Permanent Magnet Traction Motor Research Articles

Design and Manufacture of a High-Torque-Density Permanent Magnet Traction Motor for Light-Duty Electric Vehicles

Design and Manufacture of a High-Torque-Density Permanent Magnet Traction Motor for Light-Duty Electric Vehicles

Cold-Spray Additive Manufacturing of a Petal-Shaped Surface Permanent Magnet Traction Motor

Several applications require low torque pulsations as they can lead to mechanical vibrations and acoustic noise in the electric motor. Optimization of the rotor permanent magnet (PM) shape is one of the effective methods for reducing torque pulsations. Unfortunately, the low versatility of the magnet fabrication technologies limits the development of new motor geometries. Cold spray additive manufacturing can be used for shaping permanent magnets for the direct fabrication of motor parts without the need for additional assembly steps. This fabrication technique allows an increase in the design flexibility of electric machine geometries targeting improved performance. This paper investigates the performance of permanent magnet rotors fabricated using a cold spray additive manufacturing technique for radial flux surface permanent magnet synchronous machines (SPMSM). The permanent magnet rotors considered are conventional rectangular-shaped with unskewed magnets (Model A), skewed magnets (Model B), and sinusoidal-petal shaped magnets (Model C) along the axial direction. The magnitude of magnetization current pulse required to magnetize these rotors is calculated and an impulse magnetizer setup is designed for in-situ magnetization. The performance of the shaped cold sprayed permanent magnet rotors and their effects on back EMF, electromagnetic torque, and cogging torque are analyzed experimentally and comparisons are made between the different rotor designs.

Identification and Analysis of Noise Sources of Permanent Magnet Synchronous Traction Motor with Interior Permanent Magnet

The rapid development of electromobility is placing ever higher demands on new electric motor designs. This results in a gradual reduction in weight with a simultaneous increase in maximum torque. As a result, unfavorable phenomena, such as vibration and noise, can become apparent in the drivetrain. Modeling and evaluation of the acoustic noise sources of a traction motor are particularly important when it is used, for example, as the traction drive of an electric bus, where too high noise levels can have a negative impact on passengers. This article describes methods for analyzing and evaluating the root causes of noise that occurs in permanent magnet traction motors with a rotor in which the magnets have been placed inside the rotor (PMSM IPM). This paper presents an analysis of acoustic noise and forces acting in the air gap of a 240 kW motor with 60 stator slots and 2p = 10 (s60p20) as the number of pole pairs designed for bus and truck drives. To determine the dominant noise sources and evaluate their value, the forces acting in the air gap and their effect on the deflection of the outer surface of the stator yoke were calculated. The natural frequencies of the machine, their frequencies for the entire rotor speed range, and the frequency of vibration of the motor stator were calculated. Based on these data, the sound power level (A-SWL) was calculated at varying motor speeds. MANATEE software (EOMYS, 9, avenue de la Créativité, 59650 Villeneuve d’Ascq—FRANCE) from EOMYS was used to perform vibroacoustic calculations. The analysis results were also subjected to verification on a laboratory bench.

A Comprehensive Design Guideline of Hairpin Windings for High Power Density Electric Vehicle Traction Motors

The rapidly increasing demand on power density levels of electric vehicle (EV) drive systems is pushing the boundaries of traction motor performance. Hairpin windings are becoming a popular option for EV motors due to their reduced dc losses and improved heat dissipation capability when compared to traditional random windings. In this article, a comprehensive design approach of hairpin winding layouts is first presented. The flexibility and limitation of end-winding patterns are thoroughly investigated in terms of basic pin connections, special jumpers, transposition, parallel branches, terminal positions, phase shift, winding pitches, as well as slot–pole combinations. To address the challenge of much reduced practical layout options with increased slot number per pole per phase, two novel hairpin winding designs are proposed. A 160-kW, 18 000-r/min permanent magnet (PM) traction motor featuring the new winding layout with 54-slot, 6-pole is developed using a multidomain design platform, which puts special focus on the conductor size optimization. The advantages of the designed motor are clearly revealed by comparison with the more traditional 48-slot, 8-pole counterpart. Finally, a corresponding stator prototype with the proposed hairpin winding is built to validate its manufacturability.

