Skewed Permanent Magnet Research Articles

Topology-Parameter Hybrid Optimization of Skewed Permanent Magnet Motor

In this study, we present a topology-parameter hybrid optimization of a permanent magnet motor with a step-skewed rotor. This optimization simultaneously performed topology optimization of the core shape and parameter optimization of the skew angle. Simultaneous optimization provides optimized motors that are superior to those obtained by parameter, topology, and sequential optimizations. Moreover, the optimized shape was shown to be robust with respect to variations in the skew angle.

Novel Quasi-Three-Dimensional Modeling of Axial Flux In-Wheel Motor With Permanent Magnet Skew

This paper presents a characteristic analysis of axial flux permanent magnet machines (AFPMMs) for in-wheel electric vehicles. Preferentially, a novel quasi-3-D model is developed for the fast and accurate design of AFPMMs. In electromagnetic field analysis, combined with field reconstruction method, the computation time of 2-D solutions is significantly reduced. With the use of time sweeping of the basis function, only the static finite element (FE) analysis is performed to calculate the air-gap flux distribution at the entire rotor position, whereas the conventional 2-D solutions require a transient FE analysis. In the shape sweeping process of the basis function, the virtual air-gap section method is introduced to take into account that the ratio of slot opening to slot pitch is different depending on the radius of analysis plane, which causes errors in the analysis results of the conventional quasi-3-D method. The virtual air-gap sections are obtained by interpolation of the spatial field between the mapped cylindrical planes. The proposed technique reduces the number of 2-D analysis planes required for high accuracy in the conventional quasi-3-D method, and it can also predict the air-gap magnetic flux distribution for skewed permanent magnets without additional FE analysis. Finally, using the magnetic fields calculated in the proposed method, the electromagnetic performances of the AFPMM are calculated, such as load torque, cogging torque, attraction force, and back-EMF. The analysis results were verified by comparison with the measurement results.

Novel DC-Saturation-Relieving Hybrid Reluctance Machine With Skewed Permanent Magnets for Electric Vehicle Propulsion

Reluctance machines with dc excitation coils have become a promising solution for electric vehicle propulsion system because of its robust rotor structure and good field-weakening ability. However, these machines usually suffer from relatively low torque density and efficiency. To solve this problem, this article proposes a novel hybrid reluctance machine with improved torque density and efficiency. The key novelty is to introduce skewed permanent magnets (PMs) in slot openings. The tangential component of skewed PMs can be used to relieve the dc saturation in the stator iron core, so that the <inline-formula> <tex-math notation="LaTeX">$B-H$ </tex-math></inline-formula> working range can be extended and relatively high dc excitation can be applied in the proposed machine. Besides, the radial component of skewed PM provides extra torque component under flux modulation effect. Therefore, the proposed skewed PMs can achieve torque boost and core utilization improvement simultaneously. In this article, the dc-saturation-relieving effect of the proposed design is thoroughly investigated and verified by finite element analysis.

Effect of Skewing in a Variable Flux Interior Permanent Magnet Synchronous Machine

The motivation of this article is to minimize the cogging torque and the torque ripple in a 6-pole 27-slot variable flux interior permanent magnet synchronous machine (VF IPMSM) by skewing the permanent magnets (PMs) in several steps. AlNiCo9 is used as the PM material in the rotor as the magnetization level of the AlNiCo9 PM can be changed and controlled by proper current control. The optimum skewing angles to minimize the cogging torque are found analytically and verified by using the finite-element analysis (FEA). The effect of these skewing angles on the back electromotive force and the torque ripple is also studied at different magnetization levels of the AlNiCo9 magnets. An FEA shows that a step skewed PM pole significantly minimizes the cogging torque and the torque ripple in the VF IPMSM. A current pulse in the d -axis is applied to magnetize or demagnetize each step in the step skewed PM pole. The minimum optimum skewing angle is chosen such that each step of the step skewed PM pole is magnetized or demagnetized with minimum nonuniformity.

Performance evaluation of a 60kW IPM motor for medium commercial EV traction application

This paper presented the design and performance analysis of a 60kW interior permanent-magnet (IPM) synchronous motor used as traction drive in a medium commercial electric vehicle (EV), according to the traction requirements of the electric vehicle under the rated operating conditions and overload conditions. The key dimensions were calculated on the basis of the permanent-magnet (PM) motor theory, and the 2D finite element method (FEM) simulation model of the IPM motor was built by using 2D Maxwell software. The influence geometric structures of the IPM motor including the PM dimensions and skewed PMs on electromagnetic torque were investigated, and the temperature distribution of the motor under rated operating condition and the condition of maximum speed were calculated. Finally, the simulation results of the IPM motor running in various operating modes were compared with the experimental results, which demonstrated that the designed IPM motor can match all requirements of the medium commercial electric vehicle driving applications.

