Transient stability-constrained optimal power flow for online dispatch and nodal price evaluation in power systems with flexible AC transmission system devices

This study develops a new method for economic dispatch together with nodal price calculations which includes transient stability constraints and, at the same time, optimises the reference inputs to the flexible AC transmission system (FACTS) devices for enhancing system stability and reducing nodal prices. The method draws on the sensitivity analysis of time-domain transient stability simulation results to derive a set of linearised stability constraints expressed in terms of generator active-powers and FACTS devices input references. The optimal power flow (OPF) formulation based on the Newton´s algorithm augmented with the set of stability inequality constraints is applied for forming economic dispatch solution and nodal prices. The solutions obtained also include the Lagrange multipliers associated with all of the constraints. Based on the Lagrange multipliers, individual components, including those associated with stability constraints, of the nodal prices are directly identified for assisting the market participants to make investment decisions. The sensitivity technique for forming the set of transient stability constraints lends itself to parallel-computing implementation. Therefore the additional computing-time requirement is minimal, given that the transient stability simulations can be performed independently of one another and outside the OPF loop. Representative studies and results are presented here.