Interior Permanent Magnet Motor Research Articles

Numerical and Analytical Approaches to the Modeling of a Spoke Type IPM Machine With Enhanced Flux Weakening Capability

Interior permanent magnet (IPM) machines with spoke-type design are very attractive for several applications, including vehicle traction, which requires a good flux weakening performance to achieve high speed. For this purpose, a high demagnetizing current is usually injected to reduce the machine flux at high speed, with detrimental effect in terms of efficiency. This problem can be mitigated by equipping the rotor with a mechanical flux weakening device, which activates during high-speed operation by centrifugal force. This paper addresses the analytical modeling of this special kind of IPM motor through a simplified magnetic equivalent circuit (MEC) approach, which incorporates saturation and slotting effects as well as the flux weakening device operation. It is shown how the MEC model can effectively describe the IPM machine behavior despite its simplicity. Results are successfully validated by comparison both with finite element analysis, which requires much more computational resources, and with measurements from laboratory prototype testing.

Optimal design to reduce torque ripple of IPM motor with radial based function meta-model considering design sensitivity analysis

In this study, optimum design process to reduce a torque ripple was presented for an interior permanent magnet (IPM) type electric traction motor. Firstly, 2-D electromagnetic finite element analysis was conducted to analyze the characteristics of the torque ripple in a view of magnetic saturation as well as cogging torque. Then, design factors of stator shape and rotor shape affecting to the torque ripple was selected as design variables. Secondly, using selected design variables, sensitivity analysis was performed to select design variable more affecting to the torque ripple and output torque by using design of experiments method. Thirdly, radial based function meta-model was constructed based on the results of the design of experiments (DOE). Finally, the optimum design was performed by using the constructed meta-model and method of feasible direction. By using the presented optimum design process, it is confirmed that the torque ripple of the optimum design was reduced to compare with the initial design and that output torque performance of the optimum design was maintained.

Torque Enhancement for a Novel Flux Intensifying PMa-SynRM Using Surface-Inset Permanent Magnet

This paper proposes a flux-intensifying permanent magnet-assisted synchronous reluctance motor (FI-PMa-SynRM) using surface-inset permanent magnet (PM) instead of embedded PM in the rotor. The proposed FI-PMa-SynRM employs a small amount of PM that is inset on the rotor surface facing $d$ -axis instead of facing $q$ -axis as in common PMa-SynRMs. It also differs from conventional flux-intensifying interior PM motor, where the PM is embedded inside the rotor. The proposed motor enables making use of the arrangements of two types of flux barriers (FBs): the cutoff FB and the magnet FB, collectively referred to the outer FBs, to enhance the torque output and reduce the torque ripple. The first objective in this paper is to explain the principles of the proposed FI-PMa-SynRM, and the second is to analyze the proposed technique for enhancement of the torque output with small PM volume while keeping the lowest possible torque ripple. The finite-element analysis is employed to validate the proposed motor and analyses, and the results demonstrate their advantages and effectiveness.

Irreversible Demagnetization Analysis for Multilayer Magnets of Permanent Magnet-Assisted Synchronous Reluctance Machines Considering Current Phase Angle

This paper investigates the demagnetization problem of permanent magnets for permanent magnet-assisted synchronous reluctance motors (PMa-SynRM) and applies “demagnetization ratio” as an index to evaluate demagnetization of permanent magnet (PM). The PMa-SynRM is often designed with multilayer flux barriers to improve saliency and reluctance torque in the rotor. Weaker or less PM (than that for interior PM motors) is embedded into the rotor which could be demagnetized in high-performance operation. PM demagnetization involves temperature, current magnitude, current phase angle, designed PM operating point, or combined effect of the above factors. This work investigates the demagnetization risk for PMs in all the layers of PMa-SynRM rotor considering these factors. In particular, the current phase angle for flux weakening operation is often omitted in demagnetization analysis. First, the motor performance to satisfy the operation condition over a wide speed range is analyzed and the proportion of motor torque components, i.e., reluctance torque and electromagnetic torque, considering temperature is investigated. Then, the flux density distributions on PMs at each position/layer are studied and the PM operating points are obtained based on the variation of excitation current, current phase angle, and temperature in order to evaluate the demagnetization risk. The analysis suggests that the high current phase angle combining the effect of high temperature is the major cause of irreversible demagnetization. Finally, a method incorporating the index “demagnetization ratio” is proposed to redesign the PMa-SynRM to avoid demagnetization. Experiments are conducted to validate the simulation.

