No-load Back Electromotive Force Research Articles

Design and Analysis of a Hybridly Excited Asymmetric Stator Pole Doubly Salient Machine

This article presents the design and analysis of a 12/7 (numbers of stator/rotor poles) hybridly excited asymmetric stator pole doubly salient machine (HEASPDSM) with a main focus on the special topology and operational principle by using the analytical and 2-D finite element analysis. A full comparison is conducted on the average torque, torque ripples, no-load back electromotive force and flux regulation capacity under the condition of different structural parameters, which can provide good references to the machine design. A 12/7 HEASPDSM is designed and the main performance indexes are analyzed in detail. Based on the parameters, the performance of 12/7 HEASPDSM is compared with traditional 6/7 doubly salient permanent magnet machine (DSPMM) with the same volume and thermal load. Finally, a prototype of the 12/7 HEASPDSM is manufactured and tested to validate the theoretical analysis. The results fully demonstrate that the HEASPDSM possesses the merits of strong flux regulation capability, higher torque density, and wider constant power speed range benefitted from the dc field winding than the traditional DSPMM.

Reduction of Radial Electromagnetic Force Waves Based on PM Segmentation in SPMSMs

Electromagnetic vibration is excited by the electromagnetic force waves generated by the air-gap magnetic field acting on the machine core. In this article, a fast and accurate calculation method of radial electromagnetic force density of surface-mounted permanent-magnet synchronous motors (SPMSMs) is proposed, and the radial force density including amplitude, frequency, and order is obtained. Comprehensively considering that the effect of the PM segmentation on electromagnetic force waves, cogging torque, and the no-load back electromotive force (back EMF), the optimal determination of the number of PM segmentation in different slot-pole combinations of SPMSMs is summarized, and six slot-pole combinations of SPMSMs with 6p36s, 4p36s, 6p9s, 8p9s, 8p12s, and 10p12s are calculated and analyzed to verify the universality of the conclusions, which lays a theoretical foundation for the weakening of the radial electromagnetic force.

Comparative study of thrust of U-shaped ironless permanent magnet synchronous linear motor based on analytical method and finite element analysis

Due to the large transverse edge effect for U-shaped ironless permanent magnet synchronous linear motor affect the distribution of air gap magnetic field is large, it will reduce the no-load back electromotive force and thrust. This paper proposes a novel method to evaluate the effect of transverse edge effect based on Kriging surrogate model. By comparing the results of the two-dimensional and three-dimensional finite element analysis of the air gap magnetic field of the motor, it can be seen transverse length of the motor, air gap height and thickness of the permanent magnet are the main influencing factors.

A Novel 24-Slot/10-Pole Dual Three-Phase Fractional-Slot Overlapped Winding for Low Non-Working Space Harmonics and Stator Modularization

This paper proposes a novel 24-slot/10-pole dual three-phase (DTP) fractional-slot overlapped winding, which can simultaneously achieve the goals of low non-working space harmonics and stator modularization. Moreover, the proposed winding inherits the majority of the merits of conventional fractional-slot concentrated winding (FSCW), such as low cogging torque, low torque ripple and short end-windings. The winding configuration of the proposal is described first, and then its magnetomotive force (MMF) analysis is conducted to calculate the winding factors by using the star of slots. According to the theoretical analysis, the harmonic reduction mechanism of the proposal is expounded in depth. In addition, a specific case of a permanent magnet synchronous machine (PMSM) equipped with the proposal is analyzed and compared with two PMSMs equipped with DTP-FSCW and two-slot-pitch fractional-slot winding (TSP-FSW) respectively by finite element method (FEM) in terms of no-load back electromotive force (EMF), cogging torque, armature reaction field, on-load torque, efficiency, and fault tolerance. A prototype with the proposed winding is built and tested to verify the theoretical analysis and numerical simulations.

Establishment of a New Dual Rotor Flux Switching Motor Magnetic Circuit Model and Optimization of No-Load Back EMF

A novel double rotor flux switching motor with a better output torque performance is proposed. The equivalent magnetic circuit model and the simplified equivalent magnetic circuit model of the motor are established, and the equations for calculating the main flux and the main flux density of the motor are derived. Finally, the Taguchi method is introduced into the optimization design of the dual rotor flux switching motor proposed in this article. A reasonable orthogonal test is designed. By comparison and analysis of the test results, it verifies that this optimization design can not only reduce the high-order harmonic content of no-load back electromotive force (EMF) but also improve the sinusoidal degree of no-load back EMF waveform.

