IEEE Electrification Magazine - September 2016 - 37

6.4 kWh

2 kWh

activate the backup mode. In that
Energy Supply in Hybrid
case, the speed will be limited to
Mode (15 kW × 2)
5 km/h so that it will be able to
Energy for
reach the next charging point.
Hybridation
The use of the battery energy is
Security 1 kWh
critical. It must be considered that
Slow Charging in Stops:
Margin for
Backup
- Necessary Time: 2 kWh at 7 kW × 2 ≈
the capacity of the battery string is
10 min.
extremely high when compared
Energy for
- Necessary Distance→ 24 Stops
Backup
with the ultracapacitors, but the
of 25 s.
Energy Supply in
maximum charging and dischargBackup
ing power is much lower. In hybrid
Mode (50 kW × 2)
mode, the battery string is disNormal Operation of the
charged at a power rate of 15 kW/
Tramway
module (30 kW/train); in backup
mode, they can be discharged at a Figure 7. A battery usage example.
power rate of 50 kW/module
(100 kW/train). In the Figure 7, a
battery usage example is depicted. As can be observed,
when the 2 kWh reserved for hybridization are consumed, the battery is charged at slow rate in the stops. If
all the hybridization is used in a section, then the system needs 24 stops of 25 s for full recovery. With the batteries at full charge, the train can withstand 4 min in a
nonscheduled stop. It must be pointed out that the
regenerated braking power is not used for charging the
batteries but the ultracapacitors. In case the energy for
backup is used, the tram should reach the next charging
station, charge the ultracapacitors, and finish the route
until the depot, where the batteries should be completely charged at slow rate for around half an hour.

Slow Charge
(7 kW × 2)
in Depot
Maintenance
in Depot

Charging Stations
As previously mentioned, when the train operates in a catenary-free section, the ultracapacitors must be charged at
regular intervals. Basically, two different charging infrastructures have been proposed, the ground energy charging system sistema de captación inferior de energía (SCIE)
(Spanish for lower system energy capture) and the overhead energy charging system. An example of an SCIE can
be observed in Figure 8, while in Figure 9 an overhead system is represented.
The ground charging system uses a conductor rail
made of aluminum and steel supported on top of insulators. It has double drainage and water evacuation slopes,
and the central section is made of concrete and fibers (a
detailed view can be found in Figure 8). The overhead
charging system uses a conductor bar supported with an
independent steel structure or integrated in the station
ceiling, as it is the case of Figure 9. The first solution
(ground level) has a lower visual impact, and it is more
silent. On the other hand, the overhead system is better
against dirtiness, is cheaper, and its adaptation to an
existing line is easier. Basically, the charging station is
composed by the switching system (SC), the identification
and positioning system (SIP) and the monitoring and
information system (SIM).

(a)

(b)

Figure 8. A light train equipped with hybrid ultracapacitors and Li-ion
batteries and a ground-level fast charging system. (a) A ground energy
charging system and (b) underground auxiliary equipment for the
ground energy charging system. (Photographs courtesy of CAF.)

Figure 9. An overhead charging system. (Photographs courtesy
of CAF.)

IEEE Elec trific ation Magazine / S EP T EM BE R 2 0 1 6

Table of Contents for the Digital Edition of IEEE Electrification Magazine - September 2016