Open-Circuit Field Prediction of Interior Permanent-Magnet Motor Using Hybrid Field Model Accounting for Saturation

A hybrid field model (HFM) based on the combination of magnetic equivalent circuit (MEC) and exact conformal mapping (ECM) is developed to calculate the open-circuit field of interior permanent-magnet (IPM) motor. In the proposed HFM, the IPM and iron saturations are transformed into equivalent current on the rotor surface and stator bore. ECM can calculate the air-gap field analytically using the equivalent current. Once the air-gap field is obtained, the MEC in the iron region can be solved and gives the new value of equivalent current, which forms a calculation loop. Hence, iterative solving process is required to determine the equivalent current and iron permeability in the rotor and stator. In order to verify the proposed model, both finite-element (FE) analysis and experiment are performed on IPM motors with V-type rotor and conventional “-” type rotor. Their results demonstrate the high accuracy of HFM.

Perfomance IPM Motors

As the EV industry trends toward the use of interior permanent magnet motors, specialist solutions have been designed to overcome the challenge of their optimal control and testing

An Analytical Study on Iron Pole Shape Optimization in High-Speed Interior Permanent Magnet Machines

Interior permanent magnet (IPM) motors are of extensive interest in high-speed applications, where high efficiency, high power density and robustness for these motors are a challenge. However, the noise and vibration caused due to cogging torque, electromagnetic torque ripple and reluctance torque ripple can greatly affect the machine performance. The main contribution of this paper is to develop a hyperbolic form analytical expression for optimal rotor iron pole curve in IPM motors to mitigate pulsating torque components. The analytical method is based on the resolution of Laplace equation in air gap sub-domain in polar coordinate by using the sub-domain method. The proposed method is applied to the performance computation of a prototype IPM machine, i.e., a three-phase 18S-8P motor. The analytical results are validated through FEA method and experimental tests.

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.

Parallel Finite-Element Method Based on Space–Time Domain Decomposition for Magnetic Field Analysis of Electric Machines

This paper develops a parallel finite-element method based on a space–time domain decomposition method. The proposed method combines a standard space domain decomposition approach with the parallel time-periodic explicit error correction method as a parallel-in-time integration method. To clarify its parallel performance, numerical results of magnetic field analyses of an interior permanent magnet motor fed by pulse width modulation inverters are demonstrated.

Topology Optimization Accelerated by Deep Learning

The computational cost of topology optimization based on the stochastic algorithm is shown to be greatly reduced by deep learning. In the learning phase, the cross-sectional image of an interior permanent magnet motor, represented in RGB, is used to train a convolutional neural network (CNN) to infer the torque properties. In the optimization phase, all the individuals are approximately evaluated by the trained CNN, while finite element analysis for accurate evaluation is performed only for a limited number of individuals. It is numerically shown that the computational cost for the topology optimization can be reduced without the loss of optimization quality.

Cogging Torque Reduction and Offset of Dual-Rotor Interior Permanent Magnet Motor in Electric Vehicle Traction Platforms

Recently, various methods have been proposed to increase the output power density of a driving motor applied to an electric vehicle. One such method is to design a structure with two motor rotors. High output density can be obtained by applying the dual rotor to the motor. However, this increases the cogging torque, which can cause high noise and vibration. In this paper, we proposed a method for reducing the cogging torque by adjusting the angle between the magnet and the dual rotor, as well as a novel method for reducing the cogging torque by angular adjustment of the slot opening based on electromagnetic field analysis. In addition, the design was implemented by applying a split core to increase the ease of manufacturing and the dot rate in the motor. We believe that high cogging torque, which is a disadvantage of dual rotor motors, can be lowered by the methods proposed in this paper. The results of this study are expected to be applicable to electric vehicles that require high output power density.

Inductance Testing for IPM Synchronous Machines According to the New IEEE Std 1812 and Typical Laboratory Practices

Equivalent circuit parameters serve as the basis for performance estimation and implementation of power electronic drives controls and therefore their accurate evaluation is very important. Specified in the newly approved IEEE Std 1812, a short-circuit test can be employed, in combination with an open-circuit measurement, in order to determine the back emf and the synchronous inductance. In the case of interior permanent magnet (IPM) machines, this approach can be used only to determine the d -axis inductance and additional and separate measurements are required for the q -axis inductance. In this respect, various methods, inclusive of dc step response tests, on-load tests, and a widely used test in industry, which involves locked-rotor measurements at variable voltage and constant frequency supply, are studied in detail, based on two-dimensional finite element analysis. Locked-rotor methods based on dc current supply and static torque versus rotor position measurements are introduced for determining the q -axis inductance in combination with the standardized open-circuit and short-circuit tests. A critical study of the inductances determined from different tests is conducted, and experimental results on an IPM motor design with non-sinusoidal back emf, relatively high torque ripple, and low leakage are presented.

