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Direct torque control of cascaded brushless doubly fed induction generator for wind energy applications

This paper proposes a novel configuration for wind energy applications by using a cascaded brushless doubly fed induction generator (CBDFIG) controlled by direct torque control (DTC), which eliminates the slip rings and brushes associated with the conventional DFIG and features quick response. Due to the increased complexity of CBDFIG model, prior vector control for CBDFIG is complicated and relies much on the machine parameters and controller tuning. Furthermore, so far the literature regarding CBDFIG did not address the issue of grid synchronization, which is important for reducing the impacts on both grid and CBDFIG and useful for re-closing after fault is cleared. This paper investigates the analysis and design of DTC of CBDFIG for both grid synchronization and grid connected operations without changing the switching table. The influence of additional rotor circuit is investigated and it is found that this influence is small and can be neglected. The DTC developed in this paper is very simple and achieves excellent dynamic response and steady state performance. Simulation results are presented to validate the effectiveness of the developed DTC for CBDFIG.