Transmission system loading margin enhancement with ordinal optimization based STATCOM installation strategy

Owing to the constantly increased electricity demands and transactions, power systems are becoming more vulnerable to voltage instability generally incurred by over-utilized transmission facilities or any contingency. In order for transmission networks to accommodate more power transfers with less expansion cost, proper installation of Flexible AC Transaction Systems (FACTS) is a promising way. The power system loading margin enhancement problem to determine an optimal Static Synchronous Compensator (STATCOM) installation scheme can be formulated as a mixed discrete-continuous nonlinear optimization problem (MDCP). In the paper, to improve the efficiency of solving the MDCP, an ordinal optimization (OO) STATCOM installation strategy is proposed to seek a good enough solution rather than the optimal solution. In the strategy, under each N − 1 contingency with bigger risk index (RI) value, first the crude model of the MDCP is used to estimate the rough solution of each candidate in the representative set, and then the exact method is applied to a smaller set selected from the candidates with better rough solutions to determine the good enough solutions. Finally, obtained from the union of the respective good enough solutions for all considered contingencies, the scheme with the smallest number of STATCOM units or least capacity for installation enabling the network to provide required LM is recommended. The efficiency of the proposed method is confirmed with the results studied on IEEE-24 bus reliability test system.