Surface-mounted Permanent Magnet Motor Research Articles

Unbalanced Magnetic Force Analysis in Eccentric Surface Permanent-Magnet Motors Using an Improved Conformal Mapping Method

This paper introduces an improved conformal mapping (ICM) method for the calculation and analysis of unbalanced magnetic force (UMF) in eccentric surface-mounted permanent-magnet (SMPM) motors considering the static, dynamic, and mixed rotor eccentricities. Having the on-load air gap field components obtained through ICM, and by using the Maxwell Stress Tensor method, the ICM method accurately predicts the on-load components of magnetic local traction and UMF due to PMs, the armature reaction, and the mutual interaction between both fields under the rotor eccentricity. The other purpose of this paper is to illustrate the difference between the influences of static, dynamic, and mixed rotor eccentricities on the UMF using the ICM method. The influence of initial eccentricity angle and the magnitude of eccentricity on the UMF are also investigated under the static, dynamic, and mixed rotor eccentricities. The predicted results obtained through ICM are verified by comparing with the corresponding results obtained through finite element method and the frozen permeability method. The ICM method is also validated by the experiment.

The Development of Direct-drive High-speed Brushless Permanent Magnet Motors for Machine Tools

This paper describes the development of surface-mounted permanent magnet (SPM) motors for use in direct-drive high-speed spindle machine tools. For such applications, motors should be highly efficient, have low torque ripple, and minimal package size and weight. Based on average torque, torque ripple, and efficiency, four SPM motor designs were chosen for comparison. Two configurations, 2-pole with 3-slots and 2-pole with 18-slots, were selected for analysis. The Taguchi method was used to refine stator structure and to determined how well the selected motors reduced losses. The effect of magnet span angles and winding arrangements on torque ripple, average torque, and the efficiency of 2-pole/18-slot motors was also investigated. A thermal analysis was conducted to determine temperature distribution within the motors. The motor performance was also studied using a Matlab/Simulink model. Experimental measurements and finite element analysis (FEA) were used to examine and validate the results.

Analysis of thermal performance of an outer-rotor Surface-mounted permanent magnet (SPM) motor for electric vehicles

In this work, the heat distributions and maximum temperature variations of the rotor and stator in a SPM (Surface-mounted permanent magnet) motor were analyzed under different ambient temperatures (Tamb) and current densities (J). To achieve this, the conduction heat transfer between each of the motor components, the forced convection heat transfer inside the motor, and natural convection heat transfer between the inside of the motor and outside air were considered under steady state flow conditions. At the same time, copper loss and core loss, which are the representative motor losses, were also considered to simulate the heat generation inside the motor. To improve simulation accuracy and save time, only one-ninth part of the motor was investigated, using Finite element analysis (FEA). From these results, the operating limit temperature and current density conditions of the SPM motor were studied. It was revealed that the temperature inside the motor increased linearly as the current density increased due to the effects of stack length and core loss, and the cooling effect of the air gap was observed in most cases. At the same time, limit ranges for the stable operation of the SPM motor were suggested under various current densities (J) and ambient temperatures (Tamb). These results can be used as a database for the development of EV motor systems.

Analytical Prediction of Torque Ripple in Surface-Mounted Permanent Magnet Motors Due to Manufacturing Variations

In the production of surface-mounted permanent magnet machines, manufacturing tolerances also contribute to torque ripple. Additional harmonics of low electrical orders are created in the torque spectrum. Slight manufacturing variations develop asymmetry conditions in the rotor as well as in the stator. Finite element models can be used to analyze the magnitude of pulsating torque generated due to these asymmetries. However, due to its random nature, lack of periodicity, and symmetry, it is time consuming to study the problem with numerical methods for its uneven geometry that does not allow reduced geometrical models. Moreover, the experimental verification of all possible variations would be very challenging as it would require part dimensioning and part sorting a large quantity of motor builds and finally testing of all samples. Therefore, in this paper an analytical model is presented to study the effect of such imbalance on the torque ripple. The model shows an agreement against finite element models and also with experimental results when predicting torque harmonics that come from asymmetries.

Comparative study and performance evaluation of analytical methods for surface mounted permanent magnet brushless motors

Analysis and determination of magnetic field distribution of surface mounted permanent magnet (SMPM) motors has always been a topic of research. Though a number of methods like two-dimensional numerical and analytical methods have been proposed to evaluate the magnetic field and parameters of radial flux SMPM motors, the methods developed for axial flux permanent magnet motors are mainly three dimensional. Numerical methods provide accurate results but are not suitable for initial design analysis. The analytical methods are known for their accuracy, convenience, as well as are less time consuming than numerical methods. The analytical methods like conventional design method, magnetic equivalent circuit, generalised machine theory and Fourier analysis present in the literature for SMPM motor have been investigated in this study and the results obtained are compared and evaluated for radial flux SMPM and axial flux SMPM. Experimental results are included to demonstrate the percentage error obtained from different methods and denote the accuracy. From the comparison of different results, it can be concluded that the Fourier transform method is more realistic approach and is capable of computing the performance as well as field distribution simultaneously.

