| With the popularization of DC power supply appliances and the gradual maturity of industrial frequency conversion technology,a large number of DC loads are connected to the existing power network.DC microgrid has the advantages of low transmission loss and no need for multi-stage converter conversion for DC load power supply.Many countries and regions have carried out in-depth research on it.However,the DC distribution network mainly relies on the power electronic components for control and transformation.It cannot maintain the mechanical inertia and kinetic energy of the system inertia like the traditional alternator,and the overall inertia of the system is much lower than that of the AC micro-grid.In order to solve the problem of low inertia of DC micro grid,the research of inertia control strategy for DC micro grid has become a hot topic.The four-terminal DC micro-network of the photovoltaic power generation system and the storage system is taken as an example to analyze the response characteristics of the virtual inertia control strategy under the two conditions of the system steady state operation and inter-pole fault.Firstly,topological model and mathematical model of each unit are introduced and established.The virtual inertia control theory of DC microgrid is further analyzed by comparing the frequency regulation mode of AC system.In order to solve the problem of voltage change of DC bus after load change due to low inertia of the system,an adaptive control strategy of DC microgrid based on virtual inertia control technology is proposed in this paper under the stable operation state of the system.The effects of virtual capacitance and virtual damping parameters on the response characteristics and stability of the system are analyzed,and an adaptive inertial parameter control method is proposed according to the power quality requirements of the system.Through the simulation results,the influence of the control strategy on the dynamic characteristics of the DC micro-grid response is compared and analyzed,and the effectiveness of the proposed control strategy on the dynamic characteristics optimization when the system power fluctuation occurs is verified,and the time of the system voltage fluctuation is shortened while the system inertia is guaranteed.In the system fault state,this paper analyzes the characteristics of the fault development process of different converters under the condition that the Insulated Gate Bipolar Transistor(IGBT)is not locked.In this paper,the inter-pole fault’s response characteristics of grid-connected unit and energy storage unit are firstly analyzed.Then,the influence of the virtual inertia control strategy on the dynamic response characteristics of the system after inter-pole fault is analyzed through the MATLAB/Simulink platform.It is verified that the proposed control strategy has a certain ability to restrain the fault development speed,and can effectively prolong the zero crossing time of the bus voltage. |
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