Hybrid modeling of DFIGs for wind energy conversion systems

The synchronous reference frame is widely used in Doubly Fed Induction Generation (DFIG) modeling. In a DFIG, it is usually assumed that slip control is in place at the rotor-side converters to make sure that the injected rotor voltage at slip frequency gives a constant stator frequency (60 Hz or 50 Hz). In the analysis, the injected rotor voltages are directly expressed in the synchronous reference frame. In the cases where slip control is not available, the above modeling will not work. This paper implements a hybrid model (dqabc) of a DFIG. The key modeling idea is to use the frequencies of the injected rotor voltages as explicit inputs and further transform the injected rotor voltage into the synchronous reference frame. This allows one to model and simulate scenarios including: (i) acceleration via rotor injection, (ii) harmonic simulation for six-pulse rotor injection, and (iii) negative sequence compensation using rotor injection. Matlab/Simulink is used to perform the simulations of three cases listed above. Laboratory experiments on two of the cases confirm the validity of the model and simulation results.