Micro-grid Optimized Operation Control And Differential Protection Including Wind Energy,Photovoltaic Energy,Fuel Cells And Energy Storage

In recent years,with the continuous development of society and economy,there is an increasingly prominent contradiction between energy demand and environmental pollution.The adoption of new energy sources to reduce and replace traditional fossil energy is a major measure to adhere to sustainable economic and social development and protect the ecological environment.Each country has shifted the focus of research from traditional power grids to distributed generation(DG)composed of wind power and photovoltaic power.DG contains a variety of new energy generation methods,which can effectively use energy and protect the environment.However,it is inherently random and energy output is intermittent.Micro grid can fully make up for these shortcomings.As a micro system that can realize self-management and control,it is mainly composed of different types of micro power supply,load,energy storage system and control scheduling system.The reliable operation between micro grids and the effective protection of micro grids have become an important and hot topic in the world.In order to effectively analyze and study the micro-grid operation optimization control and reliable protection problems,this thesis conduct a micro grid solar photovoltaic power generation system,fuel cell,wind turbine,the super capacitor energy storage system and micro source such as battery energy storage system model description from the perspective of distributed units.In view of the security and stability of the operation of the wind-solar fuel storage micro-grid,as well as the economic efficiency of the operation,this thesis studies and proposes the overall framework of the optimal operation control of wind-solar fuel storage micro-grid,namely the two-layer control strategy of the wind-solar fuel storage micro-grid.On the one hand,it can make the system predict the size of output power for optimization and adjustment,on the other hand,it can complete the automatic distribution of transient power fluctuations,and improve the system operation adaptability of the whole solar energy storage micro grid.In this thesis,a control strategy based on fuzzy PID droop control is adopted for the main control layer of the wind and solar energy storage micro grid.The automatic power distribution ability is further improved through the inverter,and the instantaneous power of each micropower source is evenly distributed.At the same time,the power optimization control strategy of wind-solar storage and combustion micro-grid based on improved particle swarm optimization algorithm is proposed.The improved particle swarm optimization algorithm is used to take the power generation cost as the objective function,and the operating conditions such as the charge and discharge characteristics of the storage battery and the number of charge and discharge cycles are introduced as the constraints for each micro-source and equipment capacity configuration,and the micro-power sources and each device are further optimized.The output power is verified by simulation results,which can greatly improve the overall economic efficiency of the wind-storage micro-grid.In view of the difference between micro-grid protection and traditional power grid protection,a differential protection method based on characteristic cosine is proposed by analyzing the characteristic cosine values of different bus bars.The uniform behavior of voltage and current is quantified by elliptic equation and least square method.By analyzing the direction of fault current and characteristic cosine of typical micro-grid in different locations,the difference between the position of fault segment and that of normal segment can be obtained.Based on the characteristic cosine differential protection method,the differential direction is defined and the fault section position is detected by the differential direction.Simulation results show that the method is effective.This method can effectively calculate the difference direction under different operation mode,grounding resistance,fault type,fault section position and noise influence,and has high protection accuracy.In this thesis,three micro-grid systems composed of two AC and DC micro-grids are designed and built,and a three-layer control structure is proposed,namely the micro-grid dispatching layer(upper layer),power optimization layer(middle layer),and local control layer(lower layer).Among them,the micro-grid dispatching layer(upper layer)can not only guarantee the independent operation of the three subsystems,but also realize the energy optimization configuration and flow interconnection operation among the three systems,and ensure the safe,stable and reliable operation of the whole system.The successive construction of micro-grid demonstration projects at home and abroad has enabled the rapid development and improvement of micro-grid operation control and micro-grid protection,but there are still many difficulties to be overcome.At the same time,it is the need for researchers to continuously explore and delve into.