Research On Stability Analysis Of DC Microgrid Based On Virtual Inertia Control

The DC microgrid is a low-inertia network dominated by power electronic converters,causing the DC bus voltage is susceptible to power fluctuations,which results in low DC voltage quality.In order to solve the problem,the virtual inertia control of DC microgrid has been widely discussed.However,systems under different types of virtual inertial control may show different characteristics.And the stability issues caused by the interaction of multiple converters under virtual inertial control have not been discussed yet.To explore and analyze these above problems,the main work of this paper is as follows:(1)In order to explore the impact of different types of virtual inertia controls on DC microgrid stability,small signal models of converters in power source side and load side are established in this paper.The impedance characteristics and dynamic response of the grid-side and the battery-side interfaced converters are analyzed respectively,when different virtual inertia control strategies are adopted.Considering the stability issues caused by multi-converter interaction,an equivalent impedance model of DC microgrid is built.Then,based on impedance matching principle,the influence of parameters on system stability is analyzed for different control modes.According to stability analysis results,it is concluded that a better dynamic characteristic and stability margin can be obtained when the virtual generator type inertial control is applied to battery-side converter.And the parameter of the virtual generator-type inertia control is limited based on stability and dynamics of system.(2)Accroding to the small-signal impedance model of converter,a DC microgrid stability analysis method based on the node impedance matrix is proposed.This method is suitable for multi-node DC microgrid structures.Accroding to this criterion,the characteristics of the system when analogous virtual synchronous generator(AVSG)control is applied to multiple converters are analyzed.Based on sensitivity analysis,it is concluded that the main crux which affects the stability of system is the proportional coefficient of PI controller.Therefore,the coefficients of PI controllers are designed according to the controller bandwidth design principle to avoid the improper selection of controller parameters to affect system stability.(3)Considering that the energy storage unit works under a state of charge(SOC)imbalance,it may cause over-discharge of energy storage equipment and shorten the life of energy storage system.In order to protect energy storage unit,avoid over-discharge of the energy storage unit,and realize the coordinated distribution of the power of energy storage unit when DC microgrid operates in transient and steady states,a SOC-based virtual inertia allocation control and a SOC-based droop coefficient constraint control are proposed.(4)DC microgrids simulation model is established on Matlab Simulink and RT-LAB real time simulation platform respectively,and relevant theoretical analysis is verified.