Research On Dynamic Enhancement Of Cascaded Dc-dc Power Electronic System With Virtual Impedance

With the advantage of huge transmission capacity and high power supply quality,DC distributed power sources have been widely used in space stations,shipboards,hybrid vehicles,and renewable energy systems.Most DC power distribution systems are organized as a cascaded converter system that is composed of source and load converters,and may experience a system oscillation due to the negative impedance effect of constant power loads.The load-side virtual impedance method is a possible solution to such stability problem,which however increases the voltage ripple caused by the load changes and thus increases the requirement of the filter capacitance.Based on the background,a two-stage source-load cascaded DC power electronic system is taken as the research object.A detailde introduction of the proposed source-load cascaded DC power electronic system,designs method and simulink verfication is produced firstly.However,the system may be unstable after cascading two converters which are stable seperately.Thus,the virtual impedance(VI)control method is proposed to enhance stability.Then,the source-load cascaded DC power electronic system with VI control method is analyzed.The design and modeling of virtual impedance control is proposed to compare with the system without VI control method,which implies that VI control method can stabilize the system,however,it causes negative affect on its dynamic performance.Finally,on the basis of the system with VI control method,an auxiliary circuit that is connected to the output port of the load converter is proposed such that the stability and the transient performance of the power electronic system can be simultaneously enhanced by using the virtual impedance method and the auxiliary circuit.Small signal modeling and the design of parameters is introduced.Compared with system only with VI control method,the transient performance has been significantly improved.Compared with other methods which improve the dynamic response performance,the method significantly degrates the voltage ripple and reduces the size of the system as well as eliminates large-capacity electrolytic capacitors.In this paper,a detailed introduction of the structure and principle,parameter design and control method of three cascaded DC power electronic systems is given..An example design with the simulation analysis and the experimental results is given to verify the feasibility of the proposed method.With the auxiliary,the capacitance requirement of the system for an expected transient deviation of the output voltage is significantly reduced by offsetting the additional voltage fluctuation caused by the VI control method.The prototype of the cascaded DC power electronic system is designed,and experimental waveforms and measurement results verify the feasibility of the designed control method and parameter design methods,which also indicates the auxiliary circuit has significant effects on improving the dynamic response of the system.