Overvoltage Analysis Of AC/DC System Utilizing Two-Time-Scale Separation

As of 2021, more than 20 HVDC ties are deployed in the Chinese power system, transmitting a large trunk of electric power over distance. When an AC large disturbance occurs, a DC blocking is likely to occur. Due to the time it takes to disconnect reactive power compensators connected to the blocked HVDC, the surplus reactive power will lead to a transient overvoltage on the rectifier bus, threatening the safe operation of the AC/DC system. An equivalent sending-end multi-convertor model is constructed to reveal the transient overvoltage mechanism caused by adjacent DC blocking. Then the two-time-scale characteristics of AC/DC system are explored to decompose the complex system into simple fast and slow subsystems with the help of singular perturbation. On this basis, the three stages of HVDC overvoltage evolution are discussed, and the main reason for the dynamic voltage rising after a short time is verified to be affected by the synchronous generators. The inhibition effect of time constant of generators for overvoltage is analyzed.