Sensorless predictive DTC for the PM synchronous machine

A predictive DTC algorithm calculates the switching instants of two optimum active voltage space phasors (AVSPs) that build torque demand one step in advance. After that, the trajectory of the stator flux is predicted for the two preselected AVSPs and the AVSP that leads to the best trajectory of the stator flux at the end of the cycle will be applied to the machine at the next control cycle. With this control scheme is possible to obtain similar dynamic performance as with the conventional DTC scheme, with the advantages of inherently constant switching frequency and equidistant control sampling times for easy digital implementation. As an enhancement of this predictive DTC an encoderless strategy is proposed here. The rotor position is pre-dicted through the future value of the stator flux which is estimated by using the measured stator currents and reconstructed stator voltages. Then, the estimated rotor position is processed by means of a Quadrature Phase-Locked Loop observer, so that, easy digital implementation and stable operation can be achieved. Simulated and experimental results confirm the theoretical work.