Hybrid Electric Vehicles

HYBRID ELECTRIC VEHICLES
• Hybrid electric vehicles (HEVs) incorporate more than one propulsive power source to energize
the vehicle.
• They have the ability to optimize the propulsive energy of the vehicle by effectively utilizing dual
power sources and achieve higher mileage and reduce greenhouse gas emissions.
• HEVs are integrated with an internal combustion engine and electric machines, which are
energized by on board electric battery, ultracapacitor, or a combination of both.
• The dual-mode operating capability of the electric machine (function as motor as well as
generator) is one of the primary advantages of the HEVs in terms of recovering energy during the
braking phase of the vehicle.
• Also, the electric propulsion system provides higher acceleration performance at low speed, which
cannot be achieved in conventional vehicles due to the various mechanical constraints of the IC
engine.
• Owing to the increased number of propulsive components and complexity, the power management
and control system in the HEVs plays a vital role in maximizing its overall energy efficiency and
achieving higher operating performance, while significantly reducing emissions.
Primary components of (a) Conventional vehicle and (b) hybrid electric vehicle.
HEV TECHNOLOGIES
• Micro Hybrids – vehicles with the start–stop or idle–stop systems, which automatically shut
down the engines when vehicles are coasting, braking, or stopped according to certain road
conditions, and restart the engines when the speed is regained.
• Mild Hybrids – consist of electrical motor–generators between the engine crank shafts and the
transmission input shafts.
• The added motor–generators provide the vehicle with the start–stop function, regenerative
braking function, and additional electric power to drive the accessories.
• Full Hybrids – vehicles that can run on either engine-only mode, battery-only mode, or a
combination of the two.
• In addition to the functions that micro hybrids and mild hybrids are capable of, full hybrids
can also operate on an all-electric range where only electric motors are used to propel the
vehicle and supply all the internal power loads
MILD HYBRID ELECTRIC VEHICLES
• Mild hybrid electric vehicle incorporates a smaller electric propulsion system and generally it is
integrated in the IC engine.
• The flywheel system of the IC engine is designed as an electric machine; therefore, the IC engine can
be started by electric propulsion and the electric machine can also power assist the IC engine when the
power demand increases.
• Also, it can recover a certain amount of kinetic energy during the braking phase of the vehicle.
PARALLEL HYBRID ELECTRIC VEHICLES
• Significant portion of the propulsive power in parallel hybrid electric vehicle is supplied by the electric
machine.
• Typical electromechanical integration of the parallel hybrid electric vehicle has two independent propulsive
power low paths such as electrical and mechanical paths.
• Therefore, depending upon the propulsive power requirement of the vehicle, electric only, mechanical only,
or a combination of both can be chosen.
Operating modes of parallel hybrid electric vehicles: (a) IC engine supplies the propulsive torque/power
demand; (b) electric machine is the only propulsive medium; (c) IC engine and electric machines supply the
propulsive torque/power demand; (d) regenerative braking mode of the vehicle.
SERIES HYBRID ELECTRIC VEHICLES
• Series hybrid vehicles incorporate two electric machines and an IC engine in the propulsion system.
• One electric machine is directly attached with the IC engine and most of the time it functions as an electric
generator (during starting of the IC engine, it acts as an electric motor).
• Another electric machine is integrated with the transmission system to deliver the propulsive power
requirement of the vehicle.
Operating modes of series hybrid electric
vehicles:
a. Electric machine is the only propulsive
medium;
b. IC engine is supplying the propulsive
torque/power demand;
c. IC engine and electric machines are
supplying the propulsive torque/power
demand;
d. regenerative braking mode of the vehicle
e. IC engine supplies the propulsive
torque/power demand of the vehicle;
f. IC engine charges the battery system
(also, battery can receive power from
regenerative braking).
SERIES-PARALLEL HYBRID ELECTRIC VEHICLES
• Incorporates two electric machines and an internal combustion engine for propulsion purposes.
• Contrary to the series hybrid electric vehicles, series–parallel hybrid electric vehicles use low-power
electric machines and both of them can act as motor and generator.
• Two electric machines and an IC engine are connected to the drive axle via a planetary gear system.
• The ingenious arrangement of this gear system allows the propulsive system to have much more flexibility
while achieving different propulsive requirements.
Planetary gear system and the connection diagram of propulsive systems in series–parallel hybrid
electric vehicles.
Operating modes of series–parallel hybrid
electric vehicles:
a. IC engine is the only propulsive medium.
Here part of the power produced by the
IC engine is converter via motor
generator to the traction wheels.
b. IC engine and electric batteries are
supplying the propulsive torque/power
demand.
c. IC engine is supplying the propulsive
torque/power demand while the battery
is charging.
d. Batteries are supplying the propulsive
e. demand.
f. IC engine charges the battery while the
vehicle is standstill.
g. Regenerative braking of the vehicle.
Vehicular architectures and their electromechanical integration methods:
(a) mild hybrid electric vehicle, (b) parallel hybrid electric vehicle, (c) series hybrid electric vehicle, and
(d) series–parallel hybrid electric vehicle.
PLUG-IN HYBRID ELECTRIC VEHICLES
• Plug-in hybrid electric vehicles are generally either parallel hybrid electric vehicles or series– parallel hybrid
electric vehicles.
• The plug-in hybrid electric vehicle incorporates a bigger electric propulsion system and a smaller IC engine-
based propulsion system.
• Also, the plug-in hybrid electric vehicle incorporates an external charging adopter and it can be used to
charge the battery from the grid
Difference between parallel

and plug-in parallel hybrid
electric vehicles
Different vehicular architectures and their electric and conventional propulsion systems.
Power and energy requirement of the vehicle and their effect on HEV design.
(a) Key design parameters to define the power and energy requirements of the vehicle.
(b) Power and energy supplying components of the powertrain.
AREAS FOR RESEARCH AND DEVELOPMENT
• Design, selection, and sizing of electric machines
• Selection and sizing of the electric machine is one of the critical design processes in HEV development.
• There are mainly three electric machine technologies available, such as induction machines, permanent
magnet machines, and switch reluctant machines
• Energy storage system
• Electrical energy storage system is very critical for HEV performance.
• Depending on the expected range and required driving cycle, a particular energy storage system will be chosen
for a particular vehicle.
• In general, higher-power and energy-dense storage systems are preferred for HEV applications.
• Thermal management system
• Various propulsive systems in HEVs require different temperature controls for thermal management system
design.
• For example, the coolant temperature requirement for the IC engine is not similar to the coolant temperature
requirement for electric machines.
• In reality, some components are air cooled; some are water cooled, while others are oil cooled.
• Therefore, the thermal management system needs to be developed to meet all these requirements.

Hybrid Electric Vehicles

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