Electric Vehicle Traction Motor Research Articles

Using Machine Learning to Reduce Design Time for Permanent Magnet Volume Minimization in IPMSMs for Automotive Applications

Interior permanent magnet synchronous motors (IPMSMs) have been widely used as traction motors in electric vehicles. Finite element analysis is commonly used to design IPMSMs but is highly time-intensive. To shorten the design period for IPMSMs, various surrogate models have been constructed to predict relevant characteristics, and they have been used in the optimization of IPMSM geometry. However, to date, no surrogate models have been able to accurately predict the characteristics over the wide speed range required for automotive applications. Herein, we propose a method for accurately predicting the speed-torque characteristics of an IPMSM by using machine learning techniques. To improve the prediction accuracy, we set the motor parameters as the prediction target of the machine learning methods. We then used the trained surrogate model and a real-coded genetic algorithm to minimize the volume of the permanent magnet and showed that the design time can be significantly reduced compared with the case where only finite element analysis is used.

Analysis of an IPMSM Hybrid Magnetic Equivalent Circuit

The most common type of electric vehicle traction motor is the interior permanent magnet synchronous motor (IPMSM). For IPMSM designs, engineers make use of the magnetic equivalent circuit method, which is a lumped constant circuit method, and the finite element method, which is a distributed constant circuit method. The magnetic equivalent circuit method is useful for simple design through fast and intuitive parameters, but it cannot derive the distribution of the magnetic field. The finite element method can derive an accurate magnetic field distribution, but it takes a long time and is difficult to use for analysis of intuitive design parameters. In this study, the magnetic equivalent circuit method and Carter’s coefficient were combined for rotor structure design and accurate identification and analysis of circuit constants. In this paper, this design method is called the hybrid magnetic equivalent circuit method. Intuitive design parameters are derived through this hybrid magnetic equivalent circuit method. The air gap flux density distribution according to rotor shape, no-load-induced voltage, and cogging torque was analyzed and compared to results of the finite element method. The proposed method was found to achieve a short solving time and acceptably accurate results.

Improved Immune Algorithm Combined with Steepest Descent Method for Optimal Design of IPMSM for FCEV Traction Motor

In this paper, an improved immune algorithm (IIA) was proposed for the torque ripple reduction optimal design of an interior permanent magnet synchronous motor (IPMSM) for a fuel cell electric vehicle (FCEV) traction motor. When designing electric machines, both global and local solutions of optimal designs are required as design result should be compared in various aspects, including torque, torque ripple, and cogging torque. To lessen the computational burden of optimization using finite element analysis, the IIA proposes a method to efficiently adjust the generation of additional samples. The superior performance of the IIA was verified through the comparison of optimization results with conventional optimization methods in three mathematical test functions. The optimal design of an IPMSM using the IIA was conducted to verify the applicability in the design of practical electric machines.

Multi-Objective Optimization of Permanent Magnet Synchronous Motor for Electric Vehicle Considering Demagnetization

The irreversible demagnetization of permanent magnets causes the deterioration of the performance in permanent magnet synchronous motors (PMSMs), which are used for electric vehicles. NdFeB, which is the permanent magnet most commonly used in PMSMs for electric vehicles, is easily demagnetized at high temperatures. Because traction motors for electric vehicles reach high temperatures, and a high current can be instantaneously applied, permanent magnets of PMSM can be easily demagnetized. Therefore, it is important to study the demagnetization phenomenon of PMSMs for electric vehicles. However, since the demagnetization analysis procedure is complicated, previous studies have not been able to perform optimization considering demagnetization characteristics. In this study, we optimized the shape of a PMSM for electric vehicles by considering the demagnetization characteristics of permanent magnets using an automated design of experiments procedure. Using this procedure, a finite element analysis for each experimental point determined by a sampling method can be performed quickly and easily. The multi-objective function minimizes the demagnetization rate and maximizes the average torque, and the constraints are the efficiency and torque ripple. Various metamodels were generated for each of the multi-objective functions and constraints, and the metamodels with the best prediction performance were selected. By applying a multi-objective genetic algorithm, 1902 various optimal solutions were obtained. When the weight rate of the demagnetization rate to the torque was set to 0.1:0.9, the demagnetization rate and average torque were improved by 4.45% and 2.7%, respectively, compared to those of the initial model. The proposed multi-objective optimization method can guide the design of PMSMs for electric vehicles with high reliability and strong demagnetization characteristics.

