Modeling And One-Cycle Controlling Of High-Order DC-DC Converters

Output voltages of renewable energy sources such as photovoltaic and fuel cells are normally low,and difficult to interface power grid directly,to improve this problem,multi stages of boost converters or single-stage high-step-up converter are required for pumping voltage for connecting to power grid,which also makes high voltage converters especially single-stage high-step-up converters being widely studied and applied in renewable energy system.Therein,single-stage high order DC-DC converters with multi-cell technique is one of the feasible solutions to realize a high voltage gain with high power density,low cost and high efficiency.With an increased number of cells,however,the number of switching variables and dynamic components in multi-cell converters increase,which results in slow system response,and it will be inappropriate for the complex environment of the renewable system.In order to improve the transient characteristics of this kind of converter,it is very eagerly to conduct the study of modeling analysis and design of onecycle control(OCC)strategy.Therefore,this paper aims to conduct the modeling analysis and OCC strategy for this kind of high order DC-DC converter as follows:(1)The typical multi-cell high-order DC-DC converter is built as switched linear system models remaining the dynamic characteristics of high order DC-DC converters.The controllability of high order DC-DC converters is studied based on the proposed model,and then it is used to study the adaptability of OCC.(2)This paper proposed a novel enhanced OCC strategy which based on analysis of the structural characteristics of multi-cell high-order DC-DC converter,and successfully applies the enhanced OCC method to a typical multi-cell high-order DC-DC converter.(3)Applied in the application scenarios of ion engine,the output voltage closed-loop system is designed to ensure that this kind of high-order DC-DC converter can satisfy the requirements of dynamic stability in a multi-disturbance system.(4)An experimental prototype has been built and tested in the lab,parameters design of the main circuit and the control circuit are introduced in detail.The experimental results further verify the feasibility of the proposed enhanced OCC strategy and output voltage closed-loop system for multi-cell high order DC-DC converters.The creativity of this dissertation is to build up the switched linear system models of high-order DC-DC converter,and then based on this model,controllability of high order DC-DC converters is analyzed,and then the enhanced OCC strategy and the output voltage closed loop system are designed,which well improve the dynamic input and dynamic load response of the converter.The proposed control strategy in this dissertation offers multicell high-order DC-DC converters a wider range of applications in renewable energy systems.