Torque-speed performance analysis of fractional slot PM machines having concentrated windings using alternate methods

Due to high torque density and efficiency, permanent magnet (PM) machines are widely utilized in industrial and commercial applications for all power ranges. When they are operated at high electric loading, the influence of magnetic saturation is usually large. Furthermore, due to the geometric structure of some PM machine topologies, e.g. interior PM machines, such influence can be even more significant. The partial cross-coupling model, which considers that the PM flux is a function of q-axis current and the d- and q-axis inductances are functions of d- and q-axis currents, respectively, is simple but neglects the saturation to some extent. However, as shown by the frozen permeability method in this paper, it can accurately predict the torque-speed characteristics of fractional-slot PM machines having concentrated windings. The analysis is confirmed by experimental results.