Research On The Double-sided Primary Permanent Magnet Linear Motor With Yokeless Secondary

Based on the requirements of linear motors used in electromagnetic launch system,a novel double-sided primary permanent magnet linear(DSPPML)motor with yokeless secondary is proposed in this paper.In the proposed motor,the permanent magnets and armature windings are all located on the long primary while the secondary is only made of low cost iron.The secondary is designed without yoke core in order to reduce the mover mass and maximize force density and load capacity.Hence,the proposed motor can not only maintain the advantages of simple mover structure of linear induction motors,but also inherit the merits of high efficiency and large force density of linear permanent magnet synchronous motors.And this motor can offer an efficient and reliable solution for electromagnetic launch system and has a good application prospect.Firstly,a new DSPPML motor with yokeless secondary is proposed,in which its primary and secondary pole pitch ratio(?p/?s)is 7/6.The operation principle of the proposed motor is investigated and its force production mechanism is revealed.It ca be found that more than 95% of thrust force in the motor is contributed by several dominating harmonics.Secondly,based on the complementary magnet circuit theory,some topologies of DSPPML motors with yokeless secondary and differnent primary and secondary pole pitch ratios(?p/?s = 3 or 13/12)are investigated and compared by finite element analysis(FEA).Besides,the two best DSPPML motors with ?p/?s = 3 and ?p/?s = 13/12 are compared with the DSPPML motor with ?p/?s = 7/6.The comparison results show that the motor “AABBCC” with ?p/?s = 13/12 can offer largest force density,smallest force ripple and cogging force,relatively high efficiency and power factor,which is the best topology.Thirdly,a high-power DSPPML motor with yokeless secondary is presented and the influence of the secondary type on the launch performance of this DSPPML motor is investigated.In addition,two double-sided linear induction motors are designed based on the same overall dimensions of the high-power DSPPML motor.Then,they are optimized and compared with the high-power DSPPML motor quantitatively in electromagnetic launch system.It can be concluded that the DSPPML motor with yokeless secondary can offer higher thrust force,smaller force ripple,simple secondary,less loss and higher efficiency and power factor.Hence,the DSPPML motor with yokeless secondary can offer a novel solution for electromagnetic launch system.Finally,a low-power DSPPML motor with yokeless secondary is prototyped.Static electromagnetic performance are measured and dynamic responses are validated by experimental results.The experiments results and the simulation results show a good agreement.