Modeling And Stability Analysis Of DC Distributed Power System Based On Floquet Theory

DC distributed power system(DC DPS)has been widely used in the applications such as international space stations,aircrafts,ships,electric vehicles,supercomputers and so on.In practical applications,due to the interaction among power converter modules in DC DPS,the stability problem of DC DPS becomes more and more prominent.However,in the complex DC DPS and some applications which request high stability,the traditional small-signal modeling and stability analysis methods are facing severe challenges.For Nyquist criterion which is used for the stability analysis of parallel DC-DC converter,the derivation of open-loop transfer function is too cumbersome and the formula is too tedious to be applied into the multi-module parallel DC-DC converter system.Middlebrook impedance criterion which is used for the stability analysis of cascade DC-DC converter is too conservative.Moreover,the solution of impedance for the subsystems in cascade DC-DC converter is too complex to be applied into the multi-stage cascade DC-DC converter system.In order to accurately and effectively analyze the stability of DC DPS composed of parallel DC-DC converters and cascade DC-DC converters,a modeling and stability analysis method based on Floquet theory is proposed in this paper.Firstly,taken the two-module parallel buck converter under average current mode control as an example,the stability criterion based on Floquet theory is derived.The comparison between the obtained stability criterion and the traditional Nyquist criterion reveals the internal relationship between the proposed criterion and Nyquist criterion.Further,Floquet theory is extended into the N-module parallel DC-DC converter,and the stability criterion of N-module parallel buck converter is derived.The simulation platform of the three-module parallel buck converter is established to verify the correctness of the obtained stability criterion.Then,Floquet theory is applied into the cascade DC-DC converter in DC DPS.Taken the two-stage cascade boost converter under voltage mode control as an example,its stability criterion based on Floquet theory is derived,and is compared with the traditional Middlebrook impedance criterion.On the basis of the analysis of two-stage cascade DC-DC converter,Floquet theory is extended into the N-stage cascade DC-DC converter,and the stability criterion of N-stage cascade boost converter is derived.Further,the simulation platform of the three-stage cascade boost converter is established to verify the correctness of the obtained stability criterion.To be more in line with the actual circuit,the stability of nonideal parallel DC-DC converter considering the parasitic parameters is analyzed based on Floquet theory.For the two cases where the circuit parameters of converter modules are identical or nonidentical,the corresponding simulation and experiment platforms are established to verify the correctness of stability analysis results based on Floquet theory.