Machine Air Gap Research Articles

Analytical-based investigation of consequent poles permanent magnet machine: improved air gap flux density formulation

Purpose This paper aims to an analytical investigation of a consequent poles (CP) permanent magnet machine, to enhance the accuracy of the predicted air gap flux density and thus of the machine performance. Design/methodology/approach The machine under study is obtained by the substitution of the poles machines (PMs) that corresponds to south poles, of a conventional surface PM (SPM) machine, by iron pieces of same geometry. First, the analytical model of the air gap flux density generated by a SPM topology is presented. To fit the CP concept, such model has been rearranged based on a virtual SPM machine. Then, an improved prediction of the CP machine air gap flux density is addressed by the incorporation of a south pole rotor correction function. Findings An improved prediction of the consequent pole PM machines air gap flux density is addressed by the incorporation of a south pole rotor correction function. Originality/value The paper proposes an original approach to enhance the prediction of the air gap flux density of consequent pole machines despite the different magnetic permeability of the north and south poles.

HARMONIC ANALYSIS OF MAGNETOMOTIVE FORCE IN THE AIR GAP OF SIX-PHASE ASYNCHRONOUS MACHINES

Asynchronous motors with six and more phases (usually n-three-phase) are increasingly accepted in electric drive systems of road transport, marine and even aeronautical transport. Multiphase machines are credited with multiple advantages such as: less torque ripple, better power distribution per phase, higher efficiency and fault tolerance capability compared to traditional three-phase machines. There are many publications, but few of them are dedicated to the in-depth study of the multiphase motor (m>3) and especially of the magnetic field in its air gap. The purpose of the present paper: the development of the mathematical model of the magnetomotive force in the air gap of the six-phase asynchronous machines, which determines the fundamental properties of the machine, the structure of the magnetic field and the torque developed, the efficiency, the error tolerance. The research is based on analytical studies and the results of suitable experimental measurements. The paper presents the mathematical model for the harmonic analysis of the magnetomotive force in the air gap of six-phase machines with possible variants of windings on the stator. Based on this study, it was demonstrated that only n-three-phase machines with asymmetrically arranged stator windings have the ability to attenuate higher harmonics with a major negative effect on the developed torque, the applicability and efficiency of traditional tools for reducing higher harmonics in the case of six-phase machines was confirmed. The results of measurements carried out on samples of six-phase machines confirm the findings and conclusions formulated in the paper.

Torque Ripple Reduction in Brushless Wound Rotor Vernier Machine Using Third-Harmonic Multi-Layer Winding

This article aims to realize the brushless operation of a wound rotor vernier machine (WRVM) by a third-harmonic field produced through stator auxiliary winding (X). In the conventional model, a third-harmonic current is generated by connecting a 4-pole armature and 12-pole excitation windings serially with a three-phase diode rectifier to develop a pulsating field in the airgap of a machine. However, in the proposed model, the ABC winding is supplied by a three-phase current source inverter, whereas the auxiliary winding (X) carries no current due to an open circuit. The fundamental MMF component developed in the machine airgap creates a four-pole stator field, while the third-harmonic MMF induces the harmonic current in the specialized rotor harmonic winding. The rotor on the other side contains the harmonic and the field windings connected through a full-bridge rectifier. The electromagnetic interaction of the stator and rotor fields generates torque. Due to the open-circuited winding pattern, the proposed machine results in a low torque ripple. A 2D model is designed using JMAG-Designer, and 2D field element analysis (FEA) is carried out to determine the output torque and machine’s efficiency. A comparative performance analysis of both the conventional and proposed topologies is discussed graphically. The quantitative analysis of the proposed topology shows better performance as compared to the recently developed third-harmonic-based brushless WRVM topology in terms of output torque and torque ripples.

