Contribution of DFIG wind turbines to system frequency control

Wind power has become the fastest growing renewable energy source around the world, and has become relatively large proportion of total system generation and this procedure will be continuing in future, because of wind power global preference. Because variable speed wind turbine generation (WTG) connects to power system indirectly through converters and other power electronic devices, this makes the generation system dynamic behavior different from conventional generations and decouples the rotor of generator from other parts of power system, so power system inertia will decrease by addition of variable speed WTG. Therefore, if renewable energy systems in today's power system don't capable of contribution in frequency control, rate of change of system frequency (ROCOF) will be increase, and loss of generation or change in system loading may result in critical conditions such as blackout in the system. Meanwhile, modification of wind energy systems inertial response characteristics, or considering internal frequency control loop is necessary to facilitate the increasing integration of wind generation level in power systems. Therefore, the complete dynamic model of doubly-fed WTG systems are implemented to investigate the possibility of their contribution in primary frequency control.