Low voltage ride through peformance of a STATCOM based on modular multilevel cascade converters for offshore wind application

Static Synchronous Compensators (STATCOMs) are being applied for offshore wind power plants to satisfy the grid codes under both normal operation and grid fault conditions. This paper investigates the performances of Modular Multilevel Cascade Converters (MMCC) for the STATCOM application, with special focus is on asymmetrical Low-Voltage-Ride-Through (LVRT) operation under grid faults. The design of an 80 MVar / 33 kV STATCOM is first presented. The electro-thermal stress of the power modules used in each type of MMCC is analyzed with voltage balancing control under asymmetrical grid faults. Finally, the reactive power compensation capability of the MMCC solutions is compared under different scenarios of grid faults, with the considerations of the device temperature limits and voltage saturation. The reactive power compensation capability among the MMCC solutions shows significant difference when the grid voltage is lower than 0.5 p.u.