Sensorless position control of linear tubular motors with pulsating voltage injection and improved position observer

The sensorless position control of permanent magnet motors can be successfully implemented by superimposing a high-frequency voltage on the control voltage. The accuracy of the method relies on a fast and accurate signal processing of the measured quantities and on the compensation of the inverter and motor non idealities. In this paper the position estimation is obtained by adding a high-frequency sinusoidal voltage at the output of the d-axis current controller. According to several methods proposed in the literature the position estimation is obtained by minimizing the high-frequency q-axis current. We propose a new approach that also exploits the analysis of the d-axis high-frequency current. Since this current has reasonable amplitude regardless the position estimation error, the proposed approach allows working with injected voltage of reduced amplitude thus reducing noise and additional losses. Moreover a simple I-type controller is used to estimate rotor position and it requires a low-effort design. Experiments on a linear tubular permanent-magnet motor prototype are presented to compare the performances of the considered estimation techniques.