Selective optimal under-frequency load shedding based on trajectory sensitivities

Abstract

This paper proposes an optimal selective under-frequency load shedding strategy to perform a corrective control action that prevents the loss of frequency stability. The proposal decomposes this optimal load shedding problem into two mutually connected subproblems: the frequency stability analysis and the optimal load shedding. These two subproblems are sequentially solved until the minimum load shedding needed to recover the center-of-inertia frequency close to its nominal value is determined. The link between those two subproblems is a frequency performance index, which indicates the frequency deviation at each generation node with respect to the nominal frequency value. To selectively perform the load shedding, two novel methods are developed to identify which nodal loads most affect the frequency dynamics and to determine how the selected loads must be shed to return the frequency close to its nominal value at the maximum rate of change. The effectiveness of the proposed method is numerically demonstrated in two benchmark power systems.