Improved Droop Control Strategy Of Microgrid Inverter

With the development of science and technology and the aggravation of the hot environmental problems,microgrid has a place in the power system of large grid as the main power supply.Each distributed power supply is connected to the micro grid through the inverter device to form a small power system.According to the operation mode of microgrid and the higher requirement of power quality,the control mode of inverter has become the most important research hotspot.In the inverter control mode,the peer-to-peer control has the characteristics of "plug and play",smooth switching,flexible operation,etc.,while the droop control has the problems of active power and reactive power coupling,power distribution when multiple inverters are running in parallel,and Microgrid operation mode switching,etc.Therefore,this paper studies the above problems.At the beginning of this paper,the research background and development status of microgrid are described.The basic structure and characteristics of microgrid and the common control methods of inverter are introduced.PQ control,V / F control,droop control are described and analyzed.The following droop control strategies are studied.On the premise of low-voltage micro grid line resistance,the mathematical model of inverter in dq coordinate system is established and droop control characteristics are analyzed.Secondly,the influence of sag coefficient,proportional coefficient and integral coefficient in current and voltage loop on the stability of the system is analyzed by using the root locus diagram.Aiming at the problem of reactive power distribution in traditional droop control,the reactive power distribution condition is deduced,and the reactive current consistency adaptive virtual impedance is added to the original control structure to satisfy the reactive power distribution equation.The influence of virtual impedance on the output characteristics of the inverter is analyzed,and thevirtual impedance is added to improve the resistive line characteristics to satisfy the power decoupling.In addition,the differential droop control and the static virtual impedance will make the systemFinally,the simulation analysis of the system model is carried out by using MATLAB software.The simulation results verify that the proposed improved droop control method can effectively improve the rational distribution of reactive power while maintaining the frequency and voltage of the system.Under the function of the synchronous grid module,the voltage amplitude,frequency and phase of the micro grid can be synchronized when the micro grid is incorporated into the large grid,which can be smoothly switched from off grid operation to grid operation.