Hybrid AC/DC Post-Contingency Power-Flow Algorithm Considering Control Interaction of Asynchronous Area

This paper presents an approach for the calculation and estimation of control interactions between asynchronous power systems coupled via multi-terminal high-voltage direct current grids using static analysis methods. This aims at possible application within online security assessment where, as of today, static analysis methods are still a common practice. Therefore, the postcontingency power flow is evaluated using an integrated approach for the solution of AC and DC systems in the power-flow algorithm. Thereby, equations for DC voltage control and AC frequency control of converter stations, generators, loads as well as wind turbines with frequency support are embedded into the extended system Jacobian. The results show that by using the proposed approach, the post-contingency power-flow situation can be accurately determined and the frequency changes in each subsystem can be sufficiently tracked. Using an application example of an offshore power system with frequency support by offshore wind turbines, all results have been validated against dynamic simulation, while simulation models and controllers are provided. It is shown that active power balancing controls of AC and DC systems could have a high impact on line loadings and need to be respected for security analyses.