A non-dissipative controllable charging equalizer for series connected high-capacity super-capacitors urban rail transport system

In the high power application of urban rail transport system, the supercapacitors are important energy storage units, which are commonly connected in series to increase the energy storage capacity and the withstanding voltage. It is critical to balance the voltage among supercapacitors so that the charging equalizer is very essential. This paper proposes a novel charging equalizer employing a push-pull forward multi-winding transformer with synchronous rectifier, which can achieve rapid equalization offering large equalizing current. In the proposed charging equalizer, the full bridge rectifier is implemented by controllable power MOSFET rather than the conventional power diode, which can increase the equalizing speed and reduce the power loss during the voltage equalization with the little conduction resistance of MOSFET. Meanwhile, this paper uses an extended Kalman filter based state of charge estimator, which is able to estimate the state of SCs online and get an outstanding balancing performance. The operational principles and equalization algorithm of the proposed equalizer are presented and the equalization performance is verified by the simulation and experimental results of a charging equalizer prototype for eight series-connected supercapacitors.