Under the two-stage voltage control architecture of provincial regulation, the superior dispatching control center directly sends the voltage command value to the automatic voltage control (AVC) sub-stations of each wind farm, and the AVC sub-stations of each wind farm in the wind power cluster independently perform voltage control without communication with each other. In this case, the AVC sub-stations of each wind farm can only obtain the operation data of the local station. The high efficiency and accuracy of reactive power allocation cannot be achieved through AVC master station, which makes the voltage regulation efficiency of wind power cluster low. In addition, due to the different response time of the energy management platform and the wind turbine, the voltage regulation response speed of the wind farm is also different. Wind farms with fast regulation speed bear more reactive power, and wind farms with slow regulation speed bear less reactive power, resulting in unbalanced reactive power and waste of reactive power regulation capacity.
Firstly, this paper analyzes the influence of reactive power regulation period and regulation step of AVC sub-station on the voltage control of wind farm grid-connected point. Considering that the operating parameters of each wind farm equipment in the actual system are relatively fixed, the reactive power regulation period is not easy to change, and the fixed adjustment step cannot take into account the adjustment speed and adjustment accuracy. Therefore, this paper focuses on improving the voltage regulation speed of wind farm by changing the reactive power regulation step length.
Secondly, because the voltage of the wind farm grid-connected point is not only related to the reactive power output of its own station, but also affected by the reactive power output of other stations, this paper proposes a voltage control strategy of the AVC sub-station of wind power plant based on "variable step perturbation observation". This strategy changes the output reactive power of the wind power plant, and then measures the voltage change of the grid-connected point, and evaluate the influence of voltage control of other wind farms on the wind farm grid-connected point, dynamically adjust the reactive power regulation step of AVC sub-station, improve the voltage regulation speed of the wind farm, so that the voltage of the wind farm grid-connected point can enter the voltage dead zone faster.
Thirdly, in order to improve the reactive power imbalance in the wind power cluster, the reactive power constraint relationship of the wind farm stations in the cluster is established by analyzing the voltage reactive power coupling relationship between each wind farm, and considering the difference of the reactive power margin of each wind farm station, the variable step size control strategy is improved, and an improved wind farm voltage control strategy considering reactive power constraint is proposed. The voltage regulation speed and reactive power balance of wind power cluster are considered.
Finally, based on the operating data of a wind power cluster in East China, a simulation model of wind farm convergence system is built to verify the effectiveness of the proposed strategy.