Magnet Temperature Estimation of Traction Motor in Standstill With Considering Spatial Harmonics

In this article, a magnet temperature estimation method applicable to an interior permanent magnet synchronous machine (IPMSM) at a standstill has been newly devised. First, it is analyzed that an inductance of IPMSM varies according to not only a magnet temperature but also a rotor angle, which is spatial harmonics. The analysis is verified in a small-scaled motor-generation set (MG-set), where magnet temperatures can be directly measured. Based on the analysis and experimental results, it is demonstrated that spatial harmonics can make no negligible error in the magnet temperature estimation. Therefore, the estimation method has been newly devised in this article, considering spatial harmonics. As a result, the devised method can reduce the maximum estimation error from 25.3 to 6 °C based on experimental results in the small-scaled MG-set. Additionally, the devised method has been verified as feasible for use in the small-scaled motor and the traction motor of a mass-produced electric vehicle. As a result, the proposed method can estimate the magnet temperature accurately at every rotor position of both motors. Through this online estimation, the maximum estimation error is less than 5 °C even when the stator winding temperature is varying in both a small-scaled motor and the traction motor.

Improved V‐shaped interior permanent magnet rotor topology with inward‐extended bridges for reduced torque ripple

Interior permanent magnet synchronous machines (IPMSMs) with V-shaped permanent magnet (PM) rotors are widely used as traction motors in electric vehicles because of their high torque density and high efficiency. However, the V-shape IPMSMs have the disadvantages of inevitable torque ripple due to the non-sinusoidal air-gap flux density distribution and the utilisation of the reluctance torque. In this study, with the aim of improving the torque ripple characteristics, a modified V-shaped IPMSM rotor configuration with bridges extended inwards towards the pole centre is proposed to generate a more sinusoidal air-gap flux density waveform. The proposed topology, referred to as ‘Type C’ within this study, is compared with baseline rotor configuration references, namely ‘Type A’ which is a conventional V-shaped PM rotor, as well as ‘Type B’ which is a related configuration with a mechanically non-uniform air gap. The analysis results show that the rotor ‘Type C’ exhibits significant advantages in terms of reducing cogging torque, torque ripple and radial force, without incurring additional air-gap friction losses. Finally, a prototype of the IPMSM with the proposed rotor configuration is manufactured and tested, verifying the predicted benefits experimentally.

Low-cost high-performance ferrite permanent magnet machines in EV applications: A comprehensive review

Abstract Ferrite-based permanent magnet (PM) machines have been developed for many applications due to their highly desirable features such as low costs and stable supply chain. More recently, partly driven by the rapid uptake of the electric vehicle (EV) market, and partly due to the uncertainty of the supply chain of the rare-earth metals that are key components of the EV traction motor, there have been considerable interests in developing alternative solutions to rare-earth based PM motors. Due to their intrinsic low magnetic flux and prone to demagnetization, ferrite PM motors have not been previously considered for the more stringent EV applications. Hence, there is a growing body of research studies in addressing these challenges by deploying novel design strategies with varying proportions of ferrite materials, and with varying degrees of success. To date, there is a lack of comprehensive literature review of this class of evolving and yet highly promising electric machines that will offer a viable and sustainable alternative to EV traction applications. This paper aims to fill this gap and to provide a dedicated overview of these machines with a focus on their credentials as the ‘traction motor of choice’ in future EV markets.

