切換式電容交直流轉換器應用於低頻率震動能量擷取電路

Abstract

隨著積體電路之功耗降低以及環保意識抬頭，能量擷取的重要性日益提高，近年來已有許多低功耗之感測器如RF Tags 、ZigBee……等，本論文之目的為設計新式震動能量擷取系統，並將微小能量轉換成實際可用之電源應用於不同之低功率感測器，目標為使整個系統可達到自我供電，並將系統設計成發電模組使其可方便置於震動環境或鞋具內，以獵取環境震動或人體行走時之動能。以壓電材料(PZT、PVDF)設計來說，其可將環境震動施加於PZT之應力與應變轉換成交流電壓源，然而隨著不同的機構設計與環境震動強度和頻率會產生1V之微小交流電壓或高於10V以上的交流電壓，因此在設計上將針對此兩種不同狀況，分別設計升壓和降壓式之無電池高效率的能量擷取電路。分析壓電材料之物理特性並設計發電模組機構，選擇合適之壓電材料使其達到最大發電功率，考慮發電模組於低環境震動情況下為一低電壓之間歇性能量來源，一開始透過電荷泵浦進行整流升壓並儲存於過渡電容中，中間為一功率管理電路，當過渡電容達額定電壓時則向後端之低壓降線性穩壓器供電並輸出穩定電壓，當負載電流太大時，功率管理電路會切斷傳輸路徑使過渡電容繼續充電，考慮發電模組於高環境震動情況下為一高電壓之能量來源，此時採用降壓式切換電容電路來達到額定電壓。此外也利用了商用晶片(LTC-3588)完成了切換式電感能量擷取電路，在模擬與驗證方面將以簡化之壓電模型模擬能量來源，並將設計完成之電路與壓電等校模型進行整體之系統模擬與驗證，本文將針對前端之發電機和後端能量擷取電路的設計與模擬，其設計流程為建立壓電發電模組之等校模型、電路設計、CADANCE軟體模擬修正、晶片佈局與下線、實驗量測，最後整合前端發電模組、能量轉換電路與後端感測器進行系統實驗，以達到自我供電之感測系統。

Energy harvesting materials and systems has emerged as a prominent research area and continues to grow at rapid pace. A wide range of applications are targeted for the harvesters. The distributed wireless sensor nodes with low power consumption have been developed. In this thesis, the energy harvesting systems including piezoelectric generator, harvesting circuit, storage device, and sensor node are discussed and developed. Target of this thesis is to develop an energy harvesting system with wireless sensor and no battery supplement. There have two energy harvesting circuits been developed for ambient vibration with different magnitudes in this thesis including AC/DC charge pump and AC/DC step-down switched capacitor converter. For low ambient vibration, the piezoelectric generator generates low AC voltage that needs the boost converter to transform this low AC energy to a useful DC form. For high ambient vibration, it generates high AC voltage that need step-down converter to transform this high AC energy to a useful DC form. Basic piezoelectric operation principle and material selection is introduced, and then design the best generator configuration and suitable material for optimal energy harvesting. In the first stage of energy harvesting circuit including step-up and step-down switched capacitor converter which transform AC energy to a DC form. The second stage is a power management which is using for controlling the energy transmission to the load or not. The piezoelectric generator cannot provide sufficient energy to the load while the loading current is too high, so the power management turns off the transmitted line, and then the first stag keeps charging the storage capacitor. The third stage is a low drop out regulator for providing a stable DC voltage. In the other way, the commercial IC (LTC-3588) is also developed for energy harvesting in this thesis.