Load shedding constitutes the very last resort for preventing total blackouts and cascading events. Conventional load shedding schemes, which are massively applied in industrial practice, adopt a step-wise approach which usually causes overshedding or fails to prevent frequency decay above the allowable limits. Recently proposed schemes based on real time intelligent control and neural networks achieve the control objective, but fail to minimize the amount of load to be shed due to the delay incurred in consecutive control decisions. This letter proposes a new load shedding scheme, decoupled from the conventional scheme. This scheme, based on the equivalent swing equation of the system, determines the minimal amount of load that should be shed immediately (in a single step) after the load event/disturbance occurs, in order to guarantee system stability.

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In contemporary power systems, conventional load shedding schemes are typically used. These load shedding schemes employ a preset step-level structure that identifies the amount of load to be shed. There are predefined candidate circuit breakers to be opened, based on the importance of loads, historical data for the load demand at each substation, and the operator's experience. Clearly, real conditions at the time of fault differ, resulting in the shedding of a larger or smaller amount of load and to a nonoptimal operation of the load shedding scheme. A second point to note is that adaptive load shedding schemes are usually only theoretically functional due to the large amount of real-time monitoring data required to perform satisfactorily. These data cannot be obtained on a large scale and in a cost effective manner. Last but not least, adaptive load shedding schemes do not always respond adequately against newly emerging or combinational events. In this paper, an adaptive load shedding scheme is proposed, based on a single measurement of the electric frequency of the power system. It approximates online the certain structure of the nonlinearities of the swing equation of the power system and adaptively bounds the load disturbances and the functional approximation errors of the nonlinearities. This way, a control law is extracted that "cancels" the nonlinearities and responds adequately to the load disturbances, achieving the frequency stability of the system effectively.Index Terms-Adaptive load shedding, frequency stability, smart grid, underfrequency load shedding. 1932-8184

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