Research On Microgrid Inverter Control Strategy Based On Virtual Synchronous Generator

With the rapid popularization of Renewable Energy Sources(RES),the power grid structure is changing,and inverter-based distributed generation(DG)is increasing.Since inverter-based power supplies do not have inertia like traditional synchronous motors,the introduction of a large number of DGs into the microgrid is very detrimental to the stability of the entire system.By introducing virtual inertia and damping characteristics,the inverter power supply is configured as a conventional synchronous motor.This leads to the Virtual Synchronous Generator(VSG)technology.(1)First,this article introduces the research background and significance.By analyzing the structure of the microgrid and its classic inverter control methods,the advantages and disadvantages of different methods are compared,and the concept of a virtual synchronous generator is derived.Based on the analysis of the VSG implementation principle,the effects of two key parameters of damping and inertia on the frequency and power and the operating characteristics of the single machine are studied.(2)Secondly,the operating characteristics of the microgrid inverter are analyzed.The VSG is used as the interface of the DG,which can be equivalent to a voltage source.It has two different working modes,both in grid-connected mode and Run off the grid island.Therefore,it is necessary to consider a series of problems brought by the inverter when switching between the two modes.By analyzing the conditions of VSG off / grid smooth switching,a phase-locked loop(PLL)is proposed.The pre-synchronous control strategy reduces the inrush current during the switching process and improves the reliability of grid connection.(3)Finally,the circulating current and power characteristics of VSG in parallel operation in island mode are analyzed.In the low and medium voltage microgrid lines,resistance and inductivity are the main components.The mismatch of impedance parameters of the microgrid lines results in power coupling,which is not conducive to accurate power distribution.Therefore,a power decoupling method based on improved virtual impedance is proposed,which eliminates the effect of line resistive components,makes the equivalent impedance of the VSG output inductive,reduces the degree of coupling between power,improves the accuracy of power distribution,and reduces Impact of Circulation on Parallel Systems.