Analysis of a Novel Hybrid-PM Variable-Flux Machine Using New Magnet Material CeFeB

Electric vehicle (EV) is a promising technology for saving fossil energy and reducing pollution. Hybrid-permanent-magnet (PM) variable-flux machine is a competitive candidate for EV propulsion since it has wide speed range and high efficiency at high-speed region. A novel hybrid-PM variable-flux machine with magnetic barriers is proposed in this paper, and a new magnet material CeFeB is used. The structure and operating principle are introduced, and different magnetization states of the machine are analyzed. The equivalent magnetic circuit model of the machine is established considering the influence of magnetic barriers, and the model is proven with good precision for the calculation of air gap flux density and PM operating point. The electromagnetic performances are analyzed, and compared with a traditional variable-flux machine. It is verified that the added magnetic barriers improve the distribution of air gap flux and load magnetization performance of the machine. The no-load back electromotive force, electromagnetic torque, speed range, and load magnetization ratio of the proposed scheme are all improved.

The DMCM-Based Analytical Calculation of Radial Vibration Force in a Nonsalient Pole Synchronous Generator in No-Load Conditions

In this paper, the distributed magnetic circuit method (DMCM) is used to calculate the magnetic circuit of a nonsalient pole synchronous generator and deal with the saturation effect of the iron-core material. The conformal transformation method is adopted for calculating the air-gap relative permeance to determine the slot effects of both the stator and the rotor and obtain the spatial and temporal distribution of air-gap flux density and radial vibration force wave. The results of the analytical calculation are very consistent with those of the finite-element method (FEM) and the time (8.47 s) spent on the calculation by the DMCM is much less than the time by the FEM (40 min 45 s). Through measuring the no-load back electromotive force waveform of the generator and the vibration acceleration spectrum of the generator feet, the DMCM is proved to be correct and effective, which will provide the theoretical basis for the accurate design of a magnetic circuit of the generator and for the quantitative analysis of its electromagnetic vibration.

The Influence of Stator Winding Turns on the Steady-State Performances of Line-Start Permanent Magnet Synchronous Motors

The variation of stator winding turns will directly affect the key parameters of a motor, such as winding resistance and winding reactance, which further affect the steady-state performance of the motor. In order to get excellent steady-state performance from line-start permanent magnet synchronous motors (LSPMSMs) under different load powers, taking an 11 kW LSPMSM as an example, the finite element method (FEM), combined with the steady-state phasor diagram and torque angle characteristic, are used in this paper for the optimal design of the stator winding turns of the prototype. The correctness of the model is verified by comparing the experimental data with the calculated data. First, the influences of different stator winding turns on the no-load, back-induced electromotive force (EMF), as well as on inductance and overload ability are studied, and the variation mechanism is obtained. In addition, from the perspective of the torque angle characteristic, the influence of the change in synchronous inductance caused by the number of turns on the steady-state power angle is studied. Second, the variation of the current and power factors with turn number is obtained by studying the steady-state power angle and end voltage. Based on the coupling relationship between the no-load back EMF and the power angle, the mechanism of non-linear variation of current and power factor is revealed. Finally, the variation of the number of turns on the core loss and eddy current loss is analyzed under various operating conditions, and the variation mechanism is revealed, based on the armature reaction theory.