Design advantages and analysis of a novel five-phase doubly-fed induction generator

PurposeThe purpose of this paper is to provide an analysis of the performance of a new five-phase doubly fed induction generator (DFIG).Design/methodology/approachThis paper presents the results of a research work related to five-phase DFIG framing, including the development of an analytical model, FEM analysis as well as the results of laboratory tests of the prototype. The proposed behavioral level analytical model is based on the winding function approach. The developed DFIG model was used at the design stage to simulate the generator’s no-load and load state. Then, the results of the FEM analysis were shown and compared with the results of laboratory tests of selected DFIG operating states.FindingsThe paper provides the results of analytical and FEM simulation and measurement tests of the new five-phase dual-feed induction generator. The use of the MATLAB Simscape modeling language allows for easy and quick implementation of the model. Design assumptions and analytical model-based analysis have been verified using FEM analysis and measurements performed on the prototype. The results of the presented research validate the design process as well as show the five-phase winding design advantage over the three-phase solution regarding the control winding power quality.Research limitations/implicationsThe main disadvantage of the winding function approach-based model development is the simplification regarding omitting the tangential airgap flux density component. However, this fault only applies to large airgap machines and is insignificant in induction machines. The results of the DFIG analyses were limited to the basic operating states of the generator, i.e. the no-load state, the inductive and resistive load.Practical implicationsThe novel DFIG with five phase rotor control winding can operate as a regular three-phase machine in an electric power generation system and allows for improved control winding power quality of the proposed electrical energy generation system. This increase in power quality is due to the rotor control windings inverter-based PWM supply voltage, which operates with a wider per-phase supply voltage range than a three-phase system. This phenomenon was quantified using control winding current harmonic analysis.Originality/valueThe paper provides the results of analytical and FEM simulation and measurement tests of the new five-phase dual-feed induction generator.

Power flow in the air gap of linear electrical machines by utilisation of the Poynting vector: Part 2 ‐ simulations

Different types of linear generators are simulated and their power flow in the air gap is investigated. The results are compared to the analytical expressions derived in Part 1. The simulations and the analytical expressions in Part 1 show the same general behaviour, but the magnitudes are lower for the analytical expressions. One explanation for the difference in magnitude can be that the harmonics of the electric and magnetic fields contribute to the power flow, which is not accounted for in the analytical expressions. Due to results from Part 1, it is investigated if changing the number of poles can decrease the tangential power flow while the normal power flow stays the same. As was suspected, changing the number of poles affected several other factors, which lead to an increase in the normal power flow when increasing the number of poles, even though the electrical power was the same. The tangential power flow also decreased for three out of four generators. Thereby, increasing the number of poles while keeping the same length of the machine, at the cost of reduced pole-pitch, should be done with precaution.

Computational Modeling of an Axial Airgap Induction Motor With a Solid Rotor

This article presents analytical calculations of an axial airgap or disk induction machine with a solid rotor. A quasi-3-D analytical analysis for the eddy current estimation in the solid disk rotor and 1-D and 2-D analytical analyses for the torque calculation are performed. The third-dimension effect in 1-D and 2-D analytical analyses is estimated by quasi-3-D analytical calculations of the eddy currents in the solid disk rotor. The analytical calculations are compared with the 3-D finite element method (FEM) and experimental results of a solid-rotor axial airgap induction motor. The analytical calculations are also used for the optimization of the axial airgap machine to improve torque characteristics at higher speeds.

Power flow in the air gap of linear electrical machines by utilization of the Poynting vector: Part 1 ‐ Analytical expressions

Analytical solutions and estimations for the power flow in the air gap of linear electrical machines of different geometries are derived from Poynting's theorem. The different geometries considered are flat one-sided, multi-sided, and tubular linear electrical machines. The radial power flow for all considered geometries is dependent on the area of the air gap, the electric field, the magnetic field, and the load angle. The tangential power flow for both flat one-sided and tubular linear electrical machines is dependent of the area of the air gap, number of poles, the electric field, the magnetic field, and the load angle. The number of poles could be increased to decrease the tangential power flow in flat linear electrical machines. The expression for the tangential flow in tubular linear electrical machines is so complicated that it is difficult to draw conclusions from it.

