Speed sensorless control of a long-stator linear synchronous motor arranged in multiple segments

In the case of long-stator linear drives, unlike rotative drives for which speed or position sensors are a single unit attached to the shaft, these sensors extend along the carriageway, becoming a costly part of the system. Therefore, sensorless methods are of higher concern in linear motors than in rotative ones. For long carriageways, the stator is usually divided in several independently fed segments in order to reduce the reactive power and to allow more than one vehicle to move on the same carriageway. This arrangement presents additional challenges in the implementation of sensorless methods because the position-dependent variables (as the electromotive force (EMF)] of each segment are nonperiodic signals. Moreover, the acquired speed and position information from one segment must be synchronized with the adjacent one when the mover passes over a segment transition. In this paper, a method to get a continuous estimation of the speed and position, even during the transition between segments, is proposed. This method uses an EMF observer for each active segment (i.e., where the mover is currently located, and the subsequent segment). Then, based on the addition of the observed EMF, a single speed and position observer is implemented for the mover. Using an experimental setup, validation results are attained and presented.