Back EMF, Torque–Angle, and Core Loss Characterization of a Variable-Flux Permanent-Magnet Machine

An appropriate torque–angle selection can improve the torque-to-current ratio of a machine, converter size, and provide an optimal motor operation. A precise information of the back electromotive force (EMF) helps estimating the magnet flux linkage. An accurate determination of the core loss leads to a better machine design and efficiency estimation. This paper presents the back EMF, flux linkage, torque–angle, and core loss characterization of a variable-flux permanent-magnet machine. The magnetic properties of AlNiCo 9 magnet and the process of magnetization and demagnetization are also described. The no-load back EMF, torque–angle curves, and no-load core losses are measured and simulated for a 7.5-hp variable-flux machine for three different magnetization levels. Static torque–angle curves are obtained by varying the current advance angle and the rotor position. Simulations are performed using three different machine design softwares to validate the design, software accuracy, and machine models. The core losses are also obtained using an analytical method, which is first utilized to calculate losses in M19G29 laminations, and then implemented to estimate the core losses of the prototyped variable-flux machine. The experimental results are found to be in a good agreement with the simulation and the core losses compared well with the analytical data.

Design and Analysis of Double-Air-Gap Flux-Modulated Permanent Magnet Motor Considering Leading Working Harmonics

In nature, to flux-modulated permanent magnet (FMPM) motors, the electromagnetic energy transmission is realized by abundant harmonics in the air-gap field. It means that, under the flux modulation effect, the harmonics in FMPM motors play an important role for motor performances. In this paper, by incorporating the concept of harmonics design into motor design process, a double-air-gap FMPM motor considering leading working harmonics is proposed and studied for potential applications of electric vehicles or electric tractors. First, the leading working harmonics are distinguished and chosen conveniently by evaluating the contributions of diverse harmonics to PM flux linkage. Then, a correlation design between the harmonic characteristics and geometric parameters is implemented based on the selected leading harmonics. In addition, the motor performances are evaluated by using the finite-element method, consisting of the air-gap harmonic analysis, no-load back-electromotive force, and torque performances. Finally, the theoretical analysis and computational results verify the effectiveness of the proposed motor.

Mode Recognition and Fault Positioning of Permanent Magnet Demagnetization for PMSM

This paper proposes a demagnetization fault detection, mode recognition, magnetic pole positioning, and degree evaluation method for permanent magnet synchronous motors. First, the analytical model of the single-coil no-load back electromotive force (EMF) of demagnetization fault for Permanent magnet synchronous motor (PMSM) arbitrary magnetic poles is established. In the analytical model, the single-coil no-load back EMF residual of the health state and the single magnetic pole sequential demagnetization fault are calculated and normalized. Model results are used as the fault sample database. Second, the energy interval database of the single-coil no-load back EMF residual with different numbers of magnetic pole demagnetization is established. Demagnetization fault detection and degree evaluation are performed by the real-time acquired amplitudes of the single-coil no-load back EMF residual. The number of demagnetization poles is determined by comparing the energy of the single-coil no-load back EMF residual with the energy interval database. Demagnetization mode recognition and magnetic pole positioning are realized by analyzing the correlation coefficients between normalized the single-coil no-load back EMF residual and the fault sample database. Finally, results of analysis of the finite element simulation validate the feasibility and effectiveness of the proposed method.

Optimal Slot Design of IPMSM in Railway With Independently Rotating Wheelsets

This paper proposes a quasi-semi-closed (QSC) slot design method for an open-slot-type interior permanent magnet synchronous motor (IPMSM) for independently rotating wheelsets necessary to reduce the total harmonic distortion of no-load back-electromotive force and the torque ripple in the IPMSM. Four different slot-opening models were selected-the basic model, hairpin coil model, magnetic-wedge model, and QSC-slot model-and 2-D finite-element analysis was performed under open-circuit and load operations for each of the four models. Next, the relationships among the cogging torque, the torque ripple, and the saturation phenomenon in the core were analyzed. In addition, the manufacturing process, manufacturing cost, fill factor, end-winding resistance, copper loss, and efficiency were investigated. The experimental results verify the accuracy of the proposed method.

Effects of static eccentricity on the no‐load back electromotive force of external rotor permanent magnet brushless DC motor used as in‐wheel motor

The no-load radial magnetic field and no-load back electromotive force (EMF) of external rotor permanent magnet brushless DC motor (PMBLDCM) are calculated by applying the correction coefficient of magnetic conductance here, taking into account the stator slotting and static eccentricity effects. An external rotor PMBLDCM with 51-slot/46-pole, used as in-wheel motor, is taken as an example, the analytical calculation results of the no-load back EMF are validated by the finite-element method and experiment. The influences of static eccentricity ratio on the no-load radial magnetic field and no-load back EMF are investigated based on the analytical model. The investigation shows that static eccentricity does not change the harmonic contents of no-load radial magnetic field, so it does not change the harmonic contents of three-phase no-load back EMFs. However, static eccentricity changes the space order of no-load radial magnetic field, resulting in the different total harmonic distortions of three-phase no-load back EMFs; in other words, the asymmetric distortions of three-phase no-load back EMFs are generated. The asymmetric distortions of three-phase no-load back EMFs are intensified with the increase in static eccentricity ratio.

