A high current density in the stator windings results in high copper losses and by consequence high hot-spot temperatures. To transfer the generated heat to the ambient, fins on the stator housing are commonly used. In addition, forced air cooling is employed by using a shaft mounted fan. This is to improve heat transfer from the housing fins and sometimes from the end winding and rotor surfaces. However, for high current density, the air forced cooling approach may not be sufficient and other cooling methods may be required. A water jacket in the stator housing is another possible way that enables an effective heat transfer from the stator winding active part to the coolant [25]–[29].
As we mentioned before, the stator of the SynRM is an induction motor stator that has been designed taking into account the thermal issues. The optimization of the rotor of the SynRM results in a machine with still almost the same mechanical rated power as the original induction machine. In addition, as the rotor of SynRM has much lower losses than that of the corresponding induction machine, we can be sure that no overheating will occur as long as we stick to the same rated current in the stator, the same rated speed and approximately the same mechanical power. This means that there is no need to investigate the thermal part of the SynRM. Consequently, we do not focus our study in the thermal of this machine.
For the prototype machines, the forced air cooling method is employed by using a shaft mounted fan.
3.7 Conclusions
This chapter has presented the design of synchronous reluctance motors (SynRMs), in particular the rotor design. A sensitivity analysis of the flux-barrier geometry in the rotor of SynRM is done and the effects of different rotor geometry parameters on the machine performance indicators (the saliency ratio, output torque and torque ripple %) are shown as in Table 3.12. The influence of the highest rotor parameter on the performance indicators is highlighted in the Table 3.12.
Table 3.12: Influence of flux-barriers variation on the SynRM.
Parameter Saliency ratio Torque, N.m Torque ripple%
Different angles, θbi 20.69% 10% 444%
Different widths, Wbi 109% 31.5% 152.5%
Different lengths, Lbi 9.4% 13% 75%
Different positions, pbi 23.6% 20% 72%
Moreover, a simple method (parametrized equations) for choosing the two most crucial rotor parameters of SynRMs i.e. the flux-barrier angle and width is proposed. The proposed approach is compared to three existing methods in the literature for different numbers of flux- barrier layers i.e. 3, 4 and 5 per pole. It is proved that the proposed method is effective in choosing the flux-barrier angles and widths. The SynRM torque ripple and average torque based on the proposed method are better than the considered literature methods. This results in a good SynRM design. This “starting point” design can be further optimized via FEM based optimization routines. Thanks to a good “starting point”, the required computation time for the optimization is reduced.
Finally, an optimized technique coupled with FEM to obtain an optimal selection for the flux-barrier parameters has been investigated. An optimal rotor design for the SynRM is obtained. The optimal rotor
79 Biography
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