Slip frequency phase lock loop (PLL) for decoupled P-Q control of doubly-fed induction generator (DFIG)

The paper describes an innovative slip frequency phase lock loop (PLL) which measures the rotor frequency /spl omega//sub R/ and the rotor speed /spl omega//sub m/ of a doubly-fed induction generator (DFIG). Both information are required in implementing sensorless control of DFIGs by rotor-side voltage-source converters. For decoupled P-Q control, it is necessary to align the rotor /spl gamma/-/spl delta/ axes to the axes of the stator. A new /spl gamma/-/spl delta/ axes aligner is also proposed. The information extracted are: (i) the rotor position (/spl omega//sub m/t+/spl delta//sub m/), (ii) the rotor speed /spl omega//sub m/, (Hi) the rotor frequency /spl omega//sub R/. Proofs of concepts and proofs of decoupled P-Q control of a wind turbine driven DFIG are presented from simulation studies.