Reactive power compensation capability of a STATCOM based on two types of Modular Multilevel Cascade Converters for offshore wind application

Static Synchronous Compensators (STATCOMs) have been 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 two types of Modular Multilevel Cascade Converters (MMCC) for STATCOM applications, with the special focus 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 grid faults. Finally, the reactive power compensation capability of the MMCC solutions is compared under different scenarios of grid faults, with considerations of the device temperature limits.