Mohammad Amin Aghahassani

EDLC IN TRANSPORTATION SYSTEM

PART 1• ELDC

EDLC DESIGN• This design does not have the solid dielectric that

is used in the previous designs, nor does it have the chemical reactions such as are found in batteries during charging and discharging

• A dielectric separator between the two electrodes prevents the charge from moving between the two electrodes.

 PRINCIPLE OF ELECTRICAL DOUBLE LAYER CAPACITOR (SUPERCAPACITORS)• Based on the operating principle of the electric double-layer

that is formed at the interface between activated charcoal and electrolyte.

• The applied potential on the positive electrode(made of carbon) attracts the negative ions in the electrolyte, while the potential on the negative electrode attracts the positive ions distributed over an extremely short distance (order of a few Ångströms). Such a phenomenon is known as an electric double-layer.

As Capacitance is proportional to the surface area of the electrical double layer, Therefore using activated carbon which has large surface area for electrodes(due to many minute holes made in the surface), enables EDLC to have high capacitance.

EDLC CHARGE AND DISCHARGE

The space between the two activated carbon electrodes is filled with electrolyte, and electricity is charged and discharged simply by the adsorption and desorption of ions to and from the electrode surfaces.By applying voltage to the facing electrodes, ions are drawn to the surface of the electrical double layer and EDLC is charged. Conversely, they move away when discharging EDLC.

EDLC CHARACTERISTICS

Energy density and power density Battery: high energy density, low power density EDLC: high power density, low energy density

Efficiency and lifetimeBattery: Lifetime depends on charge / discharge cyclesEDLC: High numbers of cycles, long lifetime, rapid charge / discharge

EDLC CHARACTERISTICS CONCLUSION• Supercapacitors have the highest available

capacitance values per unit volume and the greatest energy density of all capacitors. They can have capacitance values of 10000 times that of electrolytic capacitors

• existing supercapacitors have energy densities that are approximately 10% of a conventional battery, their power density is generally 10 to 100 times as great. This makes charge and discharge cycles of supercapacitors much faster than batteries

PART 2

• Transportation system

URBAN RAIL

• Metropolitan transportation is responsible for about 25% of the total CO2 emissions in the European Union (EU) (European Commission, 2011).

• Urban rail typically includes tramway, light rail and metro. A very significant portion of traction energy is wasted in the numerous and frequent braking processes.

URBAN RAIL• It plays a key role in the sustainable development

of metropolitan areas for several reasons such as energy efficiency and lack of local air pollution. The recovery and reuse of braking energy is one of the most promising measures to reduce urban rail energy consumption, on account of the numerous and frequent stops involved

REGENERATIVE BRAKING• Most modern urban rail systems are equipped

with regenerative braking technology. In those systems, the recovered energy is primarily used to supply the auxiliary functions of the rolling stock itself, whilst the excess energy is returned to the distribution line to power other vehicles within the network. However, as the energy demand of auxiliaries is relatively minor and the simultaneous braking and acceleration of different vehicles in the same electric section is unlikely to occur, a significant amount of the braking energy is dissipated into resistors.

REGENERATIVE BRAKING AND ENERGY STORAGE SYSTEM• The outstanding advances in both power

electronics and energy storage technologies have permitted ESSs to become a very promising option to manage regenerated braking energy in urban rail. ESSs can be installed either on board vehicles or at specific points along the track. The former option enables rail vehicles to temporarily store their own braking energy and reuse it for subsequent acceleration. In turn, stationary ESSs accumulate energy from any braking train nearby and release it when a power demand is detected.

HOW TO SELECT STORAGE?• The selection of energy storage technologies for

urban rail applications s will call for the following features:

• large number of load cycles • high power densities

ON-BOARD ENERGY STORAGE SYSTEMS

ON-BOARD ENERGY STORAGE SYSTEMS

ON-BOARD ENERGY STORAGE SYSTEMS

• On-board ESSs may help minimize power peaks during acceleration of vehicles. When compared to stationary systems, on-board ESSs present higher efficiency due to the absence of line losses. Moreover, the management of the recovered energy is simpler as the control is independent of traffic conditions. However, mobile storage devices typically require large spaces on the vehicle and introduce a considerable increase of weight

ON-BOARD ENERGY STORAGE SYSTEMS

• As can be seen, most of the systems are based on the EDLC technology due to its fast charge/discharge response, high power density and relatively low costs. However, the low energy capacity offered by EDLCs hinders their utilization

• Composite flywheels present satisfactory cycle life and power density, while offering fast responses. However their potential risk of explosive shattering in case of a catastrophic failure has hindered their application in urban rail

ON-BOARD ENERGY STORAGE SYSTEMSHYBRID BATTERY

• The combination of high power batteries and EDLCs appears to be a promising solution for applications where catenary-free operation is sought. Here, EDLCs can absorb the peaks of regenerated braking energy and deliver the power required for acceleration, whereas batteries can absorb the remaining braking energy and release it during coasting/rolling phases, which will increase their life and performance.

STATIONARY ENERGY STORAGE SYSTEMS

• Trackside ESSs collect the regenerated braking energy that cannot be instantaneously consumed in the system, delivering it when a vehicle is accelerating in its electric section

• In comparison with on-board devices, they have fewer installation restrictions as space and weight are normally not a big issue in trackside facilities. Besides, their maintenance does not affect the service. In contrast, stationary ESSs involve higher transmission losses in the line

STATIONARY ENERGY STORAGE SYSTEMS

• Notwithstanding, the fewer weight and volume restrictions make high-power batteries a valid option too. Moreover, the safety concerns related to flywheels are less limiting in trackside applications

CONCLUSION• ESSs have proven success as valid solutions to

manage the regenerated energy that cannot be instantaneously consumed within the system. Aside from important traction energy savings, they may significantly contribute to shave power peaks and to stabilize the network voltage. In general, EDLCs are considered to be the most adequate technology for these systems, although the combination of EDLCs and high-power batteries offers very interesting features for on-board applications that require high degrees of autonomy