Drive Control Development of Switched Reluctance Motor for Compact Electric Vehicles

<div class="section abstract"><div class="htmlview paragraph">This paper presents innovative methods to resolve the two challenges that occur when using a switched reluctance motor (SRM) as a traction motor for a compact electric vehicle (EV). Electric vehicles (EVs) are seeing a rise in popularity today and the demand for further advancement of EV technologies will continue to grow. Induction motors and interior permanent magnet motors (IPMs) are most commonly used traction motors for EVs. In this project, we focused on the development of a switched reluctance motor (SRM) as an alternative motor for compact EVs, leveraging the following benefits of SRMs:</div><div class="htmlview paragraph">1) SRMs, which require no permanent magnets, have no drag torque, enabling clutchless motor applications, and 2) SRMs demonstrate high efficiency in the high-speed rotation range. In applications of SRMs as EV drivers, however, there are two challenges to be resolved. The first challenge is that SRMs have significant torque ripples due to the principle of torque generation. As a measure to reduce these torque ripples, we have developed an effective commutation control system (Slope control of current command values) which changes current command values in a linear fashion. This system helps reduce torque ripples to approximately 40% at a maximum. The second challenge is to develop a cruise control system, which is indispensable for autonomous driving, while very few EVs equipped with SRMs are capable of cruise control. The developed cruise control system has resolved this challenge by optimizing the transition timing between power running control and regenerative braking, as proven by the road test results of a compact EV with the developed SPM maintaining a constant speed in uphill and downhill road conditions. With these two approaches, the developed SRM offers a practical solution to the insufficient torque issue and the cruise control challenge in SRM applications to compact EVs.</div></div>

Comprehensive Sensitivity Analysis and Multiobjective Optimization Research of Permanent Magnet Flux-Intensifying Motors

In this paper, two permanent magnet flux-intensifying motors are designed and optimized to realize the characteristic of Ld > Lq and the flux-intensifying effect. Compared with the conventional interior permanent magnet motor with the characteristic of Ld , the advantages of a low irreversible demagnetization risk and a wide speed range can be obtained in the motors. To meet multiple design requirements effectively, a comprehensive sensitivity analysis method is first implemented to evaluate the influence of each design variable on the selected optimized objectives of output torque, reverse saliency ratio, and torque ripple. Second, a sequential nonlinear programming algorithm is used for realizing the multiobjective optimizations of strong-sensitive design variables. Then, the performances of the two optimal motors are analyzed and compared with the initial permanent magnet motor in detail. Finally, two prototype motors are manufactured and tested. Both the simulation and experimental results verify the validity of the new flux-intensifying motors and the optimization method.

Investigation of Interior Permanent Magnet Motor With Dampers for Electric Vehicle Propulsion and Mitigation of Saliency Effect During Integrated Charging Operation

Power electronics and motor drive components existing in a conventional electric vehicle (EV) drivetrain employed to propel the EV can also be used to charge the battery under level 3 fast charging capacity. This integrated battery charging technology can be realized by employing the winding inductances of the three-phase interior permanent magnet synchronous motor (IPMSM) used for propulsion as line inductors while charging the EV's battery pack. The difference in the d - and q -axis inductances in the IPMSM offers unbalanced Thevenin impedances as viewed from stator terminals. This causes the voltages across the stator windings to become unbalanced when balanced three-phase currents synchronized with the grid utility voltages are forced into the three armature phases during charging. This paper first presents a case study employing a conventional laboratory IPMSM to illustrate the unbalanced phase winding impedance during an “emulated integrated charging” operation. Thereafter, the authors derive motivation to design and analyze an IPMSM with dampers in the rotor for propulsion and mitigation of the saliency effect, that is, the effect of unequal armature phase impedance at standstill during integrated charging. A novel design approach is presented and employed to design an IPMSM with dampers. Performance of the designed IPMSM with dampers is compared to that of the conventional IPMSM under both integrated charging and traction conditions. The proposed design is also validated experimentally using a laboratory IPMSM with dampers.

