Electric Vehicle Traction Motor Research Articles

Electric vehicle traction motors without rare earth magnets

Since the Hybrid Electric Vehicle (HEV) became main-stream with the launch of the Toyota Prius in 1997, the use of rare earth magnets in vehicle traction motors has become common. In particular the rare earth based, hard magnetic material Neodymium Iron Boron (NdFeB) has offered significant performance benefits, not possible with other technologies, enabling the development of compact, torque- and power-dense electric traction motors. This trend has continued as mass market Battery Electric Vehicles (BEV) such as the Nissan Leaf, have come to market. However in 2011–2012 the price of these materials rose significantly, owing to geopolitical concerns relating to security of supply. Whilst the price has recovered more recently closer to historical levels, concern still remains in the minds of governments and many manufacturers of hybrid and electric vehicles. Reports have also raised questions over the environmental sustainability of these materials and this has further encouraged users to consider alternatives. This paper therefore examines why these magnetic materials have been so successful in traction motor applications. It also explores the alternatives, including those which are ready for market and those which are in the process of being developed.

Dielectric Characteristics of Electric Vehicle Traction Motor Winding Insulation under Thermal Ageing

The electric motor is the heart of the electric vehicle. It is crucial that any occurring faults are detected promptly so that a catastrophic failure is avoided. At the same time, deep knowledge of the degradation mechanisms is required to allow maximum performance at minimum cost. This paper focuses on this balance. Statistical results from measurements of unaged and accelerated aged winding insulation samples provide information about the degradation processes, enabling steps toward a reliable prognosis model of the motor's remaining life.

Increasing the efficiency of a traction electric drive for operation of a trolleybus

The possibility of using autonomous motion of an electric vehicle (EV) in parts of its route that lack a source of electric power is considered. In this case, supply of energy to the EV traction motor should be carried out from a supplementary accumulator. With the aim of being able to appropriately select power plant components, experimental studies of EV motion regimes were carried out under real traffic conditions. The obtained experimental results have been systematized and processed, and major features of EV motion have been determined. Statistical methods were used to select elements of the power plant. It has been shown that EV motion regimes are characterized by irregular power consumption from a power source. In order to eliminate this problem, it was proposed to use onboard accumulators of power that can balance the irregularity of power consumption. Electrochemical double-layer capacitors can be used as such accumulators. The use of electrochemical capacitors as a buffer power source under appropriate control will make it possible to improve the conditions of operation of an accumulator battery and increase run time of an autonomous vehicle.

Effectiveness of the Adaptive PID Controller for Traction Motor in Hybrid Electric Vehicles

This paper presents a detailed derivation of permanent magnet synchronous motor (PMSM), which can be used as the prime mover for simulation of hybrid electric vehicles (HEV). A torque tracking control for the motor is developed based on the adaptive proportional-integral-derivative (APID) controller .The effectiveness of the controller has been mathematically compared with the proportional-integral-derivative (PID) controller using various input functions such as step, saw tooth, sine wave and square wave. The results show that the APID-based control is effective in tracking the desired torque with good response and is able to adapt with the desired input as compared to the PID controller. This finding supports the selection of the APID for the toque tracking control of hybrid electric vehicles.

회전자 돌극 설계를 이용한 다극 매입형 영구자석 동기전동기의 토크리플 저감 연구

Abstract The paper reports an improvement method on torque ripples of multi-pole interior permanent magnet synchronous motor (IPMSM) applied to a traction motor for hybrid electric vehicles. In the case of multi-pole IPMSM, the magnetic flux generated by a permanent magnet tends to leak through the bridge of the rotor withouta link with stator windings. The slit design on the rotor surface was proposed to reduce torque rippling and increasethe output power by reducing the leakage flux. Two design parameters for the slit are suggested for optimal designusing the response surface method. As an analysis method, the 2D finite element method (FEM) was applied to consider magnetic saturation effect. Key Words : Interior permanent magnet synchronous motor, Response surface methodology, Torque ripple reduction * Corresponding Author : Ki-Chan Kim(Hanbat National Univ.)Tel: +82-42-821-1090 email: kckim@hanbat.ac.krReceived July 10, 2014 Revised August 4, 2014 Accepted October 10, 2014

