Research On Active Damping Control Of Buck Converter Cascade System With Lossy LC Filter

With the development of new clean energy technology and the advancement of DC/DC power electronic converter,DC microgrid has been widely used as it does not involve control problems such as frequency and reactive power.The two stage cascade system which is consist of an LC input filter and a Buck converter is especially common in the DC microgrid,in order to ensure a stable voltage on the input side of the load,an LC input filter is usually added between the DC bus and the load to filter out voltage interference.In order to ensure the stability of the output voltage,the load converter in the system often applies a closed-loop voltage control.However,the closed-loop controlled load converter and the load as a whole exhibits negative damping properties to the outside,reducing the system damping as well.If the parameter value of the LC filter is not appropriate,the parameter mismatch between the filter and the load converter occurs,which causes the cascaded system voltage oscillation.Aiming at such problems,this thesis chooses the cascade system composed of lossy LC input filter Buck converter in DC microgrid as the object.The main work is as follows:The Buck converter in the studied system has been modeled,and the equivalent impedance model of the cascade system is derived.Then by using the impedance ratio criterion,the influence of the loss branch parameters in the lossy LC filter on the stability of the cascade system is analysed.In addition,for a type of cascade system with fixed parameters,the passive damping method of parallel resistors is studied,the value conditions of damping resistor is deduced in detail,and the simulation model is built on the Matlab/Simulink software to control the applied method.A simulation analysis has been carried out to verify the suppression effect of the passive damping method used on the system voltage oscillation.The passive damping method can effectively control the converter cascade system to restore the stable voltage operation state,but it will introduce additional power loss to the system.In order to overcome this defect,this paper further studies the virtual resistancecapacitance active damping control method based on the Buck converter input voltage feedforward control loop and the virtual resistance active damping control method applied to the lossy LC filter Buck converter cascade system The design process of the controller parameters for each link of the control loop in the method used is given in detail,and the simulation and result analysis are carried out on the software platform to verify the feasibility and effectiveness of the active damping method.Finally,the characteristics of the two types of active damping methods has been compared and summarized.