Research On Control Strategy Of Grid-Connected Converter Based On Virtual Inertia In DC Microgrid

As the penetration rate of renewable energy continues to increase,the microgrid becomes an effective way to absorb renewable energy.DC microgrid is efficient,stable and reliable,and has become a hot research topic.The DC microgrid grid-connected converter is the key to connecting the AC grid and the DC grid as the interface between the DC grid and the AC grid.However,the DC microgrid with the grid-connected converter as the main interface is a low-inertial network.The load and power supply frequent switching and power fluctuations in the network will affect the stability of the system.To improve the stability of the system,it is especially necessary to increase the inertia of the AC/DC system by controlling the dynamic characteristics of the converter.In this paper,the virtual inertial control strategy of DC microgrid grid-connected converter is studied.The control method of increasing the DC side and AC side inertia of grid-connected converter is given and simulated and experimentally verified.In this paper,the DC-side power-voltage relationship of the grid-connected converter is analyzed firstly,and the DC-side inertia equation is obtained.The virtual DC inertia control strategy of the grid-connected converter is designed.At the same time,this paper analyzes the power-frequency relationship of the AC side of the grid-connected converter,and combines the virtual synchronous machine control algorithm to design the virtual AC power control strategy of the grid-connected converter.On this basis,this paper combines the advantages of the two control methods to design a virtual AC-DC inertial control strategy for grid-connected converters.Secondly,the paper analyzes the modeling,parameter design and simulation of the virtual inertial control of the grid-connected converter.In this paper,the small-signal model of the grid-connected converter is established,and the current loop is designed.The small-signal model of virtual DC inertia control.virtual AC inertia control and virtual AC-DC inertial control is given.The regulator parameters are selected according to the type Ⅱ system.The design was performed and the stability was verified by the open-loop transfer function Bode plot.In this paper,the virtual inertia control simulation model of grid-connected converter is built in Psim.the validity of the regulator parameters is verified,and the influence of different inertial parameters on the dynamic characteristics of the grid-connected converter is compared.The simulation results show that after the load fluctuation,the virtual DC inertia control can effectively improve the stability of the DC system,but it has a certain impact on the AC system:the virtual AC inertia control can reduce the AC system power fluctuation.but the DC bus voltage fluctuation increases.The virtual AC-DC inertia can provide sufficient DC voltage inertia on the basis of suppressing AC power fluctuations,and has the advantages of the above two control methods.Finally,this paper builds an experimental platform to verify the effectiveness of the virtual inertial control algorithm,and analyzes the effects of different inertial parameters on the inertial characteristics.The experimental results show that the virtual DC inertia control can increase the inertia of the DC voltage,but the AC side impact increases;the virtual AC inertia control can provide AC inertia,but the voltage stability is poor;the virtual AC-DC inertial control can take into account the characteristics of both.The experimental results are close to the simulation results,which proves the effectiveness of the three virtual inertial control algorithms proposed in this paper.