Modeling and Control of a Cascaded Doubly Fed Induction Generator Dedicated to Isolated Grids

This paper deals with the control of an autonomous cascaded doubly fed induction generator (CDFIG) operating in a variable speed constant frequency (VSCF) mode. The proposed structure is a full stand-alone generating system dedicated to isolated grids for embedded systems such as aircraft or small-scale renewable-energy systems such as microhydropower generators. Compared to a traditional VSCF system based on a single DFIG, CDFIG allows suppressing brushes, leading to an easier maintenance. However, the main difficulty when working with such a structure is its inherent complexity. The major issue is to synthesize an efficient global-control strategy for these two strongly connected machines. To overcome this problem, a modeling methodology based on dynamical equivalent circuits is given in this paper for the design of the CDFIG controller. Presented simulations and experimental results validate the proposed design approach.