Bidirectional electromagnetic–thermal coupling analysis for permanent magnet traction motors under complex operating conditions

Temperature increase has a significant effect on the performance and service life of permanent magnet in-wheel motors (PMIWMs) in the traction systems of electric vehicles under complex operating conditions. Herein, we propose a bidirectional electromagnetic–thermal coupling method for analyzing the electromagnetic loss and thermal characteristics of a PMIWM considering the effect of increased temperature on the permanent magnet. The heat dissipation coefficient and electromagnetic–thermal coupling field model of each component of the PMIWM were analyzed. The distributions of electromagnetic loss and thermal loss of the PMIWM were investigated under constant-speed plus constant-torque and variable-speed plus variable-torque conditions. An 8 kW outer rotor PMIWM was used to study the electromagnetic–thermal coupling characteristics. Simulations and experimental results showed that the thermal field of each component of the PMIWM calculated using the proposed bidirectional electromagnetic–thermal coupling method was more accurate than that of the traditional unidirectional electromagnetic–thermal coupling method under complex operating conditions. The effectiveness of the proposed bidirectional electromagnetic–thermal coupling method provides solid support for the cooling design of PMIWMs operating in harsh environments.

Modified V-Shaped Interior Permanent Magnet Synchronous Motor Drive for Electric Vehicle

Electric Vehicles are one of the promising engineering areas. Among different types of permanent magnet traction motors, the Interior Permanent Magnet Synchronous Motor is the most efficient for electric vehicle applications. According to the rotor structure, the Interior Permanent Magnet Synchronous Motor is classified as an interior permanent magnet, U-shaped, V-shaped, and modified V-shaped Interior Permanent Magnet Synchronous Motor. The Modified V-shaped Interior Permanent Magnet Synchronous Motor has high efficiency, fewer core losses, fewer cogging torque, and less weight. Therefore, it is the most suitable Interior Permanent Magnet Synchronous Motor for electric vehicle applications. Among different motor controllers, the Field Oriented Control is the most suitable control technique due to less torque ripples and improved dynamics responses. In Modified V-shaped Interior Permanent Magnet Synchronous Motor, the reluctance torque is higher compared to other types of Interior Permanent Magnet Synchronous Motor. In conventional Field Oriented Control with the Constant Torque Angle method reluctance torque produced in a motor is not considered. Hence Modified V-shaped Interior Permanent Magnet Synchronous Motor with Constant Torque Angle based Field Oriented Control faces some drawbacks like poor steady-state and transient characteristics. These drawbacks are overcome with Maximum Torque Per Ampere based Field Oriented Control since it considers the reluctance torque and it has smooth steady-state characteristics. The performance comparison of Constant Torque Angle based Field Oriented Control and Maximum Torque Per Ampere based Field Oriented Control for Modified V-shaped Interior Permanent Magnet Synchronous Motor drive is presented in this paper. The entire system is validated with vehicle dynamics of E-rickshaw with a standard drive cycle. From this, it is proven that the Maximum Torque Per Ampere based Field Oriented Control is suitable for complete and efficient traction of Modified V-shaped Interior Permanent Magnet Synchronous Motor in the E-rickshaw application.

Rotor Position Estimation Approaches for Sensorless Control of Permanent Magnet Traction Motor in Electric Vehicles: A Review

Permanent magnet traction motor has the advantages of high efficiency, high power density, high torque density and quick dynamic response, which has been widely used in the traction field of electric vehicle. The high-performance control of permanent magnet traction motor depends on accurate rotor position information, which is usually obtained by using mechanical position sensors such as hall sensor, encoder and rotary transformer. However, the traditional mechanical sensor has the disadvantages of high cost, large volume and poor anti-interference ability, which limits the application of permanent magnet motor. The sensorless control technology is an effective way to solve the above-mentioned problem. Firstly, the sensorless control techniques of permanent magnet motor are classified. The sensorless control techniques of permanent magnet motor for rotor initial position, zero-low speed range, medium-high speed range and full speed range are deeply described and compared. Finally, the development trend of sensorless control technology of permanent magnet traction motor is prospected.

Design of Unskewed Interior Permanent Magnet Traction Motor with Asymmetric Flux Barriers and Shifted Magnets for Electric Vehicles

Interior permanent magnet synchronous motors (IPMSMs) are commonly used in electric and hybrid electric vehicles. Nissan Leaf electric vehicle (EV) uses skewed-rotor IPMSM as a traction motor. This motor is considered as a benchmark in this work. Although, skewing improves the torque quality of the motor by reducing the torque ripple, it reduces the average torque and increases the motor manufacturing complexity and cost. This article proposes improvements to the benchmark motor torque quality without skewing. The proposed motor uses the same stator winding and rotor magnet topologies of the benchmark motor with the same geometric constraints and magnet volume. Modifications are applied to the placement of the magnets in the rotor and the shape of the flux barriers to achieve the performance requirements. The design procedure of the proposed unskewed design is illustrated. Moreover, the electromagnetic performance of the proposed design is investigated. The design shows competitive performance in terms of the average torque, torque ripple, cogging torque, and efficiency compared to the benchmark motor. The mechanical integrity of the design is also verified. The proposed design is found to be a suitable alternative to the benchmark traction motor with a reduced rotor weight and without skewing.

