Study On Instability Phenomenon And Control Strategy Improvement Of Boost Converter

The period-doubling bifurcation phenomenon of Boost casacde converter and low-frequency bifurcation phenomenon of Power Factor Correction(PFC)Boost converter are studied in this dissertation.Morever,an effective method is proposed to solve the undesired low-frequency oscillation phenomenon in Pulse Train(PT)controlled Boost covnerter system.Firstly,the period-doubling phenomenon of Boost cascade converter operating in DCM and CCM is discussed in Chapter II.As for DCM,by simplifying cascaded Buck converter as a nonlinear resistor,the discrete mapping model is constructed,the iterative equation is derived and the stable operation feedback coefficient range is caculated.Simulation results show that Boost cascade converter will produce period-doubling and chotic phenomenon with the increase of feedback coefficient.As for CCM,with the Buck converter equal to a constant power value,the state equations are written and the model is bulit.Simulation and experimental results show that the system will produce instability phenomenon with the increase constant power value.Secondly,the low-frequency bifurcation phenomenon of PFC Boost cascade converter is studied in Chapter III.With the cascade Buck converter equal to constant power load,the negative impedance characteristics is analysed.Then a small signal model is established,and the stable operation boundary is drawn according to Routh criterion.Different sampling points on both sides are selected for test,and the results verify the influence of the cascade converter parameters on the system stablity.Lastly,as the pulse train controlled Boost converter produces an undesired low-frequency oscillation phenomenon,thus an improved Boost covnerter is designed to solve this problem effectively in Chapter IV.By adding a branch circuit to the main circuit,much more energy than before can be delivered when the output voltage is less than the reference value,while the energy delivery is suppressed when the output voltage is higher than the reference value.Hence,the low-frequency oscillation caused by laging regulation of the output voltage is corrected and the the advantages of PT control is maintained.