An Improved Dq-Axis Coordinate System Model for Interior Permanent Magnet Machines

In interior permanent magnet (IPM) machines, dq-axis coordinate system is usually employed to analysis the machine. In commonly, the d-axis is coincided with the axis of pole. However, dq-axis armature reaction will not only affect the amplitude of the PM flux linkage, but also make dq-axis offset from the position under no load condition. These will lead errors for the traditional dq-axis coordinate system model on inductances and torque calculation. In this paper, frozen permeability method is employed to analysis the effect of dq-axis armature reaction on the flux linkage excited by PMs and winding currents. And then, the analysis result is used to set up an improved dq-axis coordinate system model for the IPM machines. After that, inductances and torque of an IPM machine calculated by improved model and traditional model are compared. The results show that, the torque calculated by improved model only has 0.8% error to the torque result calculated by finite element algorithm (FEA) software. While the effect of dq-axis armature reaction on PM flux linkage is not considered, the torque calculation error is 4.5%.