Progressive Electrification of Road Vehicles
Ronald M. Dell, ... David A.J. Rand, in
Towards Sustainable Road Transport, 2014
5.3.2 Extended-range electric vehicles
The extended-range electric vehicle (E-REV) is effectively an all-electric vehicle, with all the motive power provided by an electric motor, but with a small
ICE present to generate additional electric power. Alternatively, it may be viewed as a series hybrid with a much larger battery, namely, 10–20 kWh; see Table 5.3. When the battery is discharged to a specified level, the ICE is switched on to run a generator that, in turn, supplies power to the electric motor and/or recharges the battery. With this arrangement, the range limitation that is inherent in a
BEV can be overcome. For moderate distances, E-REVs can operate in full-electric mode and are then as clean and energy-efficient as
BEVs (unlike parallel hybrids and other series hybrids with their smaller batteries and very limited electric range). For longer distances, E-REVs utilize the ICE to keep the battery charged, but consume noticeably less fuel than conventional
ICEVs for the following two reasons:
(i)
The engine of an E-REV is significantly smaller than that of a conventional ICEV – it only needs to meet average power demands because peak power is delivered by the battery pack. The engine of an ICEV, on the other hand, must also cover peak-power surges, e.g. accelerations.
(ii)
The engine of an E-REV operates at a constant, highly efficient, rotation speed; whereas that of an ICEV often runs at low or high rotation speeds during which, in both situations, its efficiency is low.
The different modes of E-REV operation are shown schematically in Figure 5.10. The vehicle begins its journey with the battery SoC close to 100%. All the vehicle power is provided by the electric motor, which draws energy only from the battery, and there are no local exhaust emissions. The battery is partly recharged with each
regenerative braking event. When the battery is depleted to a pre-ordained SoC – marked in Figure 5.10 at three levels of increasing severity, viz., green, orange and red – the vehicle switches to extended-range mode. While the vehicle is operating in this mode the ICE is switched on as and when necessary to keep the battery within the SoC range marked by the green and red dashed lines. After the journey, the battery SoC is returned to 100% with power taken from the grid.