Pulsation losses in un-skewed rotors of synchronous reluctance motors without and with ferrite magnet assistance and their measurement

Abstract:
In synchronous reluctance machines without and with permanent magnet assistance, the stator-current-excited fundamental air-gap field is modulated by the stator slot openings, resulting in a slot-frequent flux variation in the rotor iron of considerable amplitude, which especially at high current and/or high-speed causes additional rotor iron losses, called pulsation losses. These losses are negligible at low speed, full flux operation due to the low frequency and high rotor iron saturation. At field-weakening and high-speed, they may account for a significant part of the total losses, which is shown by finite element numerical calculations and measurements both for a synchronous reluctance motor prototype without and with ferrite magnet assistance. Via simulation, the current angle β and the number of rotor flux barriers Nb are found as strong influence factors. The load-dependent pulsation losses were measured for the two 4-pole un-skewed 11 kWmotors as 500 W for the motor without magnets and as 300 W with ferrite magnets at double rated speed 3000 min^-1.