ABSTRACT The voltage‐source‐converter (VSC)‐based high‐voltage direct current (HVDC) transmission technology has been increasingly adopted for power delivery from offshore photovoltaic (PV) power stations. Nevertheless, the offshore PV power stations can readily interact with the VSC‐HVDC system, leading to sub‐/super‐synchronous oscillations. In order to investigate the underlying mechanism, an accurate impedance model considering frequency‐coupling effects is developed in this paper. Then, a reduced‐order impedance for quantitative stability assessments is further derived. It has been revealed through the analysis that the PV power stations exhibit negative‐damping characteristics in the sub‐/super‐synchronous frequency range, which may trigger oscillations. Moreover, increasing the output power of individual PV units or the number of PV units connected to the HVDC system reduces the magnitude of the aggregated PV impedance, thereby increasing the oscillation risk. Time‐domain simulations reproduce pronounced sub‐/super‐synchronous oscillations, with dominant spectral components spreading around 20 Hz and 80 Hz. Furthermore, hardware‐in‐the‐loop (HIL) experimental tests validate that the oscillatory components are effectively suppressed by properly reducing the phase‐locked loop (PLL) parameters. When the PLL proportional gain is reduced to 0.8 of its setting value, the total harmonic distortion (THD) of the voltage at the common coupling is reduced from 11.8% to 0.72%. This indicates oscillation mitigation.
Ni et al. (Thu,) studied this question.