As mentioned in section I, the ultra-capacitor cell voltage is
low, usually in a range 1 to 2.SV. On another side, the power
converter operating voltage is high, usually in range from 4SV
up SOOV or even higher. To achieve such a high operating
voltage, elementary cells are series connected in a module [4]
[5]. However, because some no idealities of indi vidual cells,
total module voltage may not be equally distributed among
series connected cells. Some of the major sources of voltage
unbalance are described here.
o Dispersion of the cells capacitance, which can be +/-20%,
causes transient, short-term unbalance in voltage
distribution among series connected cells
Dispersion of the cells internal resistance causes transient,
short-term unbalance in voltage distribution among series
connected cells
Dispersion of the cells leakage current causes steady state
(long-term) unbalance in voltage distribution among
series connected cells