Power Flow Calculation Of Islanding Microgrid And Optimal Control Of Power Flow Based On Virtual Impedance

Islanding microgrid is composed of distributed power sources,energy storage equipment,local loads,monitoring and protection devices,which is one of the current research hotspots in distributed power generation applications.The clean distributed renewable energy,such as photovoltaic,is usually connected to the microgrid by the converter.The droop control is usually used by the converter to provide microgrid voltage support,realize power source "plug and play" and synchronization between power sources without communication.But with the droop control application,not only the reactive power between distributed power sources connected in parallel on the same node of the islanding microgrid cannot be distributed in proportion to the capacity of the power source,but also due to the frequency is controlled by active power,the nodes connected to the distributed power sources can no longer be equivalent to traditional ones.Therefore,the traditional power flow algorithm cannot be used to calculate the steady-state power flow of the islanding microgrid,and the power flow optimization can’t be carried out.In this paper,a small islanding microgrid composed of distributed power sources adopted droop control is the research object.The reactive power distribution of parallel power sources,microgrid power flow calculation and optimization control are studied deeply.The main research contents are as follows:Firstly,for a parallel power sources with droop control at a node of the micro grid,analysis found that when the grid-connected system impedance between the power sources does not match,the reactive power cannot be distributed in proportion to the capacity.Therefore,introduces the virtual impedance into the droop control strategy to adjust the system impedance of the power source to match the capacity,so that the reactive power between the parallel power sources is distributed in proportion.The relationship between the virtual impedance and the grid-connected point voltage is analyzed,and the virtual impedance value is reasonably selected to avoid the problem of too low grid-connected point voltage.Secondly,the distributed power source based on droop control is modeled,and based on its influence on the power flow calculation of the microgrid,the Newton Raphson algorithm is improved to be suitable for the steady-state power flow calculation of the islanding microgrid.Since the virtual impedance can regulate the distributed power sources output power of the islanding microgrid,applying the particle swarm optimization algorithm to derive the optimal value of the virtual impedance according to the results of the steady-state power flow calculation,so that the network loss of the microgrid is minimized.Finally,the effectiveness and accuracy of the islanding microgrid power flow calculation,the reactive power distribution between parallel power sources and micgrid power flow optimization based on the virtual impedance are verified by simulation and experiment respectively through Matlab and the experimental platform.