Research On Control Strategy Of An Islanded Microgrid With EVS And Shiftable Loads

With the rising of distributed energy generation in recent years,a microgrid has become an effective path for distributed energy to connect to main grid.More and more institutes started to research microgrid which can absorb and reduce the fluctuation of electric power of DER especially for RES,and enhance the reliability of power supply.In islanded mode,voltage and frequency should be kept steady and loads should be supplied with high quality power,and operation cost should be considered.This dissertation proposes a real-time control strategy which is used in islanded microgrid with EVs and shiftable loads.Quasi steady state models of typical DER,RES and power electric converter are established.Power of PV and WT can be obtained from the quasi steady models according to illumination intensity,speed of wind,and other environment parameters.The math relationship between power of MT and fuel cost is established.The loads are divided into interruptible loads,essential loads,EV loads,and shiftable loads.The related math models of EV and shiftable loads are researched emphatically.The description functions of microgrid EMS which contain objective functions and constraint functions are established based on the quasi steady models of units in microgrid.The power of RES and loads are predicted by the environment.Among lots of optimal softwares,CPLEX is chosen to find the solution.The objective functions consider the operation cost,environment cost,operation differentials,and earnings of loads.The operation cost contains fuel cost,start/stop cost,charge/discharge cost,and other punishment cost.The constraint functions are consisted of power balance,start/stop time limitation of MT,and others.The optimization software CPLEX can find the optimal solution within 3 minutes.The purpose of electric vehicles access to microgrid is to reduce the influence of accessing to main grid which are the power unbalance,difficult to optimize,poor power quality,and new project problems.When EVs connect to microgrid,some advantages are prominent which can restrain the fluctuation of RES,and improve the economy of microgrid operation,and protect the environment.Shiftable loads are the loads in which the shifted load power curves are almost the same as the objective curves.Washing machine and disinfection cabinet are the common shiftable loads.When shiftable loads access to microgrid,the whole operation economy can be increased.The difficulty of EMS of islanded microgrid with EVs and shiftable loads is to arrange the time of charge/discharge and the hierarchical control or real-time control should be researched to ensure the stability and economy of microgrid operation.A real-time control strategy is proposed based on day-ahead control strategy and rolling optimal control strategy,and the feasibility is verified in microgrid with EVs and shiftable loads.Breakpoint doesn't appear in the whole period of 24 hours.The final operation cost of real-time is equivalent to the cost of day-ahead and predicted values.The effectiveness of stabilizing the energy of ESS and microgrid operation of the proposed strategy is verified with stability and economy compared with day-ahead control strategy.In this dissertation,the transient models of micro-sources are not researched in a control period of time,and the ranges of application of the proposed real-time control strategy are needed for researched further.