Enhanced look-ahead load margin estimation for voltage security assessment

Existing methods proposed in the literature for estimating look-ahead load margin to voltage collapse do not address the limit-induced bifurcation points. Consequently, the estimated load margins by these methods are optimistic for certain types of contingencies which possess limit-induced bifurcation points. This optimism can lead to missing alarm in contingency ranking for voltage security assessment. An enhanced method for estimating look-ahead load margin to voltage collapse, due to either saddle-node bifurcation or the limit-induced bifurcation, is proposed in this paper. The estimated load margins by the enhanced method can resolve the difficulty associated with the missing alarm problem. In addition, the enhanced method contains improved schemes for accurately estimating the look-ahead load margins to bifurcation points. The enhanced method is applied to a practical 600-bus power system with promising results.