Instantaneous Electromagnetic Torque Components in Synchronous Motors Fed by Load-Commutated Inverters

This paper proposes time-domain analytical expressions of the instantaneous pulsating torque components in a synchronous machine air gap when supplied by a load-commutated-inverter (LCI) system. The LCI technology is one of the most used variable frequency drives when very high power and low speed are required in applications such as pipeline recompression and decompression, as well as liquefied natural gas compression. In such applications, synchronous motors are used because of their high efficiency resulting from a separated supply of the current to their rotor through the excitation circuit. These applications usually have long and flexible shafts, which are very sensitive to torsional vibration excitation when their natural frequencies interact with any external torque applied to the shaft. A torsional analysis is required by international standards to assess the survivability of the shaft through the overall speed range of the motor. Therefore, the magnitude and frequencies of the motor air-gap torque are needed for such evaluation. The proposed developments are supported by numerical simulations of LCI systems in a large range of operation range. From the simulation results, torque harmonic families are derived and expressed in a parametric form, which confirm the accuracy of the proposed relationships.

Condition monitoring and severity estimation of rotor demagnetisation fault using magnetic flux measurement data

This article studies and investigate the magnetic characteristics of a surface mounted permanent magnet (SPM)-type brushless direct current (BLDC) motor when subjected to demagnetisation fault conditions. The proposed research subjugates the limitation of estimating the State of Health (SoH) of a BLDC motor drive when deployed in electric vehicle (EV) applications. Demagnetisation faults adversely affect the performance of a machine and indirectly the EV drive system, bringing significant transformation in the machine’s characteristics and quantities. The novel method of measuring the radial magnetic field (Bg) across the machine airgap assists in diagnosing and estimating the % severity of faults under the subjected fault conditions. A numerical co-simulation-based model of a BLDC motor is developed to investigate the performance of the machine under both healthy and fault conditions. The BLDC motor being studied is operated using a field programmable gate array (FPGA) based control drive adopting a hysteresis current control (HCC) technique. The experimental investigation of a complete BLDC motor test drive is carried out with an FPGA-based algorithm developed on the Xilinx ISE tool. The outcomes obtained are validated with the numerical results obtained through a finite element (FE) analysis. The proposed study uses a fluxgate sensor for experimental measurement of the flux density of a BLDC motor drive, which is vital for estimating the fault severity and scheduling the maintenance accordingly. The experimental investigations are found to be in validation with the proposed techniques in estimating the health of a BLDC motor-driven EV drive system.

Multi-physics design and analyses of dual rotor synchronous reluctance machine

Dual rotor topology of synchronous reluctance machine is here proposed to improve the motor torque density and reduce the torque ripple. Thus, allowing synchronous reluctance machine to merge into EV and HEV applications. This paper presents a multi-physics design and analyses of three double rotor synchronous reluctance machine, 24/4, 36/4 and 48/4 stator slot/rotor pole combinations, through electromagnetic, mechanical and thermal analysis. First, a genetic algorithm optimization process linked to magnetic FEA has been used. The optimization is set to target the highest torque, lowest torque ripple and core loss. Mechanical study and investigation of the magnetic and rotational forces on the rotor ribs and stator tooth-tip structure have been considered to guarantee the mechanical robustness. Furthermore, the design assembly structure to ease heat dissipation from the stator has been investigated thermally. Finally, a comparison with a conventional single-rotor synchronous reluctance machine having the same size and operating conditions have been made to highlight the advantages of the double rotor synchronous reluctance machine. From the comparison it has been concluded that the double rotor machine produced 45% higher torque and 40% less torque ripple compared to its single rotor counterpart. Synchronous Reluctance Machines, Double Rotor Machine, Structural Analysis, Double Airgap Machines. • The design of a novel double rotor synchronous reluctance machine is presented. • A multi-physics design process and genetic algorithm global optimization are used. • The double rotor machine showed higher power density when compared to the single rotor. • Lower torque ripple is found in the double rotor machine when compared to the single rotor. • The higher power density and lower torque ripple are essential for automotive application.

A novel analytical calculation of magnetic field in the slotted air gap of spoke-type permanent-magnet machines using conformal mapping

This paper presented a novel analytical method for calculating magnetic field in the slotted air gap of spoke-type permanent-magnet machines using conformal mapping. Firstly, flux density without slots and complex relative air-gap permeance of slotted air gap are derived from conformal transformation separately. Secondly, they are combined in order to obtain normalized flux density taking account into the slots effect. The finite element (FE) results confirmed the validity of the analytical method for predicting magnetic field and back electromotive force (BEMF) in the slotted air gap of spoke-type permanent-magnet machines. In comparison with FE result, the analytical solution yields higher peak value of cogging torque.