Improvement of Traction Motor Performance for Electric Vehicles Using Conductors With Insulation of High Thermal Conductivity Considering Cooling Methods

This article utilizes conductors with insulation of high thermal conductivity (ThC) combining suitable cooling methods to enhance the performance of traction motors for electric vehicles. The performance of a 10 kW interior permanent magnet (IPM) motor without forced cooling is considered as a benchmark. Then, the conductors with two conventional insulation materials and two with high ThC are applied to the IPM motor windings. Two cooling methods, finned housing (no forced cooling) and water cooling, are considered here. It is found that using conductors with high ThC insulation without forced cooling can only cool the windings by several degrees; however, the temperature can be considerably reduced by combining water cooling with an appropriate flow rate. The torque and power output of the IPM motor can also be significantly improved. This indicates that forced cooling can further enhance the effectiveness of conductors with insulation of high ThC. Two induction motors using conductors with two different insulation materials (0.1 and 3 W/m·K) are tested. The experimental results validate the analysis.

Multi-objective optimization of a permanent magnet synchronous motor based on an automated design and analysis procedure

Since traction motors for electric vehicles require a variety of features to be used simultaneously, research on the design optimization of permanent magnet synchronous motors (PMSMs) has been increasing. To apply design optimization in the industrial field, it must be accurate, simple, and the design time should be minimized. This study proposes an automated design and analysis procedure to optimize the shape of a PMSM. ANSYS Maxwell and PIAnO were combined to implement automation, which are finite element analysis and design optimization software programs, respectively. The average torque and total harmonic distortion of the back electromotive force were set as a multi-objective function. In addition, the efficiency and torque ripple were set as constraints with five design variables to satisfy them. To verify the superiority of the proposed design optimization procedure, three optimization algorithms were reviewed and compared with metamodel-based design optimization. These algorithms include parallel algorithm discovery and orchestration, a progressive quadratic response surface method, and sequential two-point diagonal quadratic approximate optimization Moreover, because it is a design optimization problem with a multi-objective function, the changes in the design optimization results according to the changes in the weighting ratio were examined. Finally, the validity of the design results was verified through experiments. The research results demonstrate that the proposed design optimization procedure is more accurate, faster, and better than the conventional method.

Comprehensive Evaluation of Inter-Turn Short Circuit Faults in PMSM Used for Electric Vehicles

As a wheel traction motor used for electric vehicles (EVs), due to the requirement of high power/torque density and the poor working condition, it is more prone to cause severe inter-turn short circuit (ITSC) faults. In this paper, the ITSC faults characteristics of a permanent magnet synchronous machine (PMSM) used for wheel traction motors in EVs are deeply and comprehensively researched. The influence of fault intensity on machine’s parameters and performance are researched at different fault resistances through finite element method (FEM). Besides, factors that affect the amplitude of short circuit current are researched by mathematic formula and simulation, including load state, rotation speed, fault position and branch inductance. Then, the loss and thermal characteristics of the PMSM under different conditions are analyzed. In the last, experiments are conducted to validate the simulation results.

Back-Iron Extension Thermal Benefits for Electrical Machines With Concentrated Windings

This paper proposes a novel, low-cost, effective way to improve the thermal performance of electrical machines by extending a part of the back-iron into the slot. This modification helps in reducing the thermal resistance path from the center of the slot to the coolant; however, its thermal benefits must be clearly evaluated in conjunction with the electromagnetic aspects, due to the higher iron losses and flux leakage, and furthermore such an extension occupies space, which would otherwise be allocated to the copper itself. Taking a case study involving an existing 75-kW electric vehicle traction motor, the tradeoffs involving the losses, flux leakage, output torque, torque quality, and the peak winding temperature with and without back-iron extension are compared. Finally, experimental segments of the aforesaid motor are tested, verifying a significant 26.7% peak winding temperature reduction for the same output power with the proposed modification.

