Comparative Analysis of Electrical Stress Characteristics of Grid-Forming and Grid-Following Flexible Converter Valves

Aiming at the problem of unknown differences in electrical stress characteristics of ± 800kV/8GW converter valves for high-voltage directcurrent power transmission (HVDC) using voltage sourced converters (VSC) under grid-forming and grid-following control methods, this paper firstly investigates the true double-pole double-ended topology of ± 800kV/8GW flexure transmission and analyzes the mathematical model. Then, we compare and analyze the grid-forming (GFM) and grid-following (GFL) converter valves control strategies, and build a simulation model of ± 800kV/8GW VSC-HVDC system. Then, the electrical stress characteristics of the converter valves with GFM and GFL strategies under short-time load switching condition, grid-side three-phase short-circuit condition, and DC short-circuit condition are simulated and compared. Simulation results show that: the bridge arm current stress of GFL is 66.90% higher than GFL, capacitive voltage fluctuation rate is 142.62% higher than GFL, and the maximum circulating current stress is about 66.16% higher.