Evaluaciòn De Nùcleo De Motor Elèctrico

An Improved Formula for Lamination Core Loss Calculations in Machines Operating with High Frequency and High Flux Density Excitation
Yicheng Chen
Department of Electrical & Computer Engineering Clarkson University, Potsdam, NY 13699-5720, USA Also, Shenyang University of Technology, P.R.China yicheng@clarkson.edu

Pragasen Pillay, Senior Member, IEEE
Department of Electrical & ComputerEngineering Clarkson University Potsdam, NY 13699-5720, USA pillayp@clarkson.edu

Abstract—For electrical machine designers, core loss data are usually provided in the form of tables or curves of total loss versus flux density or frequency. These can be used to extract the loss coefficients of the core loss formulas. In this paper, three currently available formulas are discussed and compared withthe loss data supplied by lamination steel manufacturers. It is found that the dynamic hysteresis loop plays an important role in the total loss calculation, especially at high flux densities and high frequencies, and the loss coefficients should change with frequency. A new modified formula is proposed to represent the coefficient changes. The new curve is applied to the measured manufacturer’sdata, with acceptable accuracy.

According to the Steinmetz equation, measurement and calculation of core losses are normally made with sinusoidal flux density of varying magnitude and frequency. These measurements and calculations are based on the standard coil and frequently modeled by a two term function of the form

Pc = Ph + Pe
(1) = kh fB + ke f B , where f is the frequency of the externalmagnetic field, B is flux density, k h , k e and n are the coefficients, which depend on the lamination material, thickness, conductivity, as well as other factors. However, this formula is only applicable under the assumption that the maximum magnetic flux density of 1.0 Tesla is not exceeded and the hysteresis loop is under the static situation, which is not practical in electrical machines.When the magnetic flux density is over 1.0 Tesla or the field frequency becomes high, there is a big discrepancy between the calculation based on (1) and experimental results.
n 2 2

Keywords—electrical machines; hesteresis loss; eddy current loss; core loss; excess loss; high frequency excitation; high flux density excitation.

I. INTRODUCTION Core loss in a magnetic material occurs when thematerial is subjected to a time varying magnetic flux. The actual physical nature of this loss is still not completely understood and a simplistic explanation of this complex mechanism is as follows. Energy is used to effect “magnetic domain wall motion” as the domains grow and rotate under the influence of an externally applied magnetic field. When the external field is reduced or reversed from agiven value, domain wall motion again occurs to realize the necessary alignment of domains with the new value of the magnetic field. The energy associated with domain wall motion is irreversible and manifests itself as heat within the magnetic material. The rate at which the external field is changed has a strong influence upon the magnitude of the loss, and the loss is generally proportional tosome function of the frequency of variation of the magnetic field. The metallurgical structure of the magnetic material, including its electrical conductivity, also has a profound effect upon the magnitude of the loss. In electrical machines, this loss is generally termed the core loss. Traditionally, core loss Pc has been divided up into two components: hysteresis loss Ph and eddy current loss Pe.

For correction and modification, various models have been proposed [5], [6], [9], [10], [12], using the domain wall theory to explain the core loss. While such models provide useful insights into the loss mechanism, they do not, as yet accurately account for the so-called “anomalous loss”, or excess loss in a real lamination specimen, nor do they consider the flux harmonics. One of the...