Research On Micro-Grid Inverter Control Based On Virtual Synchronous Generator

The environmental damage is already very terrible now,the available energy has become scarce,and many people have become interested in new energy power generation.Micro-grid is a hot research field of power system.However,the micro-grid inverter based on power electronic devices has a fast response speed,and there is no way to have some of the beautiful qualities of the synchronous generator itself,so it is very difficult to achieve stable operation of the power grid.The Virtual Synchronous Generator control strategy has greatly improved the power system stability due to its good characteristics of Synchronous generators.In this paper,the inverter controlled by VSG is studied.(1)Based on the principle of a synchronous generator,the inverter is designed to have the characteristics of a synchronous generator.The principle of governor is used to design the active power control link,and the working principle of the exciter is used to design the reactive power control link.According to the classical control theory,the relationship between the key parameters and the system stability is analyzed respectively,which is taken as the standard of parameter selection.Then simulate the design to prove its effectiveness.(2)The microgrid can work in off-grid mode or grid-connected mode.Pre-synchronization technology is a key factor for smooth switching between these two modes.The traditional pre-synchronization control with phaselocked loop has complexity and delay,this paper proposes a presynchronization technology without phase-locked loop,which makes the microgrid voltage quickly track the grid voltage,and the calculation is simple and easy to implement.The simulation results show the reliability of the control strategy.(3)In multiple VSG parallel models,through analysis of the causes of circulating current,it is shown that the essence of circulating current is the mismatch of line impedance.With the addition of virtual impedance,there is no more circulating current.The properties of line impedance are classified,and their influence on power calculation is analyzed respectively.Thus,the power distribution can be further discussed,and the relationship between line impedance and power distribution is clarified.At the same time,the values of key parameters such as moment of inertia J and damping coefficient D must meet the allocation conditions.The simulation results show that the virtual impedance can restrain the circulating current and distribute the power accurately.(4)After the correctness of the theory is verified by simulation,in order to build the experimental platform,the real-time simulation system of RT-LAB is used.The experimental results show that the pre-synchronization control strategy and the virtual impedance technology worked.