# Topology Comparison Study of Five-Phase Wound-Field Doubly Salient Fault Tolerant Generators
## 5 Conclusions  
To present the characteristics of pole number and pole shape of the core, the five-phase Wound-field Doubly Salient Fault Tolerant Generators with symmetric phase inductance were studied and optimised in this paper, considering the split ratio, slot fill factor and core fringing effect. Two 30/24-pole and 20/16-pole Wound-field Doubly Salient Fault Tolerant Generators with low harmonic were proposed and analysed with theoretical analysis and finite element analysis method. And with the finite element analysis and experimental results, the conclusion can be drawn as follows:  
1. If the other parameters are equal, the output voltages of Wound-field Doubly Salient Fault Tolerant Generators with different poles are equal if they have the same total turn number of the armature windings. However, the pole to pole leakage effect of the 30/24-pole Wound-field Doubly Salient Fault Tolerant Generator is larger than that of the 20/16-pole, which decreases the flux linkage and the EMF amplitude. Since the number of stator poles is larger than the number of rotor poles, the stator slots are narrower than the rotor slots when the stator and rotor pole arc coefficients are the same, so the equivalent air gap length is also small. Similarly, the narrower the stator slot and the rotor slot, the smaller the equivalent air gap length of the stator slot and the rotor slot, that is, the larger the leakage magnetic flux.
2. Considering the core fringing effect, to reduce the cogging torque, as well as the harmonic content of phase flux and electromotive force, the rotor pole arc actual length should be four times the length of the air gap narrower than the ideal pole arc length. Under this circumstance, the five-phase Wound-field Doubly Salient Fault Tolerant Generator studied in this paper has the smallest harmonic content of the flux linkage and no-load electromotive force, and the minimum positioning torque is the ideal design target of the rotor pole arc length.
3. Although the total phase turn numbers are the same, the output power of the 30/24-pole Wound-field Doubly Salient Fault Tolerant Generator is smaller than the 20/16-pole one when the output current is smaller than 27A, due to the demagnetisation effect of the armature reaction. Due to the pole to pole leakage flux, the output power of the 30/24-pole Wound-field Doubly Salient Fault Tolerant Generator is larger than the 20/16-pole one when the output current is larger than 27A. The 20/16 pole Wound-field Doubly Salient Fault Tolerant Generator drops sharply due to the large demagnetization effect of the armature reaction because there are more turns of the armature winding around each pole of the 20/16-pole Wound-field Doubly Salient Fault Tolerant Generator. And this verifies the increase in the number of poles will deduce the second air gap and increase the leakage coefficient of the Wound-field Doubly Salient Fault Tolerant Generator.  
Conceptualization, L.S.; methodology, L.S.; software, L.S.; validation, L.S.; formal analysis, L.S.; investigation, L.S.; resources, L.S. and J.A.; data curation, L.S.; writing--original draft preparation, L.S.; writing--review and editing, L.S., J.A. and W.Z.; visualization, L.S.; supervision, L.S.; project administration, L.S.; funding acquisition, L.S.  
This research was funded by the National Natural Science Foundation of China (51707110, 51775320, 51875327), Taishan scholars program, and City-University Joint Research project (2018 ZBXC197).  
The authors would like to thank Prof. [PERSON] of Nanjing University of Aeronautics and Astronautics and [PERSON] of Hanyang University for their continuous support and guidance to the authors, especially in this paper.  
The authors declare no conflict of interest.