Traction Drive Technology for High Speed Traction Motors in Electric Vehicles

Traction Drive Technology for High Speed Traction Motors in Electric Vehicles

Optimum Design of Sensorless-Oriented IPMSM Considering Torque Characteristics

This article presents the design process of a sensorless-oriented interior permanent-magnet synchronous motor (IPMSM) with concentrated winding, based on spatial saliency for the traction motor in electric vehicles. The purpose of the design method is to ultimately achieve both stable rotor position detection and acceptable torque characteristics such as cogging torque and torque ripple. First, the relationship between the sensorless controllability and the electromagnetic parameters is derived through a mathematical method for a design considering sensorless drive of the motor. After describing the evaluating procedure of the sensorless controllability, the effects of the stator chamfer and notch are analyzed to figure out their effectiveness on the sensorless drive. Focusing on the analysis results of the geometric parameters, the improved model is designed through optimization, considering both sensorless controllability and torque characteristics. Response surface methodology (RSM) is used for optimization. Then, the machine characteristics including the sensorless controllability as the simulation results of the prototype and improved model are compared. It was found that the accuracy of the rotor position estimation and torque characteristics are improved simultaneously by means of the optimum design. Finally, the validity of the simulation results is verified by comparison with the test results of the prototype.

Prospect of developing Nd–Fe–B-type magnet with high electrical resistivity

Nd–Fe–B-type magnet is exclusively used as a rotor magnet in the traction motor of hybrid electric vehicle (HEV) and electric vehicle (EV), but its overly high operating temperature is a lingering problem attached to the magnet. The major cause of the high operating temperature is eddy current, which is readily generated in the highly conductive metallic magnet under alternating magnetic field from stator ripple. In this article, temperature rise in the Nd–Fe–B-type magnet with varying electrical resistivity under alternating magnetic field is discussed with the intention of highlighting the importance of enhancing the electrical resistivity for reducing the operating temperature of the Nd–Fe–B-type rotor magnet. Temperature rise in the Nd–Fe–B-type magnet (dielectric salt-added die-upset magnet) with high electrical resistivity is noticeably lower compared to the magnet (commercial sintered rotor magnet) with lower electrical resistivity, substantiating the theory that enhancing the electrical resistivity in the rotor magnet is fairly effective for suppressing the over-rise of its operating temperature during operation. Die-upset process is revealed to be particularly pertinent for the fabrication of highly dense salt-added magnet with high electrical resistivity.

Electromagnetic performance analysis and thermal research of an outer‐rotor I‐shaped flux‐switching permanent‐magnet motor with considering driving cycles

In the operation of electric vehicles (EVs), the driving conditions of frequent acceleration and deceleration, sudden start–stop, heavy load, and hill-climbing are usually required to meet the requirements of the increasing complexity of the modern transportation. Hence, the electromagnetic performance of traction motors in EVs should be investigated considering driving cycles. This study analyses the electromagnetic performance of an outer-rotor I-shaped flux-switching permanent-magnet (I-FSPM) motor with considering driving cycles. Firstly, the electromagnetic performance including the basic no-load characteristics, magnetic field distribution, and torque performances are analysed and compared under three different driving conditions. To analyse the proposed motor considering driving cycles comprehensively, the temperature rise is also calculated. Generally, the temperature rise is related to the loss characteristics. Thus, a loss prediction method considering the driving cycle for an I-FSPM motor is presented, where the New European Driving Cycle is chosen as the sample driving cycle. Also a lumped parameter thermal model is built. The predicted results of the I-FSPM motor are verified by the finite element calculations. Finally, experimental validation is carried out.

Hybrid excitation flux switching motor with permanent magnet placed at middle of field coil slots and high filling factor windings

Design and experimental studies on a hybrid excitation flux switching motor as a traction motor for hybrid electric vehicles drive are presented. A stator body of the motor consists of not only laminated silicon-iron electromagnetic steel and three-phase armature windings, but also both of field excitation coils and permanent magnets working together as a variable field magnetomotive force source. On the other hand, a rotor is composed of just laminated silicon-iron electromagnetic steel with salient poles like switched reluctance motor. To bring out the best in drive performances of the hybrid excitation flux switching motor as a variable flux motor for the application, each material adopted for the stator and rotor body should be designed properly in terms of motor efficiency, maximum torque and power densities and so forth. As some of them, in this paper, thinner silicon-iron electromagnetic steel sheet and permanent magnets with high remanent and low amount of Dysprosium used are applied for achieving higher motor efficiency. Moreover, all coils wound flatwise and edgewise using rectangular wires are introduced to realizing high filling factor for reduced copper losses. Experimental tests using a 60kW prototype of the motor demonstrates the designed motor has good motor efficiency under frequent operating points expected for the target vehicle drive.

