Research On Resonance Mechanism Analysis And Suppression Methods Of Multi-converters In DC Microgrid

With the advancement of distributed energy technology and the increase in the proportion of DC load,DC microgrid has the advantages of less power conversion,less useless loss,simple control,no need to consider frequency phase,and good compatibility.It has been widely used in many fields such as national defense,transportation,construction and so on.However,the DC microgrid contains a large number of power electronic converters,which makes the DC microgrid exhibit weak damping and low inertia characteristics.Once the output of the micro-source is fluctuated or the load is switched on and off,it will cause disturbance to the system,which will easily excite the DC bus voltage resonance,which may cause the system to crash in severe cases.In view of this,this article conducts an in-depth study on the mechanism of DC microgrid bus voltage resonance,and proposes a motor-like virtual inertia control method to effectively suppress bus voltage resonance.The control method is simple and practical,which can effectively improve the stability of the system.This article takes the DC microgrid operating in islands as the research object,which specifically includes distributed microsources,energy storage units and DC loads.The coordinated control between these units and the stability after paralleling are the prerequisites for the normal operation of the DC microgrid.Based on the state space averaging method,the small signal model and impedance model of each component under different control strategies are established,which lays the foundation for the stability analysis of the DC microgrid.Aiming at the problem of DC bus voltage resonance,the impedance ratio criterion is used to study the small signal stability of the DC microgrid system,and the phenomenon of DC bus voltage resonance is analyzed.Firstly,the common impedance ratio criteria are reviewed,and the equivalent impedance model of DC microgrid is constructed,and the relationship between disturbance and the equivalent impedance of microsource and load is theoretically analyzed.Secondly,the three operating conditions of DC microgrid are compared.The stability of the system under the following conditions is analyzed in detail,and the analysis method of the resonance mechanism of the bus voltage is studied,and the main factors affecting the resonance of the bus voltage are analyzed at the same time.Based on the structural topology of analog DC motors and bidirectional DC converters,and learning from traditional virtual DC motor control,a motor-like virtual inertia control method is proposed.Use the control loop to simulate the inertia and damping characteristics of the motor,and reshape the output impedance of the converter to change its behavior characteristics.Through the simulation analysis of the dynamic characteristics of the virtual inertia of the motor under different control parameters,and comparison with the traditional droop control,it is further proved that the proposed virtual inertia control method of the motor can effectively suppress the DC bus voltage resonance and improve the stability of the system.Finally,design and build a hardware experimental platform suitable for this subject.On this experimental platform,experiments such as DC bus voltage resonance suppression,motor-like virtual inertia control and traditional droop control are compared.The experimental results verify the effectiveness of the control method proposed in this article.