Full-Scale Modeling, Control, and Analysis of Grid-Connected Wind Turbine Induction Generators With Back-to-Back AC/DC/AC Converters

A model-based dynamic analysis of a variable-speed wind generator system consisting of an induction generator connected to the grid through a full power frequency converter is conducted. To this end, a nonlinear modeling of the entire system is used in a manner that permits a novel controller design with common structure for both the generator- and grid-side converters. The proposed controller, acting directly on the duty-ratio inputs of the converters, ensures the boundedness of the duty-ratio signals in the permitted range although its structure is independent from the system parameters and open to different control objectives. Therefore, maximum power point tracking and power factor correction are easily implemented. Furthermore, the controller is proven to guarantee stability of the whole system under field- or near-field-oriented conditions without needing any flux measurement or estimation. Hence, the main contribution established by this approach is that a rigorous stability analysis taking into account the generator, converters, dc link, and controller dynamics is presented on the basis of a complete system modeling and controller design approach. The theoretical analysis and controller effectiveness are confirmed via extended simulation results for a commercial size 2-MW induction generator operating under varied wind speed conditions and are further validated on a similar system with real-time results.