Hybrid excited claw pole generator with skewed and non-skewed permanent magnets

Abstract This article contains simulation results of the Hybrid Excited Claw Pole Generator with skewed and non-skewed permanent magnets on rotor. The experimental machine has claw poles on two rotor sections, between which an excitation control coil is located. The novelty of this machine is existence of non-skewed permanent magnets on claws of one part of the rotor and skewed permanent magnets on the second one. The paper presents the construction of the machine and analysis of the influence of the PM skewing on the cogging torque and back-emf. Simulation studies enabled the determination of the cogging torque and the back-emf rms for both: the strengthening and the weakening of magnetic field. The influence of the magnets skewing on the cogging torque and the back-emf rms have also been analyzed.

Axial Unbalanced Magnetic Force in a Permanent Magnet Motor Due to a Skewed Magnet and Rotor Eccentricities

We investigate the effect of a skewed permanent magnet (PM) with overhang on the axial unbalanced magnetic force (UMF) of a PM motor, especially in the presence of static and dynamic eccentricities of a rotor. We derive the mathematical equations of the axial UMF acting on PM motor due to the skewed PM with overhang and rotor eccentricities. We develop a 3-D finite-element model of the PM motor, not only to verify the frequency components of the proposed equations but also to determine the amplitude of the axial UMF. Further, we develop an experimental setup to measure the axial UMF caused by a skewed PM with overhang and rotor eccentricities. We confirm that the skewed PM with overhang generates an axial UMF with the harmonic of the least common multiple of pole and slot numbers. In addition, the static and dynamic eccentricities with the interaction of the skewed PM and overhang generate the axial UMF with the pole harmonics and slot harmonics, respectively.

Detent Force Compensation for PMLSM Systems Based on Structural Design and Control Method Combination

As direct-drive actuators, permanent-magnet linear synchronous motors (PMLSMs) are widely used in high velocity and high precision applications. The detent force, however, can deteriorate the performance and even excite the mechanical resonance. This paper focuses on a novel detent force compensation scheme for PMLSM systems through a combination of structural design and control method. First, due to the bandwidth constraint of the control system, eliminating high frequency ripples is unfeasible; skewed permanent magnets (PMs) considering an optimal skewing length are designed to suppress high order harmonic components. Second, based on the model of PMLSM with skewed PMs, a linearization observer is derived and applied independently to the velocity controller for further diminishing low-order harmonic components. To facilitate implementation in the digital control system, a discretization method taking account of estimated errors is designed. Through the online calculation, the estimated detent force is injected to the control system in a feedforward way. To tune the proposed scheme properly, the convergence of the algorithm is analyzed by utilizing Lyapunov stability theory. Simulation studies are performed to prove the effectiveness of the proposed method, and experiments are provided to confirm the theoretical analysis and simulation results.

Material-Efficient Permanent-Magnet Shape for Torque Pulsation Minimization in SPM Motors for Automotive Applications

This paper focuses on the design and analysis of a novel material-efficient permanent-magnet (PM) shape for surface-mounted PM (SPM) motors used in automotive actuators. Most of such applications require smooth torque with minimum pulsation for an accurate position control. The proposed PM shape is designed to be sinusoidal and symmetrical in the axial direction for minimizing the amount of rare earth magnets as well as for providing balanced axial electromagnetic force, which turns out to obtain better sinusoidal electromotive force, less cogging torque, and, consequently, smooth electromagnetic torque. The contribution of the novel PM shape to motor characteristics is first estimated by 3-D finite-element method, and all of the simulation results are compared with those of SPM motors with two conventional arched PM shapes: one previously reported sinusoidal PM shape and one step skewed PM shape. Finally, some finite-element analysis results are confirmed by experimental results.

A Study on the Novel Coefficient Modeling for a Skewed Permanent Magnet and Overhang Structure for Optimal Design of Brushless DC Motor

A novel coefficient modeling technique, using a coefficient estimation method, is introduced for a brushless DC (BLDC) motor with a skewed permanent magnet and overhang structure. To construct the novel coefficient, the 3-D FEM and a design of experiment (DOE) are utilized along with the moving least square method (MLSM). Also, to verify the accuracy of the novel coefficient modeling, the conventional coefficient modeling using LSM is constructed and compared. Then the novel coefficient is combined with an approximate model constructed by 2-D FEM for use with an optimal design algorithm. For the searching process to obtain an optimal point, the genetic algorithm (GA) is used. Three-dimensional FEM simulation is used to verify the accuracy of the novel coefficient for the optimal design.

3-D Analytical and Numerical Modeling of Tubular Actuators With Skewed Permanent Magnets

This paper considers analytical and numerical techniques to model the magnetic field distribution in a tubular actuator with skewed permanent magnets (PMs). A fast 3-D analytical model based on Fourier analysis is developed for calculation of the various field components resulting from the skewed PMs for various skewing topologies. This techniques provides means for validating the assumptions of 2.5-D multilayer methods. Furthermore, a 2.5-D analytical multilayer model is derived for calculation of the cogging force due to the slot openings including skewed PMs. The analytical methods are validated by means of 3-D finite element analysis.