Variable Structure Control Strategy Research on Regenerative Braking for a Brushless DC Motor Driven Electric Bus Cruising Downhill

To use regenerative braking to act as an auxiliary brake to maintain the constant speed of a brushless DC motor driven electric bus (BDCMEB) on downhill based on the feature of double-loop control structure of the control method for electric vehicle traction motor and the variable structural characteristics of PWM Control System for brushless DC Motor. A double-manifold variable structure control method to control regenerative braking is proposed for the bus cruising downhill. The impact of lead-acid battery's charge acceptance ability over a long charging period on the regenerative braking force of a driving motor is analyzed. Dynamic model of the bus on long downhill is established. A double-manifold variable structure controller is designed for the DCMEB on long downhill. The simulation result shows that the control system maintains enough stability and strong robustness. It may be achieved for the bus to maintain a constant speed downhill only by regenerative braking on a smaller slope. But the dynamic process is very slow. When deceleration or a constant speed is desired on a larger slope, only by electro mechanical parallel braking can the bus track the target speed precisely and quickly.

Design Considerations for an In-Wheel PM Motor with Fractional Slot Concentrated Windings for Light Electric Vehicle Applications

Design optimization of traction motors for light electric vehicles requires a comparative analysis in order to account for both performance and efficiency, while considering overall cost, size limitations and manufacturing complexity. This paper presents a comparative study on different surface mounted permanent magnet (SMPM) in-wheel motor configurations, facilitating fractional slot concentrated windings (FSCW). On a first step, different pole/ slot combinations were investigated and evaluated in terms of performance primarily. On a second step, different stator geometries were analyzed, considering both double and single layer windings and both equal and unequal stator teeth. Two different operating conditions were taken into account, i.e. nominal load and overload. The most advantageous was selected, by means of efficiency, clean interface and overall weight, using an extensive sensitivity analysis. On a third step, the final geometry was optimized, via fine-tuning of key design variables, accounting for maximum efficiency and minimum machine weight.

Design to Reduce Cost and Improve the Mechanical Durability of IPMSM in Traction Motors

The interior permanent-magnet synchronous motor (IPMSM) is often used for the traction motor of hybrid electric vehicles (HEVs) and electric vehicles (EVs) due to its high power density and wide speed range. This paper introduces the 120kW class IPMSM for traction motors in military trucks. This system, as a SHEV (series hybrid electric vehicle), requires a traction motor that can generate high torque. This study introduces a way to reduce costs by proposing a design approach that creates reluctance torque that can be maximized by varying the dq-axis inductance. If a model designed by a design approach meets the desired torque, the magnetic torque can be reduced by an amount equal to the increase in reluctance torque and consequently the amount of permanent magnets can be reduced. A reduction gear and high speed operation of motors are necessary for the miniaturization of the motor. Thus, a fairly large centrifugal force is generated due to the high speed rotation. This force causes mechanical interference between the rotor and the stator, and a design approach for adding an iron bridge is explained to solve the interference. In this study, the initial model and the improved model that reduces cost and improves mechanical durability are compared by FEA, and the models are produced. Finally, the FEM results were verified experimentally.

A Stress Analysis Method for the Rotor Design of an IPMSM Considering Radial Force

In the design of the rotor of an interior permanent magnet synchronous motor (IPMSM), the bridge between the permanent magnets helps prevent the scattering of permanent magnets and pole pieces during high-speed operation. In the design of a motor, if the bridge is too thick, its performance will be largely degraded because of flux leakage. Additionally, if the bridge is too thin, its mechanical safety cannot be guaranteed. Thus, an accurate analysis method is required to determine the thickness of the bridge. Conventional stress analysis methods determine the thickness of the bridge by only considering the centrifugal force of the rotors. In this study, however, a method that additionally considers the radial force generated by the air-gap flux density based on the conventional methods is proposed and reflected in the design of a traction motor for electric vehicles. Finally, the validity of this study is verified through a reliability test related to high-speed operation.

