Air-Gap Power-Based Sensorless Control in a DFIG Connected to a DC Link

This paper deals with the sensorless vector control of a doubly fed induction generator (DFIG) whose stator is connected by a rectifier to a dc link, which also feeds the rotor-side inverter. A noticeable reduction of the costs can be achieved by this topology, because only a single inverter and a diode rectifier are needed instead of the traditional back-to-back converter. A sensorless stator-flux-oriented control is implemented by using an observer, which directly computes the necessary slip angle based on of the air-gap power and without the need of the stator flux estimation. The direct-axis component of the rotor current is adjusted to regulate the stator frequency near the rated value. In order to track the actual stator frequency, the phase-locked-loop approach is used. The control method is validated by simulations and experimental results obtained using a small-rating laboratory setup.