Position Sensorless Control of a Permanent Magnet Linear Motor Connected Through a Long Cable

Sucker Rod Pump is a prevalent industrial solution in artificial lift applications in oil industries. Linear motors are becoming more popular as they are applied in new applications in various fields. Linear motors may be employed in artificial lift systems by placing a linear motor downhole to drive the reciprocating pump directly. This system is intended to extend the application of reciprocating pumps to deviated and offshore wells. Because of the high temperature downhole and the long distance between the drive and the motor, a position-sensorless control algorithm was selected for this project. The main challenge of sensorless control for this application is the long cable. In this paper, a model-based Luenberger observer is used to estimate the back-EMF for the position sensorless algorithm. The model utilizes a combination of the motor and cable models and a current sensor at the output of the inverter. A Phased Locked Loop (PLL) is implemented to allow starting the motor from standstill and motor speed reversal which are essential for linear motion. Experimental results verify the proposed method.