A Method to Determine Direct- and Quadrature-Axis Inductances of Permanent Magnet Synchronous Motors

The equivalent circuit constants of permanent magnet synchronous motors are needed in the calculation of operation characteristics, construction of a control system, etc. These constants can be computed from the data on structural form and materials. However, measurements are necessary to obtain highly precise values. Methods for measurement of the d- and q-axis inductances can be roughly divided into rotational and standstill methods. The standstill methods have the advantage that they are easy to carry out. However, it is difficult to consider magnetic saturation and distortion of the change in the armature winding inductance. The accuracy of the standstill method can be improved if these effects can be readily taken into account. This paper describes a standstill method for measuring accurate d- and q-axis synchronous inductances of permanent magnet synchronous motors. By utilizing the fact that the EMF interference terms in the motor voltage equation considering the distortion of the inductance change are equal to zero when the rotor is in a specific position, the proposed method determines the inductances considering both magnetic saturation and inductance distortion effects from simple off-line standstill testing. In addition, this method is capable of taking cross-magnetic saturation into account when used with the necessary testing equipment. The proposed method was implemented on a 0.4-kW interior permanent magnet synchronous motor with concentrated stator winding. The validity of the proposed method was demonstrated by comparing the measured and calculated results of the no-load and on-load characteristics. (C) 2010 Wiley Periodicals, Inc. Electr Eng Jpn, 171(3): 41-50, 2010; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/eej.20969