Comparative Thermal Analysis of IPMSMs With Integral-Slot Distributed-Winding (ISDW) and Fractional-Slot Concentrated-Winding (FSCW) for Electric Vehicle Application

Fractional-slot concentrated-winding (FSCW) interior permanent magnet synchronous motors (IPMSMs) have been attracting considerable attention due to their high power density, high efficiency, short end winding, high slot fill factor, low cogging torque, excellent flux-weakening, and fault tolerance capability. However, compared to integral-slot distributed-winding (ISDW) IPMSMs, the key challenge of using FSCW configurations is the significant rotor losses, particularly at high speed. To figure out the IPMSM with which winding configuration is more suitable for electric vehicle (EV) application, the thermal behaviors of four IPMSMs with ISDW, single-, double-, and four-layer FSCWs are comprehensively and comparatively investigated in this paper. First, electromagnetic design and loss analysis of the four IPMSMs are investigated to meet the EV traction motor requirements. Second, finite-element method is employed to investigate the thermal performance of the IPMSMs under different rotational speeds and torque overload capacities. Thirdly, experiments implemented on an ISDW prototype are carried out to validate the presented analysis method. Finally, some conclusions are drawn for a suitable winding configuration selection and the PM traction motor design.

Analysis of axial flux motor performance for traction motor applications

PurposeAnalysis of test data monitored for a number of electric machines from the low volume production line can lead to useful conclusions. The purpose of this paper is to trace the machine performance to find quality-related issues and/or identify assembly process ones. In this paper, the monitoring of experimental data is related to the axial flux motor (AFM) used in hybrid electric vehicle (HEV) and in electric vehicle (EV) traction motors in the global automobile market.Design/methodology/approachExtensive data analyses raised questions like what could be the causes of possible performance deterioration of the AFM and how many electric motors may not pass requirements during operation tests. In small and medium research units of AFM for HEV or EV, engineers came across a number of serious issues that must be resolved. A number of issues can be eliminated by implementing methods for reducing the number of failing AFMs. For example, improving the motor assembly precision leads to reduction of the machine parameters deterioration.FindingsAssembly tolerances on electric motor characteristics should be investigated during motor design. The presented measurements can be usable and can point out the weakest parts of the motor that can be a reason for the reduced efficiency and/or lifetime of the AFM. Additionally, the paper is addressed to electric motor engineers designing and/or investigating electric AFMs.Originality/valuePerformance of AFM was monitored for a number of identical motors from low volume production line. All tested motors were operated continuously for a long period of time and the tests were repeated every few weeks for half a year to check the reliability of motor design and indicate how much the motor parameters may change. The final results point how many motors fail the requirements of motor performance. A few batches of AFM were selected for testing. Each batch represents a different size (nominal power) of the same type of AFM.

Real-time simulation of scaled propulsion unit for light electric vehicles

This paper presents the implementation in a real-time simulation the Buckingham Pi theorem scaling method applied to a small surface-mounted permanent-magnet synchronous motor (PMSM) and a low-power battery pack. The goal is the entire system to behave as a light electric vehicle traction motor of 9 kW with a power supply of 652 Wh. In order to determine the optimum size of the motor and the battery pack, this method is a valuable tool. This scaling flexibility can be used to build a relatively low-cost test bench where a propulsion unit can be tested for different motors and batteries, using the same components but with different scaling gains. The scaling method is applied to calculate the appropriate scaling gains. For the PMSM traction motor, the field-oriented control is applied. The models of the control PMSM and the battery are built using MATLAB/Simulink and converted into a dynamic-link library file in order to be uploaded into the real-time processor of the Embedded Controller NI PXIe-8135 2.3 GHz Quad-Core. Different simulation scenarios are applied using NI VeriStand. In LMS Amesim software, a model for the vehicle was built. In the model, the traction motor used is the scaled PMSM and the power supply is the scaled battery. For the complete vehicle, the urban dynamometer driving schedule was applied to test the complete system.

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>