Toward a Generic Torque and Reactive Power Controller for Doubly Fed Machines

A novel shaft-position sensorless algorithm for decoupled control of torque and reactive power (TRPC) of doubly fed machines, such as the classical wound-rotor induction machine (DFIM) and the emerging brushless reluctance machine (BDFRM), has been discussed and experimentally verified in this paper. The underlying control concept is derived from first principles of magnetization and torque production in the machines. For control purposes, only the grid-connected winding measurements and rough knowledge of its resistance value are required. Such a weak parameter dependence makes the TRPC inherently robust, structurally simple, and fast to execute even on low-cost DSPs. A variety of applications are possible including drive and generator systems with limited variable speed ranges (e.g., large pumps and wind turbines), where cost savings of using partially rated power electronics are significant. Two custom-designed and built BDFRM prototypes have served as case studies to evaluate the controller performance by computer simulations and through laboratory experiments.