Principle and Design of a Novel Lorenz Force Type Bearingless Motor with Single-Axis Actively Regulated Capability

This paper proposes a novel Lorenz-force-type bearingless motor with single-axis actively positioned functionality. The novel motor consists of two slotless surface-mounted permanent magnet(SPM) motors, which have six skewed coils for each motor to constitute 3-phase windings and are in tandem along axial direction so as to achieve actively regulated axial motion. Additionally, two repulsive permanent magnet bearings (RPMBs) are used to passively stabilize radial- and tilting movements of the rotor. The slotless stator iron is employed for arrangement of the skewed coils in toroidal form. Compared with state-of-the-art single-axis actively controlled bearingless motors utilizing field weakening or strengthening effect of d-axis current to regulate axial movement, perhaps suffering irreversible demagnetization of permanent magnets especially at the time of start-up, the merit of this proposed motor is beneficial to prevent the demagnetization risk of permanent magnets. To verify the novel concept, firstly, theoretical analysis is carried out for modeling back electromagnetic force (back-EMF), axial force, drive torque. Followed by the analytical model, a detailed design process by integration of analytical method and finite element analysis (FEA) for the structural parameters are revealed. At last, 3-D FEA is performed to validate the correctness of analytical model, design process as well as to evaluate the performance of proposed motor.

On-line parameter identification of SPM motors based on MRAS technique

ABSTRACTThis article proposes a new parameter estimation method for surface-mounted permanent magnet (SPM) motors by employing the model reference adaptive system (MRAS) technique. The proposed algorithm is applied to an SPM motor used in washing machines. To determine washing and dewatering patterns, a washer tries to detect the size of load in the beginning of the operation. Hence it requires an accurate estimation of system parameters. The proposed estimation method identifies stator inductance and flux-linkage by using d- or q-axis current error, and its value is used for estimation independently with respect to each parameter. Therefore, the proposed scheme can get rid of the instability in inductance and flux estimation caused by the cross-coupling between d- and q- quantities. In this article, the stator resistance is detected by using the recursive least square (RLS) method to reduce measurement noises and to eliminate dead-time effect. Simulation results show that the proposed scheme tracks the parameters well even when there is transient states in rotor speed and the load conditions, and experimental results verify the validity and efficacy of the proposed algorithm.

Study of IPMSM Interturn Faults Part I: Development and Analysis of Models With Series and Parallel Winding Connections

In this study, the interturn fault (ITF) models of interior permanent magnet synchronous motors (IPMSMs) employing series and parallel winding connections were developed through the addition of saliency modeling to the surface-mounted permanent magnet motor models presented in a previous work. The saliency model was obtained by using deformed flux models based on both the fault winding flux information and inductance variations caused by cross-flux linkages that depend on the distribution of same-phase windings. By assuming a balanced three-phase current injection, positive and negative sequence voltages, and the fault current are obtained in the positive and negative synchronous reference frames. The output torque models were developed by adding the magnet and reluctance torques, which were derived from the developed models. To verify the proposed IPMSM models with an ITF, a finite element method-based simulation and experimental measurements were performed; the results are presented in this paper.

Analytical Model for Predicting Effects of Manufacturing Variations on Cogging Torque in Surface-Mounted Permanent Magnet Motors

In a mass production environment, due to the manufacturing tolerances, additional orders of cogging torque are created in addition to the fundamental components. The tolerances lead to asymmetry conditions both in the rotor as well as in the stator. Finite-element models can be used to analyze the cogging generated due to these asymmetries. However, it is extremely time consuming to study this uneven geometry numerically since periodicity and symmetry conditions cannot be used to reduce the model. Moreover, the experimental verification of all possible variations would be very challenging, as it would require part dimensioning, part sorting, a large quantity of motor builds, and finally testing of all samples. Therefore, in this paper, an analytical model is presented to study the effect of such imbalance on the cogging torque. The model is validated against finite-element models and also with experimental results.

Magnet Shape Optimization of Surface-Mounted Permanent-Magnet Motors to Reduce Harmonic Iron Losses

Surface-mounted permanent-magnet (PM) synchronous motors are widely applied to electric vehicles, where iron losses reduction is a crucial target. This paper proposes a new method of PM shape optimization to reduce the harmonics of magnetic field and, hence, iron losses. The proposed method is based on the analytical calculation of magnetic field distribution with a non-uniform PM shape, which can save much computation time compared with the parameter sweep method. The validity of the method is verified by 2-D finite-element analysis.

