Permanent Magnet Excitation Research Articles

Characteristic Thermal Parameters in Electric Motors: Comparison Between Induction- and Permanent Magnet Excited Machine

The thermal modeling and design process of highly utilized electric machines is a complex task. The main heat paths within an electric drive are influenced by a variety of different thermal interfaces, that can mainly be described by thermal conduction and convection. The proper selection and estimation of these design parameters is challenging especially in the early design stage. This paper provides a systematic investigation evaluating inaccuracies and design influences of single thermal resistances, such as the convective heat transfer in the rotor-stator annulus, in the cooling jacket or interfaces between different machine components. Within the study, electromagnetic finite element models and thermal lumped parameter models of two traction drives are developed and validated using test bench measurements. The thermal design parameters are varied in a range resulting from intensive literature research and own laboratory experience. The influence of the design parameters in different operational points of the drives are studied in a sensitivity analysis.

Investigation of Regenerative Braking Performance of Brushless Direct Current Machine Drive System

The brushless direct current (BLDC) machines which are preferred in light electric vehicles (LEVs) come forward as high regenerative braking capability machines due to their permanent magnet excitation and relatively simple operation. In this paper, the regenerative braking capability limits of BLDC machines and their drive circuits are examined by taking into account nonlinear circuit parameters and battery internal resistance variation. During energy recovery from mechanical port to electrical port, the inverter of BLDC machine is operated as a boost converter which enables power flow to a battery. However, the regeneration performance is also heavily dependant on the battery condition, particularly the temperature. By means of the developed detailed circuit model including the non-ideal effects of the boosting converter and the increase of the internal resistance variation which is caused by the temperature variation of the battery and ambient temperature, the specific duty cycle can be determined. The specific duty ratio is then applied in a proposed approach for various operation scenarios. The experimental tests are implemented by a 400 W BLDC machine drive system controlled via a TMS320F28335 digital signal processor. The experimental results show that the proposed comprehensive model presents a proper performance estimation of regenerative braking system under varying battery temperature.

Combined Random Forest and NSGA-II for Optimal Design of Permanent Magnet Arc Motor

This article presents an optimization design method for a double-stator hybrid excited permanent magnet arc motor (DS-HE-PMAM). The proposed optimization method combining the machine learning algorithm random forest (RF) and the nondominated sorting genetic algorithm-II (NSGA-II) contributes to achieving high average torque, low torque ripple, high back electromotive force (EMF), and low total harmonic distortion of the back EMF. First, the motor structure and working principle of the DS-HE-PMAM are illustrated. The selection of parameters to be optimized is determined based on an analytical model. Then, a variable importance measure-based new sensitivity analysis method is implemented to evaluate the influence of each structural parameter on the selected design objectives. The finite-element analysis (FEA)-based DS-HE-PMAM model is developed to obtain the sample data regarding input structural parameters and output design objectives. Based on the sample data, a powerful machine learning algorithm called RF is employed to fit the function relationship between output design objectives and input structural parameters. After that, an intelligent search algorithm named NSGA-II is introduced to search for the optimal solution to the structural parameters combination and obtain the optimal motor performances. Finally, the electromagnetic characteristics of the initial and optimized models of the DS-HE-PMAM are compared and analyzed, and both FEA and prototype experiments verify the feasibility and superiority of the proposed optimization method.

Design and Optimization of a Hybrid Excitation System for Magnetically Driven Rotating DC Arc Plasma Generators

To eliminate the disadvantages of both the uncontrollability in the magnetic field of a permanent magnet excitation system and the high energy consumption of an electric excitation system in a traditional magnetically rotating arc plasma generator, a novel topology of a hybrid permanent magnet and electrically excited coil system is proposed. The proposed system will generate a large enough magnetic field to drive the arc rotation with a minimum consumption of materials and electric energy in the normal operation duty, and will guarantee a nearly zero magnetic field in the arc triggering stage. To optimize the hybrid excitation system, a comprehensive analysis and an optimization methodology; by combining finite element analysis, the moving the least squares approximation and an adaptive weighted particle swarm optimization, are proposed. Finally, a prototype hybrid excitation system is optimized with promising results in views of both saving a huge amount of electric power consumptions and ensuring a nearly zero magnetic field in the arc triggering.

