Coordinated Fault-Ride-Through Strategy of Modular Multilevel Matrix Converter in Low-Frequency AC Transmission System for Offshore Wind Power

The offshore low-frequency AC transmission (LFAC) has high power electronic characteristics, and unable to satisfy the grid-connected requirements of the system only by the single-side crossing control of the wind turbine. In this paper, a coordinated fault ride-through (FRT) strategy of Modular Multilevel Matrix Converter-Permanent Magnet Synchronous Generators (M3C-PMSG) for different fault degrees is proposed to achieve hierarchical FRT. Primarily, the model of M3C is analyzed, and the control of M3C is optimized by means of filter circuit. Secondly, based on the performance of the LFAC, the change of M3C unbalanced power during the fault is revealed. Subsequently, according to the characteristics of system voltage and power change, M3C remote control PMSG is set to reduce output and maintain the system operation stability. Finally, the LFAC simulation model based on M3C is built in PSCAD. The FRT capability of the system is verified for different fault conditions, which proves the feasibility and effectiveness of the control strategy in this paper.