Alain Cassat

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.

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.

A new passive methodology for controlling the noise in electrical machines: Impact of some parameters on the modal analysis

This paper presents an initial state of the art about the most important techniques for reducing noise in an electrical machine. The FEM 3D modal analysis (realized with the software Ansys 11.0) is then proposed to study and reduce the acoustical power radiated by a brushless machine 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.

New Estimation of Electromagnetic Sound Power Radiated by a PM Machine: an Active and Passive Control Guideline

This paper presents an initial state of the art about the estimation of the sound power emitted by electrical machines. The paper proposes a new method, more accurate, to evaluate the sound power emitted by a PM machine by a 3D FEM mechanical analysis. It also takes into account tangential forces applied on the teeth. Finally the papers shows the impact of any harmonic force in the global emitted sound power in order to establish the most disturbing force. It proposes a guideline for active and passive noise control.

Power Supply of Long Stator Linear Motors - Application to Multi Mobile System

In large cities, due to expensive land price, high-rise buildings are built, in which the space dedicated to the elevators is considerable and reduces the rented surfaces. To decrease these lost surfaces, a multi mobile system is proposed. It consists of several moving cabins in the same shaft, permitting also horizontal motions. The use of direct linear motor drives without counterweight is requested. The direct linear drives are defined by a long stator along the lift cage and by a linear PM magnetic way on each cabin. This paper focuses on the power supply of such a system. As the long linear stator is energized per sector, a methodology is proposed to study the complete system. New modules of Simsen software are developed, as Simsen is well adapted for the study of complex power systems and adjustable speed drives. The obtained results confirm the interest of the presented approach.

Advances in precise positioning using the electrostatic glass motor

This paper reports the continuation of the authors work in the field of linear and rotary sub-micrometric positioning using electrostatic glass motors. Electrostatic glass motors, a development where a glass rotor, once polarized using a static electrostatic field, is synchronously following a moving electrostatic field, have been described previously. The potential application to precise positioning was proven feasible and promising. The present report describes a fully operational rotary prototype, featuring remarkable performances. It is shown that sub arc-second positioning is possible in open loop operation, over an infinite operation range and over a very broad speed range. After a brief recapitulation of the propulsion principle, the realized system is presented and characterized, its performance experimentally determined and discussed.