Investigation of Novel Doubly Salient Hybrid Excited Machine With Non-Overlapped Field Winding

Hybrid excited machines, with synergies of permanent magnet (PM) and wound field (WF) excitations, exhibit high torque density as well as controllable flux and are perceived as promising candidate for variable speed application. A novel doubly salient hybrid excited (DSHE) machine with non-overlapped field winding is presented in this paper. It inherits simple structure of conventional doubly salient PM (DSPM) machine and facilitates the regulation of magnetic field by field winding. The electromagnetic performances of the proposed machine with different stator and rotor pole number combinations are investigated by finite element method (FEM), confirming these advantages. Furthermore, the effect of iron bridge on the hybridization between PM and WF excitations is analyzed to obtain a trade-off between high torque density and wide flux regulation range with the frozen permeability method (FPM). It is revealed that the proposed DSHE machine possesses higher power and fault tolerance at flux weakening region compared with the DSPM machine, albeit with sacrificed torque density and efficiency with introduction of field winding. Finally, a prototype is fabricated and tested to validate the theoretical analyses.

Modern Hybrid Excited Electric Machines

The paper deals with the overview of different designs of hybrid excited electrical machines, i.e., those with conventional permanent magnets excitation and additional DC-powered electromagnetic systems in the excitation circuit. The paper presents the most common topologies for this type of machines found in the literature—they were divided according to their electrical, mechanical and thermal properties. Against this background, the designs of hybrid excited machines that were the subject of scientific research of the authors are presented.

Design and Analysis of Air Core Outer Rotor Halbach Array Compulsator

Conventionally, the capacitor-based pulsed power supply is used for the railgun. However, it cannot create zero current crossings during discharge, which leads to a large muzzle arc. This invariably leads to compulsator as a popular choice for railgun pulsed power supply. Moreover, the size of compulsator is comparatively lower than a capacitor bank of the same energy. A computer-aided design (CAD) of 10-MJ, 4-phase, 4-pole compulsator for achieving desired performance is developed and presented in this article. A six-segment Halbach array is adopted for permanent magnet (PM) excitation to remove the slip ring arrangement and to reduce voluminous design due to external excitation. The designed compulsator is simulated in Ansys electromagnetic (EM) suite for field analysis with practical design considerations along with the inclusion of armature winding impedance, PM demagnetization effects, and eddy current distribution in compensating shield. The railgun circuit analysis is carried out for the designed compulsator co-simulated using Simplorer and Ansys EM. Furthermore, various parametric studies are conducted for designed compulsator to analyze the effects on the acceleration and synchronization of the projectile’s exit from the barrel. Detailed simulation results show that the target specifications are achieved with the new design.

Analysis of Novel Hybrid-PM Variable-Flux PMSMs With Series–Parallel Magnetic Circuits

The development of traditional permanent magnet synchronous machines (PMSMs) in electric vehicle (EV) industry is limited by the unalterable permanent magnet (PM) excitation field. Variable-flux PMSMs are considered as a good candidate for EV propulsion for their ability to operate in a wide speed range with high efficiency by manipulating the magnetization state dynamically. A novel hybrid-PM variable-flux PMSM with series-parallel magnetic circuits is proposed in this article. The structure and operating principle of the proposed machine are introduced. The electromagnetic performances of the proposed machine are analyzed and compared with the series-connected and parallel-connected variable-flux machines, and the proposed machine combines the advantages of these two kinds of machines. The inductance characteristics of the proposed machine are analyzed by frozen permeability method (FPM), and the variation laws of inductance are quite different in different magnetization states and load conditions. The torque capacity of the proposed machine is analyzed. The torque ripple can be significantly reduced and the output torque can be improved by properly applying flux-weakening control.

