Research On Coordinated Control Strategies Of Microgrid Based On Distributed Generation

In recent years,with the depletion of fossil fuels and the ecological environment deterioration,distributed generation has widely used due to their features such as cleanliness and high efficiency,making microgrid also develop rapidly.During the operation of the microgrid,coordinated control of the distributed generation,smooth switching of microgrid between grid-connected and islanding operation mode,which is key to the stable operation of the system.Therefore,it is of great practical significance to conduct in-depth research on the coordinated control strategy of microgrid with multi-distributed generation.1)The thesis analyzes the working principle and control method of the common distribute power supply in microgrid.In the thesis also established the mathematical model,the inverter control system model and corresponding electromagnetic transient simulation model of micro-sources,the micro-sources include wind turbine power system,photovoltaic power system and energy storage system.The simulation analysis and verification are made by MATLAB/Simulink software to obtain the dynamic operation characteristics of micro-sources.2)The thesis from the basic structure of the inverter,based on the analysis of the principle of sine wave pulse width modulation(SPWM)modulation,the control strategy of the distributed power inverter interface: PQ control,droop control and V/f control of the basic principles elaboration are introduced.Combining adaptive droop coefficient control and voltage-current double loop control to improve the design of traditional droop control strategy.The battery storage is used as the main control power source of the microgrid,and adopt improved V/f droop control strategy when microgrid is off-grid to ensure that the voltage and frequency of the smooth switching process,in addition,it can also achieve stable operation of microgrid system after mode switching and provide high quality power to load.3)Considering the switching of the grid-connected into islanding operation,a passive islanding detection method based on detecting voltage and frequency changes at the Point of Common Coupling(PCC)is designed.The software phase locked loop(SPLL)is used to achieve voltage phase synchronization.At the same time,the output state of the micro-sources controller is controlled synchronously before and after the off-grid operation.The smooth switching of the microgrid in both operating modes is finally completed.Then,the control effect of the model has been verified from simulation software MATLAB/Simulink.4)A wind-PV-battery microgrid simulation model is built on the MATLAB/Simulink platform.Through the simulation cases of microgrid operation situation in grid-connected mode and islanded mode and the switching switching progress between two modes.The simulation results how that the feasibility of the proposed control method is verified.