Double-Switch Equalizer Using Parallel- or Series-Parallel-Resonant Inverter and Voltage Multiplier for Series-Connected Super capacitors
A double-switch cell voltage equalizer using a parallel-resonant-inverter (PRI) or series-parallel-resonant inverter (SPRI) and voltage multiplier is proposed for series connected super capacitors (SCs), such as electric double-layer capacitors (EDLCs) and lithium-ion capacitors. The double-switch operation without the need for a multi winding transformer offers simpler circuitry as well as better modularity than conventional equalizers requiring multiple switches and/or a multi winding transformer.
Generally, series-connected energy storage cells suffer from cell voltage imbalances that may lead to overcharging and over discharging of cells; the most and least charged cells in a voltage-imbalanced series connection may be overcharged and over discharged during charging and discharging processes, respectively. Non uniformity in individual cell properties of series connected cells, in terms of capacitance, internal impedance, self-discharge, is the major reason triggering voltage imbalance. Another cause that cannot be controlled in manufacturing processes is a temperature gradient among cells in practical use that exacerbate non uniform self-discharging.
In this project, a double-switch equalizer using a parallel resonant inverter (PRI) or series-parallel-resonant inverter (SPRI) and voltage multiplier is proposed for series-connected SCs. The proposed equalizer can be derived from a combination of a PRI/SPRI and a voltage multiplier. The PRI/SPRI provides an inherent constant current characteristic even at a fixed frequency, while the voltage multiplier automatically equalizes cell voltages. The double-switch configuration without the need for a multi winding transformer offers simplified circuitry and good modularity. In addition, the proposed equalizer can operate safely, even when some SC voltage is 0 V, because the inherent constant current characteristic of the PRI/SPRI automatically limits currents under desired levels. The proposed equalizer is best suitable for SCs but also can be used as an equalizer for series-connected lithium-ion batteries.
TOOLS AND SOFTWARE USED:
- MP LAB
Masatoshi Uno, Member, IEEE, and Akio Kukita, “Double-Switch Equalizer Using Parallel- or Series-Parallel-Resonant Inverter and Voltage Multiplier for Series-Connected Supercapacitors”, IEEE TRANSACTIONS ON POWER ELECTRONICS, VOL. 29, NO. 2, FEBRUARY 2014