Coordination Control For Multi-microgrid System With Parallel Structure Based On Improved Droop Control Strategy

Distributed power supply(Distributed Generation,DG)is connected to the large power grid through power electronics devices,which will cause great interference to the large power grid.microgrid solves the contradiction between distributed power supply and large power grid.however,due to the small inertia of power electronics devices,DG is vulnerable to various disturbances and then to oscillation instability.In order to solve the problem that low voltage microgrid can not design control mode and operation parameters based on traditional high voltage power grid model and is easily affected by small disturbance,this paper adopts improved droop control combined with small signal modeling and analysis to solve this problem.First of all,according to the problems existing in the traditional droop control,considering the impedance and voltage drop of low-voltage microgrid lines,a droop control optimization control strategy considering the voltage drop and voltage angle offset is proposed,which improves the control accuracy.The simulation results show that the static stability of each sub-microgrid can be satisfied due to the parallel operation of microgrid,but the dynamic stability of the system needs more accurate parameter settings to better ensure the stable operation of grid-connected disconnection.aiming at the dynamic stability of multi-microgrid,this paper establishes a small signal model of inverter and parallel system,and lists the state equations,then converts all models into common coordinate system,and analyzes the parameters that may affect the dynamic stability of multi-microgrid system.Based on the parallel operation structure of multi-microgrid,taking the grid-connected disconnection of two microgrid and distribution network as an example,this paper discusses the operation state transition of multi-microgridaccording to the possible electric power impact and frequency transformation,the energy flow between microgrid and distribution network,the micro-grid and the dynamic characteristics of micro-grid.The control strategy of grid-connected disconnection is designed.Based on MATLAB/Simulink,the simulation model of operation state transition event and process is built,and the improved control strategy and grid-connected disconnection control strategy are verified by simulation.Finally,based on the improved control strategy and small interference stability verification,the correctness of the conclusions is verified by simulation.