Back-EMF based sensorless vector control of tubular PM linear motors

A sensorless control method of a tubular linear permanent magnet motor is presented. The sensorless algorithm is based on back-EMF estimation and consists of two observer stages. First, the back-EMF vector is estimated using a modified disturbance observer. Next, a Phased Locked Loop (PLL) tracking observer is implemented to extract the position from the back-EMF vector. The algorithm does not require any external signal injection. Experimental results verified the effectiveness of the sensorless algorithm under vector control even when starting from zero speed and at speed reversal.