Analysis of permanent magnet brushless AC motor using Fourier transform approach

The paper presents an analytical model for determining performance characteristics of surface mounted permanent magnet brushless motor using Fourier transform technique. The proposed scheme assumes a simplified geometric model of surface mounted PM (SMPM) motor with dual current sheets using layer theory to analyse electrical machines. The layer theory considers regions of PMBLAC motor to be replaced by layers of respective homogeneous material properties. Isotropic model assumes stator to be sloltless while anisotropic model is also considered to account for stator slotting effect on the motor performance. The Fourier transform applicable to linear induction motor and introduced by S. Yamamura is modified and adapted for analysing PMBLAC motor. The primary stator winding and permanent magnets on rotor are replaced by their respective equivalent linear current densities. The proposed model is validated using experimental results from a 12-slot surface mounted PMBLAC motor. The proposed method is capable of calculating the effect of design parameters on the performance of the SMPM motor, thus making it suitable for design and optimisation at initial stage. Moreover, analytical validation is also presented to prove the effectiveness of the proposed method.

Comparative Study of Surface-Mounted and Interior Permanent-Magnet Motors for High-Speed Applications

This paper investigates the surface-mounted permanent-magnet (SPM) and the interior permanent-magnet (IPM) motors for high-speed applications. An SPM motor and an IPM motor are designed with the same power/speed rate and the same key dimensions. Finite-element analysis is used to compare the mechanical, electromagnetic, and antidemagnetization performances of the two motors, and lumped parameter thermal networks are involved to compare their thermal performances. It can be concluded from the comparisons that the IPM motor has comparable electromagnetic performances with the SPM motor in high-speed operations, and its costs and torque per PM weight are superior to those of the SPM motor. However, its rotor structure is not as robust and is prone to irreversible demagnetization.

Irreversible Demagnetization of Permanent Magnet in a Surface-Mounted Permanent Magnet Motor With Overhang Structure

The overhang structure is an effective solution to increase the performance of a surface-mounted permanent magnet (SPM) motor using a ferrite PM. If a ferrite PM, which can be demagnetized through a large armature reaction, is used for an SPM motor controlled by the field-weakening method, the ferrite PM can suffer from irreversible demagnetization. Moreover, if an SPM from the overhang structure is directly exposed to the armature reaction by the winding of the stator, a ferrite PM of an SPM motor could be partially demagnetized. Because of this, when the field-weakening method is used for the control of the SPM motor with the overhang structure, PMs are disadvantageous to the irreversible demagnetization. To solve these problems, a novel structure is proposed, which can increase the motor performance through the overhang structure without irreversible demagnetization in the overhang part.

Correction to “Magnetic Equivalent Circuit Model Considering Overhang Structure of a Surface-Mounted Permanent-Magnet Motor” [Mar 15 Art. ID 8201004

The information in the published version of [1] contained incorrect information about the affiliation of the authors. The correct affiliations are listed above.

Multi-objective optimization of an in-wheel electric vehicle motor

The present work deals with the optimization of an in-wheel surface mounted permanent magnet motor (SMPM) with outer rotor and concentrated windings. The main objective of the optimization procedure is tofind the optimum design geometry by maximizing the machine efficiency and minimizing its weight. To reach this goal, two objective functions are used. The first leads to a design with high output torque capability and then high efficiency. The second is a requirement imposed by the fact that the machine is directly integrated inside the vehicle wheel, and therefore a light weight is requested. In order to carry out this study, five multi-objective optimization algorithms were applied: the Genetic Algorithm (GA), the fast elitist multi- objective Genetic Algorithm (NSGA-II), the Adapting Scatter Search for Multi-objective Optimization algorithm (AbYSS), the improved PSO- based Multi-Objective Optimization and a new PSO-based Metaheuristic for Multi-objective Optimization. The reason of testing several intelligence artificial techniques is to find a fast and efficient technique for electrical machines optimization. Based on the objective functions design and the machine constraints, the results obtained by the five algorithms are compared and analyzed. In order to carry out this study, an analytical model describing the geometric, the magnetic and the electric properties of the studied design was firstly developed. Moreover, an optimized machine is chosen and studied by means of finite element analysis (FEA) tool. Then FEA results are compared with those obtained by the optimization procedure. Based on this comparison, a good concordance between the two results is shown.

