電力線磁能採集與充電系統

Abstract

隨著社會上對環保與節能觀念的重視，以及半導體電路在低功率方面的進展，環境中存在一些很低的能量源，在上述兩項進步的影響下，將此類環境能量接收並轉化為可用電力的各種能量採集技術(energy harvesting technology)或稱為獵能技術也逐漸受到重視。而在一個能量採集的系統中通常需要有三個部分，能量採集電路，能量儲存模組與後端的整流電路才可以作為一個獨立供電的系統。本論文中提出一個應用於電力線磁能感應的能量採集與充電系統的設計，對應以上的系統說明，本論文分成三個部分，包含磁能採集電路，電池充電模組以及後端的直流對直流(DC-DC)轉換電路。以上三個電路的設計的要點分別為：最大化輸入能量，降低充電所需時間以及最小化電路功率消耗。在磁能採集電路中，不同於以往文獻中的設計，針對能量源感應線圈(current transformer)的特性設計新式電路控制以及採集能量的方式，並依此新式設計觀測輸入與輸出的狀態，進行持續性動態調整至最大輸出功率。最大功率擷取(maximum power extraction)控制方式，有別於常見的阻抗模擬(resistance emulation)方式，更符合感應線圈的特性。由理論與量測證實，在相同的輸入狀況下所提出的方式相較於傳統方式可以擷取更多至120%的能量。在充電模組部分，以鋰電池做為目標儲存的元件，以其特性來設計提出一個連續內部阻抗偵測(continuous build-in resistor detector)機制，應用於切換式充電電路中，可以克服電池電壓偵測時，內部阻抗帶來的誤差，進而達到大電流充電時間延長，縮短充電時間的效果。由理論與量測證實可以節省最多40%的充電時間。並於充電模組中提出一自動能量傳輸控制(automatic energy deliver control)的功能，可以動態分配能量同時供給系統以及電池能量，以方便應用輸入源的最大能量。在直流對直流轉換電路的方面，針對極低功率的控制方式進行最佳化，應用非連續導通方式(discontinuous conduction mode)控制並使用一個新式的動態開關時間(dynamic on-off time)機制去除傳統耗電的零電流偵測(zero current detection)電路，並配合校正電路以達到在微瓦功率輸出時，仍能保持高效率。加上動態相位領先電路(adaptive phase lead)，可改善在低電流下比較器的延遲造成的輸出電壓負載電壓不穩定的現象。在實驗結果中也證實了本論文所提出的三個電路的功能正確完整具有高轉換效率，符合電源管理與獵能系統晶片設計的要求。

This thesis presents a power line magnetic energy harvesting and charger system with the circuit blocks of magnetic energy harvesting (MEH) circuit, switching-based charger circuit and nano-power buck converter. First, the proposed MEH circuit harvests magnetic power on power wires through power sensing current transformer (CT). The MEH circuit includes the direct AC-DC rectifier and the maximum power extracting (MPE) control circuit. The MPE control fits the characteristic of magnetic energy source and continuously tracks the maximum power of the CT. Thus, 120% harvesting power improvement can be achieved under the same CT’s sensing current. Second, the proposed switching-based charger circuit charges the Li-ion battery with the novel continuously built-in resistance detection (CBIRD) function to achieve fast charging. The CBIRD dynamically adjusts the mode transition voltage during the charging procedure and extends the period in constant current (CC) mode to effectively reduce charging time. Besides, the proposed automatic energy deliver control (AEDC) technique manages charging current according to the loading system’s requirement and input supply energy. The charger system can save up to 40% of charging time with 87% of peak power efficiency at a rated 1A charging current. Third, the nano-power buck converter provides regulated power from the battery to the back-end system. The proposed dynamic on/off time (DOOT) control with the α-calibration scheme can predict on/off time at different input voltages without a power consuming zero current detection (ZCD) circuit, as well as suppress static power in idle periods. Furthermore, the adaptive phase lead (APL) mechanism can improve inherent propagation delay attributable to low-power and non-ideal comparator Experimental results show 95% peak efficiency, low static power of 217nW. The test chips of the MEH circuit, switching-based charger circuit and nano-power buck converter were fabricated in 0.25μm CMOS process with chip area of 0.98 mm2, 3mm2 and 0.39 mm2, respectively.