Development of a High-Efficiency Double Air Gap Axial Flux Synchronous Reluctance Motor for Electric Vehicles: Effect of Magnet Assistance

This article deals with the design of high-speed synchronous reluctance motors for electric vehicle applications. The need to enhance the power density and to lower the cost leads to research on high-speed motors with a reduced amount of rare earth. Pure synchronous reluctance motors potentially operate at high speed and exhibit a cost-effective rotor compared to permanent magnets and induction motors. Nevertheless, they present reduced performances in deep flux weakening operations, in particular when the so-called radial ribs are introduced to increase the mechanical robustness of the rotor. In this article, the introduction of the radial ribs and the related design challenges are investigated and discussed. The adoption of the topology optimization tool that is able to optimize the amount, the positioning, and the sizing of suitable structural ribs is presented. A design flow integrating the topology optimization is presented. The approach leads to an original positioning of the radial ribs able to preserve the performance of the motor at high operating speed enhancing the mechanical integrity of the rotor.

This paper deals with the design of high-speed Synchronous Reluctance motors for electric vehicle applications. The need to enhance power density and lowering costs leads to the design of high speed motors with a reduced amount of rare earth. Pure synchronous reluctance motors potentially operate at high speed and exhibit a low cost rotor compared to PM and induction motors. Nevertheless, they present reduced performances in deep flux weakening operations in particular when the so-called radial ribs are introduced to increase the mechanical robustness of the rotor. In this paper the adoption of the radial ribs in the related design challenges are investigated and discussed. The adoption of a suitable commercial optimization tool able to optimize the placement and the sizing of the radial ribs is presented. The approach leads to an original positioning of the radial ribs able to preserve the performances of the motor at high operating speed enhancing the mechanical integrity of the rotor.

In this paper, Switched Reluctance Motor (SRM) for electric vehicle (EV) is designed using finite element method (FEM). The static torque of SRM is estimated with the magnetic field analysis. The temperature rise with time of SRM is estimated with the heat transfer analysis. First, the static torque and temperature rise with time of 600W SRM for sample machine are measured in the experiment, and they are compared with the calculated results using FEM under the same conditions. The validity of magnetic field analysis and heat transfer analysis is verified by the comparisons. Then, the 60 [kW] SRM for EV, which has the output characteristics equal to 1500 [cc] gasoline engine, is designed with the magnetic field analysis and heat transfer analysis.

With the development of the economy and the deepening of the energy crisis, electric vehicle has now become the hotspot of the global automotive industry. Therefore, as the key part of electric vehicle, the design and research of drive motor has become the focus of attention of engineers and technicians. Because of its simple structure, easy maintenance, high output power, high output torque, wide speed range, and high efficiency, the switched reluctance motor (SRM) has been one of the first choice of electric vehicle driving motors. According to the performance requirements of electric vehicle driving motors, a 3-phase 24/16 pole with rated power of 30 kW switched reluctance motor (SRM) for electric vehicle has been designed in this paper by using Motor-Cad which can be used to optimize the parameters of motor to make the overall structure of the motor more reasonable. In order to reduce the torque ripple of switched reluctance motor, appropriate stator polar arc and rotor polar arc design are used in the motor. To realize the speed control of switched reluctance motor in a wide range, PWM control mode is adopted in this paper, which has fast motor response speed, high power factor and excellent dynamic and static performance. The simulation results show that the performance indexes of the switched reluctance motor meet the design requirements completely.

In this study, a high-power synchronous reluctance motor (SynRM) was designed for the traction motor of electric vehicle (EV) and its double-stage optimization was performed. Genetic algorithm and sensitivity analysis methods were used to obtain the best design parameters. Double-stage optimization was carried out to minimize the torque ripple and obtain the targeted torque, speed, and power values of the SynRM. In the first stage, the genetic algorithm method was used to improve the design parameters of the stator and rotor. With the improved design parameters, it was observed that the torque ripple decreased. In the second stage, the sensitivity analysis method was used. In this method, the effect of changing the skew angle of the stator on the torque ripple was investigated. The performance of the designed motor was examined in the optimization process. It was observed that the targeted torque, power, speed, efficiency, and torque ripple minimization values are successfully achieved with the best stator and rotor parameters. The results showed that SynRM produces high torque and high power with high efficiency and low torque ripple over wide speed range. It is quite proper to use the designed SynRM as a traction motor of new generation electric vehicles.

