The inertia of the power system changes when the generators in the system are disturbed or tripped. However, in some systems, there is no control center or communication device falling behind. It makes real-time inertia difficult to obtain and affects the adaptive under frequency load shedding (UFLS) scheme. This paper proposes an adaptive decentralized UFLS scheme based on load information to overcome this problem. First, a calculation method is derived according to the load information after the disturbance to identify the real-time of load equivalent virtual inertia. Then, the power deficit of load is estimated and the optimal adaptive load shedding scheme is obtained. Finally, compared with conventional UFLS schemes, the proposed scheme can be performed merely by load information. Hence, the requirement of communication conditions and the dependence on the control center are reduced. The simulation is carried out on the island utilizing the IEEE39-bus system. Furthermore, the accuracy of real-time identification of load equivalent virtual inertia and the validity of the load shedding scheme are verified. INDEX TERMS Load information, power deficit, inertia calculation, frequency stability, real-time calculation.

This paper addresses the issue of power system transient stability assessment and control (TSA&C) based on phase plane representation of the power angle and rotor speed. First, the relationship between transient stability–instability and concavity–convexity of the phase‐plane trajectory is found and proved based on the single machine infinite bus (SMIB) system, and a transient instability criterion is derived for real‐time instability detection. Second, with the aim that the phase‐plane trajectory swings back before the unstable equilibrium point (UEP) once instability is detected, near‐optimal control size of generator tripping to stabilize the system is determined based on the relationship between unbalanced power and the slope of the phase‐plane trajectory. Finally, the instability detection and control technique is extended to a multimachine power system based on SMIB equivalent transform. The proposed method is independent of the network structure and operation mode, which can be applied for real‐time emergency control based on wide area measurement system (WAMS). The simulations in the Institute of Electrical and Electronics Engineers (IEEE) 39‐bus system and the Sanhua Power Grid (in China) validate the accuracy and efficiency of the proposed method. © 2019 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

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