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 rota-ry-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.