Enhancing Linearity of Permanent Magnet Synchronous Linear Motor Based on Thrust Coefficient Identification

There are lots of actual factors that cause the thrust nonlinearity (or thrust fluctuation) of permanent magnet synchronous linear motor (PMSLM), which increases the difficulty of controller design for precision motion. The existing methods to reduce thrust nonlinearity include structure optimization, mathematical model improvement, and the use of intelligent controllers, all of which have limitations. This article proposes a novel drive method to calculate and assign the coil currents which can reach higher thrust linearity so that provides the high-quality controlled plant. It makes PMSLM output accurate thrust by modeling and identifying the thrust coefficient of each phase coil separately, and calculating the corrected coil currents in real-time. This method does not require changes to the existing motor structure, does not rely on the nominal motor model, and its correction algorithm runs in the drive instead of the controller, hence it has the advantages of low cost, high precision, and fast dynamic response. The experiment results show its ability to identify the high-order harmonics and the nonperiodic component of the thrust coefficient and the detent force, significantly reducing the thrust nonlinearity and the controlling error of precision trajectory tracking.