Magnetic Field Analysis in Eccentric Surface-Mounted Permanent-Magnet Motors Using an Improved Conformal Mapping Method

This paper presents an improved conformal mapping (ICM) method for magnetic field analysis in one typical surface-mounted permanent-magnet (SMPM) motor considering the static, dynamic, and mixed rotor eccentricities. The ICM method accurately accounts for the slotting effect, the winding distribution, the armature reaction, the magnetic saturation effect, and the working point variation of PMs throughout their volume. The ICM method is also very rigorous to separate the onload air gap field components. First, the slotless model of an eccentric SMPM motor is mapped to one concentric model using a new form of bilinear conformal mapping, and the field solution is then obtained through applying Hague's solution in the main canonical domain. Second, the slotted air gap magnetic field is obtained through the modulation of air gap magnetic field in the slotless physical domain using the complex relative air gap permeance. The ICM method is also used to investigate the influence of rotor eccentricity on the flux linkage of the stator coils. This developed model is validated through comparing with the corresponding results obtained through finite element method and the frozen permeability method. This method can also be used as a tool for design and optimization of electrical machines.

Kriging-Assisted Multi-Objective Design of Permanent Magnet Motor for Position Sensorless Control

This paper presents a novel multi-objective evolutionary algorithm (MOEA) based on surrogate models. Kriging surrogate models are created and updated with the solutions from the MOEA for reducing the number of evaluations of the computationally expensive finite-element analysis models. The proposed method is applied to solve a multi-objective design problem of a surface-mounted permanent magnet motor in order to improve its sensorless control capability without comprising other performances, such as output torque and torque ripple. The Kriging-assisted MOEA is proved to have the potential of providing good solutions with a limited computation time budget.

Advanced simulation model for IPM motor drive with considering phase voltage and stator inductance

ABSTRACTThis paper proposes an advanced simulation model of driving system for Interior Permanent Magnet (IPM) BrushLess Direct Current (BLDC) motors driven by 120-degree conduction method (two-phase conduction method, TPCM) that is widely used for sensorless control of BLDC motors. BLDC motors can be classified as SPM (Surface mounted Permanent Magnet) and IPM motors. Simulation model of driving system with SPM motors is simple due to the constant stator inductance regardless of the rotor position. Simulation models of SPM motor driving system have been proposed in many researches. On the other hand, simulation models for IPM driving system by graphic-based simulation tool such as Matlab/Simulink have not been proposed. Simulation study about driving system of IPMs with TPCM is complex because stator inductances of IPM vary with the rotor position, as permanent magnets are embedded in the rotor. To develop sensorless scheme or improve control performance, development of control algorithm through simulation study is essential, and the simulation model that accurately reflects the characteristic of IPM is required. Therefore, this paper presents the advanced simulation model of IPM driving system, which takes into account the unique characteristic of IPM due to the position-dependent inductances. The validity of the proposed simulation model is validated by comparison to experimental and simulation results using IPM with TPCM control scheme.

On-Load Field Component Separation in Surface-Mounted Permanent-Magnet Motors Using an Improved Conformal Mapping Method

This paper introduces an improved conformal mapping (ICM) method for the separation of the on-load air-gap magnetic field components in surface-mounted permanent-magnet (SPM) motors under loading conditions. The ICM method can model the magnetic induction inside a permanent magnet (PM) due to the armature reaction and the relative recoil permeability. The ICM method can also consider the simultaneous influences of the armature reaction, the slotting effect, the magnetic saturation, and the relative recoil permeability in the determination of operating points of the PM in its different parts. Therefore, this proposed method can be useful for an on-load performance analysis of SPM motors. Three conformal mappings are used to reach the main canonical domain: two logarithmic complex functions and the Schwarz–Christoffel (SC) mapping. The field solution in the slotless domain is then mapped back into the slotted domain using the complex air-gap permeance. The field solution in the slotted domain is used to calculate the on-load air-gap field components due to the PMs and the armature reaction. These on-load field components allow the calculation of the on-load PM flux linkage, the on-load PM back-EMF, and the on-load torque components. The influences of electric loading on the on-load torque components and the on-load PM back-EMF are studied using the ICM method. The on-load cogging torque periodicity is confirmed to change due to the magnetic saturation, and the harmonic content of torque components and the PM back-EMF is also altered due to the electric loading. The accuracy of this developed model is verified by comparing the results obtained through the ICM method with the respective results obtained through the finite-element analysis and the frozen permeability method.

Comparison of Claw-Pole Machines With Different Rotor Structures

Due to the global winding and 3-D flux, the claw-pole machine (CPM) can exhibit higher torque ability than other types of electrical machines. Using the powder metallurgical technology, the manufacture cost of CPMs made of soft-magnetic composite (SMC) material can be much lower than that of the conventional machines, especially with the low density cores. The performance of SMC motor was improved as the material has undergone through substantial improvement in the last decades. To seek better performance, CPMs with different permanent magnet (PM) rotor structures and SMC cores, including the surface mounted PM motor, surface inset PM rotor, V-type PM rotor, and flux concentrating PM rotor, are designed and the performances compared. The magnetic parameters of these machines are obtained by the 3-D finite-element method, and the analysis method is verified by the experiment of a surface-mounted PM CPM with SMC core.