應用於壓電能量擷取系統之具最大功率點追蹤的同步電壓反轉與電荷擷取介面電路

Abstract

物聯網的興起大幅改變了現代人的生活，而無線低功耗傳感器在物聯網中扮演著至關重要的角色，透過無線傳感器偵測分析物體周邊的資訊並傳遞分享出去，得以讓物聯網中的物體可以彼此溝通交流資訊，不需仰賴任何人機互動，達成現實世界的數位化。然而無線傳感器的供電是一大問題，若是透過傳統電池來供電的話，人力維護及環境污染的成本會過高。為了解決此問題，因此有了從環境中擷取能源供傳感器使用的研究出現。 壓電能源作為擷取環境能源的一種，相較其他能源，具有能量密度高的優勢，因此很適合用來作為傳感器的電能供應來源。使用壓電材料製成之壓電片，當其處於振動環境中，可透過壓電效應產生交流電源。然而實際應用需透過介面電路將交流電源整流後，才可供電給傳感器做使用。傳統上最簡單的介面電路為使用全橋整流器，優點為架構簡單、不需額外控制電路即可運作，缺點則是輸出功率不高，因為全橋整流器包含四顆二極體，會導致有大量能量被浪費。 同步電壓反轉與電荷擷取介面電路(Synchronous Inversion and Charge Extraction, SICE)就是因應此問題而被提出，然而若要將此介面電路操作在輸出功率最大值，需要透過手動量測、計算寄生電容與外接電感的LC共振路徑上之電壓反轉因子(Voltage inversion factor)，大幅增加操作上的困難度。因此本論文提出應用於同步電壓反轉與電荷擷取介面電路之最大功率點追蹤控制電路，讓控制電路可以自動根據介面電路之電壓反轉因子設定最佳電壓反轉次數，大幅降低將介面電路操作在高功率點的操作複雜度。 本論文之設計晶片是使用台積電180 nm 高壓BCD製程，根據量測結果，在電壓反轉因子為0.804時，輸出功率增益為632%，透過最大功率點追蹤控制電路讓電壓反轉次數操作在4次；在電壓反轉因子0.645時，輸出功率增益為491%，透過最大功率點追蹤控制電路讓電壓反轉次數操作在2次。最大功率點追蹤演算法於電壓反轉因子超過0.6時，最大功率點追蹤效率可超過92%；於電壓反轉因子超過0.8時，最大功率點追蹤效率可超過98%。

The rise of the Internet of Things (IoT) has significantly changed modern life, and wireless low-power sensors play a crucial role in the IoT ecosystem. By detecting and analyzing information from the surrounding environment, wireless sensors enable the communication and exchange of data between IoT devices. This process requires no human-machine interaction, thereby facilitating the digitalization of the physical world. However, the power supply for wireless sensors remains a significant challenge. If traditional batteries are used, the maintenance efforts and environmental pollution costs become prohibitively high. To address this issue, research into energy harvesting from the environment to power sensors has emerged. Piezoelectric energy, as a form of energy harvesting, has the advantage of high energy density compared to other energy sources, making it an ideal candidate for powering sensors. When piezoelectric materials are used to create piezoelectric plates, they can generate an AC power source through the piezoelectric effect when subjected to vibrations. However, in practical applications, an interface circuit is required to rectify the AC power before it can be used to power the sensors. Traditionally, the simplest interface circuit is the full-bridge rectifier. The advantage of this approach is its simple structure and the fact that it operates without the need for additional control circuits. However, the downside is that the output power is not very high because the full-bridge rectifier, which includes four diodes, results in significant energy loss. To address this issue, the Synchronous Inversion and Charge Extraction (SICE) interface circuit was proposed. However, in order to operate this interface circuit at its maximum output power, the voltage inversion factor in the LC resonance path involving parasitic capacitance and external inductance needs to be manually measured and calculated, which greatly increases the complexity of operation. Therefore, this paper proposes a Maximum Power Point Tracking (MPPT) control circuit for SICE, which allows the control circuit to automatically set the optimal number of voltage inversions based on the voltage inversion factor of the interface circuit. The proposed MPPT control circuit significantly reduces the complexity of operating the interface circuit at high output power point. The chip designed in this paper was fabricated using TSMC 180 nm high-voltage BCD process. According to the measurement results, when the voltage inversion factor was 0.804, the output power gain was 632%, and the voltage inversion was optimized to 4 times through the MPPT control circuit. When the voltage inversion factor was 0.645, the output power gain was 491%, and the voltage inversion was optimized to 2 times using the MPPT control circuit. The MPPT algorithm can achieve a tracking efficiency exceeding 92% when the voltage inversion factor is greater than 0.6, and exceeds 98% when it is greater than 0.8.