Operational Reliability Evaluation of an MTDC-Based Hybrid AC–DC Power System Considering Conditional-Dependent Faults

The ever-growing applications of the multiterminal direct current (MTDC) systems have introduced interdependence in terms of operation conditions between ac and dc systems. When considering such a conditional dependence, the outage probabilities are affected by the previous fault events in hybrid ac–dc power systems and thus no longer independent, rendering the results from conventional reliability evaluation techniques to be inaccurate. This article provides a method to evaluate the operational reliability of the MTDC-based hybrid ac–dc power systems considering the conditional dependence between the ac and MTDC systems. First, a conditional-dependent fault analysis model is developed to describe the entire temporal fault process. In the proposed model, dynamic state models for components are built considering system parameters that affect their outage probabilities. A redispatch model for the hybrid ac–dc power system is then established to characterize the variation of operation status between different periods. After that, a framework to evaluate the operational reliability of a hybrid ac–dc power system considering conditional-dependent faults is formulated by combining the conditional fault analysis model and the Monte Carlo simulation technique. The impacts of conditional dependence on the reliability of hybrid ac–dc power systems are quantified by the modified reliability indices. Finally, the proposed method is validated by modified IEEE-RTS systems with different MTDC topologies and ac–dc coupling levels to demonstrate the impact of conditional-dependent faults.