Comparison of inertia control methods for DFIG-based wind turbines

Doubly fed induction generator (DFIG)-based wind turbines are nowadays used widely in large wind farms. Due to the fact the control system of DFIG is not based on the power system frequency, the whole inertia of the power system is reducing rapidly with the penetration of wind generation increasing. This is extremely bad for the stability of the system frequency. Thence, ancillary inertia control strategies of DFIG need to be developed to compensate for this deficiency. At the beginning of this article, the vector control system of DFIG-based wind turbines is described briefly. The inertia control methods making use of that model could later be designed out. Then, a concept called controllable virtual inertia is put out and the derivation of its formula is given in details. After the two inertia control strategies of DFIG are described fully, the mechanism that how the virtual inertia of DFIG can be manipulated is revealed: the parameters (K1, K2and K3) contained in the inertia control schemes determine proportionally the virtual inertia level of DFIG. Finally, through the simulations in Matlab/Simulink, the two strategies of inertia control for DFIG-based wind turbines which have been utilized in this work are effective for the system frequency support and the concept named as controllable virtual inertia has theory worth for further research.