Research On Control Strategy Of Parallel Inverter Based On Improved Droop Control

As the shortage of traditional fossil energy and environmental degradation have become increasingly prominent,the continuous development of distributed power generation technology has been promoted.Renewable energy sources such as wind and solar energy continuously and efficiently due to their intermittent and unpredictable characteristics.Microgrid is an effective way.As the basic power electronic interface unit of the microgrid,the microgrid inverter is directly related to the performance of the microgrid how to achieve reasonable and effective control.This paper takes the low-voltage microgrid system as the research object,focusing on the three-phase inverter closed-loop control strategy and the smooth switching between microgrid control modes.This paper first conducts an in-depth study on the traditional droop control microgrid three-phase inverter,and establishes the small signal model of the power loop and the voltage outer loop and current inner loop according to its mathematical model.On this basis,the dynamic characteristics and stability of the active-frequency and reactive-amplitude droop coefficients are analyzed separately,and the stability and dynamic characteristics of the system are mainly related to the droop coefficient and the design of the LC filter.The droop coefficient and the design method of the power filter are presented.Then,the PR control is used to improve the stability of the inverter closed-loop control system of proportional resonance control and improve the system performance.In addition,an experiment platform in which two inverters are connected in parallel is used for simulation,and the simulation experiment is performed to verify it.Secondly,the impedance of the low-voltage microgrid line is resistive and inductive,which will result in the failure of parallel inverters to achieve power sharing,causing circulating currents between the inverters and reducing power quality.Therefore,this paper adopts virtual resistance loop to realize active and reactive power decoupling control,which improves system stability and reduces the actual line impedance and inductance value.However,the introduction of virtual resistance loop will make the output voltage be affected by harmonics and consider that traditional droop control cannot be effectively suppressed.Circulation,this paper proposes a new and improved droop control to replace the traditional linear droop control.By improving the accuracy of the droop control and shortening the compensation time,the effect of the circulation suppression is better improved.Finally,it analyzes and improves the operating characteristics of droop control microgrid inverters in islanding and grid-connected modes,and proposes a grid-connected pre-synchronization control strategy to achieve smooth switching between micro-grid dual modes.Then,a microgrid simulation model was built through Matlab/Simulink to verify the effectiveness and feasibility of the proposed strategy.