Direct Eigen Control for Induction Machines and Synchronous Motors

3

Interior Permanent Magnet Synchronous Motor

We now are able to follow the same approach as that we proposed for a surface mounted permanent magnet synchronous motor (SMPM-SM), with an interior permanent magnet synchronous motor (IPM-SM).

We will establish electrical equations for the synchronous motor with permanent magnets set inside magnetic steel rotor sheets. This motor can have a smooth rotor surface, but the rotor magnetic reluctance is not the same, depending on whether the stator magnetic field penetrates in the rotor through the pole of a magnet or between two magnet poles. This motor thus presents an electromagnetic saliency. This magnetic anisotropy is due to the difference between the relative permeability of magnets and that of the magnetic steel sheets of the rotor, but also to notches in the steel sheets which avoid magnetic short-circuits of the permanent magnets themselves. Many and various arrangements of magnets in the rotor have been propounded by technical papers (Moritomo et al., 1996).

Figure 3.1 is one of many examples of a rotor realization of this kind of motor, in this case with two pole pairs. The main field lines of two magnet pairs are represented, as well as the leakage flux of one magnet. The stator leakage flux is shown here for only one ­stator notch.

Saliency can be a direct one if the reluctance is less through the magnet poles (d axis) than that following the axis between magnet poles (q axis), or a reverse one in the opposite case. It depends ...