Steady-state Fault Current Calculation Method of LFTS with Offshore Wind Farm Integration Considering Converters' Control Strategy

Low frequency transmission system (LFTS) has become a competitive method for long-distance offshore wind power transmission. The fault current of LFTS is strongly coupled with the control strategy of converters. This paper proposes a novel steady fault current calculation method considering strategies including modular multilevel matrix converter (M3C) and grid-side converter (GSC) of an offshore wind farm. Firstly, the fault equivalent circuit model based on external characteristics of converters is derived, which is used for phase current calculation at both ends of the submarine cable. Then, the expressions of arm currents in M3C are derived. The distribution of high-frequency component and low-frequency component among nine bridge arms is influenced by the control strategy of M3C. Finally, simulation results show the correctness and high accuracy of the proposed calculation method. The fault current calculation method can be applied to equipment selection and relay protection of LFTS with offshore wind farm integration.