同步切換半主動式功率開關電路於能量汲取與功率損耗之研究與設計

Abstract

本論文以壓電薄板與懸臂樑結合成為壓電發電機，將壓電發電機應用於能量汲取技術(Power harvesting)上，利用壓電材料之正壓電性質，將機械能轉換成電能，再以電力電路的技術將電能儲存至儲能元件之中。為了提升輸出功率，將壓電發電機與切換電路結合，切換電路最基本有兩大類，分別是同步開關切換汲取電路-串聯式(SSHI-S)、同步開關切換汲取電路-並聯式(SSHI-P)，功率開關導通時機為懸臂樑位移最大時，其餘時間都為截止，當開關導通時電路上電感會與壓電薄板內之靜態電容，產生了LC 諧振，使得電壓波形與電流波形為同相位，使得實功率上升，降地虛功率，大幅的提升了輸出功率，提升了標準型電路4 至9倍。但一切的事物都會有正反兩面，壓電發電機卻產生了高頻訊號，原因是為了使壓電薄板產生之電壓與電流同相位，使得壓電電壓波形瞬間極性翻轉，極性翻轉此現象作用於壓電發電機之上，如同是對壓電發電機掃頻，而產生了高頻模態訊號，高頻訊號無法被同步切換電路所吸收，則將能量轉換成聲能擴散至空氣之中，使得在汲取能量過程中，壓電發電機會產生高頻訊號，為了降低高頻訊號，挑選較大的電感值，電感值大會使得開關時間拉長，使得極性翻轉此現象較為和緩，也降低了壓電發電機被激發出的高頻模態能量。同時地，切換電路上電子元件損耗也提升，MOSFET 功率開關損耗消耗最多，降低元件損耗的方式是挑選品質因數較高的電感，品質因數高的電感使得電路輸出功率提高，也有較少的電路損耗。

Piezoelectric generator is a combination of cantilever beam and piezoelectric thin slip. The property of piezoelectric material has two basic characteristics, which are Direct Piezoelectric Effect and Converse Piezoelectric Effect. Direct piezoelectric effect turns mechanical energy into electric energy. Direct piezoelectric effect is being applied in Power Harvesting technology. Combined with piezoelectric generator, semi-active power harvesting circuitry is adopted to raise the output power harvested. There are two basic circuitry configurations adopted in semi-active power harvesting technology. One is SSHI-P (Synchronized Switch Harvesting on Inductor-Parallel) and another is SSHI-S (Synchronized Switch Harvesting on Inductor-Series). The above-mentioned circuitry configuration gets 4~9 times the power gains than the standard passive power harvesting circuit on average. Piezoelectric generator produces high frequency signal which happens while the switch is turned on during the harvesting process. As the voltage of piezoelectric produces inversion when switch turns on, piezoelectric generator is excited by voltage inversion that produces high frequency signal. Choosing high-value inductor reduces high frequency signal, but power dissipated on the electrical element of circuitry actually increases. Choosing inductor with high quality factor not only rises output power but also reduces the power dissipated on the electrical elements.