This thesis deals with the design and measurement of inverter-fed synchronous reluctance motors without and with ferrite magnet assistance. For the design of the synchronous reluctance rotor, direct methods, based on analytically determined dimensioning rules and parameter studies, and the multi-objective optimization are investigated. In terms of a high power factor required to operate at the voltage limit of the frequency inverter, both methods lead to similar rotor designs. Therefore, the less computationally intensive direct method is used to design a prototype reluctance rotor for the stator of an existing 2p = 4-pole, fan-cooled, totally-enclosed PN = 11 kW standard induction motor. However, the multi-objective optimization is used to design the synchronous reluctance rotor with ferrite magnets, since the parameterization of the rotor geometry can be more easily adapted to the use of commercially available standard magnet dimensions. Due to the risk of irreversible demagnetization of the ferrite magnets (low coercive field strength), numerical calculations (finite element method) of the three-phase sudden short-circuit are carried out. Accordingly, in the worst case of low magnet temperature (positive temperature coefficient of coercive field strength), there is even a risk that the magnets near the airgap are magnetized in the opposite direction to the original magnetization direction. As a possible measure to remagnetize the ferrite magnets, the switching-on of an externally driven motor, already rotating at synchronous speed, to a three-phase sinusoidal grid is investigated. Both the partially irreversible demagnetization caused by the three-phase sudden short-circuit and the successful remagnetization are confirmed by measurement results. Further measurements show, that the directly determined efficiencies of the synchronous reluctance motors measured at the rated point (nN = 1500 rpm, MN = 70 Nm) in inverter operation are η = 92,4% (cos ϕ = 0,80) without and η = 93,6% (cos ϕ = 0,88) with ferrite magnet assistance and are higher than the efficiency of the original squirrel-cage induction motor η = 87,5% (cos ϕ = 0,85). This is also true for the partially irreversible demagnetized prototype after the three-phase sudden short-circuit η = 93,2% (cos ϕ = 0,83). However, due to the lower magnetization, the efficiency in the constant power range (2nN = 3000 rpm and MN/2 = 35 Nm) decreases for this prototype from originally η = 90,0% (cos ϕ = 0,93) to η = 88,1% (cos ϕ = 0,79) after the three-phase sudden short-circuit, which is significantly higher than for the pure synchronous reluctance motor with η = 83,8% (cos ϕ = 0,68). | English |
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