Research On The Droop Control Strategy Of Micro-grid Based On Line Impedance Matching

In the current society,traditional energy sources are depleted and environmental pollution problems have become increasingly prominent.In order to alleviate environmental pollution problems and the energy crisis,new energy sources such as wind energy and solar energy have attached more and more attention.New energy power generation,also known as distributed generation,has the advantages of geographical dispersion and flexibility,and mutual backup with large power grids,but it also has shortcomings.In this thesis,the power sharing of multi-parallel inverters is difficult to control and the circulation problem between multiple parallel inverters is analyzed in depth,and an improved method is proposed.As for three-phase voltage source type grid-connected inverters,this thesis establishes their mathematical models in three-phase a/b/c stationary coordinate system and two-phase d/q rotating coordinate system,analyze the relevant characteristics of LC filters,and design the relevant parameter.Based on the analysis of inverter droop control principle and the power sharing condition of parallel inverter,the influence of line impedance on power distribution is studied;then the characteristics of traditional drooping method and traditional inverted drooping method are also investigated in detail to analyze the shortcomings of these methods and design the power controller and voltage/current double loop controller.Considering the difference between the impedance of the power line in different voltage levels,the relationship between the traditional droop coefficient and the active/reactive power of the inverter output is studied,and an improved drooping strategy for multi-voltage levels microgrids is proposed based on the analysis of the equivalent power line impedance's impact on the power sharing.Aiming at the proposed self-adaptive integrated droop control method,a high/low voltage microgrid simulation model based on different impedance characteristics is established.Finally,the parallel system is simulated under the different conditions including steady state,sudden increase load and sudden decrease load,which is compared with the traditional droop control strategy under the same working conditions to verify the power equalization and circulation suppression effect.