Study on the Traction Motor Characteristic for Hybrid Electric Vehicle

The basic characteristic for traction motor of hybrid electric vehicle affected the dynamics, economy as well as reliability performance for the vehicle directly. The paper derived all kinds of requirements for traction motor according to how improve the overall performance for vehicle. The control mode, static characteristics and dynamic characteristics for the traction motor were separately proposed, and performance index for traction motor were quantitative or quantitative analyzed. As a result, theoretical principle was supplied for parameter matching and evaluation for traction in this paper.

A Carrier-Based Neutral Voltage Modulation Strategy for Multilevel Cascaded Inverters Under Unbalanced DC Sources

This paper proposes a pulsewidth-modulation strategy to achieve balanced line-to-line output voltages and to maximize the modulation index in the linear modulation range where the output voltage can be linearly adjusted in the multilevel cascaded inverter (MLCI) operating under unbalanced dc-link conditions. In these conditions, the linear modulation range is reduced, and a significant output voltage imbalance may occur as voltage references increase. In order to analyze these effects, the voltage vector space for MLCI is evaluated in detail. From this analysis, the theory behind the output voltage imbalance is explained, and the maximum linear modulation range considering an unbalanced dc-link condition is evaluated. After that, a neutral voltage modulation strategy is proposed to achieve output voltage balancing as well as to extend the linear modulation range up to the maximum reachable point in theory. In the proposed method, too large of a dc-link imbalance precludes the balancing of the output voltages. This limitation is also discussed. Both the simulations and the experiments for a seven-level phase-shifted modulated MLCI for electric vehicle traction motor drive show that the proposed method is able to balance line-to-line output voltages as well as to maximize the linear modulation range under the unbalanced dc-link conditions.

Inductance Calculation in IPMSM Considering Magnetic Saturation

The design of a motor with a large armature reaction, such as the electric vehicle traction motor, can be implemented using a trial-and-error method based on the finite element method (FEM). The base model-design method that uses conventional magnetic equivalent circuits is quite inaccurate. To avoid such inaccuracy, this study proposes a method that accurately calculates the inductance values at a practical operating point considering the control issue. To achieve this objective, the flux linkage due to the current phase angles in each section is modeled using magnetic equivalent circuits. The result is used to calculate the inductance, assuming relative permeance waves. Finally, the validity of this study is verified by FEM simulation and testing.

Characteristics Comparison of a Conventional and Modified Spoke-Type Ferrite Magnet Motor for Traction Drives of Low-Speed Electric Vehicles

Rare-earth magnets have been widely employed for traction drive motors of hybrid and electric vehicles (EVs) due to high energy density. Nevertheless, the magnets have critical problems such as unstable supply and high cost. Recently, in order to solve the problems, a variety of motors not using rare-earth materials have been reviewed, such as an induction motor, a switched reluctance motor, and a spoke-type ferrite magnet motor (FMM). In this paper, a modified spoke-type FMM with a novel rotor configuration was presented for a traction motor of low-speed EVs. The characteristics of the modified spoke-type FMM are numerically compared with a conventional spoke-type FMM at the same design condition. Finally, the modified spoke-type FMM is fabricated and tested in order to verify its performance and feasibility.

A Power Presizing Methodology for Electric Vehicle Traction Motors

This paper proposes a methodology for presizing the power of an electric vehicle traction motor. Based on the vehicle desired performances, the electric motor optimal power can be calculated. The final objective is to meet the design constraints with minimum power under the European urban (ECE-15) and sub-urban (EUDC) driving cycles. The power presizing methodology is validated through extensive simulations for different induction motor-based electric vehicles.