Low - speed generator with permanent magnets and additional windings in the rotor for small power wind plants and micro hydro power plants

Recently due to the worldwide population grows much attention has been paid to increasing total electricity generation. However, traditional power plants, which are used hydrocarbon fuels, cause one of the challenging problems like environmental contamination and global warming in the world. In this case, renewable or alternative energy sources can be a promising replacement for traditional hydrocarbon fuels. Uzbekistan has lots of small rivers and water reservoirs and the use of these potentials in the perspective to generate power it is a unique decision of the problem. Usually in small power plants use low-speed generators and efficiency of these type generators are very low. Hence, the main objective of this study is to increase the efficiency of the low power generator by improving and optimizing the specifications and parameters of the low power generators. The use of low-speed generators with permanent magnet excitation for micro-hydroelectric power plants and wind turbines is relevant in terms of providing good weight and size indicators, simplicity of construction, lack of sliding contacts, with the ability to perform a generator of low rotation speeds, which causes low cost and high reliability. In this study, the natures of the influence of the main geometric dimensions of the mass-dimensional parameters and the air gap on the energy indicators of the generator are estimated. Theoretical and experimental research results are submitted.

ОСОБЕННОСТИ ПРОЕКТИРОВАНИЯ ВЕТРОГЕНЕРАТОРОВ ПОВЫШЕННОЙ МОЩНОСТИ (600÷3600) кВт С ВОЗБУЖДЕНИЕМ ОТ ПОСТОЯННЫХ МАГНИТОВ

В основу работы положены результаты расчетов ряда синхронных безредукторных ветрогенераторов модульных конструкций [1] с возбуждением от постоянных магнитов NdFeB мощностью (600÷3600) кВт при принятой за рубежом расчетной скорости ветра – 12,5 м/с. Такой подход исследования машин позволяет оценить сложную взаимосвязь их параметров при минимуме допущений, в частности, учесть насыщение наиболее нагруженных участков магнитной цепи и определить целесообразность применения некоторых возможных вариантов обмоток, которые обеспечивают наибольшую электромагнитную мощность генераторов с учетом технологичности их выполнения; показаны особенности изменения зубцовой зоны машин повышенной мощности, обусловленные низкой скоростью вращения генераторов в безредукторных установках и обоснована по этой причине возможность применения "меандровой" обмотки.
 В такой обмотке каждая фаза выполняется в виде одного непрерывного проводника, что позволяет исключить соединение секций в фазе, имеющее место в традиционных обмотках, уменьшить сопротивление обмотки благодаря отсутствию одной лобовой части в сравнении с витком секции. При решении технологии изготовления таких обмоток в виде шины возможно повышение коэффициента заполнения пазов и мощности генератора в определенных габаритах. Возможно изготовление такой обмотки кабелями, в этом случае трехфазная обмотка будет представлять три кабеля, что позволит упростить её изготовление, но коэффициент заполнения пазов будет меньше. 
 В работе проведено сравнение различных вариантов меандровых обмоток с целью упрощения их изготовления и традиционных всыпных обмоток с различным количеством пазов на полюс и фазу с целью увеличения зубцового шага и упрощения изготовления пакета статора и обмотки. Библ. 9, табл. 1, рис. 5.

Nonlinear Analytical Solution of Magnetic Field and Performances of a Spoke Array Vernier Permanent Magnet Machine

This article presents a nonlinear analytical (NA) solution based on subdomains for predicting magnetic field and performances of a spoke array vernier permanent magnet (SAVPM) machine which has spoke array type permanent magnet (PM) excitation. On one hand, equivalent current sheets replace tangentially magnetized PMs to make the magnetic vector potential in the region with PMs satisfy a Laplace's equation, which simplifies the problem and reduces the workload of numerical calculation. On the other hand, in contrast to the existing literature, regions of soft-magnetic material such as a tooth and a rotor pole are subdivided into small pieces, and are no longer a whole with a single permeability for considering local magnetic saturation. Poisson's and Laplace's equations with the given permeability of soft-magnetic material are analytically solved by separation technique of variables in seven subdomains, and nonlinear iteration is used to determine the solution of NA and update soft-magnetic material permeability. NA solves the magnetic field and performances of a SAVPM machine. Frozen permeability method (FPM) is used to determine PM flux linkage and d-axis inductance under load. Results from the NA model have been compared with those from FEA and experiments.

