Interior Permanent Magnet Motor Research Articles

Analysis of Torque Ripple and Cogging Torque Reduction in Electric Vehicle Traction Platform Applying Rotor Notched Design

Drive motors, which are used in the drive modules of electric cars, are interior permanent magnet motors. These motors tend to have high cogging torque and torque ripple, which leads to the generation of high vibration and noise. Several studies have attempted to determine methods of reducing the cogging torque and torque ripple in interior permanent magnet motors. The primary methods of reducing the cogging torque involve either electric control or mechanical means. Herein, the authors focused on a mechanical method to reduce the cogging torque and torque ripple. Although various methods of reducing vibration and noise mechanically exist, there is no widely-known comparative analyses on reducing the vibration and noise by designing a notched rotor shape. Therefore, this paper proposes a method of reducing vibration and noise mechanically by designing a notched rotor shape. In the comparative analysis performed herein, the motor stator and rotor were set to be the same size, and electromagnetic field analysis was performed to determine a notch shape that is suitable for the rotor and that generates reasonable vibration and noise.

Torque Ripple Reduction in Five-Phase IPM Motors by Lowering Interactional MMF

This paper proposes a torque ripple reduction method for a five-phase interior permanent magnet (PM) motor by shifting asymmetrical rotor poles. The key of this method is to consider the PM torque ripple, reluctance torque ripple, and cogging torque simultaneously from two aspects. First, the main interactional harmonic, contributing to PM torque ripple, between stator magnetic motive force (MMF) and rotor MMF is developed. Then, the appropriate combination of unequal pole arcs is adopted to eliminate the main interactional harmonic. Second, the asymmetrical rotor pole-pair is selected as a repeating unit which produces cogging torque and reluctance torque with consistency in waveforms and phases. Then, three methods for shifting asymmetrical rotor pole-pair are proposed showing that the torque ripple can be reduced greatly and the lower-order harmonics of radial force is acceptable when the shifting angle of the repeating unit is 4.5 mechanical degrees. Through theoretical analysis and experimental test, it is verified that the proposed motor can offer lower torque ripple even under deep flux-weakening region.

Simulation and Experimental Study on No-Load Loss Distributions of an IPM Motor Under the Conditions of Both Sinusoidal Supply and Converter Supply

In this paper, each component of the no-load loss of interior permanent magnet motors under the conditions of both sinusoidal supply and converter supply is investigated by the finite-element method and experimental method. The no-load loss is calculated at different rotation speeds, two different slot and pole combinations and different converter parameters. The wireless temperature sensor embedded in the interior rotor is used to test the temperature of the permanent magnet under no-load condition, and the permanent magnet loss is calculated according to the slope of the initial temperature–time curve. Then, the mechanical loss of the prototype is measured by dragging a nonmagnetic rotor. The total tested losses are subtracted from the copper loss, the mechanical loss, and the permanent magnet loss to obtain the test results of core loss, and the experimental results of each loss and permanent magnet temperature rise are compared with the corresponding calculated results to verify the correctness of the simulation results.

Design and Analysis of Rotor Shapes for IPM Motors in EV Power Traction Platforms

The recent increase in the use of permanent magnet rotor motors underlines the importance of designing a rotor with an interior permanent magnet (IPM) structure, high power, and high efficiency. This study analyzed the rotor shapes of IPM motors for electric vehicles. Five types of motor rotors for automobiles were analyzed, including two hybrid vehicles. In order to minimize the number of variables in the analysis, the size of the motor stators was fixed and only the rotor shapes were modified to compare torque, torque ripple, efficiency and back-electromotive voltage. When the motor properties were compared as a function of rotor shape, the rotor shape with the smallest magnet volume exhibited excellent results for torque, efficiency and torque ripple.

Quantitative Comparison of Vernier Permanent-Magnet Motors with Interior Permanent-Magnet Motor for Hybrid Electric Vehicles

In this paper, three Vernier permanent-magnet (VPM) motor, namely the inner-rotor VPM (IR-VPM) motor, the outer-rotor VPM (OR-VPM) motor and the OR consequent-pole VPM (OR-CP-VPM) motor are proposed for the hybrid electric vehicle (HEV) applications. Owing to employment of toroidal-winding arrangement, the OR-VPM and the OR-CP-VPM motors can enjoy better material utilization and easier manufacturing process than its IR-VPM counterpart. Meanwhile the OR-CP-VPM motor can utilize the consequent-pole topology to minimize flux leakage that exists in conventional design. With the support of finite element method (FEM), the motor performances among the VPM motors and the profound interior permanent-magnet (IPM) motor can be compared quantitatively.

