Research On Inverter/Grid-Connected Control Of Low Voltage Microgrid Inverter

With the global energy shortage and environmental pollution problems becoming increasingly serious,more and more attention has been paid to clean energy.The power generation mode of distributed power can effectively realize the use of renewable energy.However,due to the randomness and discontinuity of photovoltaic power generation and wind power generation,the reliability of power supply for distributed new energy generation is reduced.The inverter is in the "core position" in the microgrid,and its two ends are connected to the distributed power source and users and the main grid.Therefore,the research of inverter control strategy is the most core part of the entire microgrid system.First,by analyzing the topology of the inverter,the parameters of the main circuit are designed,and the mathematical model of the inverter is derived in a twophase rotating coordinate system.In addition,the characteristics of the traditional droop control strategy are analyzed,and the output power calculation module,droop control module,and voltage and current double-closed-loop module are analyzed and parameterized.The simulation results verify the correctness of the above model.Then,through the parallel equivalent circuit diagram and formula derivation of the inverter,it is analyzed that the droop control strategies of P-f and Q-U are not suitable for low-voltage AC systems.In order to solve this problem,a control strategy for the virtual impedance is derived.In addition,it analyzes that when a microgrid inverter parallel system is operated in an off-grid island,voltage drops will occur due to the line impedance,which leads to the problems of inaccurate reactive power distribution and excessive reactive circulating current.In order to solve this problem,an improved droop control strategy is proposed.For voltage drop caused by line impedance and virtual impedance,a voltage compensation link and voltage feedback link are designed to eliminate it,so as to achieve accurate distribution of reactive power and suppress reactive circulating current aims.Finally,when the microgrid is connected to the grid,it will analyze the huge impact if the grid connection conditions are not met.In order to suppress the excessive impact,a presynchronization controller is designed.In addition,it is necessary to realize the presynchronization controller by designing a phase locked loop to lock the phase angle of the power grid.After analysis of simulation results,the correctness of the proposed control strategy is verified.