  Since cascading outages are major threats to power systems, it is important
to reduce the risk of potential cascading outages. In this paper, a risk
management method of cascading outages based on Markovian tree search is
proposed. With the tree expansion on the cascading outage risk, risk gradient
is computed efficiently by a forward-backward tree search scheme with good
convergence, and it is then employed in an optimization model to minimize
control cost while effectively reducing the cascading outage risk. To overcome
the limitation with linearization in computing risk gradient, an iterative risk
management (IRM) approach is further developed. Tests on the RTS-96 3-area
system verify the accuracy of the computed risk gradient and its effectiveness
for risk reduction. Time performance of the proposed IRM approach is tested on
the RTS-96 system, a 410-bus US-Canada northeast system and a 1354-bus
Mid-European system, and demonstrates its potentials for decision support on
practical power systems online or on hourly basis.
