Research On Control Strategy Of Parallel Inverters In Microgrid

The Distributed Generation combine with the energy storage device and the energy conversion device usually connect to the large power grid in the form of the microgrid or Suplly Electric energyr to the load,and the Distributed Generation scheme with parallel inverters to connected the microgrid bus.thus the inverters acts as the microgrid core device of electric energy conversion,which parallel control system work stability is very improtant.The droop control has been widely studied and utilized for its advantages of plug-and-play characteristics and high reliability.Firstly this paper summarizes the development background and current situation of microgrid,and analysis several control strategies of parallel inverter in-depth which been widely used at present.Then compare the advantages and short-board between different control strategies and choice the droop control as the main control method of the inverter parallel system.Secondly,the island microgrid model and the three-phase inverter mathematical model with LC filter are established,set the LC filter parameters,several commonly used control strategies of the Distributed Generation are analyzed,then focus on the analysis of power transmission characteristics of Distributed Generation parallel inverters which used droop control.Summarize the shortcoming of the droop control in microgrid.Setting the parameter selection principle of the droop control factor.Design double closed loop controller of voltage and current and set the parameter.By using the Bode diagram,the effects of resistive virtual impedance and inductive virtual impedance on the equivalent output impedance characteristics of the inverter are analyzed,and the shortcomings are summarized.A combination of virtual negative resistance and virtual inductance is proposed.The new virtual negative impedance technology uses the virtual negative resistance to cancel the resistive part of the system impedance,the output impedance amplitude been reduced,reduce the output voltage drop,then combine the virtual inductor to correct the inverter output impedance characteristics to pure inductive.The power decoupling is realized,and se the principle of the value of the virtual negative impedance parameter.The stability analysis of the control system is carried out by Establishing the root locus of the controlling system function.Last,the independent hybrid microgrid system model of Photovoltaic cells and energy storage batteries was established,and the photovoltaic cell model and energy storage battery simulation model were built in MATLAB/Simulink.The parallel simulation of double Distributed Generation inverters was used to verify the effectiveness of the virtual negative impedance control strategy.The results show that the virtual negative impedance of improved droop control strategy can keep the power quality of the system output under the condition of both Power balance and circulation inhibition.