Today’s automotive industry has focused its studies on electric vehicles (EVs) or hybrid electric vehicles (HEVs) rather than gasoline-powered vehicles. For this reason, more investment has been made in electric motors with high efficiency, high torque density, and high-power factor to be used in both EVs and HEVs. In this study, an outer-rotor permanent-magnet-assisted synchronous reluctance motor (PMaSynRM) with a new rotor topology was designed for use in an EV. The design has a transversally laminated anisotropic (TLA) rotor structure. In addition, neodymium-iron-boron (NdFeB) magnets were used in rotor topology. The stator slots were designed as distributed windings, so torque ripples are minimized. At the same time, the maximum electromagnetic torque was achieved. The analysis of the designed motor was carried out using the finite element method (FEM). Optimal values of motor parameters were obtained by improving the rotor geometry of the three-phase PMaSynRM in order to obtain maximum torque and minimum torque ripple in the design. The motor is in a 48/8 slot/pole combination, a speed of 750 rpm and a power of 1 kW. The simulation results showed that the design achieved maximum torque and minimum torque ripple.

Electromagnetic Design of Synchronous Reluctance Motors for Electric Vehicles Considering Mechanical Stress

Synchronous reluctance motor is a cost-effective solution for existing motors such as PMSM, BLDC, and switched reluctance motors used for electric vehicle applications. A Synchronous reluctance motor with high efficiency, good power factor, better speed, and rotor with high mechanical integrity is required for the electric vehicle. The performance enhancement of a 35 kW synchronous reluctance motor for an electric car is proposed in this paper. An average vehicle speed of 60 km/hr is considered for the speed calculation of motor. The performance analysis and enhancement of the synchronous reluctance motor are analytically designed and virtually developed in the Ansys platform. The performance analysis is carried out using the simulation of the virtually developed motor with two types of flux barrier named hyperbolic-curve and hyperbolic-polyline. Among them, synchronous reluctance motor with hyperbolic-polyline shows better efficiency. The performance parameter such as power factor and efficiency of synchronous reluctance motor with hyperbolic-polyline flux barrier is analyzed by changing the flux barrier alignment in the rotor geometry. The proposed alignment method of flux barrier improves the saliency ratio, power factor, efficiency, and reduces the cost due to savings of material in the rotor of synchronous reluctance motor.

In this study, the Axial Flux Synchronous Reluctance Motor (AF-SynRM) with multiple barriers in its rotor is designed and it is aimed to compare the performance with the Axial Flux Induction Motor (AF-IM) with the same stator structure and dimensions. For an equal comparison, the motor dimensions and stator structure are chosen the same, only the rotor is changed. In the preliminary study of the designs, machine dimensions are calculated analytically and modeled with the 3D Finite Element Method (FEM). To optimize the saliency ratio, which is the most important factor affecting AF-SynRM performance, Genetic Algorithm (GA) based optimization is performed and the rotor geometry is changed. Thus, a suitable model is created for comparison. Torque, efficiency, input power, power factor, total loses and torque per amper parameters are analyzed. With the proposed comparison method, AF-SynRM obtains higher efficiency, power, torque per ampere and lower losses than AF-IM at the same power rating (2.2 kW). The AF-SynRM rotor will be a good alternative in applications where high efficiency and torque are required, with low cost-maintenance costs due to the absence of a squirrel cage and its structure without magnet.

A uniform magnetic density distribution in the air gap is key for the Lorentz magnetic bearing to achieve high precision control and large torque output. To overcome the small magnetic field strength in an explicit magnetic bearing and a high magnetic density fluctuation rate in an implicit Lorentz magnetic bearing, a second air gap design method is proposed based on the maximum magnetic density distribution in the winding area. A novel Lorentz bearing with a double second air gap is designed. The maximum magnetic field strength in the winding area is calculated by the finite element method, and the structure of the double second air gap is designed. To reduce the calculation error of the magnetic field strength, the division of the reluctance by the magnetic induction line is proposed. The reluctance calculation formula is given. Based on Ohm’s law, the calculation of the magnetic field strength is obtained. Finally, a prototype of the novel Lorentz magnetic bearing is made. The magnetic field strength in the winding area and the magnetic density fluctuation rate are measured with a magnetic density measurement instrument. The maximum magnetic flux density in the winding area is 0.631 T, and the magnetic field strength is 0.58%. Less difference is found between the measurement result and the finite element result.

