Ryuya Tanabe

Optimal operation solutions of power systems with transient stability constraints

The computation of an optimal operation point in power systems is a nonlinear optimization problem in functional space, which is not easy to deal with precisely, even for small-scale power systems. On the other hand, the emergence of competitive power markets makes optimal power flow (OPF) with transient stability constraints increasingly important because the conventionally heuristic evaluation for the operation point can produce a discrimination among market players in the deregulated power systems. Instead of directly tackling this tricky problem, in this paper, OPF with transient stability constraints (OTS) is equivalently converted into an optimization problem in the Euclidean space via a constraint transcription, which can be viewed as an initial value problem for all disturbances and solved by any standard nonlinear programming techniques adopted by OPF. The transformed OTS problem has the same variables as those of OPF in form, and is tractable even for the large-scale power systems with a large number of transient stability constraints. This paper also derives the Jacobian matrices of the transient stability constraints and gives two computation algorithms based on the relaxation scheme. The numerical simulation verified the effectiveness of the proposed approach.

Two novel screening methods to decide network configurations to maintain voltage stability using sensitivity analysis

This paper discusses screening methods in the planning stage which are able to find suitable power network configurations to maintain voltage stability. The electrical characteristics of power systems depend strongly on network configuration. However, to find the best network configuration is difficult because there are many objectives and constraints. In this paper, the relation between reactive power loss of transmission networks and voltage sensitivity is made clear to screen out suitable network configurations for maintaining voltage stability from among many candidates; the voltage sensitivity expresses the variation of node voltage magnitude when a unit active power supply is increased from one of the nodes. Two screening methods in the planning stage are proposed. The first method uses linear programming techniques and decides transmission lines which could be disconnected without deteriorating voltage stability; disconnection of transmission lines is effective for reducing the short circuit current though it may worsen the voltage stability. The second proposed is the use of new index called the generator installation site index. The index can be used to determine where a new generator should be installed to best improve the voltage stability. This index is calculated from variation of total demand voltage sensitivity when a unit of active power is supplied from one of the nodes.