System-Level Optimization of Hybrid Excitation Synchronous Machines for a Three-Wheel Electric Vehicle

In this article, a two-level methodology is proposed to optimize the design of a hybrid excitation synchronous machine (HESM) for a given electric vehicle (EV) over an arbitrary-selected driving cycle. We are looking at a huge analysis problem of finding an optimal hybridization ratio (HR) between the two excitation sources, namely, permanent magnet (PM) and wound excitation (WE). To find the optimal HR, the HR is scanned from 0 to 1 or from pure WE to pure PM excitation. For each HR, the motor is optimally designed at the component level, its cost is minimized, and its global efficiency over the selected driving cycle is calculated. Then, at the system level, the global efficiencies associated with each HR are compared in order to find the optimal HR. The complexity of the design optimization at the component level is addressed by nondominated sorting genetic algorithm II (NSGA-II). To make a compromise between the accuracy and speed of calculations, a nonlinear 3-D dynamic magnetic equivalent circuit (MEC) model is developed and evaluated by commercial finite element analysis (FEA) software. Following the proposed methodology and due to 300 h of computations with 48 CPU cores in parallel, the final HESM design can achieve up to 18.65% higher global efficiency than pure WE and 15.8% higher than pure PM excitation.

Characteristic analysis of parallel-rotor hybrid generator based on exciter types

In this paper, a characteristic analysis and a performance comparison of a permanent magnet (PM) exciter and a conventional winding exciter for a parallel-rotor-type hybrid generator is presented. The proposed rotor of the hybrid generator comprises two separate structures, a PM and a field winding. The two rotors are attached in parallel to improve the efficiency and self-starting characteristics. Using this configuration, the PM rotor produces base flux to generate enough no-load voltage and the field winding rotor is used to regulate that output voltage. Because of the PM rotor flux, the automatic voltage regulator can self-start the generator by taking the voltage induced by the PM flux, regardless of the exciter. The self-start capability, dynamic response and efficiency of both exciters are compared and investigated. It can be confirmed through experiments that the PM exciter shows better efficiency and dynamic response with reduced mechanical complexity.

Research on a hybrid excitation PM synchronous generator with stator third harmonic winding excitation

This study presents a hybrid excitation permanent magnet synchronous generator (HEPMSG) with a stator third harmonic winding to solve the problems of adjusting the air-gap magnetic field of the permanent magnet synchronous machine (PMSM) and simplify the excitation system structure. The electromotive force (EMF) of the stator third harmonic winding, induced by the inherent third harmonic magnetic field in the air gap, provides the adjustable field current for the rotor field winding via the controllable rectification. The proposed machine structure is described, and the generation mechanism and the excitation principle of the stator third harmonic EMF are analysed. The conditions for maximum excitation current output are discussed, and the integrated design methods of the stator third harmonic winding and the rotor excitation winding are described. Based on the finite element method, the performances of the third harmonic excitation system are numerically compared for different stator third harmonic windings, and the open-circuit voltage regulation characteristics under different control angles are analysed. A 2.5 kW HEPMSG prototype with a stator third harmonic winding is manufactured and tested. The predicted and experimental results are in good agreement, which verifies the correctness of the excitation principle of the proposed HEPMSG.

Cogging Torque Reduction in Double-Rotor Hybrid Excited Axial Switched-Flux Permanent Magnet Machine

In this paper, a novel double-rotor hybrid excited axial switched-flux permanent magnet (DRHE-ASFPM) machine incorporating the advantages of the axial switched-flux permanent magnet (PM) machine and wound field synchronous machine is investigated. Similar to the switched-flux PM machine, there is a large undesired cogging torque in the DRHE-ASFPM machine because of high air-gap density and strong flux-focusing effect. This paper presents and compares three cogging torque reduction techniques in the DRHE-ASFPM machine, including stator/rotor teeth notching, stator slot chamfering, as well as stator slot chamfering and teeth notching (SCTN). The analytical expression of the cogging torque is derived and three methods are analyzed and compared in detail. As verified by 3-D finite element (FE) method, the SCTN technique can effectively reduce the cogging torque extremely, but slightly decrease the output torque under both PM and hybrid excitation modes. Finally, an optimized prototype machine with SCTN structure is manufactured, and the experiment is performed to validate the FE predicted results.

