INTERIOR PERMANENT-MAGNET MOTOR HAVING SEVERAL IMPROVED FEATURES

The no-load airgap flux density distribution of most conventional perm anent magnet motors is square in shape. The rotor configurations havin g interior magnets employed in these machines also lead to vastly diff erent saliencies along the d- and q-axes giving a quadrature axis indu ctance larger than the direct axis inductance. A modified rotor config uration is presented that produces a near sinusoidal airgap flux densi ty distribution which is achieved by shaping the rotor airgap pro file while keeping the interior magnets rectangular in shape. As a result of this shaping the quadrature axis inductance is reduced significantl y while there is almost no change in the direct axis inductance. It is also shown that the new rotor configuration leads to significantly re duced cogging torque and less saturation along the q-axis which assist s in maintaining a linear torque versus current relationship in field oriented control employing the quadrature axis current. Airgap flux de nsity levels, inductances and static torque characteristics obtained u sing the finite element simulation work are presented comparing them w ith those for a uniform airgap machine. There has been good agreement between the experimental and simulation results. The operational advan tages gained by the improvements made are also briefly discussed.