全域式主動互補平衡電路開發

Development of an Globally Active Balance Circuit

鋰鐵磷電池具有高能量密度、高充放電電流、無記憶、效應與自放電率低的特性，可解決電動船長久以來續航力不足的問題，但磷酸鋰鐵電池於串聯應用時，會因各電芯內阻或容量的不同，而出現各電芯電壓不一致的問題，此問題會導致部分電芯提早過充或過放，為了避免電芯因過充或過放而造成永久地損壞，必須切斷電池組迴路以停止充電或放電，但此舉將造成電池組電量不足或續航力降低，本研究針對此問題提出全域式主動互補平衡系統，此系統利用切換開關電路針對電壓較低的電芯進行平衡的動作，將此電芯之電壓拉抬至設定值，直到所有電芯之電壓維持一致為止，透過此全域式主動互補平衡可降低部分電芯出現提早過充或過放的機率，電池組於充電時能盡可能達到滿電量；於放電時能完全善用電池組內的能量，達到提高電池組之效率與續航力的目的。 Lithium iron phosphate (LFP) cells have been demonstrated to possesses good cell characteristics of high energy storage density, high discharging and charging currents, no memory effect, and low self discharge rate. With these good cell characteristics, LFPs have been hoped to finally resolove the short range anxiety for battery powered boats. Due to inconsistencies of internal resistance or capacity among LFP cells, cell voltage varies in a LFP battery pack in series. Cell voltage variation could lead to earlier cell overcharge or earlier cell over discharge. Both cases will either damage to the cell or lower effective storage energy in the stack. In order to protect the overcharged or over discharged cells, battery management systems cut off the battery circuit to stop charging or discharging completely. Range covered by the vehicle will be negatively affected due to the cell protection function. This study proposed a new active balance circuit, which balances the cell voltages in a global manner. This new balance scheme designed a switching circuit, composed of a matrix of photo DMOS relays, to select the cell with minimu cell voltage and moving electrical energy from the whole stack to the selected cell until it reached a preset voltage. Cell voltage compensation continued until a balanced state was reached among all the cells in the series. From the extensive tests of this study, this active balance circuit could reduce the possibility of over discharging or overcharging. The range realized by the battery stack with the new balance circuit was therefore increased. Lifecycle achievable by the battery stack with the new balance circuit was also extended.