新式微機電升壓轉換器設計

Abstract

本論文提出一種新型MEMS boost converter設計。Boost converter利用儲能元件將輸入的電能以其他形式的能量儲存，並在輸出時將能量釋放，藉此提高輸出電壓達到升壓的目的。傳統的boost converter有將輸入電能以磁能儲存在電感的switch-mode boost converter，以及以靜電能儲存在電容的charge pump。然而switch-mode boost converter在切換時會有電壓突波及電子雜訊的產生，且電感的尺寸過大也不利於空間利用。而charge pump改善了前述使用電感的缺點，但其所需的電容數量隨著升壓倍率提高而增加，因此在高升壓倍率的應用下，過多的電容數量也將造成尺寸大幅增加。 MEMS boost converter是利用靜電式微致動器將輸入電壓的電能以機械能形式儲存，並在升壓時利用儲存的機械能減少電容值，使儲存在電容中無法流走的電荷因電容值變小而提高電壓，藉此僅透過一個電容即可升壓，避免像charge pump為了提高升壓倍率而增加電容數量。然而該設計在儲存能量時為避免靜電力消耗掉機械能，因此會將電容短路使靜電力消失，然則也將使儲存的靜電能浪費掉，造成效率低落的問題。而本論文提出的設計將以兩個大小不同的電容交錯產生方向不同的靜電力矩，將能量以機械能儲存，並讓電荷能在電容與電壓源間流動，避免短路損失靜電能。接著藉由大電容的負極電壓改變將儲存的電荷推往小電容使小電容電壓提升，再利用機械能減少小電容的電容值，使電壓再次提升。 本論文將以Simulink的一個工具箱「simscape」進行模擬驗證。模擬結果此設計可將輸入電壓2.5V提升到14.35V，且在輸出電壓為5.5V時能量輸出效率為92.73%。接著我們增加小電容的數量，使大電容儲存的電荷能繼續流往增加的小電容，再將小電容串聯疊加電壓。如此可將輸入電壓2.5V提升到27.35V，且在操作頻率11.23KHz、輸出電壓25V、輸出平均電流37.1μA的條件下，只需要400μm×300μm，相較於傳統設計的面積縮小許多。

This thesis proposes a novel MEMS boost converter. A boost converter transforms the input electric energy into another kind of energy stored, and releases the energy to raise output voltage. There are two kind of conventional boost converters, one is switch-mode boost converter which stores energy in inductors, another is charge pump which stores energy in capacitors. But, switch-mode boost converter has voltage spike and electronic noise when switching, and the inductor size will occupy too much area to use. Charge pump overcomes above disadvantages, but the higher voltage boost ratio we need, the more capacitors we use. So, in the high voltage boost ratio applications, the capacitors will occupy much area, too. MEMS boost converter transforms input electric energy into mechanical energy by electrostatic micro actuator, and uses the stored energy to decrease capacitance. The charges stored in capacitor will raise voltage. So, it can use an only capacitor to raise voltage unlike as charge pump. However, this design will short the capacitor to cancel the electrostatic force to avoid consumption mechanical energy when opposite moving. So the electrostatic energy will be wasted and cause low efficiency. This thesis proposes a novel design, which uses two different size capacitors to produce electrostatic torque by turns to store mechanical energy, and make charges flow between capacitors and voltage source to avoid wasting energy. Then, changing the negative voltage of large capacitor, charges will flow to small capacitor to raise its voltage. And the mechanical energy will decrease the capacitance of small capacitor to raise its voltage again. This thesis uses a Simulink toolbox 「simscape」 to simulate and verify. The simulation results show that this design can boost input voltage 2.5V into 14.35V, and the output efficiency gets 92.73% when the output voltage is 5.5V. Then we add the number of small capacitors and make the rest charges in the large capacitor flow to the new adding capacitors. Connecting all of the small capacitors and summing up the voltage. This design can boost input voltage 2.5V into 27.35V. When it operates in 11.23 KHz, input voltage 2.5V, output voltage 25V and average output current37.1μA, just need the area 400μm×300μm. It is much smaller than conventional design.