Direct drive permanent magnet (PM) motors have become a very attractive choice for electric vehicles. Generally, PM motors are divided into PM synchronous motors (PMSMs) and PM flux‐modulated motors (PMFMMs). High torque density is the main requirement of direct drive motors, therefore, the structure of conventional PM motors is modified to boost the torque. Increasing the number of poles is a structural modification to achieve high torque density in PMSMs; however, a large number of poles affects motor characteristics such as power factor, flux weakening, losses, and efficiency. The other way to have high torque is to use PMFMMs, which have a high intrinsic torque density. This paper first compares the performance of PMSMs with different number of poles. Then the performance of PMFMMs and PMSMs are compared to show their differences. The performance of PMFMMs with different teeth modulators and magnetic gear ratios are predicted to show their effects upon its performance. The simulation results using finite elements method|finite element method (FEM) are presented, and finally, a PMFMM with 36 slots and 40 poles as case study is subjected to an experimental test and its results are compared with FEM.The cover image is based on the article Comparison of permanent magnet synchronous machine and permanent magnet flux‐modulated machine in direct drive considering number of rotor poles by Saeed Abareshi et al., https://doi.org/10.1049/elp2.12500.

The demand of fossil fuel vehicles has decreased due to carbon emissions. Recently, electric vehicles (EV) with electric motor propulsion have gotten attention due to their zero carbon emissions and high efficiency. In this study, an outer rotor in wheel switched reluctance motor (IWSRM) with 18 poles on the stator and 24 poles on the rotor, designed for the propulsion of electric vehicles, is investigated in two-dimensional Finite Element Method (FEM). The magnetic field distributions of IWSRM for different rotor positions at nominal current are obtained. Then, the torque and phase inductance are calculated. As a result, the designed IWRSM provided low torque.

The 3-D finite element method (FEM) has been widely used for accurate analysis of winding loss with winding axial transposition angle considered. However, its application is limited due to long computation time and complex modeling processes. To address these problems, this article proposed a 2-D equivalent permeability modeling method (EMM). First, according to the proposed method, the 3-D winding model with axial transposition angle could be equivalent to several segmented 2-D models. Through equivalent axial length coefficients, 2-D models with different axial lengths could be solved in one project. Using appropriate segment and equivalent coefficients, to a great extent, the inherent error of the 2-D model could be reduced. Second, with equivalent permeability and conductivity, current density distribution and winding ac loss could be calculated. To verify the correctness and robustness of the proposed method, the study was conducted in the five-parallel-strand model. Single-tooth models with concentrated windings were built to verify the evaluated winding loss. In addition, a 20-kW 12/8 high-speed switched reluctance motor was manufactured, and the temperature rise was tested to verify the effect of winding loss on the temperature rise. Through the comparison of experiments and FEM, the EMM is verified to be with high accuracy and computational efficiency to analyze the ac loss and current distribution.

The SynRM stands for synchronous reluctance machine. The machine rotor has no windings, no conducting bar and no permanent magnet. Its rotor loss is negligibly small so that it has higher efficiency than the traditional induction motor and satisfies the high standard on efficiency such as IE3, IE4 or IE5. In addition, it has lower cost than the permanent magnet motor. Therefore, it is increasingly used in electrical vehicles. The article presents a method to design a synchronous reluctance motor. The sizing equation is presented and discussed. The motor is initially designed using analytical equations then the design is refined by using time-stepping transient finite element method (FEM) including rotor motion. The concept to make automatically transient FEM is given out. The influence of design parameters on torque ripple is investigated.

Motor design can be said as multi-modal optimization problem, as many performances should be considered. In addition, a time-consuming finite element method (FEM) is required for accurate analysis of the motor, and such computational burden becomes worse when the FEM is applied to multi-modal optimization problem. In this paper, adaptive-sampling kriging algorithm (ASKA) is proposed to relieve the computation cost of multi-modal optimization problem. The ASKA utilizes kriging interpolation model with generated samples by Compact Search Sampling (CSS) and Exclusive Space-filling Method (ESM). The CSS improves the accuracy of the solutions by generating samples near the expected solutions, and the ESM guarantees the diversity of solutions by generating samples far from existing samples, avoiding solution-near area. Using CSS and ESM, the ASKA adjusts the number of samples effectively and reduces function call considerably. The superior performance of the ASKA was verified by mathematical test functions with complex objective function regions. To validate the feasibility of actual electric machines, the ASKA was applied to optimal design of permanent magnet assisted synchronous reluctance motors for electric vehicles and optimum design with diminished torque ripple is derived.