Determination of Steady-State and Dynamic Control Laws of Doubly Fed Induction Generator Using Natural and Power Variables

A doubly fed induction generator model is presented whereby the natural and power variables are the state variables. The natural variables are the electromagnetic torque $(T_{e})$ , the reactive torque $(T_{r})$, the magnitude of the rotor flux linkage $(\lambda_{r})$, the magnitude of the stator flux linkage $(\lambda_{s})$, and the rotor speed $(\omega_{r})$. The power variables are the real power $(P_{f})$ and reactive power $(Q_{f})$ generated/absorbed by the grid-side converter into/from the grid. Simulation of the dynamic natural variable model of the induction machine is compared with a vector variable simulation. Steady-state operating regions are established for various power factor operations. The optimal stator power factor operation is estimated. A direct control of torque and power variables is developed. The robustness of the developed control against rotor parameter variation is investigated using small signal analysis and is compared with vector control. Results are shown for a 5-hp machine.