Performance Analysis of an Axial Magnetic-Field-Modulated Brushless Double-Rotor Machine for Hybrid Electric Vehicles

The series–parallel hybrid electric vehicles (HEVs) are widely developed due to the advantages of high fuel economy and good driving performance. The electronic continuously variable transmission, which is a key part of the HEV, can be based on planetary gear or compound structure machine (CSM). The axial magnetic-field-modulated brushless double-rotor machine (AMFM-BDRM), which can be connected with a traditional permanent-magnet synchronous machine to form a CSM, is investigated in this paper. The axial tilting torque is analyzed, and the necessary condition for avoiding it is given. Compared with the single-sided topology, the double-sided AMFM-BDRM is recommended to eliminate the axial tilting torque. The influences of winding turns, diameter ratio, ferromagnetic block and permanent-magnet (PM) dimensions, air-gap length, phase current, and internal power-factor angle on the power factor and electromagnetic torque are analyzed, and it is found that the increase of power factor is sometimes at the expense of sacrificing the electromagnetic torque. The effects of speed and PM segmentation on losses are investigated, and the circumferentially double-segmented PM is selected. The influences of dissymmetry on air-gap flux density, no-load back electromotive force, electromagnetic torque, and axial magnetic force are analyzed, and it is found that the offset, tilt, and PM position deviation of the PM rotor have different degree effects on machine performances. Experiments are carried out, and the correctness of the analysis and simulation results are verified.

Comparison of the Electromagnetic Characteristics of Single-Phase Linear Oscillating Machines according to Magnetic Flux Flow

Linear oscillating machines are typically classified according to flux flow, as longitudinal and transverse flux type devices. In longitudinal flux linear oscillating machines, the direction of the current flow is perpendicular to the direction of the moving part, while the direction of the current flow in transverse flux linear oscillating machines is parallel to the direction of the moving part. Since the direction of the magnetic flux and the current are different in the two models, their electromagnetic characteristics can also be expected to be different. In this paper, we compare the electromagnetic characteristics of these two types of linear oscillating machines. For a fair evaluation of these characteristics, both models are designed to have the same stator outer diameter, permanent magnet volume, and no-load back electromotive force. In characterizing the devices, we analyze air gap flux density, flux linkage, and inductance, as well as the electromagnetic loss.

Winding Design and Analysis for a Disc-Type Permanent-Magnet Synchronous Motor with a PCB Stator

The stator structure of a disc-type permanent-magnet synchronous motor is a printed circuit board (PCB). The design of stator windings has a direct influence on motor performance and the utilization rate of the stator. However, in some respects, PCB processing technology limits the development of the disc-type electric motor with a PCB stator. For example, the wiring of the stator winding and the connections of the ends are single. In this paper, an improved winding was designed to improve the output power. The analytic expressions for the back electromotive force (EMF) and other parameters such as power, winding resistance, and eddy loss are established, respectively. According to finite-element theory, the characteristics of the improved winding and distributed winding under no load and load were simulated and analyzed. It is concluded that the improved winding not only improves no-load back EMF, along with output power and efficiency under load, but also the utilization rate of the stator was greatly improved. Finally, a prototype was made to verify the design that has a certain reference value for the design of a disc-type permanent-magnet motor with a PCB stator.

