Research On AC Microgrid Networking Technology Based On Droop Control

With the increasing prominence of environmental problems,the rational and efficient use of renewable energy has become an important issue in the transformation of the energy system.As an important way for the efficient use of renewable energy,microgrid networking technology needs to have the characteristics of high reliability and flexibility,so as to achieve high-quality power supply from renewable energy.This paper takes the key technology of multi-source networking control as the theme.The parallel mode switching,reactive power distribution and inertia effect in the process of networking in the microgrid are regarded as the main research content of this article.Aiming at the demand for smooth switching of voltage source inverters in parallel in the process of microgrid networking,this paper proposes a variable step-length pre-synchronization scheme based on droop control.The scheme generates an adaptive adjustment step size according to the stage of the pre-synchronization process.At the same time,the phase angle optimization judgment is added in the parallel transient state to avoid the phenomenon of power backflow.In order to reduce the influence of droop control active power distribution on the system frequency,the droop equation is adjusted in the parallel transient state to achieve smooth switching of operating modes.Aiming at the problem that it is difficult to achieve proportional distribution of reactive power among power generation units in microgrids,the mechanism of reactive power distribution of voltage source inverters and the influence of virtual impedance technology on the operating characteristics of voltage source inverters are described in this paper.At the same time,an iterative optimization algorithm for virtual impedance is proposed in this paper.During the networking process,each voltage source inverter automatically matches the best virtual impedance to achieve proportional distribution of reactive power.Aiming at the problem of power generation unit disconnection caused by excessive frequency change rate in microgrid.First,the inertia effect and influencing factors of the voltage source inverter are analyzed.Then an improved inertia control technique that limits the frequency change rate is proposed in this paper to limit the inverter output frequency change rate.Finally,the stability analysis of the proposed control scheme is carried out,and the selection method of key parameters is studied.The optimization strategy proposed in this paper can realize the smooth transition of parallelism in the networking process,the reactive power is distributed proportionally,the inertia is adaptively adjusted,and the stability of the islanded microgrid network operation is enhanced,which can be verified by the PLECS software.