| The lower outputs of the solar energy and biological energy in the renewable power generation system can not satisfy the requirements of gird connecting and application in DC microgrid.It is necessary to lift up the output of the photovoltaic panels with high step-up DC/DC converters.Due to the advantages of high step-up ratio,simple structure and low cost of the high step-up DC/DC converters with coupled inductors,these converters have good application prospect.The dynamic characteristics of the DC/DC converter are determined by its control strategy to some extent.However,the investigations on control strategies of the high step-up DC/DC converters with coupled inductors are lagged behind researches on their topological structures,which has become an important factor of limiting the application of these converters.Therefore,control strategies of the high step-up DC/DC converters with coupled inductors are further studied in this thesis and the main works are as follows:First,the Boost-Forward converter with coupled inductor is chosen as the research object and its operating principle is analyzed.Power circuit parameter design for the converter is realized,in which the parameter design and winding method for the coupled inductor are studied in detail.More important,simulation verifications on the designed power circuit are implemented and the correctness for the circuit is achieved.These provide a solid foundation for the preparation of the high step-up converter and research on its control strategies.Second,the peak current control method for the Boost-Forward converter is studied.With the switching device averaging method,the small-signal model for Boost-Forward converter operating in peak current mode is derived.Control loop design for the converter is finished.Furthermore,transient characteristics for the converter,such as disturbances in the input and output,are simulated to verified the control results of the designed control loop.Third,the one-cycle control method for the Boost-Forward converter is investigated.By introducing the theory of switched linear system,the periodic switched linear system model for Boost-Forward converter is established,and the controllability for the converter is analyzed.Then,the one cycle controllability for the converter is proved by theoretical calculations.Based on the designed power circuit,the simulation model is built.The one cycle controllability for the converter is verified by the simulation results.Final,two prototypes for the Boost-Forward converter under one-cycle control and peak current control are prepared.The input,output and peak power of the prototypes are 48 V,380V and 150 W,respectively.Results of steady state and transient tests on the prototypes verify the correctness of theoretical analysis.Studies in this thesis have high reference value for applied researches on high step-up DC/DC converters with coupled inductor. |
