“…, a pair of filament current paths on the core surface is substituted for each coil from “1” to “5.” The substitution represents the effect of the iron core, i.e. the concentration of the magnetic flux that is yielded by each coil . According to the Lorentz force law, an electromotive force (emf) and a torque emerging in a pair of filament current paths are, respectively, expressed by Here, ω is the rotational angular speed defined by ω = d θ 0 /d t ; q is a serial number for the five coils or the five pairs of current paths; I q is the current of each coil; and Φ q is the flux linkage (per radian) defined by where N is the number of windings per one coil; a and l are the radius and depth of the iron core, respectively; and are the angles of the inflow and return current paths, respectively; B r ( θ , z ) is the radial component of B ( a , θ , z ); and B ( r , θ , z ) is the magnetic flux density yielded by the permanent magnets.…”