Study on the Necessity and Role of Inertia in Power System Frequency Response

As the penetration of renewable energy (RE) in power systems continues to increase, synchronous generators (SGs) are being replaced by power electronic interfaced RE sources with no or little equivalent inertia, which results in the decline of power system synchronous inertia. Previous studies mainly recommend adding virtual inertia control in RE to increase system inertia. However, we find that the essence of inertia is a form of fast response energy storage (FRES). Proper forms of FRES such as droop control can also alleviate the problem of inertia decline if maximum frequency deviation is considered as the main index to measure frequency dynamics. This conclusion is based on our recognition that FRES is vital for power system frequency security and synchronous physical inertia is one form of FRES and can be replaced by other forms of it. If the responding speed and capacity of energy storage are guaranteed, power system frequency security will be good. Relevant achievements broaden the way to improve the frequency security of power system with high penetration of RE. Simulation results verify the conclusion.