Christophe Espanet

Analytical Solution of the Magnetic Field in Permanent-Magnet Motors Taking Into Account Slotting Effect: No-Load Vector Potential and Flux Density Calculation

We present a general computation taking into account the slotting effect on the no-load magnetic field distribution in multipole surface mounted permanent-magnet motors (SMPMM). A new analytical solution based on 2-D analysis in polar coordinates is developed. It includes both radial and parallel magnetization and the main originality is to consider the stator slotting. The saturation effect of the magnetic circuit is neglected. The 2-D analytical calculation of the no-load magnetic field with the slotting effect has been validated by a corresponding finite-element analysis (FEA). The analytical results are in very good agreement with those obtained by the FEA, considering both amplitude and waveform.

Specifications and Design of a PM Electric Variable Transmission for Toyota Prius II

This paper focuses on an analysis of technical requirements for the design of a permanent-magnet-type electric variable transmission (PM-EVT), which is a novel series-parallel hybrid electric vehicle (HEV) powertrain concept. Similar to the planetary gear train used in Toyota Prius II, the EVT also realizes the power-split function. However, it is implemented in an electromagnetic way rather than in a mechanical way, as is the case for Prius II with a planetary gear. In this paper, a procedure to define the technical requirements of an EVT is presented. Since Toyota Prius II is a well-known series-parallel HEV, this vehicle is chosen as a reference. The engine, battery, and other necessary components are kept as input data. A dynamic simulation was performed to take into account different driving cycles. Then, based on an analysis of the simulation results (torque, speed, and power) the technical requirements of the PM-EVT are defined. Finally, the PM-EVT machine is designed. The PM-EVT design results are presented and validated using the finite-element method (FEM).

BLDC motor stator and rotor iron losses and thermal behavior based on lumped schemes and 3-D FEM analysis

Many industrial applications refer to BLDC motors applied at their potential limits. Two cases related to the motor configuration lead to high possible iron losses and consequently to the necessary knowledge of the thermal behavior of the motor. Referring to the motor synchronous frequency: the first case corresponds to a relative low speed, but a high number of pole pairs (torque motors used in direct drive applications); the second case to a low number of pole pairs, but a high speed (mass storage applications, for example). The iron losses are a key issue since the considered frequencies are over the usual range of the known field of magnetic material vendor characteristics. Because the excitation flux and the slot geometry introduce high harmonic frequencies, rotor losses are a key issue of the investigation. This paper considers a torque motor with a high number of slots and poles. The authors present two different methods to model the iron losses and the thermal behavior. The first method uses two lumped schemes: the first scheme permits determination of the flux distribution as well as the stator, magnet and rotor yoke iron losses. The temperature gradient distribution is computed using an original lumped thermal scheme of the motor. The second method uses FEM analysis with a 2D model for the magnetic behavior and a 3D model for the thermal behavior. A testing bench for a BLDC torque motor has permitted measurement of the iron losses at no load generating operation and the temperature using thermal probes and infrared camera. Then simulations and measurements results are compared to characterize the accuracy of the two methods. The main interests of the presented work consist in the computation of the whole iron losses in the stator as well as in the rotor yoke and the magnets and in the 3D FEM computation of the thermal behavior.

Improvement of an EVT-Based HEV Using Dynamic Programming

Automotive engineers and researchers have proposed different topologies for series-parallel hybrid electric vehicles (SP-HEVs). The Toyota Hybrid System (THS) is the best known SP-HEV-based vehicle, but alternative solutions, such as electric variable transmission (EVT), have been also proposed. An efficient comparison between these different solutions is a key point to estimate the added value of each topology. This paper presents the application of optimal control to two series-parallel hybrid architectures for efficiency assessment purposes. The dynamic programming method is applied to the THS and to a virtual hybrid vehicle with an EVT. The way to take into account the supplementary degree of freedom provided by the decoupling of the wheels and the engine in both topologies is presented. The optimal fuel consumption is then compared on different driving cycles and brings out an overconsumption of the EVT topology. Then, a parametric study shows that inserting an appropriate gear ratio on the internal-combustion-engine (ICE) shaft can improve the EVT efficiency that becomes close to the THS efficiency.

