Research On Frequency Adjustment Optimal Control Of Micro-grid Based Hybrid Energy Storage System

As one of the effective ways to promote the local consumption of uncontrollable distributed generation,the flexible and economic power supply mode of micro-grid has become an important supplementary means for China’s large power grid.However,the randomness and intermitence of the output of wind power,photovoltaic and other uncontrollable distributed generation have become the main reason to curb the development of micro-grid.In recent years,the growing maturity of various energy storage technologies has brought new opportunities to solve this problem,especially in the aspect of micro grid frequency modulation.The fast and accurate power tracking ability of energy storage and powerful power throughput provide a new auxiliary section for micro grid to maintain system frequency stability.Based on this,this paper firstly analyzes the research status of micro-grid frequency control and energy storage system participating in micro-grid frequency adjustment,comprehensively considers the advantages and disadvantages of various energy storage systems,and proposes a hybrid energy storage system composed of battery array and superconducting magnetic energy storage system to participate in micro-grid frequency adjustment,in order to absorb clean energy as much as possible,through the complementary advantages of each energy storage system,it has the advantages It can effectively maintain the frequency stability of micro-grid.Secondly,through the analysis of the topology and model of micro-grid,the detailed modeling analysis of wind power generation system,photovoltaic power generation system,energy storage battery,superconducting magnetic energy storage system and diesel engine in micro-grid is carried out,which lays the foundation for the research on the active power output characteristics of distributed generation and frequency regulation characteristics of frequency regulation unit in micro-grid.Through the modeling analysis and theoretical derivation of distributed generation in micro-grid,it is concluded that the moment of inertia of wind power generation system and photovoltaic power generation system to the system presents the characteristics of "weak inertia" or "no inertia".With the increase of wind power and photovoltaic installed capacity,the equivalent moment of inertia of micro-grid will be reduced,and the randomness of its output will seriously affect the frequency stability of micro-grid Rate stability.The hybrid energy storage system is composed of battery and superconducting magnetic energy storage system.The superconducting magnetic energy storage system has strong power throughput,fast change rate and flexible response,so it is very suitable to bear the high-frequency component of system power shortage;the output power of battery system has a small change range and slow change rate,but it can be charged / discharged for several hours,so it is suitable to bear the system power The low frequency component of the rate gap.Finally,the hierarchical control architecture of micro-grid frequency control is proposed : the first layer proposes the power increment factor droop control considering cost function by improving the traditional power frequency droop control.The second level control is based on the secondary frequency regulation of micro-grid.Through the improved consistency weighted algorithm,the battery cells that bear the part of frequency regulation power shortage can allocate power adaptively to avoid the state of charge and output power exceeding the limit.The third level of power flow is used to minimize the cost of each power source.Finally,the correctness and effectiveness of the proposed strategy are verified by simulation.