Analytical Calculation of Armature Reaction Field of the Interior Permanent Magnet Motor

The energy crisis and environmental concerns worldwide have helped usher in the age of electric vehicles (EVs) and hybrid EVs (HEVs). The interior permanent magnet motors (IPMMs) are widely used in these vehicles. The analysis of the armature reaction field is the most critical issue in the study of IPMMs since it determines the characters of torque, efficiency, vibration, and the radiated acoustic noise. This paper provides a calculation method of the armature reaction magnetic field (ARMF) of an IPMM. First, the formulas of ARMF without magnetic barrier are derived. Second, the relative permeance function of an IPMM is calculated. Third, the analytical solution of the ARMF of an IPMM is derived by applying the armature reaction magnetic field with unsaturated rotor multiplied by relative permeance function. Finally, several results of comparisons between the calculation method proposed in this paper and the finite element method are presented. Based on the calculation method proposed in this paper, the magnetic barrier’s influence on the ARMF is studied. The spatial harmonic orders and time harmonic orders of the ARMF of IPMM are revealed respectively.

Multiphysics Design of a V-Shape IPM Motor

In this paper, a multiphysics model is proposed for a multi-V-shape interior permanent magnet motor with concentrated winding. This paper develops a nonlinear magnetic model that computes the flux density in the motor. The analytical model includes several novel aspects: it takes into account the local saturation near the iron bridges, it proposes a method for modeling the concentrated tooth winding, and it calculates the slot tangential leakage flux and includes it in the flux linkage calculation. The magnetic model is coupled with an electrical model that computes the power factor and the voltage at the motor terminals. A loss model is developed in order to calculate the copper and the iron losses. They are used as inputs to a nodal thermal model that introduces a thermal circuit for concentrated end-winding and computes the temperature of the motor. A mechanical model is developed. It evaluates the mechanical constraints encountered by the structure. The models are verified using finite element computations and numerical calculations performed with dedicated software. Besides, the coupled analytical model is experimentally validated using a prototype motor. Finally, two multiphysics bi-objective optimizations are carried out in order to design the motor for high-torque and low-speed application.

A Combined Control for Fast and Smooth Performance of IPM Motor Drives Over Wide Operating Conditions

This paper presents a new combined vector and direct torque control (CC) system for interior permanent magnet motor drives to achieve improved motor performance. High-performance motor control systems are always aimed at fast and smooth motor performances. Also, simplicity and parameter independence are much anticipated in motor control systems. The proposed system uses fast production of torque producing current command and smooth production of flux producing current command, in connection with a switching table. The CC enjoys minimal parameter dependence and controller tuning challenges. Analysis of motor performance under the control system shows rapid motor dynamics with low torque and flux linkage ripples and current harmonics, in addition to rather uniform inverter switching. Simulation and experimental results obtained from a 1 hP motor under the proposed control system confirm the above-mentioned performance merits. Also, extensive simulation results show the control performance superiority in comparison with vector control, direct torque control, and an existing CC.

Computationally efficient permanent magnet traction motor loss assessment

PurposeThis paper aims to introduce a computationally efficient hybrid analytical–finite element (FE) methodology for loss evaluation in electric vehicle (EV) permanent magnet (PM) traction motor applications. In this class of problems, eddy current losses in PMs and iron laminations constitute an important part of overall drive losses, representing a key design target.Design/methodology/approachBoth surface mounted permanent magnet (SMPM) and double-layer interior permanent magnet (IPM) motor topologies are considered. The PM eddy losses are calculated by using analytical solutions and Fourier harmonic decomposition. The boundary conditions are based on slot opening magnetic field strength tangential component in the air gap in the SMPM topology case, whereas the numerically evaluated normal flux density variation on the surface of the outer PM is implemented in the IPM case. Combined analytical–loss evaluation technique has been verified by comparing its results to a transient magnetodynamic two-dimensional FE model ones.FindingsThe proposed loss evaluation technique calculated the total power losses for various operating conditions with low computational cost, illustrating the relative advantages and drawbacks of each motor topology along a typical EV operating cycle. The accuracy of the method was comparable to transient FE loss evaluation models, particularly around nominal speed.Originality/valueThe originality of this paper is based on the development of a fast and accurate PM eddy loss model for both SMPM and IPM motor topologies for traction applications, combining effectively both analytical and FE techniques.

