Design and analysis of a new linear wound field flux reversal machine

Linear permanent magnet (PM) machines are more and more attractive for direct-drive systems due to the merits of high power density and efficiency . Also, in comparison with the conventional rotary-to-linearly drive system, the linear drive system takes the advantages of high reliability and low vibration and noise because of the absence of the linear-to-rotary device . However, for the long stroke applications such as railway traction, the PMs or windings should be mounted on the long stator which results in high cost . Recently, a new class of linear PM machine, i .e ., the linear flux reversal PM (FRPM) machines has been developed [1], [2], in which both magnets and coils are placed on the short mover, and the long stator is only manufactured of iron with salient poles . Thus, the cost for long stroke applications can be definitely decreased [1]-[4] . However, it still suffers from the uncontrollable PM flux, as well as conventional PM machine, which limits the constant power speed range (CSPR) . Consequently, a hybrid excitation FRPM machine is proposed in [4] . By employing additional field excitation windings, the flexible air gap flux adjustment and wide speed range can be achieved . Nevertheless, due to the risk of irreversible demagnetization of PMs, its field weakening capability is still limited . Furthermore, it uses a large quantity of rare earth material which significantly increases the manufacturing cost [5] . In order to reduce the cost further and enable a wide CSPR, a new linear wound field flux reversal (WFFR) machine is proposed in this paper .