Sensorless Predictive DTC of a Surface-Mounted Permanent-Magnet Synchronous Machine Based on Its Magnetic Anisotropy

This paper introduces a sensorless predictive direct torque control (PDTC) scheme for surface-mounted permanent-magnet synchronous machines, which is able to operate at a wide range of speeds. At very low and zero speeds of operation, the identification of the rotor position is carried out by applying test voltage signals in order to detect the machine saliency produced by the stator magnetic saturation. Then, the acquired signals that contain the information of the rotor position are digitally processed by means of a quadrature phase-locked-loop tracking observer. At middle and high speeds, the angular position of the rotor is estimated by using a closed-loop sliding-mode observer of the stator flux which uses reconstructed stator voltages and measured stator currents. Then, a gradual changeover between both algorithms is used for coupling both estimated values of the rotor position. Following this strategy, no extra hardware, special current transducers, or additional connections are required in comparison with a standard drive with an encoder. Experimental results in a wide speed range verify high performance of the proposed encoderless PDTC scheme.