Research On The Effect Of Hazheng UHVDC Commutation Failure On Wind Power

With the large-scale development of wind power in our country, ultra high voltage direct current transmission will become an important way for delivering wind power in the future. The built of ±800kV Hami-Zhengzhou ultra high voltage direct current transmission project (Hazheng UHVDC) is beneficial to transporting wind power in Hami to central China, which could effectively relieve the supply pressure of central China power grid. However, there are still some security and stability problems at the start of the DC operation. Due to the anti-jamming ability of the wind farms is poor than the conventional power plants, the operation of the wind turbines will be destroyed under the circumstance of AC overvoltage caused by DC commutation failure. In very severe cases, the large-scale wind turbines may disconnect from the grid, which threatening the stability of the system. This problem has also become one of the important factors that limits the transmission capacity of HaZheng UHVDC. Therefore it is very necessary to study the impact of HaZheng UHDVC commutation failure on Xinjiang wind power.According to the actual engineer parameters of Hazheng UHVDC, a simplified Northwest power grid model is built based on PSCAD/EMTDC. It contains Xinjiang, Gansu, Qinghai provinces. This paper introduces how to build the model of generator, transmission lines, transformer, load and the model of double-fed induction generator (DFIG) with large capacity. The mechanism of AC overvoltage caused by DC commutation failure is researched in depth based on the simulation model. The transient overvoltage levels of wind farms in Hami are checkcd under different conditions. This paper analyze the influencing factors of the overvoltage level of the wind farms, including the power transferring after failure, the level of DC power, the fault type leading to commutation failure and the operational mode of the AC system.On the basis of the simulation results, the improvement suggestions about the standard of wind turbines high voltage ride through (HVRT) in Xinjiang are proposed. The measures which can suppress the transient overvoltage are developed through installing static var compensator (SVC) in parallel with the wind farms and improving the parameters of DC constant current control VDCOL. The effectiveness of the proposed strategies is verified by simulation.