## 5 Conclusions  
This paper investigated the effect of BCS on dynamic and fatigue characteristics of modern wind turbines. Considering the increase of the slenderness ratio and the flexibility of wind turbine in the development of wind energy, it is very significant for the safety of wind turbine structure to accurately calculate the wind-induced dynamic responses of the support structure and blades. Based on FAST code, two different cases with BCS and without BCS are simulated with various wind conditions, from cut-in to cut-out wind speed. By comparing the mean and maximum values of wind turbine dynamic responses between the two cases, we found that the mean values of the displacement and load components increase with the increase of wind speed in No. 1, while the mean values increase below the rated wind speed and then decrease over the rated wind speed in No. 2, and there are mean values reductions of over 68% in No. 2 at the cut-out wind speed compared to No. 1. The maximum values of the displacement and load components have the same trend with the mean values in the two cases except for the simulation results of tower when the wind speeds are around the cut-in speed. There are maximum values reductions of over 42% in the cut-out wind speed in No. 2 compared to No. 1. To more accurately describe the relationship between the wind speeds and structural dynamic responses when the BCS working, the corresponding fitted curves are carried out and provided, which is helpful to better understand the dynamic features of wind turbine subjected to wind loads during normal operation. In the cut-in wind speed range for No. 2, the 3P of the rotor speed is close to the first tower FA natural frequency, which causes the increase of structural dynamic responses and fatigue loads of the tower when compared to No. 1. By comparing the binned range rainflow cycles of the four load components between the two cases, we found that compared with BFX and BMY, the effect of BCS on the number of rainflow cycles in the high load range on TBFX and TBMY is more obvious. By comparing the COVs and DELs of major load components between the two cases, we found that values of DEL and COV in No. 2 are larger than those in No. 1 in most conditions, especially for TBFX and TBMY around the cut-in speed. In addition, the obvious influence of BCS was clarified by comparing the BFX and TBFX with the azimuth position of the blade and frequency analysis between the two cases for four typical wind scenarios. According to the simulation results, it is concluded that the traditional method analyzing the dynamic responses of wind turbine blades and tower without considering the BCS will overestimate the mean and maximum values of structural responses while underestimate the fatigue loads. Therefore, to improve the safety and reliability of wind turbine structure, the BCS should be considered for design, structural dynamics, and fatigue analysis. Since the BCS plays an important role in the safe operation of modern wind turbines, future research efforts can be focused on BCS optimization, such as the influence of Tip Speed Ratio on control results and a more effective fatigue analysis method. Conceptualization, methodology, software, validation, formal analysis, investigation, data curation, writing original draft, C.Y. ; supervision, writing-review and editing, J.L. ; supervision, writing-review, and editing, Y.X. ; supervision, methodology, W.B. ; Methodology, J.W. All authors have read and agreed to the published version of the manuscript. This research was funded by the Key Research and Development and Promotion Project in Henan Province (Grant No. 212102310269), National Natural Science Foundation of China (Grant No. 51679092) and Scientific Research Project of North China University of Water Resources and Electric Power (Grant No. 201811007). Not applicable. Data Availability StatementData underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.