Severe disturbances in a power network can cause the system frequency to exceed the safe operating range. As the last defensive line for system emergency control

under frequency load shedding (UFLS) is an important method for preventing a wide range of frequency excursions. This paper proposes a hierarchical UFLS scheme of “centralized real-time decision-making and decentralized real-time control for inter-connected systems. The centralized decision-layer of the scheme takes into account the importance of the load based on the equivalent transformation of kinetic energy (KE) and potential energy (PE) in the transient energy function (TEF)

while the load PE is used to determine the load shedding amount (LSA) allocation in different loads after faults in real-time. At the same time

the influence of inertia loss is considered in the calculation of unbalanced power

and the decentralized control center is used to implement the one-stage UFLS process to compensate for the unbalanced power. Simulations are carried out on the modified New England 10-generator 39-bus system and 197-bus system in China to verify the performance of the proposed scheme. The results show that

compared with other LSA allocation indicators

the proposed allocation indicators can achieve better <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{nadir}$ and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$t_{d}$. At the same time

compared with other multi-stage UFLS schemes

the proposed scheme can obtain the maximum <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">$f_{nadir}$ with a smaller LSA in scenarios with high renewable energy sources (RES) penetration.