Yves Perriard

Very-High-Speed Slotless Permanent-Magnet Motors: Analytical Modeling, Optimization, Design, and Torque Measurement Methods

This paper presents a very-high-speed (VHS) slotless permanent-magnet motor design procedure using an analytical model. The model is used to design the optimal prototype (target: 200 kr/min, 2 kW). The multiphysics analytical model allows a quick optimization process. The presented model includes the magnetic fields, the mechanical stresses in the rotor, the electromagnetic power losses, the windage power losses, and the power losses in the bearings. VHS machines need a new torque measurement method. This paper presents the developed method. It also presents a ball bearing friction torque measurement method designed particularly for VHS machines. Remarkably, the method allowed us to design a prototype which operates beyond the target of speed and power. The results given by the model are compared with the measurements of the prototype.

Contactless power and information transmission

In some applications, contacts between two devices are the first cause of dysfunctions. The aim of this study is to transfer contactless power energy to add new functions to a tool (a drill machine for example). A bi-directional communication is also needed. This is realized with an ironless high frequency transformer for both power and information transmission. Different coil geometries have been studied to reduce mutual inductance between power and information coils. This new solution enables to build low cost and smart energy transfer systems including communication.

Reducing the cogging torque in brushless DC motors by using conformal mappings

We present an exact model for determining the cogging torque in a brushless DC (BLDC) motor. It is based on the conformal mapping (CM) method, by which the motor configuration is transformed to a configuration where the magnetic field can be determined. Then, by integrating the field over the stator surface, the cogging torque is determined. By varying some motor parameters, which is easy to do, an optimal configuration with the minimal cogging torque is obtained. We have confirmed the results by the finite-element method (FEM). The model produces results much faster than FEM alone.

Optimization Design of a Segmented Halbach Permanent-Magnet Motor Using an Analytical Model

We present an optimization design of a slotless permanent-magnet brushless dc motor (400 W, 6000 rpm), with two-segment Halbach arrays. The optimization is based on a motor analytical model which is obtained by solving the magnetic scalar potential using the Fourier series. We show that the iron-cored Halbach configuration is better than the classical one and that the air-cored Halbach configuration is even better. This means that the rotor iron can be completely omitted. We verify the results by using the finite-element method.

Slotless Permanent-Magnet Machines: General Analytical Magnetic Field Calculation

This paper presents a general analytical model for predicting the magnetic field of slotless permanent-magnet machines. The model takes into account the effect of eddy currents in conductive regions and notably in conductive permanent magnets without neglecting their remanent field. The modeling of this effect is important for the design of very high speed slotless permanent-magnet machines, as the power losses are linked with the frequency of the field. The model takes into account any number of layers. It implies that, for one, the fields can easily be calculated in a design including a permanent magnet and a conductive retaining sleeve. The model is applicable both to internal rotor and external rotor permanent-magnet machines. The effect of the relative permeability and of the conductivity of the permanent magnet or of the yoke on the magnetic fields is also taken into account. Any magnetization can be taken into account, in particular a Halbach type permanent magnet, or a radially magnetized permanent magnet can be considered.

Force and Torque Analytical Models of a Reaction Sphere Actuator Based on Spherical Harmonic Rotation and Decomposition

This paper presents an analytical model for the force and torque developed by a reaction sphere actuator for satellite attitude control. The reaction sphere is an innovative momentum exchange device consisting of a magnetic bearings spherical rotor that can be electronically accelerated in any direction making all the three axes of stabilized spacecrafts controllable by a unique device. The spherical actuator is composed of an 8-pole permanent magnet spherical rotor and of a 20-coil stator. Force and torque analytical models are derived by solving the Laplace equation and applying the Lorentz force law. The novelty consists in exploiting powerful properties of spherical harmonic functions under rotation to derive closed-form linear expressions of forces and torques for all possible orientations of the rotor. Specifically, the orientation of the rotor is parametrized using seven decomposition coefficients that can be determined noniteratively and in a linear fashion by measuring the radial component of the magnetic flux density from at least seven different locations. Therefore, force and torque models for all possible orientations of the rotor are expressed in closed form as linear combination of mutually orthogonal force and torque characteristic matrices, which are computed offline. The proposed analytical models are experimentally validated using a developed laboratory prototype.

Analytical Solution for Rotor Eddy-Current Losses in a Slotless Permanent-Magnet Motor: The Case of Current Sheet Excitation

We present an analytical solution for the magnetic field, induced eddy currents, and the corresponding losses generated in the rotor of a slotless permanent-magnet (PM) motor. The field excitation is a current sheet placed at the stator interior surface. The solution is based on an analytical solution of the diffusion equation using double Fourier series and in the complex domain. The first and the second Fourier series correspond to the time and space harmonics, respectively. We have analyzed the effect of each time harmonic in detail, and verified the results with FEM software.

fMRI compatible haptic interface actuated with traveling wave ultrasonic motor

We are developing haptic interfaces compatible with functional magnetic resonance imaging (fMRI) for neuroscience studies. The presented prototype with one rotary degree of freedom is actuated by a traveling wave ultrasonic motor operating under admittance control. Torque is sensed from the deflection of an elastic polymer probe via light intensity measurement over optical fibers. This concept allows us to place all electronic components outside the shielded MR room. Hence, the device can be used in conjunction with fMRI, providing torque and motion feedback simultaneously with imaging. Its compactness and simplicity facilitate the construction of multiple degree of freedom systems.

Optimization of electric motor for a solar airplane application

This paper presents a method to model and optimize brushless dc motor for a solar airplane. In order to obtain the optimal solution for the given specifications, all free parameters are analyzed globally in one go. For this, the commercial optimization software Pro@Design is used. The method is fully analytical and deterministic. The actual multiphysic model comprises electromagnetic, thermal, and propeller models. Different results of the design of solar airplane motor using this method are presented

A New Standstill Position Detection Technique for Nonsalient Permanent-Magnet Synchronous Motors Using the Magnetic Anisotropy Method

This paper describes a new method to estimate the standstill position of permanent-magnet synchronous motors (PMSMs). The method is based on the anisotropic properties of permanent magnets and is therefore referred to as a magnetic anisotropy method (MAM). It differs significantly from all standard standstill position detection methods previously presented in the literature. It is totally independent of saliency and saturation effects and can therefore be used in many types of PMSMs where the standard methods would fail. The paper fully explains the experimental results and briefly analyzes the physical phenomena behind the method