The determination of the stability regions and sequential transient stability analysis of integrated AC-DC power system consisting of bipolar DC lines via the controlling unstable equilibrium points

Abstract

In this paper, a sequential transient stability analysis of an integrated AC-DC power system consisting of bipolar MTDC is accomplished by taking into account the variation of the amplitude of the bus voltages during transient. This variation of the bus voltages is provided by the sequential AC-DC load flow algorithm of the AC-DC power system with respect to the active power modified at each integration step. The algorithm has two superiority. Firstly, as DC system variables tire not included in Jacobian matrix the convergence time of the algorithm and necessity of computer memory is little. Secondly, both this algorithm has been developed for bipolar system and this algorithm also can be run with current controlled, voltage controlled and power controlled terminals without making any changes in proposed method. Thus, the AC-DC transient stability analysis is accomplished considering the true value of the ratio of the reactive power absorbed from the converters to the active power transferred through DC line by the sequential approach. In the transient analysis of the system, the DC lines loads are represented as the current injections to the buses where they are connected and its effect is reflected at the internal buses in the form of additional bus power injections. The effect of these is again reflected at the internal buses in the form of additional bus power injections. Thus, the problem in constructing a valid Lyapunov function due to the transfer conductance is eliminated.