共振式無線能量傳輸系統之功率震盪器設計與實現

Abstract

近幾年來，隨著手持式、醫療以及工業裝置的迅速發展，人們對行動裝置的使用率越來越高，為了有更安全方便的充電方式，發展無線充電技術的重要性也逐漸增加。一般行動裝置常見的無線充電方式分為感應式與共振式。感應式利用兩線圈靠近時由磁場產生的互感進行能量傳輸，缺點為線圈距離需較近以及虛功造成額外的損耗；共振式則是將兩線圈以電容補償至相同共振頻率，消除虛部阻抗產生近似純電阻的負載，也可以達到較好的傳輸距離。共振式主要分成Qi及AirFuel Alliance兩個聯盟制訂規格，AirFuel Alliance使用ISM band中的6.78 MHz頻帶，其優點是距離及線圈擺放位置對傳輸效率的影響較低。 本論文實現的無線能量傳輸系統包含三部分，第一部分對兩共振耦合線圈進行分析，包含串聯-串聯共振線圈形式及串聯-並聯共振線圈形式。第二部分是使用E類功率放大器作為無線能量傳輸系統之傳輸端電路，並推導E類功率放大器公式及設計參數，使用串聯-並聯共振線圈傳輸能量，根據量測結果，於線圈距離2公分時E類功率放大器輸出功率約為1.89 W，效率可達83.66 %，線圈傳輸效率可以達到80.52 %，系統整體效率可達67.36 %。第三部分為減少無線能量傳輸端之電路複雜度，省去額外的訊號產生電路以及驅動電路，將E類功率放大器以回授方式做成功率震盪器，使用串聯-並聯共振線圈傳輸能量，根據量測結果，於線圈距離0.5公分時功率震盪器輸出功率約為2.22 W，效率可達73.38 %，線圈傳輸效率可以達到92.84 %，系統整體效率可達68.13 %。

Due to the development of portable, medical and industrial devices, the usage of mobile devices is getting higher and higher. To charge safely, the technology of wireless power transfer is needed. The common wireless charging methods for mobile devices are inductive coupling and resonant coupling. The inductive coupling uses the mutual inductance generated by the magnetic field when the two coils are close. The disadvantages of inductive coupling are the short coil distance and additional loss caused by reactive power. The resonant coupling is to compensate the two coils to the same resonant frequency with capacitors. Eliminating the imaginary impedance to create a load close to pure resistance, and a good transmission distance can be achieved. The resonant coupling alliances include Qi and AirFuel Alliance, and the AirFuel Alliance uses the 6.78 MHz ISM band. The advantage is that the distance and coil placement have lower impact on transmission efficiency. The wireless power transfer system implemented in the thesis is divided into three parts. The first part is the analysis of two coupling coils, including series-series coupling and series-parallel coupling. The second part is to use the Class E power amplifier to drive the coil of the wireless power transfer system, deriving the formula and design parameter for Class E power amplifier, and using series-parallel coupling to transmit power. According to measurement, the output power of the Class E power amplifier is about 1.89 W and efficiency is up to 83.66 %. The coil transmission efficiency is 80.52 %. The overall system efficiency is 67.36 %. The third part is to reduce the complexity of transmitter, eliminating the need for additional signal generator and driving circuits. The Class E power amplifier is made into a power oscillator by LC feedback, and using series-parallel coupling to transmit power. According to measurement, the output power of the power oscillator is about 2.22 W and efficiency is up to 73.38 % when the coil distance is 0.5 cm. The coil transmission efficiency is 92.84 %. The overall system efficiency is 68.13 %.