利用散熱技術提升壓電功率轉換裝置輸出能量之實現

Abstract

本研究致力於利用創新散熱技術，有效提升壓電變壓器的輸出能量，實現高功率 密度之壓電式電力轉換器裝置。不同於以往利用外部電路控制或整流器電路設計 來提升壓電變壓器之輸出效能，本論文探討溫度所造成的非線性現象如何直接影 響並限制壓電變壓器之輸出效能，進而影響電力轉換器之功率密度。本論文詳細 透過理論分析與實驗驗證詳述壓電變壓器之熱穩定問題為提升整體效能的核心關 鍵，尤其在大功率應用。本研究主要分為四大部分：1. 首先進行壓電變壓器熱傳 導之理論分析，並結合等效電路模型介紹隨溫度變化之非線性熱阻與壓電變壓器 可承受的溫升限制；2. 透過設計不同層數的多層壓電變壓器，探討不同結構設計 壓電變壓器可承受的最大限流及輸出效能，並與加入散熱層後(由鋁片及石墨散熱 膠帶組成)同體積之多層壓電變壓器比較兩者輸出功率；3. 由加入散熱層之研究， 發現增加散熱效能之重要性後，本研究提出數種創新並有效之散熱方式提升壓電 變壓器整體效能，如利用薄型鋁製散熱裝置、致冷晶片、超薄型壓電風扇等，成 功提升壓電變壓器本身在55°C 可容許溫度限度下之輸出電流及輸出功率達三倍， 效率亦維持在良好情況；4. 最後本研究亦將壓電變壓器應用至直流對直流轉換 器，探討外接整流電路(如倍電流整流器電路)提升整體系統輸出能力之功效，並同 時加入散熱裝置之系統相互比較。使用薄型化散熱裝置之系統輸出效能提升近兩 倍，可以取代需要使用大電感元件之倍電流整流電路，並同時達到薄型且高輸出 兼具之效能。藉由本研究之成果，可成功突破壓電功率轉換裝置以往皆侷限在高 電壓、低電流之藩籬，藉由此散熱機制可實現壓電功率轉換裝置在大功率使用環 境，並適用於高電流、低電壓之不同使用需求，並且同時兼具大環境之薄型化設 計之需求。

The objective of this study was to increase the output current and power in a piezoelectric transformer (PT) based DC/DC converter by adding a cooling system. It is known that the output current of PT is limited by temperature build-up because of losses especially when driving at high vibration velocity. Excessive temperature rise will decrease the quality factor Q of piezoelectric component during the operational process. Simultaneously the vibration energy cannot be increased even if under higher excitation voltage. Although connecting different inductive circuits at the PT secondary terminal can increase the output current, the root cause of temperature build-up problem is not solved. This dissertation presents the heat transfer technology to deal with the temperature build-up problem. With the heat transfer technology, the threshold vibration velocity of PT can be increased and thus the output current and output power (almost three times). Furthermore, a comparison between heat transfer technology and current-doubler rectifier applied to the piezoelectric transformer based DC/DC converter was also studied. The advantages and disadvantages of the proposed technique were investigated. A theoretical-phenomenological model was developed to explain the relationship between the losses and the temperature rise. It will be shown that the vibration velocity as well as the heat generation increases the losses. In our design, the maximum output current capacity can increase 100% when the operating condition of PT temperature is kept below 55°C. The study comprises of a theoretical part and an experimental proof-of-concept demonstration of the proposed design method.