Rotor Shape Optimization for Improving Torque Performance of PMAssisted Wound Field Synchronous Machine

Wound field synchronous machines (WFSMs) utilize rotor windings to generate flux without magnet. However, the current in field winding causes much copper loss, thereby the efficiency is decreased and temperature rise is increased. With the development of the permanent magnets (PMs), the permanent magnet synchronous machines (PMSMs) have been widely used in many industry applications instead of the WRSMs. But its development is restricted by the high cost of PMs and the limited supply of the rare earth magnets [1]. And another problem is that once the magnet is magnetized, it is difficult to achieve flux weakening control [2]. Furthermore, the danger of the demagnetization should be considered when PMSMs design. To overcome these problems, many kinds of hybrid excited machines have been developed. Inserting PMs into rotor's slot opening, there are two kinds of assist effects: one is the reduction of the magnetic saturation, and the other is the direct flux linkage increase of the armature windings from the permanent magnets. And the total assisted effects are ensured for wide load condition [3]. The demagnetization analysis of the assisted-PM is evaluated due to sudden three-phase short circuits in [4]. Meanwhile, it can be benefit for the motor's reluctance torque and affect the operation range. In paper [5], the optimized single flux barrier is introduced in the WRSMs. It is an effective and simple method to improve the motor's reluctance torque and widen the operating region. In this paper, PM was introduced in a WRSM with a single flux barrier configuration for high quality wide load condition and wide operating range, then the rotor shape of PM-Assisted Wound Field Synchronous Machine (PMa-WFSM-B) was optimized for improving torque characteristic and decreasing torque ripple under constant permanent magnet (PM) volume and motor size. The optimization method mainly includes Kriging method and genetic algorithm (GA). Then, JMAG-Designer is used as the tool of 2-D finite-element analysis to confirm the validity.