Research on Inverter Side AC Fault Ride-through Strategy for Hybrid Cascaded Multi-terminal HVDC System

Hybrid cascaded multi-terminal HVDC system is usually located in developed areas, and the load centers are relatively close, so the AC systems on the inverter side will inevitably be electrically coupled. At this time, when the AC system of a single converter fails, it will also cause the AC bus voltages of the remaining converters to drop to varying degrees at the same time, which is likely to cause the cascading failure reaction of each VSC's output power limitation and high-end LCC commutation failure. As a result, the low-end VSCs on the inverter side have sub-module overvoltage due to power surplus. The inverter side AC fault ride-through characteristics of hybrid cascaded multi-terminal HVDC system is analyzed firstly, and the mechanism of VSCs' sub-module overvoltage is clarified. Then, an inverter side AC fault ride-through strategy composed of inverter side AC voltage based rectifier side DC current limiting and LCC commutation failure prediction based rectifier side DC current fast response is proposed to quickly suppress the sub-module overvoltage of the VSCs. Finally, a simulation model of a ± S00kV/S000MW hybrid cascaded multi-terminal HVDC system is established in PSCAD/EMTDC, and the effectiveness of the proposed control strategy is verified by simulation comparison.