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Journal of SA Electronics
Volume 1, Issue 1
Published: January, 2021
Hybrid Electric Vehicles (HEV): classification,
configuration, and vehicle control
Muneer Mujahed Lyati
January, 2021
Abstract
: Public and private transport play a significant role in the economy, development and progress of a
country. A well-functioning transportation system allows for expansion of markets and strengthening existing
markets. It enables and promotes the strong economic growth that leads to global competitiveness. An inefficient
system causes an increase in commute congestion, a decrease in productivity, and loss of social relations. The
objective of this study is to present the classification such as Series HEV, Parallel HEV, combination HEV. This
research also discusses the configuration, and vehicle control. To achieve the research objective we review the
relevant literature on the Hybrid Electric Vehicles (HEV).
Keywords
: HEV, HEV classification, HEV configuration, HEV vehicle control, Series HEV, Parallel HEV,
combination HEV.
Author:
Muneer Mujahed Lyati is a Graduate
from College of Technology in
mechanical engineering as a bachelor
of science in mechanical engineering
with major Engines and Vehicles. His
research mainly focuses on
automotive factors, hybrid cars,
electrical cars, engines, and artificial
intelligence https://muneerlyati.com/
El ectric Vehicles (EVs) & Hybrid Vehicles (HVs) Definition
First of all, a distinction between' traction' and' propulsion' is required. Traction is provided by the motor while propulsion
is provided by the combination of engine systems. When a car with an electric motor receives the energy it needs from a
battery pack, it is considered an all-electric vehicle. This vehicle requires recharging stations that correspond with how far
it can travel on a charge. If the electric motor is fed by the battery and a thermal engine, it is considered to be a hybrid
vehicle. In reality, this vehicle is a water–fuel cell hybrid. Despite the fact that electric vehicles (EVs), either all-electric or
hybrid, reduce emissions in local areas, they do not do the same for the rest of the world.
HYBRID ELECTRIC VEHICLES.
At least two energy converters, such as internal combustion engines (ICE), electric motors, hydraulic drives, etc., are
combined in a hybrid electric vehicle (HEV). The ultimate aim of the HEV is to have the same power, range and protection
as a traditional vehicle while reducing fuel consumption and harmful emissions that are harmf ul for health (Sanghvi and
Gordon, 2021). Hybrid vehicles have the ability, including the following, to realize many benefits:
1. Higher efficiency of the electric machine: The electric machine is a simpler and more powerful machine compared
with the ICE. For example, an electrical machine's moving parts consist primarily of the armature (DC motor) or
rotor (AC motor) and bearings.
2. Regenerative braking: A regenerative brake is an energy system that decreases the speed of a vehicle by
transf orming some of its kinetic energy into a future storable type of energy, rather than dissipating it as heat as
with a conventional brake.
3. Improved torque characteristics: Electric machines are more suitable for automotive applications, with low-speed
high torque and lower cruising speed torque.
4. Reduced emissions - through smoothing and idle removal of transients.
5. For selected setups, optimum engine operation - run the engine in its 'sweet spot', staying close to its best output
hand.
6. Engine downsizing could be necessary in order to cope with average load (not peak load) and thereby reduce the
weight of the engine and powertrain.
7. It is possible to shut the engine off, thus reducing fuel consumption, pollution and NVH.
8. Accessory electrification enables the operation of parasitic loads on the necessary basis.
HEV drawbacks, however, include:
1. Powertrain and electronic complexity increased
2. Increased mass of the vehicle due to additional components
3. Increased cost due to extra components and power management difficulty
4. Overall system reliability can be lower due to increased complexity
5. If not optimized for the appropriate drive cycle, benefits may not be f ully realized.
In order to comply with various applications, a variety of different device architectures are considered. They are generally
categorized as split sequence, parallel, and strength. Device design selection depends primarily on the program. The car
manufacturing organization is obliged to reduce the intensity of adverse effects on nature, as well as to increase the level of
safety of its products, such as cars (Tengiz, 2020b) (Tengiz, 2020a). Besides, due to the complexity of many car
manufacturing companies structures, a mathematical modeling becomes necessary in order to simplify reality using models,
thereby increasing the ability of car producers to make the right decisions.(Magradze, 2020a) (Magradze, 2020b).
How Hybrids Work
Hybrid electric vehicles (HEVs) combine the benefits of gasoline engines and electric motors. Th ey can be designed to meet
different goals, such as better f uel economy or more power.
