Stability Analysis Of DC Micro-grid With Virtual Inertia Control

With energy shortages and increasingly serious environmental problems,distributed power sources account for a larger proportion of the power grid.DC microgrid is increasingly attracting attention by virtue of their ability to take full advantage of distributed power.However,a large number of power electronic devices lead to the DC microgrid is a low inertia system.Under the condition of random power disturbance,the voltage quality becomes very poor.Therefore,virtual inertial control is widely studied,but the stability of virtual inertial control for DC microgrid needs to be analyzed in depth.Therefore,the main work and achievements of this paper are as follows:(1)Introduce the structure of DC microgrid,establish mathematical models of wind power unit,energy storage unit,grid-connected converter and load unit.Working principle and control strategy is analyzed.The construction of the DC microgrid system containing the above four parts will provide a theoretical basis for subsequent research.(2)Taking the DC microgrid controlled by virtual inertia as the research object.The small-signal model of the grid-connected converter and the constant power load is derived,and the output impedance and load input impedance of the power supply side are obtained.According to the frequency analysis method and impedance matching criterion,the influence of virtual inertia coefficient and constant power load on system stability is analyzed.(3)In order to solve the problem of additional virtual inertia control and constant power load weakening system damping,resulting in high-frequency resonance of DC bus voltage,from the perspective of impedance matching,using the idea of active damping,the grid-connected converter is connected in series.The method of impedance.Analyze and extract the peak amount of the output impedance,and compensate the peak function to the original impedance in the form of virtual impedance in the control system to reduce the output impedance.According to different virtual inertia coefficients and load power,the specific calculation process of virtual impedance is given.The stability of the system after series virtual impedance is judged by Middlebrook criterion.(4)The DC microgrid model is established in Matlab/Simulink and time domain simulation is carried out.The experimental test is carried out on the RT-LAB real-time simulation platform to verify the correctness of the stabilit y analysis and the effectiveness of the tandem virtual impedance method.