INTERIOR PERMANENT MAGNET MOTOR HAVING SEVERAL IMPROVED FEATURES

Abstract

ABSTRACT The no-load airgap flux density distribution of most conventional permanent magnet motors is square in shape. The rotor configurations having interior magnets employed in these machines also lead to vastly different saliencies along the d- and q-axes giving a quadrature axis inductance larger than the direct axis inductance. A modified rotor configuration is presented that produces a near sinusoidal airgap flux density distribution which is achieved by shaping the rotor airgap profile while keeping the interior magnets rectangular in shape. As a result of this shaping the quadrature axis inductance is reduced significantly while there is almost no change in the direct axis inductance. It is also shown that the new rotor configuration leads to significantly reduced cogging torque and less saturation along the q-axis which assists in maintaining a linear torque versus current relationship in field oriented control employing the quadrature axis current. Airgap flux density levels, inductances and static torque characteristics obtained using the finite element simulation work are presented comparing them with those for a uniform airgap machine. There has been good agreement between the experimental and simulation results. The operational advantages gained by the improvements made are also briefly discussed.