Finite Element Calculation of Inductances of Internal Permanent Magnet Motors

Increasing power density and torque capability of permanent magnet synchronous machines can be achieved by a specific design of the rotors. The consequences of the complicated rotor structure are often the strong dependency of the inductance on the electric loading of the machine. The detailed finite element-based analysis of the inductances is described in this paper. It is shown by the comparison of the calculated values of inductances and flux linkages in the rotor coordinate system (d-q), that besides the inductances, the stator current significantly affects the permanent magnet (PM) flux linkage. As expected, the negative direct-axis current increases the permanent magnet flux linkage, but the quadrature-axis current excites the opposite quadrature-axis PM flux linkage. This additional flux linkage related to the exciting current can be desired as a part of the inductance and significantly affects the design of the machine and the traction characteristics.