Modeling and Power Control of Cascaded Doubly-Fed Induction Generators Using a fractional-order PIλ controller

This paper deals with the power control of the cascaded doubly-fed induction generator (CDFIG) for wind energy applications. using a fractional order proportional integral (FOPI) controller within a field oriented control (FOC) scheme. The FOPI controller has a similar structure to the classic proportional-integral (PI) controller but FOPI controller considers non integer integration orders in determining the control action. This allows obtaining responses of the controlled system with different characteristics such as oscillations, stability and rise time. In this study FOPI strategy is simulated within a FOC scheme using a mathematical model of cascaded doubly-fed induction generator (CDFIG).    The system can be an attractive alternative to conventional double output wound rotor induction generators. Cascaded doubly-fed induction generator examined in the paper consists of two identical wound rotor induction machines having their rotors mechanically and electrically coupled.    The system employs two cascaded induction machines to eliminate the brushes and copper rings in the traditional DFIG.         In this case, Cascaded induction generators require lower maintenance. In CDFIG both stators of connected machines are accessible. The control strategy for flexible power flow control is developed. The independent control of the active and reactive power flows is achieved.