Study on Operation Characteristics of Offshore Wind Farm Integrated to Weak AC Systems via VSC-HVDC

VSC-HVDC has the ability to supply power to weak systems and is a common grid connection method for offshore wind farms. However, the operating characteristics of offshore wind farms connected to weak receiving end AC systems via VSC-HVDC remain to be clarified. This paper established a model of an offshore wind farm based on DFIG connected to a weak receiving end system via VSC-HVDC, and analyzed the VSC steady-state operating range and its influencing factors. And the change rule of the theoretical value of the system critical short-circuit ratio was summarized. On this basis, the influence of the access of doubly-fed wind turbines on the short-circuit ratio was discussed. The critical short-circuit ratio under different output conditions of the wind farm was obtained by using the control variable method of increasing the equivalent reactance of the receiving end system and the output of the wind farm. Finally, a simulation is carried out based on the PSCAD/EMTDC, and the results show that the strength of the receiving end systems is a key factor affecting the grid-connected capacity of offshore wind power. Taking appropriate reactive power compensation measures can improve the safe and stable operation of the system.