Application of Finite-Element Method to a PMLSM with Non-Sinusoidal Electromotive Force

Abstract

Remy Ghislain Non-member (L2EP, ENSAM Lille, ghislain.remy@lille.ensam.fr) Tounzi Abdelmounaïm Non-member (USTL, ENSAM Lille, mounaim.tounzi@univ-lille1.fr) Barre Pierre-Jean Non-member (L2EP, ENSAM Lille, barre@lille.ensam.fr) Piriou Francis Non-member (USTL, ENSAM Lille, francis.piriou@univ-lille1.fr) Hautier Jean-Paul Non-member (L2EP, ENSAM Lille, hautier@lille.ensam.fr) Keywords: PMLSM, non-sinusoidal electromotive force, finite-element analysis Nowadays industrial applications such as machine-tools applications require high speed and high precision. Fig.1 shows a prototype designed for high speed laser cutting. To improve the performances of linear motion systems, classical solutions used are to adapt more powerful linear motors, or to reduce the moving weight. But in the meantime, ripple forces induced by harmonics of Back-EMF are amplified as the power of the linear motor increases; consequently, the mechanical system is more and more perturbed by the force ripple and a high precision positioning becomes more difficult to reach. One solution is to improve the control strategy of such systems: to control permanent magnet linear synchronous motors (PMLSM) in an optimal way, the knowledge of the real waveform of different electrical characteristics is required. Thus, control strategies can be built on accurate values and yield reliable processes, notably on the thrust control. One of the electrical characteristics needed is the electromotive force (emf). This can be sinusoidal or not, which implies different control approaches. Furthermore, it is generally difficult to obtain this emf from measurements. Nowadays, the threedimensionnal finite-element method (3D-FEM) is widely used to model PMLSMs. Then, it can be helpful to determine the electrical characteristics of a PMLSM when it is difficult to measure them. It can also be used, in virtual prototypes, to quantify their electromagnetic variables in order to foresee the machine control or to modify the geometrical characteristics of the prototype to yield the desired results. The PMLSM studied is a LIMES400/120 from Siemens (Fig. 1). Measures and estimations of Back-EMF are made in realtime with a dSPACE 1005 card. Fig. 1. PMLSM PrototypeWe used the finite-element method to study the non-sinusoidal EMF of a PMLSM. Firstly, the finite-element method is introduced; as there are severals solutions to solve the Maxwell equations, two classical potential formulations are presented to express and solve the electromagnetic problem. Results presented give some advice to make the choice between the two formulations regarding to the studied system.Previous studies have shown that the high number of poles decreases the end effects and the dissymetry of the inductances. Consequently, it is possible to use the geometric periodicity to model only a part of the machine and then to limit the computation time without any effect on the accuracy of the results. We presented the elementary part modelled and the geometrical characteristics. Then, the several cases have been in...