Engineering Data Analysis of Sub/Super-Synchronous Oscillation between Wind Farm and MMC in Zhangbei Project

To analyze the problem of subsynchronous and supersynchronous oscillation in the operation of Zhangbei renewable energy flexible DC power grid project, the voltage and current waveforms obtained from on-site recording data are analyzed. Fourier analysis shows the oscillation frequency is 44 Hz and 56 Hz. But in the dq-rotating coordinate, the curves of Id, Iq, Ud and Uq are all composed with 6 Hz oscillation. At the same time, there is also a 6 Hz oscillation on the recording curve of DC current and DC voltage. It can be inferred that the 6 Hz oscillation on AC side and DC side is coupled with each other. This paper believes that this power oscillation phenomenon is due to the lack of DC current control. When the wind power rises rapidly, the capacitor voltage of VSC station is oscillated caused by control delay. This is the reason of oscillation of DC and AC voltage.