Investigation of the transient and steady state operations of two Line Start Permanent Magnet Motors (LSPMMS) with different rotor configurations

This paper investigates the transient and steady state operations of two Line Start Permanent Magnet Motors (LSPMMs) with different rotor types. The calculations showed that both designs can reach a higher efficiency than comparable induction motorsof the same size. The loading capability of the Surface Permanent Magnet (SPM) rotor is better than the Interior Permanent Magnet (IPM) rotor on asynchronous rotation as it has lesser torque ripples. However, IPM rotor had less flux leakage and copper losses at the synchronous operation under the same loading conditions.The results of the investigation also show that IPM motor attains a higher speed responses than SPM motor but SPM motor synchronizes faster than the IPM motor under the same loading conditions. During the asynchronous period, the chracteristics of both machines display similar features at a lower load torque less than 50N-m. The ripple contents of IPM is greater than that of SPM as can be observed in the run-up speed characteristics where IPM shows spontaneous overshoot. The pull out torque for SPM and IPM occurred at the time of 6 and 10 second respectively with same load increments. Keywords: synchronous, asynchronous, motor, permanent magnet, torque

Voltage minimization control of vector controlled interior permanent magnet motor

Maximum Torque Per Voltage trajectory has been utilized only during field weakening operation of Interior Permanent Magnet (IPM) motor. In this paper, the voltage minimization control from zero-speed is proposed. Voltage minimization results in maximum torque per voltage control of IPM motor. The control implementation is also simple in comparison to current minimization, as the operation is always along the current-limit locus irrespective of operation in field-weakening. Voltage minimization technique minimizes the core losses whereas current minimization would minimize the copper losses. The mathematical model of IPM motor following voltage minimization is derived and the solution to the 4th order quartic equations is obtained using Ferrari’s method. The solution obtained is utilized to develop a look-up table for vector control of IPM motor. A comparative analysis of voltage minimization and current minimization is established which is supported by simulation results and demonstrated by detailed experimental results.

Finite Element Approach of Interior Permanent Magnet Motor Acoustics Noise

IPM (Interior Permanent Magnet) motors produce torque based on two different mechanisms. The first of them is permanent-magnet torque, which is generated by the flux linkage between the PM (Permanent Magnet) rotor field and the electro-magnetic field of the stator. It is the same torque as produced by SPM (Surface Permanent Magnet) motors, however, IPM designs produce another force known as reluctance torque. The second one, the shape and location of the slots in the rotor laminations are designed to channel magnetic flux so that even if the slots were left as air gaps, the rotor would experience a force to align the magnetic flux lines with those generated by the stator coils. IPM motors are now very popular in industrial and military applications by providing high power density and high efficiency compared to other types of motors. This paper presents the use of finite element method harmonic analysis for investigation of IPM motor acoustics noise. This method is useful for DC (Direct Current) motor designs in many industrial and military applications.

Comparative Design and Analysis of New Type of Flux-Intensifying Interior Permanent Magnet Motors With Different <italic>Q</italic>-Axis Rotor Flux Barriers

In this paper, two new flux-intensifying interior permanent magnet (FI-IPM) motors owing the characteristic of Ld > Lq are proposed for extended operating speed range. The feasible approaches of realizing Ld > Lq are first discussed to emphasize rotor flux barrier design. According to the feasible approaches, interior flux barriers and surface flux barriers combined with different PM placements are adopted in these two motors. To verify the proposed approaches and the validity of motors, a comprehensive investigation and comparison between the two motors are carried out, including both electromagnetic performances and mechanical performances. By comparison, a prototype motor possessing lower torque ripple, lower magnetic saturation, wider speed range, and more robust mechanical property is manufactured and tested. The experiment results verify the characteristics of the proposed motors and the validity of the proposed approaches in FI-IPM motor design.

On-Line Inter-Turn Short-Circuit Fault Diagnosis and Torque Ripple Minimization Control Strategy Based on OW Five-Phase BFTHE-IPM

This paper proposed an on-line inter-turn short-circuit (ITSC) fault diagnosis approach by observing the dc component in the torque deviation for the open-end winding (OW) five-phase brushless fault-tolerant hybrid-excitation interior permanent magnet motor (BFTHE-IPM). To eliminate the impact of ITSC fault on torque and guarantee a disturbance-free operation, the strategy of torque ripple minimization is proposed, in which the virtual direct-quadrature axis current feedforward compensator is adopted. Moreover, the compensation is obtained by measuring the zero-sequence current without calculating short-circuit turns ratio and short-circuit current. Therefore, computational quantity and complexity of the algorithm are greatly reduced. Simulation and experimental results verify the effectiveness of the proposed method.