Most hybrids use several advanced technologies:
• Braking Regenerative. During coasting or braking, regenerative braking restores energy normally lost. It uses the
wheels' forward motion to spin the engine. This provides energy which makes the car slow down.
• Drive/Assist Electric Motor. In order to help the engine accelerate, move, or hill climb, the electric motor provides
power. This enables the use of a smaller, more -efficient engine. The electric motor alone propels the vehicle in
some hybrids at low speeds, where gasoline engines are the least powerful.
• Stop/Start Automatic. When the car comes to a halt, the engine automatically shuts of f and restarts when the
accelerator is pressed. It minimizes wasted energy from idling.
Figure 1. Functionality of Hybrid cars
Classification:
HEV can historically be categorized into three types: HEV sequence, HEV parallel, and HEV combination.
2.1.1. Configuration of Series HEV.
We can see from Figure 1 that the HEV series consists of the ICE, generator, power converter, motor, and battery. There is
no mechanical connection between the ICE and the transmission, so the ICE will work at the maximum efficient point by
controlling the output power of the battery to fulfill the vehicle's required power. However, the power from the ICE is
transf erred via the generator and the engine, so much more energy is lost. Because the engine is the final and sole drive unit,
the engine must be sufficiently large to meet the vehicle's output, so the regenerative braking power can almost be stored
by the engine in the battery. (Butler, Ehsani and Kamath, 1999)
Figure 2. Configuration of Series HEV.
In the HEV series, when it has to be recharged, an electric motor, coupled to an ICE, supplies electricity to the electric
machine to drive the vehicle and to the energy storage system. One of the main benefits of the series is that the speeds of
the engine and car are decoupled. As a result, the engine will run at its peak, substantially reducing the consumption of fuel.
However, because the electrical machine is the only one connected to the wheels and the engine/generator set is sized for
sustained grade power, this design includes a large pack of energy storage device, electrical machine and engine, adding
inefficiencies and weight.
Configuration of Parallel HEV.
We can see from Figure 2 that the parallel HEV allows both the electric motor and ICE to deliver power to drive the vehicle
in parallel, i.e. the ICE and motor can drive, respectively, or together. There is a mechanical relation between the ICE and
the transmission, unlike the HEV series, and therefore the rotational speed of the ICE depends on the driving cycle, so that
the ICE can run on the optimum running line by controlling the battery output power. (Tei et a l., 2003)
Figure 3. Configuration of parallel HEV.
Both the electric vehicle and the engine have mechanical connections to the wheels of parallel hybrids. Since both the
electric machine and the engine are directly connected to the wheels, the power can be shared during accelerations.
Compared to series hybrids, it is also possible to downsize both the engine and the electric motor. Since the ICE speed is
linked to the vehicle speed, the ICE can operate close to its best efficiency curve only under certain conditions. However,
since both mechanical and electrical energies can be used to directly propel the vehicle, the powertrain efficiency is
increased compared to series configuration during most operating conditions.
2.1.3. Configuration of Combination HEV.
From Figure 3, we can see that the HEV combination combines the features of both series and parallel HEV, adding an
additional mechanical link between ICE and transmission compared to the hybrid series, and also adding an additional
generator compared to the parallel hybrid between ICE and power converter. Although structural complexity contributes to
more costly production.
Figure 3. Configuration of Combination HEV.
To build an incredibly successful method, the HEV mix blends the best elements of both series and parallel hybrids. This
system splits the power of the engine into two routes: one goes to the generator to generate electricity and one goes to drive
the wheels via a mechanical gear system. In general, the series path is avoided as it is less efficient. The key additional
characteristic is that the speeds of the engine, generator and motor are decoupled, allowing additional power independence.
A HEV combination system (transmission), two electrical machines and an engine make up the most common configuration,
called an input split. Several variants of the HEV combination have been added, each offering various benefits:
o The first electric machine is used to regulate the engine speed in a single HEV combination hybrid mode, while the
second one provides the remaining power needed to track the vehicle track.
o A two mode power system is composed of a compound mode, in addition to the input mode. I n this case, the size
of the electric machine can be reduced as each motor is used to control the engine speed in various conditions. In
addition to minimizing the electric machine power requirements, the system performance can be further increased
by reducing the energy recirculation by the use of the f ixed gears.
2.2. Main Issues of HEV.
For the following purposes, the HEV can save fuel compared to traditional vehicles.
1. The HEV may store part of the kinetic energy of the vehicle in the battery during braking or downslope, where the heat
of the conventional vehicle is otherwise incinerated in the brake drums.
