Development of ESS for Regenerative Energy of …

1 Development of ESS for Regenerative Energy of electric Vehicle Hanmin Lee, Gildong Kim, Changmu Lee Korea Railroad Research Institute, Uiwang-City, Gyeonggi-Do, Korea Abstract The Energy storage system is considered to be one of the useful devices for Energy storing and recycling. The Energy storage system reduces primary Energy consumption without affecting transport capacity and punctuality. Also the Energy storage system can stabilize the system voltage. This paper presents the Development of the Energy storage system.

2 Namely, effect of the Energy storage system for Energy saving, applying EDLC as the storage unit of the Energy storage system, the Energy storage system design, installation and field tests. Introduction The electric railway is a clean and Energy saving system, because it requires relatively less Energy than automobiles by transporting the same passengers or goods. Six thousands of vehicles are operated on Korean urban transit system. This system is 95% of regeneration system. Especially, the VVVF-Inverter vehicle has a merit of the highest regeneration rate.

3 Energy consumption is 90% for traction and 10% for auxiliary supply. Braking Energy is about 30% of Energy consumption. Up to 30% of the tractive power of vehicles capable of returning Energy to the power supply can be regenerated during braking and that this Energy can be used to feed vehicles which are accelerating at the same time. The Energy generated by braking vehicle would simply be converted into waste heat by its braking resistors if no other vehicle is accelerating at exactly the same time.

4 Such synchronized braking and accelerating can not be coordinated, the ESS( Energy storage system, here after) stores the Energy generated during braking and discharges it again when a vehicle accelerates. The ESS creates optimum conditions for Energy regeneration in urban transit system. The ESS is able to store and discharge Energy extremely quickly, consequently enabling a complete exchange of Energy between vehicles, even if they are not braking and accelerating at precisely the same time, as is most frequently the case in everyday service.

5 The ESS reduces primary Energy consumption without affecting transport capacity and punctuality. In addition, the ESS can stabilize the system voltage. The ESS is considered to be one of the useful devices for Energy storing and recycling. This paper presents the Development of the ESS. Namely, effect of the ESS for Energy saving, applying the electric double layer capacitor(EDLC, here after) as the storage unit of the ESS, The ESS design, installation and field tests. ESS( Energy Storage System) The recent environmental protection trend requires more strict Energy saving, therefore every transportation system should reduce Energy consumption to the minimum value.

6 High-efficiency operation system, Energy saving and CO2 emissions shall be addressed as important issue in railway system. These issues are the most essential factors of railway, major public transportation system. Recently, saving Energy in the electric railway system is studied. For such new Energy saving, the ESS is considered for storing Energy . Energy saving is possible by efficient use of regenerated Energy . Regenerated Energy is recycled amongst vehicles by mean of charge and discharge corresponding to powering and braking of electric vehicle operations.

7 This Energy saving contributes to cut CO2 to reduce greenhouse gas emissions. Recycling regenerated Energy demonstrate significant effect on peak cut of consumption Energy in railway substation. Absorption of excess Energy avoids regeneration failure due to high traction voltage. EDLC( electric Double Layer Capacitor) In urban transit system, about 40% of the traction power fed for powering vehicle is converted to braking Energy and dissipated as heat. The ESS provides ideal Energy -saving for railway system, by means of storage and recycle of braking Energy .

8 For such new Energy saving, the EDLC of huge capacitance is considered for storing Energy . And then the EDLC is considered to be one of the useful devices for Energy storing and recycling. The ESS is developed by applying EDLC, which is attracting widespread attention as a large-capacity Energy storage medium. The EDLC, which does not rely on chemical reactions, suit to frequent rapid charge/discharge, and everlasting in principle. The EDLC contains no heavy-metal parts and so is environment-friendly.

9 If the electrodes of an electrolytic capacitor are dipped into an electrolyte, thin insulated layers form in the electrolyte that is in contact with the electrodes. As a result, two pairs of what are known as electric double layers are formed between the electrode and the insulated layer. If the allied voltage is lower than the minimum voltage that electrolyzes the electrolyte, the layers are maintained and the gap between them is extremely thin, so that a large amount of Energy can be stored. The structure of an electric double-layer capacitor is shown in Figure 1.

10 The electrolyte constitutes the two layers and a middle layer. Porous carbon is used so that the electrodes offer a large surface area, and organic liquid often used as an electrolyte. The general equivalent circuit of an electric double-layer capacitor is indicated with a capacitance(C) and a resistance(R) connected in series. This is a good approximation of any real capacitor if long-term processes are excluded. The terminal voltage of the capacitors v and the charge/discharge current of the capacitors I can be expressed by the following equation.