Online Evaluation Of Voltage Stability Of Multi-infeed HVDC System

Due to the fact of complex national conditions in China,such as long distance between the energy resource base and the load center,the high voltage direct current(HVDC)transmission technology is widely used because of its advantages,such as long distance,large capacity,asynchronous interconnection,and controllable power flow.Its outstanding advantages make it play a key role in Chinese national strategy of “transmitting electricity from the west to the east” and “Regional interconnection”.In China,there have been dozens of closely spaced high-voltage DC systems integrated into the same receiving AC power grid.Different types of HVDC systems and receiving AC power grids have been combined into Multi-Infeed HVDC(MIDC)System or Hybrid Multi-Infeed HVDC(HMIDC)System.As the size of the HVDC feed into the receiving AC grid is getting larger and larger,and some conventional generator units are shut down,the receiving AC grid 's ability to support the dynamic reactive voltage of the HVDC system is gradually decreasing.Compared with traditional AC power systems,The problem of voltage stability of MIDC system is more prominent.How to accurately assess the voltage stability of the MIDC system online,this paper has carried out in-depth research on the establishment of a MIDC system simulation model,the proposed voltage stability index,and the verification of an example.First,MIDC system and HMIDC system are reduced respectively as equivalent single-infeed system model and generalized dual-infeed system model.Secondly,based on the above equivalent system model,the power sensitivity factors,such as equivalent nodal power sensitivity factor(ENPSF)and hybrid power sensitivity factor(HPSF),are derived based on the equivalent system model.Then,short circuit ratio index for steady-state voltage stability analysis,such as equivalent operating short circuit ratio(EOSCR)and hybrid generalized short circuit ratio(HGSCR),are respectively proposed based on the power sensitivity factor.Thirdly,with the power sensitivity as the medium,the mathematical and physical relationship between the proposed short-circuit ratio index and steady-state voltage stability and the mathematical relationship with the traditional short-circuit ratio are established.Finally,based on PSCAD / EMTDCTM,dual LCC-HVDC feed system models and a hybrid tripple-infeed system model were built to verify the proposed indicators.