Environmental Engineering Reference
In-Depth Information
2.1 Series configurations
Series powertrain architectures have found favour in larger vehicles such as heavy-
duty trucks and locomotives. For a series propulsion system to be viable it must
possess an overall high efficiency in total power processing. Generally, in pas-
senger vehicles this has not occurred due to component inefficiencies or driving
cycles or both. Vehicles following fixed routes such as city buses, locomotives and
the like have well-defined usage and can be optimized for it. Passenger vehicles, on
the other hand, are more difficult to make a case for series propulsion systems
because of the generally much higher additional weight associated with a dedicated
engine generator set, a separate electric M/G for traction and some amount of
energy storage. Large vehicles such as buses and trucks are much less sensitive to
the added weight of series hybridization and appear to benefit from this archi-
tecture. Figure 2.3 illustrates the series architecture.
Energy
storage
Power
rectifier
e-
mtr
Power
inverter
Gen.
Figure 2.3 Series hybrid propulsion system architecture
A series hybrid vehicle has only an electric transmission path between prime
mover and the driven wheels. As Figure 2.3 shows, the engine generator power is
rectified to dc then reconverted to variable frequency and variable voltage by the
power inverter for delivery to the electric motor on the driven wheel axle. An
energy storage system of high turnaround efficiency is required. The energy storage
system may have low capacity or capacity sufficient for electric-only range. In the
case of low capacity, such as 1-3 kWh, the vehicle architecture is classified as load
tracking because the engine generator must respond to propulsion power level
changes due to the road load with relatively fast dynamics. A high capacity energy
storage, on the other hand, more closely resembles a battery-electric vehicle (BEV)
with range extender. In fact, a high storage capacity, series hybrid may have a
downsized engine that provides mainly base load, or average cruising power, plus
passenger amenities and a storage system provides peaking power.
2.1.1 Locomotive drives
Locomotive drives are perhaps the oldest series hybrid propulsion systems in
existence. In this architecture, similar to that shown in Figure 2.3, a naturally
