Abstract
Refurbishing electrical machines to have a higher performance and/or reliability is a clear trend in the circular economy. This paper investigates the gain in efficiency, torque density and reliability with replacing the windings and the iron of the stator of existing three-phase synchronous reluctance machines (SynRMs), resulting in a multiphase machine. The stator housing, shaft, bearings and the rotor are not changed, to keep the cost of refurbishing low. As the housing and rotor are kept, logical constraints are to have the same inner and/or outer stator diameters, air gap length and axial length. In the new windings, an identical copper volume is considered as a constraint. An optimization technique is coupled to 2D finite element method to select the optimal slot dimensions. Case studies showed that it is possible to replace the stator of existing three-phase SynRMs with a better performance multiphase one. It is found that the average torque, efficiency and power factor of the five-phase SynRM are increased by 11.78%, 0.72% and 5.54%, respectively, compared to a three-phase SynRM at rated conditions. At higher speeds (three times rated value), the efficiency and average torque are greatly improved by about 3.64% and 33.67%, respectively, compared to the three-phase SynRM. Moreover, a faulty case of one phase opened is also investigated. The five-phase SynRM works at 75.45% of the healthy rated torque of the three-phase SynRM, whereas the three-phase SynRM works at only 43%. Measurements on an existing 5.5-kW, three-phase SynRM confirm the observed results.
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Abbreviations
- a :
-
Number of parallel circuits
- a c :
-
Conductor cross-sectional area
- A sn :
-
Stator slot area for n-phase machines
- b s0 :
-
Slot width at opening
- b s1 :
-
Slot width at top conductor
- b s2 :
-
Maximum slot width (at bottom)
- b t0 :
-
Teeth width at tip
- b tb :
-
Teeth width at bottom
- D :
-
Stator inner diameter
- D o1 :
-
Stator outer diameter
- h s0 :
-
Slot opening height
- h s1 :
-
Slot height above conductors
- h s2 :
-
Slot copper height
- h s3 :
-
Slot bottom height
- K f :
-
Slot filling factor
- l :
-
Mean length per turn
- N cn :
-
Number of conductors per slot for n-phase
- n :
-
Number of phases
- P :
-
Number of pole pairs for the rotor
- q n :
-
Number of slots per pole per phase for n-phases
- R ph :
-
Resistance per phase
- S n :
-
Stator slots number for n-phase machine
- ρ :
-
Resistivity of copper
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Acknowledgement
The authors acknowledge the Special Research Fund of Ghent University (BOF) for the financial support during this work.
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Appendix
Appendix
Table 8 shows the geometrical parameter for the reference machine.
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Tawfiq, K.B., Ibrahim, M.N., EL-Kholy, E.E. et al. Refurbishing three-phase synchronous reluctance machines to multiphase machines. Electr Eng 103, 139–152 (2021). https://doi.org/10.1007/s00202-020-01064-w
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DOI: https://doi.org/10.1007/s00202-020-01064-w