BLDC motor stator and rotor iron losses and thermal behavior based on lumped schemes and 3D FEM analysis

Many industrial applications refer to BLDC motors applied at their potential limits. Two cases related to the motor configuration lead to high possible iron losses and consequently to the necessary knowledge of the thermal behavior of the motor. Referring to the motor synchronous frequency: the first case corresponds to a relative low speed, but a high number of pole pairs (torque motors used in direct drive applications); the second case to a low number of pole pairs, but a high speed (mass storage applications, for example). The iron losses are a key issue since the considered frequencies are over the usual range of the known field of magnetic material vendor characteristics. Because the excitation flux and the slot geometry introduce high harmonic frequencies, rotor losses are a key issue of the investigation. This paper considers a torque motor with a high number of slots and poles. The authors present two different methods to model the iron losses and the thermal behavior. The first method uses two lumped schemes: the first scheme permits determination of the flux distribution as well as the stator, magnet and rotor yoke iron losses. The temperature gradient distribution is computed using an original lumped thermal scheme of the motor. The second method uses FEM analysis with a 2D model for the magnetic behavior and a 3D model for the thermal behavior. A testing bench for a BLDC torque motor has permitted measurement of the iron losses at no load generating operation and the temperature using thermal probes and infrared camera. Then simulations and measurements results are compared to characterize the accuracy of the two methods. The main interests of the presented work consist in the computation of the whole iron losses in the stator as well as in the rotor yoke and the magnets and in the 3D FEM computation of the thermal behavior.

Design of a permanent magnet electric variable transmission for HEV applications

This paper focuses on a permanent magnet (PM) machine based electric variable transmission (PM-EVT) for HEV applications. The basic idea of EVT is firstly given as well as a state-of-the-art. To choose an appropriate PM-EVT structure, a detailed description of possible architectures is presented and the specifications are defined based on the well-known Toyota Prius hybrid car. Main design procedure and equations are presented. The first design is finished, some preliminary results are given.

PMSM and inverter sizing compromise applied to flywheel for railway application

In this paper the authors study the first step of power inverter and permanent magnets synchronous machine (PMSM) sizing, considering the application to a flywheel energy storage system. Knowing the operating characteristics of the drive defined by the application, our approach is based on determining the evolution of both machine torque and power converter current as functions of the rotational speed. It is shown that those curves strongly depend on the relative speed range of constant power and constant torque operations. The authors explain how to choose ©t1 (the rotational speed corresponding to the beginning of the constant power working) in order to obtain a good compromise between the inverter power and the PMSM torque. Finally the authors detail the influence of a real cyclic working on the design of the flywheel system.

Forces and vibrations analysis in industrial PM motors having concentric windings

Industrial applications involving torque BLDC motors require high efficiency over a large speed range. In order to achieve such specifications, the flux weakening is necessary, which could lead to relative high mechanical vibrations and consequently to audible noise. Furthermore, to decrease cogging torque and to satisfy motor manufacturing constraints, concentric windings are usually considered. Such motor configurations lead to harmonics of the electromagnetic forces being the sources of mechanical vibrations. This paper focuses on the electromagnetic forces created in SMPM and IPM motors for two concentric windings: one and two coils per slot. These forces are determined using a lumped magnetic scheme and 2D FE simulations. 3D FE simulations permit to determine the mechanical modes and the acoustic power. The acoustic measurements confirm the analysis and the proposed improvement.

A New Passive Methodology for Reducing the Noise in Electrical Machines: Impact of Some Parameters on the Modal Analysis

This paper presents a 3-D finite-element modal analysis to reduce the acoustical power radiated by a brushless permanent-magnet synchronous machines and avoid any resonance phenomena. The method is able to analyze the impact of some design parameters on all the resonance frequencies for reducing the total sound power and gives some guidelines to their choice. A less noisy prototype has been analyzed in simulation without any acoustic calculation and then built and validated with experimental results.

Design of an Axial-Flux Interior Permanent-Magnet Synchronous Motor for Automotive Application: Performance Comparison with Electric Motors Used in EVs and HEVs

The use of permanent-magnet (PM) machines for electric vehicles (EVs) and hybrid electric vehicles (HEVs) has grown substantially in recent decades. This is due to their high torque/power performances, especially when rare-earth PMs are used. Furthermore, high efficiency and, with adequate control, large speed operation range can be reached. In this paper, an axial-flux (AF) machine type interior PM (IPM) is designed to be used in HEV application. Machine performances will be described and compared to those of conventional IPM motors used in current commercialized EVs and HEVs.