使用氮化鎵場效電晶體之高功率密度返馳式轉換器設計與實作

Abstract

受氮化鎵場效電晶體於高效率高功率密度電能轉換技術之潛力所驅，本論文致力於研究使用氮化鎵場效電晶體設計一高功率密度之返馳式轉換器。本論文實作一雙脈衝測試電路研究氮化鎵場效電晶體高速切換行為之模擬與量測。透過比對實驗與模擬結果，本論文確立了數個高速量測之技巧；並且，本論文亦證實，利用一包含了關鍵寄生電感的集總式模擬電路模型，可預測氮化鎵場效電晶體之切換行為至一合理的精確度。本論文進行分析以最佳化基於氮化鎵元件之傳統硬切換式返馳式轉換器之設計。分析的焦點為兩個影響變壓器體積甚鉅的主要設計參數，即切換頻率Fsw及最低線電壓下之臨界負載電流值IoB(Vin_min)。本論文分析了變壓器體積及損耗成分隨Fsw及IoB(Vin_min)的變化趨勢，並以效率/體積變化圖及損耗分布，研究通用線電壓輸入、19.5V/45W輸出、基於氮化鎵元件之硬切換式返馳式轉換器之性能限制。分析發現切換損耗在高切換頻率與高線電壓下仍然嚴重，限制了切換頻率至數百千赫茲。本論文實作了一600kHz之原型電路，達到22.53W/in3之功率密度以及84%之最高效率。實測效率與估計效率彼此是接近的，證實本論文中的分析是可信的。

Motivated by the potentials of gallium nitride field effect transistors (GaN FETs) in high-efficiency high-power-density switching power conversion, this thesis is devoted to the design of a high-power-density flyback converter using GaN FETs. A double-pulse tester was built to investigate the simulation and measurement of the fast switching behavior of GaN FETs. By comparing experimental and simulation reaults, several high-speed measurement techniques were established; also, it was proved that a lumped simulation model including critical parasitic inductances can predict the switching behavior of GaN FETs to a reasonable extent. Analyses were conducted to optimize the design of a GaN-based traditional hard-switched flyback converter. The focus was on two major designer’s choices that affect greatly the transformer volume, i.e., the switching frequency Fsw and the lowest-line boundary-load current IoB(Vin_min). The varying trends of the transformer volume and loss components with Fsw and IoB(Vin_min) were analyzed, and the performance limit of a universal-line-input, 19.5V/45W-output GaN-based hard-switched flyback converter was studied by efficiency/volume maps and loss distributions. It was found that the switching loss is still severe at high switching frequencies and high line voltages, limiting the switching frequency to several hundred kilohertz. A 600kHz prototype reaching a power density of 22.53W/in3 and a peak efficiency of 84% was built. Measured and estimated efficiencies are close to each other, validating the analyses in this thesis.