Design Of A Modern Tram Charging Device Based On Super Capacitor

As an up-and-coming energy storage element, super capacitor has large capacity and power density. It can achieve high-current fast charging. Apart from this, it doesn’t have memory effect. So it is increasingly favored by the market. Moreover, the super capacitor is also flexible to be deployed, easy to be designed to be modular. And it has a long life, wide operating temperature range and environment-friendly, maintenance-free advantages. These advantages make the super capacitor possible for harsh working environment. In recent years, with the continuous development and updates of C nanotechnology, the manufacturing cost of super capacitor reduces highly. These further expand and accelerate the application of super capacitor in the new electric energy storage aspect. The application scenarios of super capacitor are also more and more broad.The super capacitor has be used in urban rail transit abroad, but in China, it just starts. In the urban rail transit, the super capacitor has two working modes. One is that the super capacitors are connected in series in OCS. The super capacitors will absorb the braking energy of the trains for avoiding wasting the energy. When the voltage of OCS declines, the super capacitors release the stored energy for ensuring the voltage stability. This working mode is called ground type. The other one is that the super capacitors are installed in the trains. When trains stop at the platform, the charging device will charge the super capacitor, the charging time is short. This working mode has no OCS. Every platform has a set of charging device. It is called train type.The paper designed a set of charging device for the Wuhan T1 line. And the author verified the feasibility of the charging device. At first, the author built the single super capacitor model, simulated and verified its performance. No matter what kind of working mode, the single super capacitor’s max voltage and energy density are relatively small. This situation is insufficient to meet the working requirements. So the single super capacitor needs to be in series and parallel to achieve the energy and voltage rating requirements. In this paper, the author offered the power restriction way and the energy restriction way. Based on the two ways, the author obtained the single super capacitor’s number and the way of series and parallel. Moreover, the charging device needs a DC/DC converter device to charge the super capacitor. And the DC/DC converter device must be able to choose the constant current charging mode, constant voltage charging mode or constant power charging mode flexibility according the complicated condition. Contrary to ground-mounted and vehicle-mounted working mode, the paper compared and analyzed the topology and the working principle of the DC/DC converter device. The author calculated and chose the suitable storage inductor and filter capacitor. In addition, in order to let the charging device can select different charging mode according to different condition at work, the author established a mathematical model of Buck charging circuit, obtained the state equation and transfer function, and given the current inner and voltage outer control strategies. At last the paper described the structure, working principle and operating logic of the charging device of the tram, and built a model of charging device. The author calculated the voltage and current waveform of the super capacitor energy storage module at the process of charging by means of simulation. Compared the result of simulation to the actual waveform of the experimental prototype, the charging device achieves the desired design requirements. Also the author gave the fault protection of AC side and DC side.