Ring losses evaluation in ringed pole PM motors

In this paper, the ringed pole surface-mounted permanent magnet machine is investigated from the point of view of the ring losses. The rings around the poles are interested by the high frequency signal injection, that is useful to detect the rotor position. Such signal injection causes losses in the ring itself. Further, the rings are interested by other changing fluxes that can induce losses. This paper investigates the effect of other two sources of losses in the rings, in addition to the losses due to the signal injection. The first is constituted by the harmonics in the airgap magnetomotive force, which are not synchronous with the rotor and so they induce currents and losses in the rings. The second is the effect of the airgap flux fluctuation, due to the stator slotting. An investigation on both small size and large size machine is addressed. An analytical model is also proposed for evaluate the ringed pole feasibility.