Investigation of Open Circuit DC Winding Induced Voltage Reduction Techniques in Five Phase Non-Overlapped Wound Field Flux Switching Machines

The induced voltage pulsation in DC winding can generate various issues in five phase wound field flux switching (WFFS) machine such as DC current ripples, unsteady field excitation, deteriorates the DC power source and challenges for control performance of machine. In this paper, the simplest five phase WFFS machine having the 5 stator slots with 7, 6, 4 and 3 rotor poles are analyzed and investigated for open circuit DC winding induced voltage. The phenomena of the DC winding induced voltage is briefly analyzed and explained. Three reduction techniques i.e., rotor pole chamfering, rotor pole arc optimization and rotor pole axial pairing, are investigated and optimized to reduce the open circuit DC winding induced voltage and cogging torque for WFFS machine while the average electromagnetic torque is kept greater than 90% of its initial value. The Finite Element (FE) results show that the reduction achieved in peak-to-peak value of open circuit DC winding induced voltage is 70.84%, 73.65%, 70.13%, and 63.42% as compared to its initial values by performing the rotor pole chamfering for the five phase WFFS machine having the 7, 6, 4, and 3 pole rotors, respectively. For rotor pole arc optimization, DC winding induced voltage peak to peak value is effectively reduced to 60.18%, 74.91%, 64.74%, and 64.10% for the 7, 6, 4, and 3 rotor-poles machines, respectively, while its reduction for axially paired rotors is 42.70%, 68.05%, 68.64%, and 56.09%, respectively. The 5-stator-pole/6-rotor-pole five phase non-overlapped WFFS machine with the initial rotor, chamfered rotor, optimized rotor, and axially paired rotor are prototyped to validate the FE results.