Determination of steady state control laws of doubly - fed induction generator using natural and power variables

A doubly - fed induction generator (DFIG) system is presented in terms of its natural and power variables as the state variables. The natural variables are the electromagnetic torque (T_e), the reactive torque (T_r), the magnitude of rotor flux linkage (λ_r), the magnitude of stator flux linkage (λ_s), and the rotor speed (ω). These are used in modelling the induction machine and the machine side converter (MSC) of the system. The real power (P_f) and reactive power (Q_f) that the grid side converter (GSC) exchanges with the grid make up the power variables of the system and are used to model the GSC. Simulation of the dynamic natural variable model of the induction machine is carried out and the results are compared with a conventional induction machine simulation technique. Steady state analysis is presented for various power factor operations. A method of predicting an optimal stator power factor operation is proposed.