| Along with the development of modern microgrid architecture,the proportion of new energy generation is constantly rising,causing the microgrid frequency modulation pressure to be significantly increased in the island operating mode.Reducing frequency fluctuations is the research focus to ensure the safe and stable operation of the microgrid.When the microgrid is in island operation mode,there may be a disturbance in different channels from the control input during actual operation.The traditional control method is not ideal for load frequency control.At the same time,in each subsystem,the load frequency will fluctuate due to the randomness of its local load and the intermittence and uncertainty brought by access to new energy generation.Especially when the impact load occurs in the microgrid,due to the increase of the proportion of new energy generation,the response speed and reserve capacity of traditional units will not meet the requirements of frequency regulation.How guarantee the stability of the load frequency of the microgrid is of great importance in the mode of the island operation.This thesis is in light of the load frequency stability of the islanded microgrid with wind power,photovoltaic,and energy storage to conduct research.First of all,aiming at the disturbance existing in the traditional microgrid in island operation mode,a load frequency control model composed of generator-load,prime mover,governor,and other component models is established,and the load frequency control strategy for the traditional islanded microgrid is designed based on the strong robustness of the sliding mode variable structure control method to the disturbance.The stability of the system is analyzed by the Lyapunov stability theory.Under this strategy,the balance of the active power and frequency of the system can be achieved.The simulation verifies the antiinterference ability and response speed of the system.The sliding mode variable structure control method adopted can ensure the reliability of the microgrid island operation,and the system state can quickly converge and maintain stability.Secondly,on the basis of the traditional islanded microgrid load frequency control,in order to suppress the impact of the fluctuation and intermittence of new energy power generation on the load frequency,the islanded microgrid taking into account the wind and photovoltaic power generation fluctuations is modeled for load frequency control,the disturbance observer is designed to estimate the disturbance due to the wind and photovoltaic power generation fluctuations,furthermore,the load frequency controller is designed and the system stability is analyzed based on this strategy.When the load frequency of the islanded microgrid is affected by wind and photovoltaic power generation fluctuations,the proposed strategy can guarantee the system’s stability.Simulation of the control process with MATLAB is carried out,and the result is validated when the load frequency fluctuates due to the impact of new energy generation access.Finally,the energy storage link is introduced to assist the frequency modulation,and the dynamic load frequency control model is established for the islanded microgrid with wind power,photovoltaic,and energy storage.Based on the disturbance observer,the load frequency controller is designed,and the adaptive reaching law is used to improve the performance and speed of the system.Simulation results show that the method is feasible for the islanded microgrid with wind power,photovoltaic,and energy storage assisted frequency modulation and can effectively reduce the deviation of load frequency,reduce the frequency modulation pressure caused by the increase of the proportion of new energy generation,and can adaptively reduce the chattering phenomenon according to the system status.It is shown that the proposed method can improve the robustness and operational stability of the islanded microgrid with wind power,photovoltaic,and energy storage. |
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