Model-Switching Drive of Line-Start Permanent Magnet Linear Synchronous Motors

Permanent magnet linear synchronous motors (PMLSM) have their line-start performance enhanced with a conductive ladder arrangement in the “line-start PMLSM” design. However the thrust oscillation during the synchronisation in the non-salient structure is significant. To achieve stable synchronisation in practice, this paper develops a model-switching direct thrust and flux control (model-switching DTFC) theory for the line-start PMLSM. A general model is first established, which considers the longitudinal end effect and the eddy current produced by the conductive material of the ladder arrangement during transients. Then a conventional model is simplified into during steady-state periods at synchronous speed. Importantly conditions at which switching between models occurs are determined by the differential stator voltage between the general and the conventional model, with which the model-switching DTFC is designed. The proposed theory is applied to a prototype setup. Using experimental results, the model-switching DTFC is demonstrated to improve the kinetic performance of the line-start PMLSM. Both the overshoot and the steady-state ripple in the mover velocity can be improved by a factor of 2; 80% of underdamp and 50% of the thrust error can be eliminated. Therefore, the major contribution of this paper is improved control precision during reversals for the line-start PMLSM.