2.The Voltage-balancing between single cells in supercapacitor module
The method of voltage-balancing are mainly passive balancing and active balancing.
When the supercapacitors are connected in series, voltage imbalance between single cells may happen. That’s mainly affected by the capacity and self discharge, so modules are grouped according to strict capacitance selection to ensure the voltage balance at constant current charging.
Meanwhile, each capacitor is connected in parallel with a resistor to eliminate the influence of self discharge. Because self Passive Balancingdischarge of each capacitor are not the same, it will cause the voltage difference between single cells after a period of charge storage. The difference will become larger after repeated charge&discharge, and some capacitor voltage may exceed rated voltage, which will influence module life. By measuring the leakage current, the equivalent parallel resistance of the capacitor can be calculated. The voltage balancing resistor is selected according to the equivalent parallel resistance value to achieve the purpose of voltage balancing.
Beside selection of each capacitor’s capacitance, equalizing circuit at both ends of each capacitor in parallel connection are adopted. Do it like this:
A voltage comparator with a set value (usually at 2.6V) is needed. If the capacitor voltage is less than the set value, the discharge circuit does not work; otherwise the other side of the voltage comparator conduct, making the discharge resistor be in parallel to the capacitor. Through discharge of resistor, the capacitor voltage will drop. When the voltage drops below the set value, the voltage comparator switch to the other side, then the discharge will stop.
Supercapacitor module comprised of high- capacity capacitor mainly adopt this method. The main form of circuit is as follows:
5.The voltage balancing between modules
When connected, supercapacitor modules with the same range of capacitance should be selected as much as possi
ble to ensure voltage consistent within a certain range when charging. Based on that, equalization circuit are mainly adopted to achieve the overall voltage balance.