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 ω_R and the rotor speed ω_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 γ-δ axes to the axes of the stator. A new γ-δ axes aligner is also proposed. The information extracted are: (i) the rotor position (ω_mt+δ_m), (ii) the rotor speed ω_m, (Hi) the rotor frequency ω_R. Proofs of concepts and proofs of decoupled P-Q control of a wind turbine driven DFIG are presented from simulation studies.