Estimation of the rotor position of a servo drive at zero stator frequency

This paper introduces a technique to estimate the angular position of the rotor of an industrial servo motor with rotor saliency. The estimation technique is based on injection of Test Voltage Signals (TVSs). The TVSs generate stator current transients which are exploited in order to acquire the required rotor position information. Then, the obtained information is processed through a tracking observer to extract useful position signals. Following this strategy no extra hardware, especial current transducers or connections are needed in comparison with a standard servo drive with an encoder. The technique is effective at zero and very low stator frequencies of operation, where the back EMF is very low and model based sensorless techniques commonly fail. Experimental results at very low and zero stator frequency of operation verify the effectiveness of the investigated sensorless strategy.