Design And Implementation Of Energy Management System For Off-grid Microgrid

In today’s world to the rapid development of economy,the energy crisis and environmental pollution problems become increasingly serious.With the proposal of low-carbon economy,in order to achieve sustainable development of human beings,the search for new energy has become a top priority.Solar energy,wind energy and other renewable energy sources not only perform excellently in solving the energy crisis,but also perfectly "live in harmony" with the ecological nature.Renewable energy can be connected to the power grid in the form of distributed energy.However,due to the large impact of the environment and the large voltage fluctuation caused by the connection to the power grid,the reasonable development of renewable energy is hindered.Therefore,the concept of micro grid is proposed.Microgrid is divided into off-grid type and grid-connected type.Off-grid microgrid has no support from large power grid,so its voltage amplitude and frequency are far less stable than grid-connected microgrid.However,it has certain advantages in self-sufficiency and flexible construction compared with grid-connected microgrid,and can maximize the performance of microgrid.In order to solve the problems mentioned above,this paper mainly studies the distributed energy in off-grid micro grid.By analyzing the power generation characteristics of photovoltaic cells,wind turbines and batteries,the equivalent circuit is constructed and the equivalent mathematical model is obtained.Finally,the output characteristics are fitted in the simulation environment.In this paper,distributed energy resources are designed in Matlab/Simulink software environment.Because of the power instability in the off-grid microgrid,this paper proposes to replace the large grid with batteries.The main battery outputs a stable DC voltage on the DC side in the form of DC/DC.Through the inverter V/f control mode,the three-phase alternating current required by the system is obtained.The maximum power tracking point(MPPT)technology is used from the micro source,mainly wind turbine and photovoltaic cell.Theinverter adopts PQ and droop control methods to control the power output of each micro source.Based on the coordinated control of distributed energy made a lot of research,on the basis of the master-slave control,introducing hierarchical control strategy,mainly to the micro source coordination work,formulate the corresponding coordination control constraints,control the network voltage amplitude stability,frequency stability,power balance,eventually to build the whole micro power grid model.In the case of load fluctuation and distributed energy output fluctuation,the effectiveness of the system is verified,which provides a theoretical basis for the actual work of the microgrid.In addition,in the study of the inverter,due to its high voltage utilization rate,small loss of switching devices and other advantages,mainly space vector pulse width modulation research,through the control of switching devices on and off,using the principle of mean value equivalence,the generation of the system given voltage vector,synthesis of three-phase electrical sine wave.In the end,this paper carries out simulation analysis on the energy of an island micro power grid,and adjusts the power balance in the network by means of electricity price adjustment,load adjustment,etc.,so as to make maximum use of distributed energy.