Calculation of D- and Q-Axis Inductances of Pm Brushless Ac Machines Accounting for Skew

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IEEE TRANSACTIONS ON MAGNETICS, VOL. 41, NO. 10, OCTOBER 2005

Calculation of d- and q -Axis Inductances of PM Brushless ac Machines Accounting for Skew

Y. S. Chen1;2 , Z. Q. Zhu2 , Senior Member, IEEE, and D. Howe2

College of Electrical Engineering, Zhejiang University, Hangzhou, P.R. China 310027 Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield S1 3JD, U.K.

A hybrid two-dimensional (2-D) finite-element/analytical technique is described for predicting the -axis and -axis inductances of permanent magnet (PM) brushless ac machines, with due account for the influence of skew. Predicted inductances are compared with measured values for two machines having identical stators, which are skewed by one slot-pitch, but which have different rotor topologies, one having surface-mounted magnets and the other having interior magnets. Index Terms—Brushless machine, permanent magnet (PM), permanent magnet (PM) machine, winding inductance.

I. INTRODUCTION

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HE -axis and -axis inductances have an important influence on both the steady-state and dynamic performance of permanent magnet (PM) brushless ac machines [1]. Thus, their accurate prediction is essential, not only for predicting performance aspects such as the torque and flux-weakening capabilities, but also for designing control systems, in order to maximize the efficiency, power factor, etc. The influence of magnetic saturation is usually accounted for by determining current-depenand . dent inductances [1], [2], i.e., However, since high local saturation may occur due to the combined influence of the PMs and the armature reaction field, especially in interior-magnet rotor machines, analytical methods for determining the winding inductances are often inadequate, and a numerical method must be employed. When the stator slots or rotor magnets are skewed, however, three-dimensional (3-D) calculations are required, which remain time consuming. In this paper, the influence of skew...