Two fuzzy-based direct power control strategies for doubly-fed induction generators in wind energy conversion systems

This paper proposes two novel (direct power control) DPC strategies for a doubly fed induction generator (DFIG)-based wind energy conversion system based on a (fuzzy logic controller) FLC. At first, the mathematical model of the DFIG in the synchronous reference frame is derived. Then, based on this model, two novel FLC-based DPC strategies, called (fuzzy-based DPC) FDPC and (fully fuzzy-based DPC) FFDPC are proposed. In the FDPC, the required rotor voltages to eliminate power errors within each fixed sampling period are directly calculated based on the FLC, the measured active and reactive powers, the stator voltage and some machine parameters. On the other hand, in the FFDPC, the rotor voltages are directly calculated from the FLC. The control structures of proposed methods are very simple. Compared to the conventional switching table-based DPC, in the proposed methods, the hysteresis comparator and the switching table are replaced by a simple FLC and a PWM (pulse width modulation) modulator. The converter switching frequency is constant which simplifies the practical implementation. Also the proposed methods are robust against machine parameters mismatches and grid voltage disturbances. Extensive simulations in Matlab\Simulink are performed to confirm the effectiveness of the proposed methods under transient and steady state conditions.