Influence of winding topologies and encapsulation materials on FSPM machine thermal performance

This study investigates the thermal impact of using different winding topologies and different winding encapsulation materials on dual-stator 6/4 flux-switching permanent magnet (FSPM) machine with water jacket cooling. The thermal performance of four different design cases are compared using lumped-parameter thermal network models. The modelling of the heat transfer in the stator slot, machine air gap and water jacket channel are presented. It is shown that FSPM machines with circumferential winding and toroidal winding have different thermal limiting components and the winding encapsulation material has a different impact on the thermal performance of the two winding topologies. Prototype motors are built and tested to validate the thermal models.

Design and fault tolerant analysis of five-phase permanent magnet synchronous motor

<span lang="EN-IN">This paper presents a design of 15-slot/12-pole, five-phase, surface-mounted permanent magnet synchronous motor (PMSM). The five-phase PMSM can be an attractive solution to few applications that demand fault tolerant capability such as in aerospace engineering and electric propulsion. The motor model is first investigated based on the implementation of analytical method. The analytical method derived from the subdomain model of the permanent magnet machine is initially applied to estimate the magnetic flux density distributions for the radial component <em>B</em><sub>r</sub> and the tangential component <em>B</em><sub>t</sub> in the machine air gap. Other important motor characteristics such as phase back-EMF, line back-EMF, cogging torque and electromagnetic torque are also calculated. The analytically calculated results are then compared with the numerical method in a 2D finite element analysis. Additionally, the capability of this PMSM model against faulty conditions are further investigated. The results show that the analytical model of the 15-slot/12-pole, five-phase PMSM provides very accurate motor performance within acceptable error margin. For instance, the average electromagnetic torques, inclusive of the cogging torque, as computed by the analytical and numerical methods are 5.53Nm and 5.33Nm respectively, yielding an error of 3.6%. During faulty conditions, the PMSM can possibly continue to operate with lower output torque, about 60% to 80% of its rated torque, when one-phase or two phase windings are out of service.</span>

Thermal Deformation Analysis of Water Cooling Doubly Salient Brushless DC Generator With Stator Field Winding

Thermal deformation changes the length of a variable reluctance machine's air gap; this change has a significant effect on the machine's power density and efficiency. The variable reluctance machine usually has a small air gap, which may cause scrapping failure (due to thermal deformation). Therefore, it is necessary to study the influence of thermal deformation on air gap length in order to avoid scrapping failure and to choose an optimal air gap length. The doubly salient brushless dc (DSBLDC) generator is a variable reluctance machine with stator field winding. Water cooling is the usual method for cooling a DSBLDC generator (as all excitation sources are mounted on the stator). In this paper, a water-cooling DSBLDC generator is employed to analyze thermal deformation. First, the configuration of the DSBLDC generator is introduced and the thermal distribution characteristics of the water-cooling DSBLDC generator are given. Second, the DSBLDC generator is separated into a yoke and pole in order to investigate its thermal deformation. A theoretical calculation model and a three-dimensional finite-element model are then proposed to analyze the thermal deformation. The influence of thermal deformation on the stator, rotor, and air gap length is further analyzed under different temperature distribution conditions. Finally, thermal deformation's influence on output performance is discussed and the calculation and analysis of thermal deformation are verified through experimental results.

Fault-Tolerant Operation of Wound Field Synchronous Machine Using Coil Switching

This paper proposes a fault tolerant operation of a wound field synchronous machine (WFSM) under the loss of excitation (LOE) fault in the rotor field winding. A two-mode field excitation scheme is presented, where the rotor of the WFSM was modified, and an additional harmonic winding is introduced with a rotating bridge rectifier. Mode I is the conventional direct dc supply field excitation using slip-rings and brushes, whereas mode II, is the brushless field excitation under an LOE fault, resulting in an unregulated field current. During mode II, a special coil switching is performed in the stator. Consequently, the stator winding creates an additional sub-harmonic component of the magneto-motive force (MMF) in the machine air gap along with the fundamental MMF component. The additional sub-harmonic MMF is induced in the rotor harmonic winding. A rotating diode bridge rectifier mounted on the rotor periphery rectifies the harmonic winding ac, and a stable dc was supplied to the rotor field winding. The decoupling between the additional rotor harmonic winding and stator winding is analyzed. The 2-D finite-element analysis (FEA) was performed to analyze the proposed idea. The FEA results were validated by experiments based on a 1-kW prototype.

