An interior permanent magnet machine with shaped poles

This thesis presents the results of investigations into an interior permanent magnet (IPM) machine having characteristics which are superior to those available from an existing type. The improvements are made to a conventional IPM machine having radially mounted magnets on the direct axis, by shaping the rotor airgap profile. In the new machine the airgap length is gradually increased towards the quadrature axis in comparison to the airgap length along the direct axis. Finite element simulations show that a near sinusoidal distribution of airgap flux density due to the magnets can be achieved while reducing the quadrature axis inductance (Lq). It has been shown that the shaped pole machine has significantly reduced cogging torque. The torque pulsations in the total torque and also in the reluctance torque versus load angle characteristics are reduced in the case of shaped pole machine. It is shown that the shaped pole machine has a higher total torque within the normal operating mode in comparison to that of the uniform airgap machine. The new machine also gives a linear torque versus current relationship even at currents much higher than the rated current. The simulation results show that the saturation effects are less in the new shaped pole machine. The reduced Lq of the new IPM machine may provide an advantage in vector control using controlled quadrature axis current making the machine fast responding. The reduced Lq will impose a reduced voltage rating on the current controlled inverter supplying the machine.