3D analytical field calculation using triangular magnet segments applied to a skewed linear permanent magnet actuator

PurposeThe purpose of this paper is to present novel analytical expressions which describe the 3D magnetic field of arbitrarily magnetized triangular‐shaped charged surfaces. These versatile expressions model that the field of triangular‐shaped permanent magnets (PMs) are very suitable to model skewed slotless machines.Design/methodology/approachThe analytical 3D surface charge method is normally used to provide field expressions for PMs in free space. In this paper, the analytical surface charge integrals are analytically solved for charged right‐triangular surfaces. The resulting field is compared with that obtained by finite element modeling (FEM) and subsequently applied in two examples.FindingsThe comparison with FEM shows that the 3D analytical expressions are very accurate and exhibit very low‐numerical noise. These fast‐solving versatile expressions are therefore considered suitable to model triangular‐shaped or polyhedral‐shaped PMs.Research limitations/implicationsThe surface charge method assumes that the relative permeability is equal to 1 and therefore soft‐magnetic materials need to be modeled using the method of images. The PMs are assumed to be ideal in terms of homogeneity, magnetization vector, permeability, demagnetization, and geometrical tolerances.Practical implicationsMany applications, such as the subclass of slotless synchronous linear actuators with a skewed PM structure and planar magnetic bearings, are very suitable to incorporate this modeling technique, since it enables the analysis of a variety of performance data.Originality/valueAs an addition to the common 3D analytical field expressions for cuboidal or cylindrical PMs, this paper presents novel expressions for magnets having triangular surfaces.

Calculation of Position-Dependent Inductances of a Permanent Magnet Synchronous Machine With an External Rotor by Using Voltage-Driven Finite Element Analyses

This paper discusses finite element analyses of a skewed permanent magnet synchronous machine (PMSM) with an external rotor regarding the magnetic saliency. Since the machine is fed from a voltage source inverter (VSI), a simulation as close as possible to the regular operational behavior is intended. Therefore, a voltage-driven finite element model with a strong circuit coupling excited with the time-dependent voltages according to the space vectors of the VSI will be applied. This approach directly allows for a comparison of the numerically obtained phase currents with those obtained from measurements. Afterwards, the inductance characteristics depending on the rotor position can be evaluated from the time-dependent phase currents in order to obtain the suitability for a sensorless control algorithm.

Three-dimensional finite element analysis of permanent magnet brushless DC motor drives-status of the state of the art

This paper reviews advances in the state of the art of applying three-dimensional finite-element (3-D-FE) magnetic field computation techniques to the analysis and quantification of parameters and performance of permanent magnet (PM) brushless DC motors as components of brushless DC drives. The application of the powerful 3-D-FE formulation based on the coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) concept to a case study PM brushless DC motor with skewed permanent magnet mounts is reviewed and summarized. This large-scale simulation of such a motor drive system is shown to be successfully implementable using workstation type computer environments.

Three dimensional magnetic field computation by a coupled vector-scalar potential method in brushless DC motors with skewed permanent magnet mounts-the formulation and FE grids

A three dimensional finite element (3D-FE) method for the computation of global distributions of 3D magnetic fields in electric machines containing permanent magnets is presented. The formulation of this 3D-FE method including 3D permanent magnet modeling, which is based on a coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) approach, is given. The development of the necessary 3D-FE grids and algorithms for the application of the method to an example brushless DC motor, whose field is three dimensional due to the skewed permanent magnet mounts on its rotor, is also given here. A complete set of results of application of the method to the computation of the global 3D field distributions and associated motor parameters under no-load and load conditions are detailed in a companion paper. >

Three dimensional magnetic field computation by a coupled vector-scalar potential method in brushless DC motors with skewed permanent magnet mounts-the no-load and load results

The coupled magnetic vector potential-magnetic scalar potential (CMVP-MSP) method of computation of 3D magnetic fields by finite elements (3D-FE) is applied here to a brushless DC motor with skewed permanent magnet mounts on its rotor. Results of the CMVP-MSP and 3D-FE computation of the magnetic field and associated motor parameters (EMFs and armature inductances) are detailed in this paper. These results demonstrate vividly the three dimensional nature of the computed flux distributions, caused by the torque ripple reduction design employing skewed magnet mounts on the rotor. Experimental evidence supporting the validity of the BD-FE field computations, through comparison between computed and measured armature EMF waveforms is also provided in this paper.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

Modeling and experimental verification of the performance of a skew mounted permanent magnet brushless DC motor drive with parameters computed from 3D-FE magnetic field solutions

This paper contains a comparison between actual laboratory-measured performance of a brushless DC motor drive system, with skewed permanent magnet mounts on its rotor, and two computer-simulated motor drive system performance characteristics. These simulated motor drive system performance results were once obtained using motor parameters computed from rigorous three dimensional-finite element (3D-FE) magnetic field solutions detailed in two companion papers and once obtained using motor parameters from more conventional 2D-FE magnetic field solutions. The comparison demonstrates that 3D-FE based motor parameters lead to drive system performance simulations which are much closer to test results for this type of brushless DC drives with skewed permanent magnet mounts. Torque ripples computed from 3D-FE based and 2D-FE based motor parameters are also included. The results clearly show advantages to basing the drive system simulations on 3D-FE computed motor parameters.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>