Performance Analysis of Permanent Magnet Motors for Electric Vehicles (EV) Traction Considering Driving Cycles

This paper evaluates the electromagnetic and thermal performance of several traction motors for electric vehicles (EVs). Two different driving cycles are employed for the evaluation of the motors, one for urban and the other for highway driving. The electromagnetic performance to be assessed includes maximum motor torque output for vehicle acceleration and the flux weakening capability for wide operating range under current and voltage limits. Thermal analysis is performed to evaluate the health status of the magnets and windings for the prescribed driving cycles. Two types of traction motors are investigated: two interior permanent magnet motors and one permanent magnet-assisted synchronous reluctance motor. The analysis results demonstrate the benefits and disadvantages of these motors for EV traction and provide suggestions for traction motor design. Finally, experiments are conducted to validate the analysis.

Field Weakening Characteristics Computed with FEM-Coupled Algorithms for Brushless AC Motors

Finite Element Method (FEM) analysis tools are the most adopted in the design of brushless alternating current motors due to the advantage of considering multi-physics effects with dependencies of variables such as cross-coupling, saturation and others that are not possible to be modeled analytically with high precision. During the design process designers compute operation points such as maximum torque per ampere or flux weakening characteristics that cannot be targeted directly on the FEM tool. Therefore, designers make a sweep of simulations and post-processed the data in order to obtain the results, this is repetitive particularly in the conceptual phase of the design where features of the motor are still not defined. This paper presents nine algorithms as an alternative to compute with iterative methods operation points that cannot be targeted directly on a FEM tool. The algorithms must be coupled to the FEM tool and can compute complex points such as the characteristic current and modes of operations limits within acceptable range of error and times of execution for practical purposes. Validation of the algorithms using Jython is presented with results for the three types of brushless motors (non-salient, interior permanent magnet and reluctance motor).

Design and Optimization of IPM Motor Considering Flux Weakening Capability and Vibration for Electric Vehicle Applications

As motor design is key to the development of electric vehicles (EVs) and hybrid EVs (HEVs), it has recently become the subject of considerable interest. Interior permanent magnet (IPM) motors offer advantages such as high torque density and high efficiency, benefiting from both permanent magnet (PM) torque and reluctance torque. However an obvious disadvantage of IPM motors is that operation at high speed involves difficulties in achieving the required flux-weakening capability and low vibration. This study focuses on optimizing the flux-weakening performance and reducing the vibration of an IPM motor for EVs. Firstly, flux-weakening capability, cogging torque, torque ripple, and radical vibration force are analyzed based on the mathematical model. Secondly, three kinds of motors are optimized by the genetic algorithm and analyzed, providing visible insights into the contribution of different rotor structures to the torque characteristics, efficiency, and extended speed range. Thirdly, a slotted rotor configuration is proposed to reduce the torque ripple and radical vibration force. The flux density distributions are discussed, explaining the principle that motors with slotted rotors and stator skew slots have smaller torque ripple and radical vibration force. Lastly, the design and optimization results have been validated against experiments.

Nonlinear Analytical Model for a Multi-V-Shape IPM With Concentrated Winding

This paper presents a nonlinear analytical model of a multi-V-shape interior permanent magnet (IPM) motor with nonoverlapping concentrated winding. The model relies on Ampere's theorem and the flux conservation law in order to compute the flux density in the different parts of the motor. This article proposes a saturated analytical model of the stator and the rotor. The analytical model is used to calculate the average torque, the power factor, and the voltage of the motor. It is five times faster than the 2-D finite element analysis (FEA). The results are compared with 2-D FEA simulations and experimentally validated using a prototype motor.

Simplified current minimization control of vector controlled Interior Permanent Magnet motor

This paper presents a simplified current minimizing technique for Interior Permanent Magnet (IPM) motor. This is primarily achieved by utilizing normalized 2D-Look Up Table (LUT) that is parameter independent except for saliency ratio. In addition, torque-flux reference frame is considered for implementation to reduce the complexity generally present in conventional methods utilizing ids − iqs current reference frame. The proposed algorithm also incorporates both the aspects that lead to field weakening operation, i.e., increase in speed and reduction of dc link voltage. A novel compensation method for incorporating saturation effect is also addressed. The current minimizing technique is analyzed in detail, supported by experimental results.

