Research On Collaborative Control Of Offshore Wind Power System

In recent years,with the rapid development of wind power construction in China,onshore wind power gradually tends to be saturated,meanwhile offshore wind power is becoming the new trend of wind power development.The offshore wind resources in our country are abundant,and close to the center of the economically developed southeast coastal load.Therefore,offshore wind power will become the focus of wind power market development and an important component of the strategic emerging industry in China in the future.This thesis mainly studies on the MPPT and LVRT perfprmance of a direct drive offshore wind farm,with a synergetic control method applied.Firstly,a PMSG wind farm model is established,the components of which include wind turbines and transmission chain,PMSG,and VSCs.Based on the control principle of PMSG wind farm,the control strategy of machine side converter and grid side converter are put forward in order to realize MPPT.Then a PMSG wind farm grid connecting system simulation model is built in Simulink,to analysis the operation characteristics of the PMSG wind farm.Secondly,a synergetic control is applied to the direct drive offshore wind farm.According to the mathematical models and control equations of PMSG and its converters,the synergetic control equations of the system are deduced.The Simulink simulation model was established,and the MPPT scheme was tested to prove the good operation performance of MPPT when the synergetic control is applied.Thirdly,in order to solve the overcurrent and overvoltage problems when voltage drop happens,the pitch angle control method is needed to reduce the power output of wind turbine and keep the power balance between machine side and grid side.In the Simulink simulation model,the variable pitch control is realized,and a three-phase grounding fault is simulated.The simulation analyzes the synergetic control of the offshore wind farm in the process of LVRT,and the effectiveness of synergetic control method is verified.Finally,the offshore wind farm with VSC-HVDC interconnection system model is introduced.A double loop control method is adopted in the two converters of VSC-HVDC,between which the WFVSC uses the constant AC voltage control in the outer loop,while the GSVSC uses the constant DC voltage control,and in the inner loops of them are mainly current controllers.In order to improve the control performance,the VSC-HVDC converter also adopts the synergetic control.The simulation model of direct-drive offshore wind farm via VSC-HVDC is established in Simulink,and the simulation results show that the synergetic control can stabilize the wind power system.Along with the development and utilization of wind energy,offshore wind farm will have a longer transmission distance and a larger capacity.This thesis studies the synergetic control method of the direct-drive offshore wind farm grid system,complied with the development trend of the offshore wind farm,and has a certain role in promoting the further development of offshore wind energy.