Back-EMF Analysis of a Variable Flux Machine for Different Magnetization States

Abstract

This article presents the effect of different magnetization pulse widths and methods on the back electromotive force (EMF), no-load losses, and minimum inverter rating at different operating conditions of a variable flux permanent magnet synchronous machine (VF-PMSM/VFM). Precise information of the back-EMF helps to estimate the cogging torque and torque ripple. An accurate determination of the core loss leads to a better efficiency estimation and machine design. An experimentally determined minimum inverter rating reduces the cost of the motor drive system. An adaptive nonlinear filter is used to estimate the VFM back-EMF during the motoring mode. The VFM is often demagnetized and remagnetized by injecting a current pulse to achieve the high-speed and high-torque requirements. The sudden injection of a <italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">d</i> -axis current pulse will change the magnet flux linkage and back-EMF harmonics. In this article, harmonics present in the machine back-EMF due to different magnetization and demagnetization current pulse widths and magnetization methods are analyzed. Besides, the quality of the back-EMF for different speeds and machine no-load losses are presented for different magnetization levels. The minimum inverter current rating is determined for magnetizing current and magnetizing current at full load considering the minimum pulse amplitude and width to magnetize the VF-PMSM.