Design evaluations of the new double rotor interior permanent magnet machine

Among various types of electric motor, permanent magnet motor is competent for high torque applications. Its torque producing point is resultant of air gap flux linkage between permanent magnet inbuilt in rotor and the stator winding. The reduction in air gap length improves the flux linkage, however it can only be reduced to a certain extend due to torque pulsation occurrence that increases cogging torque due to strong attraction of magnetic flux. A novel double rotor interior permanent magnet motor is proposed for improved torque performance. The key to this proposed structure is by introducing an additional outer rotor to the conventional permanent magnet motor. Consequently, this double rotor structure provides higher torque generation through an increase in torque producing point by utilising the flux linkage at stator yoke, meanwhile allowing the reduction of air gap length as the attraction of magnetic flux is distributed evenly from the inner and outer rotor. An electromagnetic analysis on the effect of torque producing capability to utilize the stator yoke flux is analysed using finite element method. An improvement of 22% of the motor constant square density value with an increase of 26% of average torque value in comparison than that of the conventional motor is reported in this paper