Encoderless Predictive Direct Torque Control for Synchronous Reluctance Machines at Very Low and Zero Speed

As an enhancement of a predictive direct torque control (PDTC) scheme for synchronous reluctance machines (SynRMs), an encoderless PDTC scheme that is able to operate at very low and zero speeds is introduced in this paper. At very low speeds, the angular position of the rotor can be estimated by injecting test voltage signals (TVSs) to detect the spatial orientations of existing position-dependent rotor anisotropies. The TVS produces transient stator current changes, so that stator current derivatives can be estimated in a digital way. In a SynRM, the stator current derivatives contain useful information that can be used to estimate the angular position of the rotor. The obtained information is processed by means of a quadrature phase-locked loop observer to extract the angular position of the rotor without detriments in phase and frequency. Following this strategy, no extra hardware, special current transducers, or connections are needed in comparison with a standard drive with an encoder. Based on the proposed strategy, an encoderless PDTC scheme for SynRMs is implemented. Experimental results using a digital signal processor and a field-programmable gate array embedded in the same board verify the effectiveness of the proposed control scheme.