An algorithm for contingency analysis of the AC-DC networks using modified Z-bus technique

Abstract

The steady state Contingency Analysis (CA) utilizes non-iterative distribution-factors (DFs) based linear estimation method of current-redistribution, to deliver approximate solutions in a shorter timeframe, which is favored over recurrent usage of iterative power flow-based non-linear techniques. However, the established principles of conventional DF-based CA cannot be directly implemented on burgeoning AC-DC networks. The DFs obtained from single unified Z-bus constructed for the entire AC-DC network leads to erroneous estimation of current redistribution post any contingency event. The reason being unified Z-bus built overlooked the characteristics of AC and DC lines. As a paradigm change toward a co-existing AC-DC network emerges, an adequate framework for understanding contingencies within such a network becomes critical. We present a quick non-iterative DF-based approach for the CA of any AC-DC network in this research by merging the use of separate AC and DC impedance matrices while accounting for the intertwined implications of the AC and DC networks. The interlinking converters (ILCs) are simulated using a reactive current bypassing approach. The proposed CA method is capable of handling contingencies occurring within ILCs, AC and the DC networks. The ETAP simulations and the Newton-Raphson (NR) technique for the AC-DC network have been utilized to corroborate the results.