Topology deduction and platform design of non-isolated high step-up DC-DC converters
[Objective]To accommodate the global shift in electric energy consumption,the total volume of new energy generation,primarily from photovoltaic and fuel cells,is steadily on the rise.However,the input voltage level for these new energy power generation systems typically ranges from 20 to 50 V,while the DC bus voltage of the traditional three-phase grid-connected system requires 380 V.As a result,high step-up,high-efficiency,and high power-density DC-DC converters have become a pivotal research topic.[Methods]Current methods of boosting technology include cascade,multilevel,switched-inductor,switched-capacitor,coupled-inductor,and voltage multiplier cells.Among these,switched-capacitor boost technology stands out owing to its scalability and ease of integration,given the absence of magnetic components in the converter.Coupled inductors,with their high power density and excellent voltage regulation characteristics,are also frequently employed in high step-up DC-DC converter topologies.There are a wide variety of high step-up boost converters based on coupled inductors and switched capacitors.Herein,we use a class of units consisting of diodes,capacitors,and magnetic elements.Characterized by their high efficiency and low cost,these units serve as voltage multiplier cells.To help students cultivate a deeper understanding of these converters and master their topology laws,this study adopts the idea of"voltage multiplier cell-converter topology-evolution law."We aim to provide a comprehensive summary of the evolution laws of nonisolated high step-up DC-DC converters.[Results]A series of coupled-inductor,switched-capacitor,and center-tap coupled-inductor switched-capacitor voltage multiplier cell structures are also presented for derivation.The general structure of the high step-up converter is derived and summarized in relation to the converter topology and the derivation law.Taking the coupled-inductor high step-up boost converter with a Y-source structure as an example,we conduct a modal analysis and voltage gain derivation.To verify the steady-state and dynamic characteristics of the proposed high step-up DC-DC converter,we have designed an experimental prototype with an output power P0=200 W.At the same time,we considered the design of the main circuit,the driver circuit,and the sampling circuit to ensure that the converter works stably and efficiently.Steady-state experimental results show that the efficiency of the rated power(P0=200 W)is 95.81％at a voltage gain B of 10.55.At a voltage gain B of 13.57,the efficiency of the rated power(P0=200 W)is 94.76％.The highest efficiency is achieved at half of the rated power(P0=100 W),with efficiencies of 98.06％and 97.35％,respectively.These results demonstrate the high efficiency of the proposed converter.[Conclusions]Dynamic experimental results indicate that the proposed converter can stabilize the output voltage in response to sudden changes in the input voltage and load resistance.This proves the reliability of the PID closed-loop control.This paper helps students gain a more intuitive understanding of the high step-up DC-DC converter in power electronics and increases their ability to summarize information.The DC-DC converter is a crucial part of power electronics technology,offering an excellent opportunity for students to hone their theoretical analysis and hands-on experimental skills.
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