Volume 61 Issue 2 (2011) - Годишник на ТУ - София - Технически ...

4. ImplementationBLDC motor pole is investigated (Fig.3-a) for optimal shape determination. The poleface should be shaped in such way that cogging torque has a minimum value. 2D finiteelement field magnetic model is implemented and applied for optimal shape determinationfor the given cogging torque.(a)(b)Fig.3 Permanent magnet poleObjective Function (OF) used by optimization process is (1):OF min(CT ) (1)where CT represents calculated cogging torque. The value of OF is minimized (ideally,to set it to zero) by changing pole face, so that the cogging torque declines fromthe prescribed one.Pole shape is described by eleven variable points from the top which have symmetricalposition underneath (Fig.2-b). One fixed point is used as pole shape constraint.Variable point’s coordinates are parameters of optimization process. In that case multiparametricoptimization problem is solved.Calculated cogging torque value by Femm is used in objective function (1).5. ResultsMagnetic field distributions obtained by Femm are shown in Fig.-Fig. 5-7. These resultsrepresent the field distribution for important stages of optimization process. OnFig.5 is shown magnetic field distribution with poles initial shape. Magnetic field distributionduring shape optimization process is presented on Fig.6. Finally obtained resultcan be seen on Fig.7, where BLDC motor magnetic field distribution whit polesbest shape is demonstrated.108