns in Fractional-Slot Permanent Magnet Machines

Machine design problems are often solved under the assumption of no-load when calculating iron flux densities. However, it is particularly important to account for the fluxes from the stator currents, the armature reaction, in fractional-slot machines. The fluxes from the permanent magnets and the armature reaction both vary in time with the electrical frequency. By studying the flux that flows along the stator yoke behind every slot in such a machine, it is revealed that the armature reaction flux does not have the same amplitude behind all slots. In addition, it is revealed that the time-varying no-load and armature reaction fluxes are shifted in time, with different phase shifts behind different slots. The sum of the no-load and armature reaction fluxes, namely, the load flux, depends on both the amplitudes of the fluxes and the phase shift between them. The resulting load flux behind each slot varies significantly. In four investigated machines, the ratio of the highest to the lowest load flux amplitude ranges between 1.6 and 6. The load flux can be significantly higher than the no-load flux. The flux calculations are verified through finite-element analysis in all four machines, and the error in the maximum load flux ranges between 2% and 6%.

Asymmetrical Geometries in Electrical Machines

This paper describes and classifies possibilities of using asymmetric geometry solutions in slotted electrical machines with nonlinear soft magnetic core. These asymmetrical optimizations can reduce cogging torque and torque ripple at the nominal load. Additionally, some of them can improve overload capability, and field weakening capability by proper optimization of over-saturated regions of soft magnetic core. In this paper it is shown that the geometry of the soft magnetic core regions of TC-PMSMs, exhibiting strong saturation due to the interaction of PM- and armature reaction fluxes, has a significant impact on the torque quality. Therefore, by their modifications (including asymmetrical) it is possible to improve the machine characteristics. Two types of PMSM rotor arrangements (embedded-magnet rotor PMSM and rotor-surface magnet PMSM) were simulated with 2D FEM. The results showed that slight modification of the TC-PMSMs soft magnetic regions near by the air gap which exhibit the strongest saturation can lead to significant torque quality variation as well as to synchronous inductance changes.

On-Load Voltage Distortion in Fractional-Slot Interior Permanent Magnet Machines

The mechanism and the influence of the on-load terminal phase voltage distortion by the armature reaction in interior permanent magnet (IPM) machines with fractional-slot concentrated windings (FSCWs) are investigated in this paper, by taking a 12-slot/8-pole machine as an example. The phenomenon is presented first, which shows that the peak voltage will be much higher than the fundamental value, especially under the flux-weakening operation. Then, the mechanism is investigated with the aid of the frozen permeability method. Due to the geometric feature of the FSCW IPM rotor, the armature reaction flux will asymmetrically enhance the local magnetic saturation in the tooth-tips and the rotor lamination region near the rotor ribs, which disrupt the smooth variation of phase flux linkage and lead to a voltage distortion. With the increasing of current advancing angle ( $\beta $ ), this effect will become more obvious and result in the higher distortion level. Furthermore, the influences of voltage distortion on the machine torque performance are investigated, which show that it will only contribute to the torque ripple in the constant torque region, but will largely reduce the flux-weakening operation region compared with the ideal one calculated by the fundamental voltages only. Finally, a prototype is manufactured and tested to validate the analyses.

Rotor eddy loss in high‐speed permanent magnet synchronous generators

Analytical and transient finite element analysis (FEA) methods are used to calculate on-load rotor eddy current power loss in permanent magnet machines taking into account the effect of the reaction of eddy currents. The effect of the phase advance angle between the back electromotive force, and the phase current on rotor eddy current power loss is investigated. Both magnet flux tooth ripple and magnetomotive force harmonics are considered in the analytical calculation of rotor loss; the harmonics of the magnet tooth ripple flux and armature reaction flux are added vectorially. Good agreement between analytical and FEA results is observed when the stator laminations are assumed to have a linear BH curve. However, a significant discrepancy is observed between the analytical and FEA solutions when a non-linear BH curve is used.

A fault location method using air‐gap fluxes of synchronous generator

AbstractThis paper deals with an experimental investigation of a novel fault location method using air‐gap flux distributions of a synchronous generator connected to a power system. Air‐gap fluxes are the sum of field fluxes and armature reaction fluxes. Changes in armature current and field current at a fault contribute directly to the armature reaction fluxes and field fluxes, then resultant air‐gap fluxes. Therefore, air‐gap fluxes can be utilized to locate a fault. Wavelet analysis is applied to the induced voltages of search coils, which are wound around a stator tooth top for measurement of the air‐gap flux. It is shown that the fault type and location can be estimated based on the change in the search coil voltages measured during the fault. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 20–27, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20707

Design and Test of an Axial Flux Permanent-Magnet Machine With Field Control Capability

We designed and tested a new axial flux permanent-magnet machine (AFPM) with field weakening capability. This paper provides a summary of key design features, optimization, and test results of an AFPM prototype. The proposed field weakening method is based on the control of the d-axis component of the armature reaction flux. The paper focuses on the air-gap flux control capability of the topology.

同期発電機の空隙磁束を利用した送電線事故標定手法

This paper deals with an experimental investigation of a novel fault location method using air-gap flux distributions of a synchronous generator connected to a power system. Air-gap fluxes are the sum of field fluxes and armature reaction fluxes. Changes in armature current and field current at a fault contribute directly to the armature reaction fluxes and field fluxes, then resultant air-gap fluxes. Therefore, air-gap fluxes can be utilized to locate a fault. Wavelet analysis is applied to the induced voltages of search coils, which are wound around a stator tooth top for measurement of the air-gap flux. It is shown that the fault type and location can be estimated based on the change in the search coil voltages measured during the fault. © 2009 Wiley Periodicals, Inc. Electr Eng Jpn, 167(3): 20–27, 2009; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20707

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.

Synchronous machines with contrarotating armatures: steady-state behaviour

A synchronous machine can be constructed with two armatures and one field. If the armatures contrarotate, the armature-reaction flux in the quadrature axis, ideally, is eliminated. The machine therefore operates with a high saliency ratio. The voltage regulation for a unity power-factor load is then only affected by winding resistance and leakage reactance. This unique feature allows the machine to have a peak power capability several times that of conventional machines of the same size. Two contrarotating machines have been designed and tested. One of the arrangements has steady-state behaviour approaching the expected ideal behaviour. The test machine built has three rotatable machine elements which allows the examination of a number of operating modes.

Three‐dimensional analysis of inductances and magnetic fields in the air‐cored armature windings of a superconducting synchronous machine

Although the inductances of an iron-cored synchronous machine can be calculated precisely by established conventional methods, it is not easy to calculate the inductances and flux distribution of air-cored synchronous machines. The flux distribution is greatly affected by the structure of the winding and, therefore, it is very important to clarify the three-dimensional distribution of the magnetic field taking into acount the shape of the windings. Two types of air-cored armatures are presented. These are the diamond type and the helical type. The magnetic flux distribution, inductances, and other performances of the diamond-type winding are compared to the helical-type winding. The results from the analysis to derive calculation formulas for armature reaction flux and winding inductances are presented.