A new sensorless torque and reactive power controller for doubly-fed machines

A novel sensor-less algorithm for decoupled control of torque and reactive power of a class of doubly-fed machines like the conventional wound rotor induction machine (DFIM) or the emerging brushless reluctance machine (BDFRM), has been proposed in this paper. The control concept has been derived from the first principles of torque production and magnetisation of the machines and requires only the grid-connected winding measurements. The sensitivity analysis presented has shown an inherent robustness of the flux estimator to resistance variations making the overall control scheme practically parameter independent and structurally simple and as such suitable for implementation using low cost DSP platforms or micro-controllers. Potential target applications include variable speed drive and generator systems with limited speed ranges (e.g. large pumps and/or wind turbines) where the cost benefits of partially-rated power electronics can be fully exploited. A custom-designed BDFRM prototype has served as a case study to illustrate the good control performance through computer simulations.