Multidomain Optimization of High-Power-Density PM Electrical Machines for System Architecture Selection

The power density of electrical machines for transport applications has become a critical aspect and target of optimization. This paper looks at the development of an intelligent, rapid, flexible, and multidomain tool to aid for system-level optimization of electrical machines within next-generation high power density applications. The electromagnetic, thermal, and mechanical aspects are wholly integrated, thus enabling the optimization including the nonactive mass. The implementation and overall architecture of the tool are described, and using a case study drawn from the aerospace industry, the tool is used to compare the power density of various surface permanent magnet topologies including single airgap and dual airgap machines, highlighting the particular suitability of the dual rotor topology in achieving the best power to mass ratio. Finally, the accuracy of the tool is highlighted by practical realization and experimental validation.

Winding Function Approach for Winding Analysis

The winding factor is an operand in order to consider the effect of winding distribution and chording on the spatial distribution of the magnetic field in the air gap of synchronous and induction machines. The sinusoidal functions for winding factor calculation presented in literature are not defined and valid for every irregular winding, e.g., single-layer fractional-slot, combined star-delta, multilayer (greater than two), and asymmetrical windings. Although the summation of induced voltage phasors (star of slots) is the most accurate method, asymmetrical windings require to be decomposed in symmetrical components. In this paper, in addition to deriving the symmetrical components for asymmetrical multiphase windings, the analytical formulation is presented to relate the harmonic content of winding functions to winding factors. The harmonic leakage factor is accurately formulated from the winding function instead of the Gorges diagram without the need for summing up an infinite number of normalized winding factors quadratically. Without restriction of the number of layers and the distribution of the winding, including full-pitch, chorded and fractional-slot symmetrical and asymmetrical windings, the suggested analysis method is validated with the star of slots and sinusoidal functions of distribution and pitch factors, where applicable.

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.

Getting Rare-Earth Magnets Out of EV Traction Machines: A review of the many approaches being pursued to minimize or eliminate rare-earth magnets from future EV drivetrains

There are now more than 1.5 million plug-in hybrid electric vehicles (HEVs) and battery electric vehicles (BEVs) that have been commercially produced in the world during the past 11 years, and it is likely that the number produced during 2016 exceeded 700,000, a new record. A large percentage of those electrified vehicles use ac permanent magnet (PM) synchronous machines for the traction machines used in their drivetrains. Even more specifically, nearly all of these PM synchronous machines fall into the class of interior PM (IPM) synchronous machines. The origin of this name becomes apparent by inspecting the cross section of a typical IPM machine in Figure 1 that has been simplified to highlight the key features. This figure shows that the magnets are buried in cavities inside the rotor, and the cavities are carefully shaped, often in V configurations, to concentrate more of the PM magnetic flux into the machine's air gap.

Потери от вихревых токов в массиве постоянных магнитов магнитоэлектрических вентильных двигателей

Higher harmonic components of magnetic field in the air gap of permanent-magnet electrical machines cause eddy currents to occur in the bodies of permanent magnets, due to which the latter become heated and partially demagnetized. Expressions for the coordinate components of magnetic induction and eddy current density in the magnet body (given the known value of the n-th harmonic component of magnetic inductance on the magnet external surface) are obtained proceeding from analytical solution of the well-known Maxwell equations for the n-th harmonic component of magnetic field. It is shown that the electromagnetic wave energy enters into the magnet through the external cylindrical surface and lateral radial flat edges. It is also found that the power flux surface density in the first channel is constant, whereas that in the two other channels decreases exponentially in the radial direction. Therefore, it is not expedient to subdivide the pole magnet into elementary tiles in the transverse direction from the viewpoint of losses, because the losses in the first channel remain unchanged (i.e., they are invariant to decomposition), whereas the losses in the second channel increase (the total number of tile lateral edges increases in decomposing the magnet). The article presents a quantitative assessment of losses in samarium-cobalt magnets of a switched motor with a capacity of 15 kW due to a slotted stator surface outline, a non-sinusoidal waveform of the frequency converter voltage, and higher harmonic components of the stator winding MMF.