Direct Power Control of DFIG Wind Systems Based on Nonlinear Modeling and Analysis

A complete new modeling approach for doubly fed induction generator (DFIG) wind energy systems is provided in this paper. The model incorporates all the system component dynamics, i.e., the ones of the induction generator and the ac/dc/ac frequency converter, and is developed on state space with the state vector including directly as states the stator-circuit and grid-side converter active and reactive powers. This innovation, combined with a voltage-oriented model deployment, permits the design and application of simple feedback PI direct power controls (DPCs). Hence, the proposed design approach becomes independent from the flux measurement or estimation under the cost of requiring a rigorous stability analysis, caused by the fact of not using field-oriented vector control techniques. Using recent advanced nonlinear methods, this analysis is completely performed on the entire closed-loop nonlinear system to conclude input-to-state stability and convergence to the desired equilibrium. Thus, a fully analyzed design approach for DPC is provided with guaranteed stability, further evaluated through extensive simulation results on a commercial 2-MW DFIG wind system.