Research On Control Strategy Of Low Voltage Microgrid Inverter

In order to cope with the global energy reform,China has adopted the idea of green development,deepened the field of new energy,adopted new energy strategies,pursued new modes of economic growth and social progress,and put forward higher requirements for the further development of electric energy.In order to realize the environmental goal of "Beautiful China",support the distributed energy storage power generation system,the grid connection of microgrid and large grid,and adapt to the response strategy under new demands,the transformation of traditional power grid becomes very important.This paper studies the control strategy of low-voltage microgrid inverter to solve the problems of power distribution,reactive circulation and islanding detection in traditional droop control.Firstly,the topology structure of microgrid inverter system is analyzed and the mathematical model is established.Coordinate transformation of the mathematical model of the inverter is carried out to realize the conversion from AC component to DC component of the system.The control principle of traditional droop controller is analyzed,and a microgrid simulation model based on traditional droop control is built.Secondly,in order to improve the power distribution accuracy of microgrid parallel inverter,the traditional droop control is improved,and a virtual impedance loop is added to the droop controller,so that the line impedance is still in an inductive state under low voltage conditions.In view of the introduced virtual impedance part,the neural network adaptive control algorithm is used to control the virtual impedance value,which solves the voltage drop problem,the problem that power cannot be distributed proportionally and the problem of reactive power circulation caused by inconsistent feeder impedance,realizes the rational distribution of system power,ensures good power quality and improves the reliability of the system.Finally,aiming at the problem of current impact when the microgrid is connected to the grid,the phase-locked loop is improved in the pre-synchronization control module,and the double second-order generalized integrator is adopted to reduce the influence of unbalanced current in the system on the accuracy of the phase-locked loop,so as to realize the smooth switching from islanding mode to grid-connected mode.According to the principle of the active frequency shift method of islanding detection module,the working process is analyzed,and the positive feedback link is added to the active frequency shift method,so as to reduce the blind area of islanding detection after improvement.Particle swarm optimization is used to adjust the positive feedback coefficient in the active frequency shift method,so as to improve the reliability of the system in detecting islanding effect.Finally,the simulation verifies the effectiveness of particle swarm optimization control.