Maximum power per VA control of vector controlled interior permanent magnet motor

Maximum Torque Per Ampere is the commonly used technique for operating interior permanent magnet (IPM) motor while little work is reported towards maximum power-factor operation i.e., Maximum Power Per Volt-Ampere (MPVA). The MPVA operation allows maximum-utilization of the drive-system. The control technique is developed using detailed mathematical model of IPM motor in MPVA, and the solution to the quartic equations involved is derived and analyzed. The solution is utilized to develop LUT for implementation of MPVA control. The comparison of MTPA and MPVA technique is established to demonstrate its merits and demerits. The proposed algorithm is supported by simulation and experimental results on a 5.5 KW vector controlled IPM drive.

The Role of Temperature-Dependent Material Properties in Optimizing the Design of Permanent Magnet Motors

The effects of temperature-dependent material properties, including those of silicon steel and permanent magnet (PM) materials, on the design process of inverter-fed PM motors are investigated in this paper. The magnetization curves of these materials are measured experimentally at different temperatures and are imported into a finite-element package. Then, a statistical study of an integrated motor-drive system consisting of an interior PM motor connected to a space vector modulated inverter is performed by assigning four different temperatures and building a design space of various objectives including the integrated system efficiency, speed limits, motor startup quality, torque ripple, total harmonic distortion, and power factor as the geometrical dimensions are varied. The results reveal that incorporating the realistic material properties into the design process is essential. Moreover, different motor-drive performances have totally different variation rates as the material properties are changed. Finally, a set of optimal designs at different temperatures is proposed to show the effect of changing material properties.

Shape Optimization Procedure of Interior Permanent Magnet Motors Considering Carrier Harmonic Losses Caused by Inverters

An automatic shape optimization procedure that estimates the inverter carrier harmonic losses generated at cores and magnets has been developed in order to improve the performance of interior permanent magnet motors used for variable speed/load applications. In the proposed procedure, an electromagnetic field analysis coupled with armature voltage equation is iteratively carried out at each rotor shape. The input of this analysis is the theoretical inverter voltage, which is determined by both the rotor shape and the driving conditions of the motor. The proposed procedure is applied to a 100 kW-class interior permanent magnet motor, in which the carrier harmonic losses become dominant under frequent driving conditions. It is clarified that the carrier harmonic losses can be reduced by more than 10%, whereas the other important characteristics are not deteriorated.

Fast Numerical Analysis of Electric Motor Using Nonlinear Model Order Reduction

The problem of the computationally efficient analysis of the electromagnetic system with nonlinearity is considered in the proposed work. Unlike the previously proposed proper orthogonal decomposition (POD)-based model order reduction (MOR), the proposed method based on the dynamic mode decomposition works well even under the highly nonlinear system. Using the proposed method, a highly saturated interior permanent-magnet (IPM) motor model is analyzed. Comparisons in terms of the radial air-gap flux density and torque are made with that of the full and POD-based models. The results show that the proposed method is capable of giving a good approximation of the full model of the IPM motor. Also, a reduction in the computational time can be achieved compared with that of the traditional POD-based MOR.

Topology Optimization Using Basis Functions for Improvement of Rotating Machine Performances

This paper presents a new topology optimization method based on basis functions for design of rotating machines. In this method, the core shape of a given rotating machine is represented by the linear combination of the basis functions. The shape is then freely deformed by changing the weighting coefficients to the basis functions to find the optimal shape. The proposed method is compared with the conventional shape optimization based on polygon morphing. The former is shown to outperform the latter in both interior permanent magnet and synchronous motor models.

A Robust Multimodal Optimization Algorithm Based on a Sub-Division Surrogate Model and an Improved Sampling Method

The characteristics analysis of an electric machine requires the finite-element method. Hence, a large amount of computation occurs in the design process to take into account uncertainties as the manufacturing tolerances. In this paper, an efficient and useful multimodal optimization algorithm using the kriging surrogate model is proposed for the robust optimization of an electric machine. However, the conventional kriging (CK) method has a memory problem in multi-dimensional problem due to the enlarged correlation matrix. Thus, a sub-domain kriging (SDK) strategy and improved Latin hypercube sampling (ILHS) are proposed not only to solve the memory problem of the CK method, but also to increase the convergence speed. In addition, a gradient-free sensitivity index is proposed for robust optimization in order to address the conventional first and second gradient index which causes a numerical error. The outstanding performance of the proposed algorithm is verified by comparing with other optimization methods via several mathematical test functions which includes multi-dimensional problem. Moreover, the proposed algorithm is applied to a cogging torque reduction design case for interior permanent magnet motor.