Intersystem fault clearing in hybrid AC/DC power systems with full bridge modular multilevel converters

摘要

The parallel routing of high voltage AC and DC systems on the same transmission tower is one new option for a timely integration of HVDC technology into existing AC power grids, enhancing the latter's flexibility. However, the rare event of an intersystem fault is a new fault type which might occur in these configurations. Previous studies indicate that existing protection concepts are necessary but need not be enhanced for fault handling in hybrid AC/DC systems and have to be adapted especially to this case. This contribution offers a conceptual approach to combine identification and classification of intersystem faults, resulting in a protection concept for hybrid AC/DC systems with subsequent fault handling. It shows that the fault current detection and localisation can be separated and run independently. Using the advantages in control of modern VSC with full bridge technology, the DC component can be removed very quickly by limiting DC fault currents and driving them to zero. Without blocking the converter it is possible to continuously stabilise the AC networks and reduce the time required to restore the normal power transmission capability after the fault have been cleared. Subsequently, the intersystem fault can be detected and classified by the DC system reliably. Since the AC system cannot detect a fault any more, it is also task of the DC system to trip the AC protection. The control was tested simulatively using EMTDC?/PSCAD?.