Force Ripple Minimization of a Linear Vernier Permanent Magnet Machine for Direct-Drive Servo Applications

Linear vernier permanent magnet machines (LVPMMs) for direct-drive servo applications are attracting more and more attentions due to its high force density, easy maintenance, rapid dynamic response, and so on. This paper proposes an LVPMM structure, which has a similar secondary as that of a regular linear PM machine, while its primary mover is composed of three modules, and the modules are separated by flux barriers. Since high-precision servo systems have rigorous demands on the force ripple of the drive motors, two methods are introduced to minimize the force ripple of the LVPMM. One is to choose an optimal length of flux barriers; the other is to change the three-phase winding connection. The effectiveness of both methods is verified by time-stepping finite element analysis. It is found that the force ripple can be reduced from 10.6% to 2.4% by the proposed two methods.