Study on the Vehicle Cabin Noise Employing the Interfacial Friction in Double Layered Frames Used in Electric Vehicle Traction Motors

Study on the Vehicle Cabin Noise Employing the Interfacial Friction in Double Layered Frames Used in Electric Vehicle Traction Motors

Investigation of the Electric Vehicle Motor Constant Power Characteristics

The characteristics of traction motor for electric vehicle is introduced here. The qualitative analysis on the relation between the base speed ratio and power is showed. The emphasis is on the analysis and comparison for permanent magnet brushless DC motor, induction motor and switched reluctance motor.

Analysis on the Charateristics of Variable Reluctance Resolver Considering Uneven Magnetic Fields

Variable reluctance (VR) resolver is widely used in traction motor for battery-powered electric vehicles (EVs), as well as for hybrid EVs as rotor position sensor. VR resolver generates absolute position signal using resolver-to-digital converter (RDC) to deliver the exact position of permanent magnets in the rotor of a traction motor to the motor controller. This paper deals with analysis methodology on a VR resolver using cosimulation analysis with RDC tracking algorithm for position-angle detection considering uneven magnetic fields. The eccentricity of the VR resolver, short-circuit conditions of the excitation and output-signal coils, and shape of rotor saliency are considered as sources of uneven magnetic fields in the VR resolver. Two-dimensional FEM is used for the SIN and COS output-signal waveforms, and these waveforms are converted into absolute position angle using RDC algorithm. To verify the analysis results of the proposed resolver, experiments on different uneven magnetic field conditions were conducted and compared with the simulation results.

Application of High-Strength Nonoriented Electrical Steel to Interior Permanent Magnet Synchronous Motor

We investigated the torque characteristics and the motor efficiency of interior permanent magnet synchronous motors (IPMSM), in which a rotor core consists of high-strength nonoriented electrical steel, as-cold-rolled nonoriented electrical steel, and conventional nonoriented electrical steel with various bridge widths. Furthermore, we analyzed deformation behavior of the rotor core during operation by finite element method. The motor of the high-strength nonoriented electrical steel generated greater magnet torque than that of the conventional nonoriented electrical steel. Although the high-strength nonoriented electrical steel had much higher iron loss than the conventional nonoriented electrical steel, the motor efficiency decreased only slightly. A reduction in the bridge width of the rotor core significantly enhanced the torque characteristics and the motor efficiency of IPMSM. The high-strength nonoriented electrical steel effectively suppressed the deformation of the rotor core with its excellent mechanical properties, and the suppression enabled us to reduce the bridge width sufficiently. Accordingly, a magnetically optimum rotor core design will be realized with the high-strength nonoriented electrical steel, and the performance of IPMSM will be significantly enhanced, particularly in traction motors for electric vehicles and hybrid electric vehicles and compressor motors for energy-efficient air conditioners.

Determination Method of Centerpost Distance of Interior Permanent Magnet Synchronous Motor for Electric Vehicle Traction Motor considering Mechanical Safety

With the active development of hybrid electric vehicle (HEV), the application of interior permanent magnet synchronous motor (IPMSM) has been expanded. As wide driving region of IPMSM for electric vehicle (EV) traction motor is required, many studies are conducted to improve characteristics of a motor in both low and high-speed driving regions. A motor in high-speed driving region generates (produces) large stress to the rotor. Thus, the rotor needs to be designed considering the mechanical safety. Therefore, in this paper, we conducted stress analysis and electromagnetic analysis to determine the centerpost's distance which is considered important during the design of IPMSM for EV traction motor in order to secure mechanical safety and satisfy specifications of output requirement.

Novel estimation of tyre-road friction coefficient and slip ratio using electrical parameters of traction motor for electric vehicles

The estimation of the friction coeffi cient and the slip ratio is crucial for advanced traction control or anti-brake control of electric vehicles. In this paper, dynamic behaviours of electrical parameters of the traction motor under road change are modelled and analysed. Novel estimation only using the measurements of the armature voltage and the current is proposed. The proposed method is much quicker than traditional methods, contributing to adjust the vehicle’s motion state more quickly and precisely. Further, it can eliminate the speed measuring devices of the wheel speed and the vehicle speed. Simulations verify the effectiveness.