壓電轉子搭配整流電路功率損耗之改善研究

Abstract

本論文探討在兩種不同旋轉模型中，壓電懸臂樑經整流電路後功率損耗之改善研究。其中，朝外(朝內)模型為壓電懸臂樑自由端朝離圓心方向(朝向圓心方向)。理論模型是本團隊透過漢米爾頓定理配合參數分佈法得出。前期研究雖然有諸多成果，但在實驗上出現兩個問題。其一，發現在交流電路中，當壓電振子在共振頻後，會出現實驗大於理論的現象，推測是因為在實驗架構中，基於實驗安全考量，會在模型周圍安裝一壓克力外罩，導致在高轉速下會產生風的擾動。因此，本研究將壓克力外罩鑽孔處理加以改善此問題；其二，因實務需求，必須透過橋式整流電路將交流電轉換為直流電。結果顯示無論是在何種模型下，實驗結果皆遠低於理論功率。經由實驗分析，橋式整流中的二極體損耗並不是造成較大誤差的唯一解釋原因。而後發現在旋轉環境下，因在週期性的外力(重力)刺激下會產生極大的電壓，造成二極體產生逆偏電流的狀況。於是設計一個修正電路，利用四個二極體搭配二個PMOS組成，減少在高電壓下逆偏電流效應，除了提升直流輸出功率外，亦有效地改善與理論的誤差。最後，透過調變附加質量大小與懸臂樑固定端至轉盤圓心之距離兩項參數，探討其中現象，並配合修正電路，提升其整流後之功率輸出。

The thesis aims to improve the electric loss from the AC-DC rectifying circuit attached to a rotary piezoelectric energy harvester. There are two kinds of configurations for rotational energy harvesting. The first (second) setup is a piezoelectric cantilever beam mounted radially on a rotating host with the outward (inward) tip direction. Both models are established based on the Hamiltonian principle and the parametric distribution method. Our previous studies indicated the experimental observations were higher than the theoretical estimate when the driving frequency is larger than the resonant frequency. In addition, the proposed model agreed with the experiment only in the case of AC power output. In other words, the experimental observations of DC harvested power were reduced significantly in comparison with the theoretical estimate. The former is viewed as the factor of wind disturbances at higher driving frequencies due to the inclusion of an acrylic cover for safety. As a result, an improved setup is proposed by drilling the acrylic cover with many more holes. The latter is viewed as the combined effect of diode loss and reverse current due to high voltage induced by 1g excitation of the beam during the rotational motion. Therefore, an improved circuit design consisting of four diodes with two PMOS is proposed for replacing the traditional bridge rectifier circuit. The result shows the significant reduction of electric loss during the rotational motion. Finally, the effects of tip mass and the distance between the fixed end and the rotational center on the harvested DC power are studied experimentally under the attachment of the improved interface circuit. The results show reasonable agreement between the theory and experiment.