Influence Analysis of DFIG Virtual Inertial Control Strategy Based on Releasable Kinetic Energy

In allusion to the defect caused by adding virtual inertia control strategy onto existing doubly-fed induction generator (abbr. DFIG) that leads to the deficiency in giving consideration to both frequency response and transient angle stability, firstly, utilizing voltage and flux linkage equations of DFIG the electromagnetic power expression was derived, and based on the conception of power angle of synchronous generator the equivalent power angle of DFIG, which was similar to the former, was derived too and the relation between the frequency regulation ability of DFIG and its equivalent power anger stability was analyzed. Secondly, in view of the fact that under different wind speeds, DFIG contained various degrees of releasable kinetic energy, a releasable kinetic energy based inertia control strategy based on was proposed, i.e., the rate of change of frequency (abbr. ROCOF) and the loop gain of the droop loop in the inertia control strategy were adjusted according to the rotor speed to make the DFIG, which was operated under a higher rotating speed, enable to release more kinetic energy, and then based on the released kinetic energy the available contribution of wind power generating set to system inertia response could be determined. On the basis of improving system frequency regulation ability, the proposed strategy could give consideration to improve transient power angle stability, and avoid too low rotor speed, thus the stable operation of DFIG during inertia control process could be ensured. Finally, utilizing simulation software RSCAD based on real time digital simulation system (abbr. RTDS), a single machine grid-connected simulation system for DFIG was constructed, and the simulation results show the effectiveness of the proposed control strategy.