Forward fly-back voltage balancing circuit for series connected super capacitors using digital control

Supercapacitor is an electrical energy storage device which offers remarkably high energy density when compared to conventional capacitors and high power density when compared to batteries. While using the supercapacitors for energy storage, the main disadvantage is their limited voltage due to contemporary technology restrictions. Therefore, for higher voltage operation supercapacitors are connected in series to achieve the appropriate voltage level. Because of the difference in the magnitude of capacitance of cells, local over-voltage appears on one or more supercapacitor cells. This over-voltage decreases the lifetime and energy storage efficiency of the associated cell, which can be improved considerably by balancing the voltages across each supercapacitor. This paper presents an active voltage balancing approach using a forward fly-back power converter. In the proposed balancing scheme, cell with the higher voltage is selected to extract the extra energy and then a proportion of this extracted energy is distributed to other supercapacitors via the proposed circuit. The feasibility of the proposed balancing scheme has been verified by computer simulation and experimental results.