An Algorithm for Effective Design and Performance Investigation of Active Cooling System for Required Temperature and Torque of PM Traction Motor

The conventional mechanical design approach of cooling jackets serves the goal of heat dissipation to keep motor temperature below the maximum allowable limit for thermal protection. However, the desired motor performance cannot be effectively achieved by this approach since it only employs heat transfer mechanism. Therefore, a detailed algorithm is developed to provide a constructive cooling design process to achieve the desired performance of a permanent magnet (PM) traction motor. In the preprocessing stage, a two-way electromagnetic (EM) and thermal co-analysis method is developed for preinvestigation of motor temperature and torque to set the goal for the cooling requirement. In the solver, a shape and size optimization method is utilized to get the optimal cooling design for fulfilling the requirement. Further, a multiphysics finite-element analysis model is developed for structural optimization to ensure safe minimal weight of cooling design for the improvement in torque and power density. In the validation step, unlike using only computational fluid dynamics (CFD) to predict motor temperature, a two-way coupling of EM and CFD model is utilized to ensure the design goals of both torque and temperature for several operating conditions. Finally, the design optimization of a cooling jacket for an interior PM synchronous motor is conducted by implementing this algorithm.

Novel Empirical Model for Calculation of Core Losses in Permanent Magnet Machines

This article presents a simple model for the calculation of core losses in permanent magnet machines based on the total flux linkage of the stator winding. In reality, the total core losses will vary as a function of permanent magnet field and the combination of $d-q$ current components even in the case when different $d-q$ currents produce the same amount of stator winding flux linkage at a given speed. The classical model with constant equivalent core loss resistance predicts constant core losses for constant flux linkage which leads to incorrect results. The model presented in this paper expands the classical core loss resistance based model with a novel additional term which corrects the classical model and calculates an additional core loss component as a function of $d$ axis current, total flux linkage of the stator winding, and two constant parameters. The accuracy of the model is confirmed by finite element simulations and core loss measurements for the cases of an interior permanent magnet traction motor and an industrial surface permanent magnet motor (only simulations).

Direct Liquid Cooling Method Verified With a Permanent-Magnet Traction Motor in a Bus

Direct liquid cooling (DLC) of electrical machine windings is a clearly effectual cooling method for high-torque and high-power-density applications needed, especially, in heavy vehicles. Usually, in electric vehicles, the stator copper winding losses are the most dominating losses during the accelerating or decelerating (recuperation) modes, and therefore, traditional windings may heat up significantly during high-torque periods. Removing the heat directly from the winding in which most of the heat is generated allows the most straightforward and effective way of cooling. This paper investigates the feasibility of the DLC in a radial-flux permanent-magnet traction motor. This case provides experimental information of the behavior of the DLC of the windings. The prototype motor equipped with DLC windings is installed in an electric bus so that typical bus load cycles can be tested.

가감속 성능향상을 위한 매입형 영구자석 견인전동기 연구

가감속 성능향상을 위한 매입형 영구자석 견인전동기 연구

Integration Principles and Thermal Analysis of an Oil-Cooled and -Lubricated Permanent Magnet Motor Planetary Gearbox Drive System

A permanent magnet traction motor integrated with a planetary gearbox is studied. A machine of this kind can be employed as a propulsion motor in off-road machines like agricultural tractors that have to produce either very high traction forces at low speeds or reach higher traveling speeds at lower torques. In principle, a constant power curve as a function of speed is desired, which means that the output torque of the drive system should be inversely proportional to the operating speed of the off-road machine. Such driving conditions are challenging as the electric motor has to be heavily overloaded at the lowest speeds. Therefore, it is essential to accurately evaluate not only the electromagnetic performance but also the thermal performance of the machine. This paper studies the integration principles of an electrical machine and a planetary gear. The integration poses some new challenges to the design. For example, also the lubrication and cooling can, and, in practice, must be integrated into the system. The thermal performance of the motor and cooling with the lubrication oil of the gear were analyzed. The long-term tests with the oil cooling system were carried out to verify the successful integration.