A Quasi-Three-Dimensional Magnetic Equivalent Circuit Model of a Double-Sided Axial Flux Permanent Magnet Machine Considering Local Saturation

This paper presents a quasi-three-dimensional (3-D) nonlinear magnetic equivalent circuit (MEC) model for double-sided axial flux permanent magnet machines (AFPMMs) with fractional slot concentrated windings. The proposed model can take into account not only the local magnetic saturation effect but also the 3-D flux distribution. A coupled variable permeance element is proposed in airgap modeling that captures both axial and circumferential airgap flux densities. With the help of the coupled variable permeance element, the transient magnetic field is considered by the time varying connection of the airgap and the rotor. The proposed model can be used to predict the performance of AFPMMs, including the 3-D distribution of no-load and armature airgap flux densities, no-load back electromotive force, and electromagnetic torque. In order to verify the reliability of the MEC model, two AFPMM prototypes are taken as examples, and the accuracy is verified by comparing the calculated parameters of the MEC model with the finite element analysis and experimental results. Finally, the effect of local saturation on the performances of AFPMMs is investigated.

Development and Analysis of a Novel Spherical 2-Degree-of-Freedom (2-DOF) Hybrid Stepping Motor

A novel spherical two-degree-of-freedom (2-DOF) hybrid stepping motor is proposed in this paper, which has a simple and compact mechanical structure and is easy to manufacture, assemble, control and apply. The motor is composed of two sub-motors, each of which is a hybrid stepping type with an arc-shaped stator and a specially designed bearing structure. The rotational axes of these two sub-motors cross at the sphere center, and this structure enables the 2-DOF motor to move in any direction. Due to the mutual influence of permanent magnet (PM) leakage flux between the two sub-motors, the 3-D magnetic field distribution inside the motor becomes more complex, and thus the 2-D equivalent magnetic field analysis method is proposed, with two types of 2-D equivalent motor models established. The accurate one can take into account of the PM leakage flux influence yet is only suitable for solving motor’s static and steady state problem, whilst the simplified one can solve all the problems and is applicable for the more typical situation where the PM leakage flux influence can be almost neglected via optimal structure design. A prototype of the proposed spherical 2-DOF motor with outside diameter of 50 mm is newly manufactured and experimented to validate the feasibility of motor’s operational principle, and the accuracy of both 2-D equivalent motor models is verified by the 3-D finite element analysis (3-D FEA) calculation results. Based on the 2-D equivalent motor models, the 2-D FEA is employed for the performance analysis, such as no-load back electromotive force (EMF), tooth-layer permeance harmonics, detent torque, pull-out torque, unbalanced force, etc., which is characterized by time- saving, high accuracy and good versatility.

Application of Particle Swarm Optimization Combined With Response Surface Methodology to Transverse Flux Permanent Magnet Motor Optimization

As a result of the 3-D magnetic field and complex structure, existing motor design programs are not suitable for the transverse flux permanent magnet motor (TFPMM). Hence, a method combining particle swarm optimization (PSO) algorithm and response surface methodology (RSM) is proposed to optimize a TFPMM. The optimization aims to maximize the no-load electromotive force (EMF) to get higher torque density in the same volume of the motor. First, central composite design method is adopted for experiments on geometrical design variables. Next, the finite-element method is utilized for simulations to determine the coefficients of the second-order analytical model for the RSM. The optimal solution of the model is then obtained by MATLAB PSO toolbox. Finally, we compare the optimized model with a prototype owning the same volume. The results show that with optimization, the no-load back EMF is improved by 10%, so is the output torque, which illustrates the effectiveness of the optimization method.

Lumped-parameter thermal network model and experimental research of interior pmsm for electric vehicle

A 25kW interior permanent magnet synchronous machine (IPMSM) applied to the electric vehicle is introduced in the paper. A lumped-parameter thermal network model is presented for IPMSM temperature rise calculation. Furthermore, a 3D liquid-solid coupling model considering the assembly clearance is compared with the 2D lumped-parameter thermal network model. Finally, a dynamometer platform for temperature rise measurement is established to verify the above-mentioned methods, which obtains the measured efficiency map at rated load case and overload case. At the same time, the measured no-load back electromotive Force (EMF), load line input voltage and load current are gathered. Thermocouple PTC100 is used to measure the temperature of the stator winding and iron core, and the FLUKE infrared thermal imager is applied to measure the surface temperature of PMSM and controller. Testing result shows that the lumped-parameter thermal network have a high accuracy to predict each part temperature.