Abstract：In order to prevent the out-of-step accident, the factors that cause the out-of-step of the vertical-moving PMLSM is analyzed, the fault symptom before the PMLSM begins to be out-of-step as well as the main electric parameters and its variation that can reflect the out-of-step fault symptom of the vertical-moving PMLSM are obtained.The measurement schemes of physicial quantities, such as the supply voltage or current, the motor thrust, the operating power angle, the operating speed, and the air gap between permanent magnets and stator armature winding are established.

Keyword：permanent magnet linear synchronous motor;the reason of out-of-step;the fault symptom of out-of-step;measurement of mover position angle;