Research On Control Strategy Of FESS Machine-Side Converter For Smoothing Wind Power Grid-connected Power

Wind power is one of the important ways to solve environmental pollution and energy crisis.However,the randomness and intermittency of wind speed will lead to fluctuations in the output power of wind turbines.With large-scale wind power integration,fluctuating power will bring many adverse effects on the safe and stable operation of the grid.Flywheel energy storage system(FESS)has the characteristics of high power density,fast response,high energy conversion efficiency,long service life and no pollution.The reasonable configuration of flywheel energy storage devices in wind power generation system can effectively suppress wind power fluctuations and improve grid-connected power quality.This paper takes the FESS applied in wind power generation system as the research object,and the control strategy of FESS machine-side converter is studied to achieve the purpose of smoothing wind power grid-connected power.Firstly,the development status of wind power generation in China is described,and the method of using FESS to improve the grid-connected power quality is proposed for the problem of wind farm output power fluctuations.By analysing the development status of energy storage technology and its application status in wind power generation system,and the research status of flywheel energy storage control strategies,the research content of this paper is determined.Secondly,the basic structure and working principle of flywheel energy storage are introduced.According to the operating characteristics of flywheel energy storage,the permanent magnet synchronous motor is selected as the flywheel drive motor,and its mathematical model is established and analyzed.The FESS is connected to the outlet bus of the wind farm in a centralized configuration,and the control strategy of each converter in the system is designed according to the smoothing principle.Thirdly,the sliding mode control is applied to the control of FESS machine-side converter for the problem that traditional PI control is difficult to meet the rapidity and accuracy of power regulation.It introduces the working mechanism of sliding mode variable structure control,and analyzes the causes and solutions of its chattering problem.An improved exponential approach law with better performance is proposed by introducing system state variables into the traditional exponential approach law and designing a switching function.The sliding mode power controller based on improved exponential approach law is designed,and compared with the traditional control method by simulation.The simulation results show that the improved SMC can improve the power tracking ability of FESS,and weaken the current chattering while enhancing the power response speed.Finally,the Kalman filter algorithm is used to optimize the control strategy of FESS in wind farm in order to prevent overcharge or overdischarge of energy storage during power smoothing.The Kalman filter is designed according to the characteristics of the wind farm output power,and by introducing the operation state of FESS into the filtering process through fuzzy reasoning,the fuzzy Kalman filter considering the operation state of energy storage is designed.The simulation model is built to study the system with traditional and fuzzy Kalman filters,and the smoothing effect of grid-connected power is analyzed by the maximum variation and fluctuation frequency.The simulation results show that the proposed control strategy can effectively smooth the wind power to meet the grid connection requirements,and maintain the speed and power of FESS within the limits during the smoothing process,which achieves the two objectives of wind power smoothing and energy storage protection.