2. Without compromising the efficiency of the vehicle, the ICE in the HEV can be configured to have a smaller
displacement.
3. By controlling the output power of the battery to satisfy the necessary power of the vehicle, the HEV may make ICE
work at the maximum efficiency point or optimum operating line.
4. HEV is a multi-energy system; the key challenge for HEV is how to maximize the flow of energy to achieve the best fuel
economy or low emissions at lower costs, also referred to as the problem of energy management (EM). The problem will
be addressed in depth in the next segment.
Vehicle Control in HEV.
The control system of the HEV is very complex. For large-scale and complex systems, multilevel hierarchical control is an
important control technique. Hierarchical regulation is thus commonly adapted to HEV control, as seen in Figure 4. (series
HEV). The HEV controller consists of an interpreter f or driver control, a vehicle system controller and an electronic
controller. The Vehicle System Controller is the level of decision to assess the torque requirements of the engine, generator,
ICE, and mechanical brake according to the torque demand of the driver, vehicle speed, and state of charge of the battery
(SOC), where the SOC is estimated by the battery management system (BMS), the sensor feeds the vehicle speed (Serrao,
Onori and Rizzoni, 2009) (Pisu and Rizzoni, 2007) The electronic controller is the execution stage at which the vehicle
system controller carries out the order to make the corresponding parts operate.
(1) Command Interpreter for Drivers. The driver command interpreter's job is to measure the torque demand of the driver
according to the desired vehicle speed and actual vehicle speed. Vehicle speed is controlled by the direction of the
accelerator pedal and brake pedal. By changing the accelerator pedal and brake pedal position, this is a feed control device
to make the vehicle obey the desired vehicle (Wenzhong and Porandla, 2005). (Yan, Wang and Huang, 2012)
(2) Vehicle System Controller. HEV is a multiple energy source compared to traditional vehicles, so how to divide the
required power between energy sources is ref erred to as EM. By using EM strategies according to command signals
obtained from the driver command interpreter and parameter information input from the electronic controller, the vehicle
system controller performs powertrain control. As shown in Figure 5, the vehicle system controller can be categorized into
three feature blocks.(Johnson, Wipke and Rausen, 2000) (Lee and Sul, 1998) (Enang and Bannister, 2017) I) Required
vehicle interpreter capacity. (ii) Methods for handling electricity. (iii) Translator of torque. The vehicle interpreter's
necessary power is a function block for translating the torque demand of the driver to power demand. HEV is a multiple
energy device, distinct from traditional vehicles that can only produce power, not only can battery output power, but also
consume energy. The hot topic among technology developers is how to divide the necessary power between two energy
sources and mechanical brakes in order to reduce fuel consumption or emissions. (Plett, 2004).
Electronic Controller (3). The electronic controller is an embedded device that carries out commands from the controller of
the vehicle system to operate the corresponding components. In Figure 4, the electronic controller comprises the engine
control unit (ECU), the engine control unit (MCU), the generator control unit (GCU), the mechanical brake control unit and
the battery management system (BMS). The engine control unit is an electronic control unit (ECU) f or ICE control; by
injecting fuel into the ICE combustion chambers, it generates the desired ICE output torque coming from the vehicle system
controller control signal. The ICE operating point can be defined by torque and velocity. There is no mechanical link
between ICE and the transmission in the HEV series, so how can ICE speed be controlled? There is a mechanical link
between the ICE and the generator, so the speed of the ICE is regulated by the torque demand of the generator. Motor is the
final drive system and is connected to the transmission by mechanical connection, and thus the speed of the motor depends
on the driving cycle, similarly, the operating point of the motor can typically be represented by torque and speed; due to
mechanical connection to transmission, the torque demand of the motor is determined by the torque demand of the driver.
Using FOC technology, the MCU normally makes the engine run at the desired torque. During braking or down slope,
engines, commonly used for traction, may also become a generator. Therefore, the kinetic energy of the engine, otherwise
burned in the form of heat in the brake drums, can be transformed into electrical energy and sent back to the battery. If the
battery is non-receptive, it will operate with the electronic braking system control unit.
Figure 4. Vehicle Control in HEV
Notation
Explanation
sd
Desired speed of vehicle
s
Speed of vehicle
Δs:
Difference of desired speed and speed of vehicle
Tdrv dm d:
Driver demand
SOC:
State of charge
Tice dmd
Torque demand of ICE
Tgc dmd:
Torque demand of generator
Tmc dm d:
Torque demand of motor
Tbh dmd:
Torque demand of braking
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