Thermal optimization of a totally enclosed forced ventilated permanentmagnet traction motor using lumped parameter and partial computational fluid dynamics modeling

In this study, we present a thermal optimization method using the overall lumped parameter (LP) and partial computational fluid dynamics (CFD) modeling for a 600-kW permanent magnet traction motor developed for high-speed trains. The motor is totally enclosed forced ventilated to achieve high power density, high efficiency, and low maintenance requirements. Considering the electro-magnetic performance, bogie space, and thermal capacity, we propose a ventilation structure with zigzag plates in sector cross-section. We focus particularly on the ventilation channels and propose an overall LP model for thermal optimization, in which the full consideration of the influence of turbulent flow is given by using a partial CFD model. Given the specific critical parameters from the optimization results, we present a complete 3D CFD model of the whole motor to obtain an accurate temperature distribution and the maximum temperature rises in local points. The benefit of zigzag plates is studied extensively using both the LP and the complete CFD models and the results are verified by equivalent thermal experiments under rated operations. Experimental results indicate that the ventilation structure fulfills the normal operational demands of high-speed trains by improving thermal performance by more than 15%. Additionally, we propose an engineering method to estimate iron loss constraint with the complete CFD model to guide the control system design.

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.

Reduction of Computational Efforts in Finite Element-Based Permanent Magnet Traction Motor Optimization

This paper presents a method for reducing computational time in constrained single objective optimization problems related to permanent magnet motors modeled using computationally intensive finite element method. The method is based on differential evolution algorithm. The principal approach is to interrupt the evaluation of inequality constraints after encountering the constraint which is violated and continue their evaluation only if better solutions are obtained in comparison with the candidate vector from the previous generation both in terms of inequality constraints and the cost function. This approach avoids unnecessary time consuming finite element calculations required for solving the inequality constraints and saves the overall optimization time without affecting the convergence rate. The main features of this approach and how it complements the existing method for handling inequality constraints in Differential Evolution algorithm is demonstrated on design optimization of an interior permanent magnet motor for the low-floor tram TMK 2200. The motor geometry is optimized for maximum torque density.

Thermal-fluid and electromagnetic coupling analysis and test of a traction motor for electric vehicles

This paper proposes a multi-phasic coupling analysis and test of a 50 kW traction motor for electric vehicles. The temperature-dependent properties of the electrical and magnetic materials of the interior permanent magnet traction motor are not negligible over a wide operation range of the vehicle. The heat produced by the electromagnetic power loss changes the motor’s properties, and in turn the motor performance changes to produce a different power loss. This two-way coupled electromagnetic and thermal-fluid analysis of the torque and speed curve and the transient thermal response at a rated operation point are simulated and compared with the traditional one-way coupling analysis. The simulation results are also compared with and proved by experiments on a prototype motor. The experimental results show that it is critical and necessary to predict the motor performance by means of the proposed two-way coupling analysis that provides more accurate information than the traditional one-way coupling analysis.

Production and Application of HPMS Recycled Bonded Permanent Magnets for a Traction Motor Application

Due to the volatility of the cost and sustainability concerns associated with the rare-earth permanent magnets, alternative product designs using less or no rare-earth contents have, recently, gained popularity. Another method to address this need is to apply a magnet recycling process, such as the novel hydrogen processing of magnetic scrap (HPMS) which can be applied to the end-of-life products such as hard drive disks. Despite the growing research on the background science of different recycling techniques, a practical make, use and evaluation of recycled magnets in a real-life application, is rarely attended. To address this gap, in this paper and for the first time, the viability of the HPMS recycled magnets for use in a permanent magnet traction motor is investigated. On this basis, a detailed description and testing of the recycling process and the magnet production for a customized traction motor design is provided. Furthermore, the behavior of the motor using the final magnet product is analyzed using simulations and prototype testing. Based on the results, the proposed recycled magnets satisfy the overall requirements, while demonstrating similar or better electromagnetic performance compared to the alternative low-cost ferrite magnets.

Dynamic Reluctance Mesh Modeling and Losses Evaluation of Permanent Magnet Traction Motor

In this paper, dynamic reluctance mesh model (DRM) combined with an improved iron losses prediction model are presented to provide fast and accurate way to evaluate the iron losses for permanent magnet (PM) motors with pulsewidth-modulated power supply. A DRM model for high-speed train PM traction motor is first built. The magnetic field distribution for one cycle is then obtained using the DRM method. An improved engineering model of iron losses prediction is applied. Finally, the simulation and testing results are presented to confirm that the proposed combined method is accurate and effective as the finite element method (FEM) model with much less time consumed.

Iron Loss Analysis of the Permanent-Magnet Synchronous Machine Based on Finite-Element Analysis Over the Electrical Vehicle Drive Cycle

Fast methods to estimate iron losses of the permanent magnet traction motor during the drive cycle of the electrical vehicle are compared. The methods use the iron loss information calculated by a finite-element analysis as a function of rotational speed both at no load and with a short-circuited stator to take into account the variable frequency and field weakening of the traction motor. The effect of iron losses on the optimal current components, providing the maximum efficiency, is studied. Several methods yield a good accuracy even based on the no-load iron loss only, but the accuracy can be improved especially in deep field weakening by including the short-circuit iron loss information in the analysis.