  In this paper, the empirical controllability covariance (ECC), which is
calculated around the considered operating condition of a power system, is
applied to quantify the degree of controllability of system voltages under
specific dynamic var source locations. An optimal dynamic var source placement
method addressing fault-induced delayed voltage recovery (FIDVR) issues is
further formulated as an optimization problem that maximizes the determinant of
ECC. The optimization problem is effectively solved by the NOMAD solver, which
implements the Mesh Adaptive Direct Search algorithm. The proposed method is
tested on an NPCC 140-bus system and the results show that the proposed method
with fault specified ECC can solve the FIDVR issue caused by the most severe
contingency with fewer dynamic var sources than the Voltage Sensitivity Index
(VSI) based method. The proposed method with fault unspecified ECC does not
depend on the settings of the contingency and can address more FIDVR issues
than VSI method when placing the same number of SVCs under different fault
durations. It is also shown that the proposed method can help mitigate voltage
collapse.
