# Design of External Rotor Ferrite-Assisted Synchronous
###### Abstract
; [PERSON], [PERSON], [PERSON] Design of External Rotor Ferrite-Assisted Synchronous  
Roluctance Motor for High Power Density  
[PERSON]; [PERSON]; [PERSON], [PERSON], [PERSON]; [PERSON], [PERSON], [PERSON] Design of External Rotor Ferrite-Assisted Synchronous  
Roluctance Motor for High Power Density  
[PERSON]; [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], S.; [PERSON], [PERSON]; [PERSON], S.; [PERSON], S.; [PERSON], [PERSON]; [PERSON], S.; [PERSON], S.; [PERSON], S.; [PERSON], S.; [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], S.; [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON]; [PERSON], [PERSON]. To further achieve higher power density, an external rotor electric motors could be a strong candidate. Depending on the optimal split ratio (ratio of stator outer diameter to rotor outer diameter) and relatively high bore diameters, an external rotor motor can offer significantly higher torque density compared to the internal rotor system [19; 20]. Also, the external rotor motors are suitable for direct-drive in-wheel applications and can save drive space with integrated drive electronics [21; 22; 23; 24; 25]. To utilize such advantages, in [26], a three-phase external rotor Fe-PMaSynRM has been proposed as a low-cost but high-power density motor in an electric two-wheeler. The fault-tolerant multi-phase (number of phase > 3) external rotor designs have also been proposed, such as five-phase ferrite-based IPM and five-phase Fe-PMaSynRM [27; 28]. It has been observed that the additional phases not only boost the fault-tolerance but also increase the torque density compared to three-phase motors. In [29], performance comparisons between five-phase RE-PM-based and RE-free external rotor PMaSynRM are presented. The RE-free design has shown comparable torque density to the RE-PM-based design at lower material costs. In [28], multi-physics analysis design optimization of external rotor PMaSynRM has been presented that considers the developed heat transfer and mechanical stress. In [30], the authors have discussed the torque ripple reduction approach for the same motor by using rotor surface notch. However, articles [28; 29; 30] have focused on some major and common concerns of external rotor PMaSynRM such as heat extraction, torque ripple reduction, and torque density increasing. The demagnetization aspects of the Ferrite PM, which are a major concern for using Ferrite-PM in external rotor PMaSynRM design, have not been discussed in detail. This paper presents the precise design procedures of a five-phase external rotor Fe-PMaSynRM for high torque density applications. Detailed design considerations such as optimal rotor and stator configurations and geometrical parameters to maintain high torque density and low torque ripple while ensuring demagnetization-free operation have been presented in detail. The proposed RE-free motor has been compared to a benchmark external rotor RE-PMaSynRM with the same outer dimensions to validate the torque density. Section 2 shows the design considerations for high power density and illustrates the risk of irreversible demagnetization. Section 3 presents the design optimization procedures for the optimal five-phase outer rotor Fe-PMaSynRM. In Section 4, the finite element analysis (FEA) simulation results are presented to compare the proposed external rotor Fe-PMaSynRM and benchmark external rotor RE-PMaSynRM. Finally, in Section 5, experimental validations are provided through tests on the proposed 3.7 kW external rotor Fe-PMaSynRM prototype.