Oscillation Between VSC-HVDC and AC Grid: Phenomena, Analysis and Solution

Several oscillation events happened between VSC-HVDC system and the AC grid in recent years, which may result in the outage of VSC-HVDC. To understand the oscillation and find solutions, this paper concentrates on the mid- and high-frequency oscillation between VSC-HVDC and the AC grid. The 1270 Hz oscillation happens in China Southern Power Grid (CSG) is firstly reviewed. Then the physical and mathematical mechanism of the oscillation is analyzed. Analysis result show that as it’s hard to eliminate the negative-real-part of VSC impedance due to the long control delay in VSC-HVDC systems, the occurrence of oscillation is the inherent characteristic of VSC-HVDC connected to the main power grid. Fortunately, the oscillation can be damped by changing the grid impedance or optimizing the VSC impedance. The influencing factors are analyzed and then the solution approaches are discussed. The analytical results are verified through simulation in PSCAD/EMTDC.