切換損失計算及改良式動態斜率技術應用於高效率多輸入單輸出系統

Abstract

在講求綠色能源的今天，因應多樣化的能源輸入而使得多輸入單輸出系統越來越受到重視，也因此並聯系統因為同時具備高輸出驅動能力而被廣泛的應用，在運用並聯輸入系統的時候，最主要會面臨的兩個問題就是因為每組直流轉換器的初始電壓不同而產生的並聯電流誤差，以及輕載時龐大的切換損耗所帶來的效率低落問題。 面對電流不均的問題，最簡單的方法就是運用斜率控制法，但是同時會帶來輸出電壓變動的問題，也因此，本篇論文提出了一正/負斜率補償系統，配合上動態斜率補償的機制，使得在進行均流的同時，輸出電壓可以維持在超過最小額定輸出電壓的準位，並增進輸出電壓的穩定性。 接著，為了增進輕載時的效率，本篇論文提出了一個切換功率損失計算電路，可以根據輸出電流的狀況最佳化並聯輸出的組數，此則為在輕載的時候，由於單組直流電壓轉換器即可供應輸出的電流，此切換功率損失計算電路將調整各組直流電壓轉換器的控制開關，將多餘的直流電壓轉換器關閉，以增進輕載時候的效率，而一旦進入了重載的輸出電流狀況，此電路則會再次調整控制開關，讓系統回復至並聯輸出的模式下，以減少傳導功率損失。換句話說，此正/負斜率補償輸出系統同時可以減少在進行均流時的輸出電壓下降，以及有良好的效率。 實驗結果證明了此電路在輕載的狀況下可以利用控制開關的調整，對於一個供應電壓為5V、操作頻率為5MHz的系統，在輕載的狀況下提升12%的功率，可以等效為每日降低105g的二氧化碳逸散。

The increasing demand of green energy in today’s electronic devices needs multiple input sources to deliver high driving capability to single output. Thus, parallel DC-DC converters are widely used to achieve large driving capability. When using parallel system, the major concern are the uniform current distribution caused by the initial output voltage difference and low efficiency at light loads caused by the large switching loss of each DC-DC converter. Considering the current-sharing issue, the simplest method is the droop technique, which has the drawback of increasing output voltage variation. Thus, the proposed Positive/Negative compensated (PNC) dynamic droop scaling (DDS) technique can effectively reduce the output voltage variation, thereby meeting the requirement of allowable minimum output voltage. Besides, the PNC method enhances the performance of output voltage stability. Furthermore, the light-load efficiency can be improved by a switching loss calculation (SLC) circuit. Actually, by means of the design of SLC circuit in the PNC-DDS system, it can decide the optimum driving solution according to the loading condition. That is, more than one input source is disabled to reduce the switching loss at light loads. Contrarily, multiple input sources are preferred to reduce the conduction loss at heavy loads. In other words, PNC-DDS system with power management can achieve low drop output voltage for current sharing issue and high efficiency over a wide load range. Experimental results show the efficiency can be improved approximately 12% at light loads when two input source are regulated at the switching frequency equal to 5MHz and 5V supply voltage while doing the good current sharing. This efficiency improvement is equal to decrease about 105g CO2 wasting per day.