Predictive Direct Torque Control for Synchronous Reluctance Machines at Very Low and Zero Speed without Mechanical Sensor of the Rotor Position

This paper presents a technique to estimate the rotor position on predictive direct torque controlled synchronous reluctance machines at very low and zero speed without position sensor. In this range of operation, the natural anisotropy of the rotor is exploited and a test voltage signal is injected in certain control cycles and during short time. The additional test voltage does not produce any undesired torque as a compensation signal is provided. The identification of the rotor position is based on the measurement of the phase currents and their time derivatives. Due to the anisotropy of the rotor the inductances depend on the rotor position, so the time derivatives of the currents contain the required rotor position information. The obtained signals are processed by means of a quadrature phase-locked loop observer to extract the rotor position signal without detriments in phase and frequency. The developed identification scheme does need any encoder or additional special current or voltage sensors. Based on the mentioned strategy a sensorless predictive direct torque control scheme for the synchronous reluctance machine has been developed and implemented. Experimental results using a DSP and a field-programmable gate array embedded in the same board verify the effectiveness of the proposed sensorless predictive direct torque control scheme.