Design methods for limiting rotor losses in a fractional slot PMSM motor with high power density

Fractional slot PMSM motors enable high power density factors to be obtained provided that their electromagnetic circuit, appropriate mechanical structure and cooling system are properly designed, as well as when operating at a high frequency of power supply voltage (400–800 Hz) with high magnetic saturation and high current loads (approx. 12–15 A/mm2). Such operating conditions, especially in the case of fractional slot motors, may be the reason for excessive rotor losses, mainly in the rotor yoke and permanent magnets. One of the conditions for obtaining high values of continuous power of the motor is the reduction of these losses. This paper presents selected design methods for limiting the value of rotor losses with simultaneous consideration of their influence on other motor parameters. The analysiswas carried out for a PMSM motor with an external rotor weighting approx. 10 kg and a maximum power of 50 kW at a rotational speed of 4 800 rpm.