Design and performance analysis of various high torque segmented rotor HE‐FSM topologies for aircraft applications

Electrical machines for aircraft applications require basic characteristics such as lightweight, high reliability, fault tolerance ability, and torque power and higher densities. Correspondingly, hybrid excitation flux switching machines (HE-FSMs) are capable of producing significant characteristics of high torque and power by improving flux strengthening in the iron core. However, magnetic flux cancellation and leakage in HE-FSMs cause the reduction of flux linkage created by permanent magnet (PM) and field excitation (FE), which leads to deterioration of electromagnetic torque. This study presents magnetic flux performance and comparison of various topologies of HE-FSMs by employing different positions of PMs and FE coils on the stator core. The purpose of a segmented rotor is to deliver a well-defined electromagnetic flux pathway for carrying magnetic flux to nearby armature coil on stator with rotor rotation to improve the flux strengthening. Moreover, magnetic performances of various proposed HE-FSMs at different positions of PMs are investigated and compared based on 2D finite element analysis. Subsequently, the enhanced HE-FSM III has successfully achieved flux strengthening of 22%, torque of 54% and power of 61% more than initial design of HE FSM I, respectively. In conclusion, the proposed HE-FSM structures show the capability to match high torque and power for aircraft applications.

Метод настройки нечеткой системы управления ветрогенератора с возбуждением от постоянных магнитов

Метод настройки нечеткой системы управления ветрогенератора с возбуждением от постоянных магнитов

Analysis of magnetic field distribution in a transverse-flux linear motor with superconducting windings

The influence of permanent magnet excitation on HTS coil in transverse-flux linear motor is analyzed. Numerical analysis using finite-element method is carried for two commonly used magnet arrays - alternating and Halbach. The influence of magnet arrangements on critical current density of HTS winding operating in temperature of liquid nitogen of 77 K is examined. The goal is to find optimal air gap size and magnet span to assure the best performance of the motor where anisotropy of superconductor is taken into account.

Design and analysis of a new partitioned stator flux‐modulation motor for direct drive applications

In this study, in order to improve the torque density of the conventional permanent magnet (PM) motor, a flux-modulation (FM) motor employing the magnetic gear effect is proposed. However, the FM motor has space conflict in the finite stator area, which limits the further improvement of torque density. Therefore, a new partitioned stator flux-modulation (PSFM) motor with separated PM excitation and armature windings is artfully proposed. The main design parameters influence on the average electromagnetic torque in the proposed PSFM motor is investigated, together with the proposed FM motor. Furthermore, based on the optimal designs for the highest average electromagnetic torque in this study, the electromagnetic performances of the three motors, including back-electromotive force performances, torque characteristics and several other performances with respect to speed are analysed by finite-element method. Additionally in the PSFM motor, torque generation mechanism and the reduction method of torque ripple are theoretically analysed. Results show that the proposed PSFM motor exhibits 29.1% higher torque density than the FM motor and 87.6% higher than the conventional PM motor with reduced torque ripple and superior loss performance. Finally, the proposed PSFM motor is prototyped for verification.

Design and Multi-Objective Stratified Optimization of a Less-Rare-Earth Hybrid Permanent Magnets Motor With High Torque Density and Low Cost

The price fluctuation and the unstable supply chain of rare-earth permanent magnet (PM) have posed potential risks for further application of rare-earth PM motors. To alleviate the consumption of rare-earth PM material, a less-rare-earth PM brushless motor with two types of PM materials is proposed in this paper. The key of this motor is that the rare-earth PM is purposely combined with a non-rare-earth ferrite PM, forming the hybrid PM excitation. To design the proposed motor efficiently, a multi-objective stratified optimization strategy is proposed, where the selected five optimization objectives of output torque, PM cost, cogging torque, torque ripple, and efficiency are divided into two levels. Then, different optimization methods are skillfully combined to meet the specific design requirements. The corresponding electromagnetic performances are analyzed and compared with the baseline rare-earth PM brushless motor. Finally, several experiments of the two motors are carried out for evaluation. Both theoretical analysis and experimental results verify the feasibility and validity of the proposed motor and the optimization method.