Study And Comparison Of Three-Phase Grid-Connected Inverter With Droop And VSG Control Methods

The structure of worldwide energy consumption is seeking for further improvement due to the urge demand of traditional fossil fuel and the environment problems brought by energy consumption.New energy sources,such as wind energy,photovoltaic energy and tidal energy have been proved feasible in improving energy consumption structure.The power generation industry,which features the largest energy-consuming industry,plays a key role in the improvement of energy consumption structure.Wind power and photovoltaic power contribute significantly to the energy consumption structure reforming process.A 10 kVA grid-connected inverter model is established basing on the RT-LAB platform and both droop control method and VSG control method are performed on the prototype.Mathematical model of the grid-connected droop-controlled inverter is given with both power control loop and voltage-current control loop taking into consideration.Based on the model of a single inverter,the full model of paralleled multi-inverters system is accordingly given and the stability is analyzed on the basis of eigenvalue curves.Traditional synchronous generator is briefly introduced and the power-loop control model of virtual synchronous generator is accordingly given.The whole model of the inverter with VSG control method is proposed and the stability of the system is analyzed based on the eigenvalue curves of different parameters.Droop control method and VSG control method are compared in the aspects of control theory,control modeling comparison and transfer function between two control methods.Simulation model of a grid-connected inverter is established in Simulink software and both droop control and VSG control are performed in the model.Simulation results are given and compared between the two control methods.A 10 kVA grid-connected inverter prototype is also established based on the RT-LAB system,both droop and VSG control methods are applied to control the inverter.The output waveforms under different control methods are given and compared to verify the conclusion in this article.