365
Hybrid Vehicles
or absorbing power from the engine when its output power is greater than
that required to drive the wheels. Better than the series hybrid, the parallel
hybrid needs only two propulsion devices—the engine and electric motor.
Another advantage over the series hybrid is that a smaller engine and a
smaller electric motor can be sized because they share the maximum output
power. Even for long-trip operation, only the engine needs to be rated for the
maximum output power while the electric motor may still be about a half.
In the series-parallel hybrid, the configuration incorporates the features of
both the series hybrid and parallel hybrid, but involves an additional mechanical link compared with the series hybrid, and also an additional generator
compared with the parallel hybrid. Although possessing the advantageous
features of both the series hybrid and parallel hybrid, the series–parallel
hybrid is relatively more complicated and costly. Nevertheless, with the
advances in control and manufacturing technologies, some modern HEVs
prefer to adopt this system.
As reflected by its name, the complex hybrid involves a complex configuration that cannot be classified into the above three kinds. It seems to be
similar to the series–parallel hybrid, since the generator and electric motor
are both electric machinery. However, the key difference is due to the bidirectional power flow of the electric machine in the complex hybrid and the
unidirectional power flow of the generator in the series–parallel hybrid. This
bidirectional power flow can allow for versatile operating modes, especially
the three propulsion power (due to the engine and two electric motors) operating mode that cannot be offered by the series–parallel hybrid. Compared
with the series–parallel hybrid, the complex hybrid suffers from higher complexity and cost. Nevertheless, some advanced HEVs adopt this system for
dual-axle propulsion.
12.3 Hybrid Vehicle Classification
Based on the hybridization level and operation features between the engine
and electric motor, HEVs have been classified as the micro hybrid, mild
hybrid, and full hybrid (Ebron and Cregar 2005). Recently, this classification
has been further extended to include the latest plug-in hybrid EV (PHEV)
and the range-extended EV (REV). Figure 12.3 depicts their classification in
terms of the energy source and propulsion device.
For the micro hybrid, the conventional starter motor is eliminated while
the conventional generator is replaced by a belt-driven integrated-startergenerator (ISG). This ISG is typically 3−5 kW. Instead of propelling the vehicle, it offers two important hybrid features. One is to shut down the engine
when the vehicle is at rest, so-called idle stop feature, hence improving fuel
economy for city driving. Another is to recharge the battery primarily during
Hybrid Vehicles
or absorbing power from the engine when its output power is greater than
that required to drive the wheels. Better than the series hybrid, the parallel
hybrid needs only two propulsion devices—the engine and electric motor.
Another advantage over the series hybrid is that a smaller engine and a
smaller electric motor can be sized because they share the maximum output
power. Even for long-trip operation, only the engine needs to be rated for the
maximum output power while the electric motor may still be about a half.
In the series-parallel hybrid, the configuration incorporates the features of
both the series hybrid and parallel hybrid, but involves an additional mechanical link compared with the series hybrid, and also an additional generator
compared with the parallel hybrid. Although possessing the advantageous
features of both the series hybrid and parallel hybrid, the series–parallel
hybrid is relatively more complicated and costly. Nevertheless, with the
advances in control and manufacturing technologies, some modern HEVs
prefer to adopt this system.
As reflected by its name, the complex hybrid involves a complex configuration that cannot be classified into the above three kinds. It seems to be
similar to the series–parallel hybrid, since the generator and electric motor
are both electric machinery. However, the key difference is due to the bidirectional power flow of the electric machine in the complex hybrid and the
unidirectional power flow of the generator in the series–parallel hybrid. This
bidirectional power flow can allow for versatile operating modes, especially
the three propulsion power (due to the engine and two electric motors) operating mode that cannot be offered by the series–parallel hybrid. Compared
with the series–parallel hybrid, the complex hybrid suffers from higher complexity and cost. Nevertheless, some advanced HEVs adopt this system for
dual-axle propulsion.
12.3 Hybrid Vehicle Classification
Based on the hybridization level and operation features between the engine
and electric motor, HEVs have been classified as the micro hybrid, mild
hybrid, and full hybrid (Ebron and Cregar 2005). Recently, this classification
has been further extended to include the latest plug-in hybrid EV (PHEV)
and the range-extended EV (REV). Figure 12.3 depicts their classification in
terms of the energy source and propulsion device.
For the micro hybrid, the conventional starter motor is eliminated while
the conventional generator is replaced by a belt-driven integrated-startergenerator (ISG). This ISG is typically 3−5 kW. Instead of propelling the vehicle, it offers two important hybrid features. One is to shut down the engine
when the vehicle is at rest, so-called idle stop feature, hence improving fuel
economy for city driving. Another is to recharge the battery primarily during