MMC-HVDC Transmission Connected Wind-PV-Thermal System, When AC transmission line breaks down, new fault characteristics will be generated. In case of failure of AC feeder line, voltage drop at common connection point of the system, current rise rapidly, Causing power fluctuations. However, inverter power supply control strategy change, and distinct fault characteristics are generated on both sides of connecting line. To solve the above problems, on the basis of establishing the four-terminal loop network model of MMC-HVDC system, the inverter power supply dual closed-loop vector control strategy, low voltage control strategy, suppression of negative-sequence current and other coordinated control strategies are adopted to keep the system stable and realize AC fault ride-through. At the same time, the characteristics of the current sequence components on both sides of the AC transmission line are studied considering the topological structure of the ring network system and the sequence separation decoupled calculation method, and the influence of transition resistance, fault location and fault type on the current on both sides of the connecting line is further analyzed. Finally, RTDS simulation verifies the effectiveness of the sending terminal AC fault ride-through scheme, and verifies the consistency between the fault characteristics and the theoretical analysis.