利用電量回復效應延長鋰電池放電壽命之研究

Abstract

由於越來越多的電子產品朝向可攜式的方向發展，而發光二極體(LED)在這方面的應用與日俱增，這對以鋰電池供電的電源系統造成極大的負擔，然而要如何最大化使用電池電量(maximize battery capacity usage)，對現今電池電源管理的設計應用而言，已經具有關鍵性的影響。本論文提出一個LED陣列模擬負載器，搭配一套鋰電池模擬器，利用這個實驗平台設計各種負載電流的變化，分析研究其對鋰電池放電特性所產生的影響。由實驗中，我們發現當負載電流以負斜率方式減少時，鋰電池在負載電流降低時獲得休息的機會，它能夠恢復部分活性物質(active species)，這是鋰電池所具備的一個非常重要的特性，電量回復( Charge-Recovery)。由於利用電量回復這個特性，可以延長鋰電池放電壽命，我們設計了一些電流斜率的變化，做一些最佳化分析，發現增快斜率可以獲得更多的放電壽命，最佳的情況下，比固定電流放電模式增加了290%的放電時間，而不同的斜率變化的放電時間，在最佳的情況下也有200%以上的差異。最後我們以實際的3.5吋液晶顯示器做驗證，在不同的鋰電池電壓下，減少背光光源之白光二極體的電流，加上調高影像亮度(video brightness)及對比(contrast)來補償背光光源的降低，結果可以得到多一倍的放電時間。整個實驗平台的設計及實驗結果都將在本論文中說明。

Now a days, more and more electronic product development emphasize on the portable design, which extremely increases the LED utilization. However, this implement results in a great burden to the entire powered by lithium battery power supply system. Therefore, how to maximize battery capacity usage becomes an essential key influence to the entire power management design. This thesis subjects a LED array simulator along with a lithium battery simulator to build up a platform to experiment. With this platform, we simulate all sorts of current changes and further to analyze how different current influences the discharge characteristics of lithium battery. From the experiment, we find out that when the simulating current decreased with minus slope, the lithium battery can take a good rest during the decrease of current and gradually recover its active species, which is a very important characteristic of the lithium battery called “Charge-Recovery”. Since to take the advantage of “Charge-Recovery” characteristic, the battery discharge life can be efficiently enlarged, therefore we design a series of current slope changes and further to analyze the data under the best condition. Thus, we achieve the conclusion that to fasten the slope can effectively gain more battery discharge life. Under the best condition, to fasten slope and increase 290% discharge time than constant current; furthermore, different slope changes also results in more than 200% battery discharge life difference. At last, we certify the above argument through realistic system integration experiments. Under different lithium battery voltage, we reduce the current of white LED then adjust the video brightness and contrast to make up the reduction of back light source. In the end, we get one time more discharge time for the battery. The entire architecture of this experiment platform and result will be further explained and described in this thesis.