Research On Direct Power Optimization Method Of Multi-terminal VSC-HVDC Offshore Wind Power System Based On Model Predictive Control

With the extensive development and utilization of fossil energy by humans,environmental pollution continues to deteriorate.As a renewable and pollution-free new energy source,offshore wind power has gradually become a new hot spot in the world today.However,with the integration of large-scale wind power to the grid,the volatility and randomness of offshore wind power have long restricted the healthy and sustainable development of offshore wind power.In addition,the regulation ability of the wind power system itself will also affect the transmission efficiency of the system.Therefore,this thesis aims to improve the stability of the multi-terminal VSC-HVDC offshore wind power system and reduce system output power fluctuations.Combined with model predictive control,a systematic study of the multi-terminal VSC-HVDC offshore wind power system is carried out.The main research work of the thesis includes:First,this thesis establishes the offshore wind power VSC-HVDC system model,and introduces the basic principles of the offshore wind power VSC-HVDC system and the mathematical models in different coordinate systems in detail,and then studies the different control strategies of the offshore wind power VSC-HVDC system.And the mathematical model,as the basis of the following research.Secondly,in view of the low efficiency of the multi-terminal VSC-HVDC offshore wind power control system,a direct power control method of the multi-terminal VSCHVDC offshore wind power system based on model predictive control is studied.This method uses a model predictive control algorithm to replace the traditional PI control algorithm.Set the objective function through the model predictive control,use the voltage vector to control the on and off of the switching device,use the error of active power and reactive power as the input of the model predictive controller,and introduce the internal model feedback correction link in each The sampling period corrects the predicted given value of the power,so as to achieve high-precision tracking of the instantaneous power.Compared with the traditional PI control,the amount of calculation is reduced,the switch is controlled at a constant frequency,and the AC side voltage sensor is not required,which saves costs.The simulation results show that the active power,reactive power,and DC side voltage fluctuations under this control method are smaller,the response speed is faster,and the stability is better.Thirdly,in view of the shortcomings of traditional model predictive control methods of low accuracy and large amount of calculation,a direct power control method of multi-terminal VSC-HVDC offshore wind power system based on finite set model control is studied.The method adds current feedback compensation and voltage and current correction.In the link,the traditional model predictive control algorithm is optimized and the amount of calculation is reduced.In addition,the converter control method has been added to give full play to the power regulation characteristics of the multi-terminal VSC-HVDC offshore wind power system.When a certain converter station exits due to disturbance or failure,the leading converter station is used to predict power compensation,take the initiative to assume the power shortage,and perform power compensation through mode switching between converter stations.When the power upper limit is reached,the operation mode is switched and then stopped,so as to achieve the purpose of stable operation of the system.The simulation results verify the correctness and rationality of this method.Finally,in view of the transient stability of the multi-terminal VSC-HVDC offshore wind power system,in order to effectively suppress the power fluctuation of the multiterminal VSC-HVDC offshore wind power system,MPC based multi-terminal VSCHVDC offshore wind power hybrid energy storage system control method is studied.Apply model predictive control to a hybrid energy storage system composed of batteries and supercapacitors to achieve independent power control.At the same time,the model predictive control system is dynamically solved based on the quadratic programming,which reduces the computational complexity of the model predictive control system and effectively reduces the amount of calculation.The simulation results show the correctness and effectiveness of the method,which can effectively suppress the fluctuation of the output power of the multi-terminal VSC-HVDC offshore wind power system,and improve the stability of the system.