The car occupies the daily universe of our society; however, noise pollution, global warming gas emissions, and increased fuel consumption are constantly increasing. The electric vehicle is one of the recommended solutions by the raison of its zero emission. Heating and air-conditioning (HVAC) system is a part of the power system of the vehicle when the purpose is to provide complete thermal comfort for its occupants, however it requires far more energy than any other car accessory. Electric vehicles have a low-energy storage capacity, and HVAC may consume a substantial amount of the total energy stored, considerably reducing the vehicle range, which is one of the most important parameters for EV acceptability. The basic goal of this paper is to simulate the air-conditioning system impact on the power energy source of an electric vehicle powered by a lithium-ion battery.
The energy production throughout the world is mainly based on the hydrocarbons combustion, and it is envisaged to increase by 60% during the 20 next years [
Since 1973, transport is the most intensive oil sector; its share in worldwide consumption increased considerably to reach more than 61.5% in 2010, whereas shares of industry and other sectors (agriculture, public and commercial services, not specified residences, and other sectors), respectively, decreased by 10.9% and of 10.7%. Indeed, the high and increasing share of transport in the oil worldwide consumption can be mainly explained by the number of the cars which more than doubled since 1973 [
Unfortunately, hydrocarbon combustion has a major impact on the global environment because it is responsible for 80% of the greenhouse gas emissions, which are the principal cause of climate warming and air pollution [
To overcome these problems, the governments and automobile manufacturers are obliged to develop a new generation of vehicles based on environmentally-friendly technologies of energy utilization [
Most of the commercial zero emission vehicles (ZEV) available today are pure electric vehicles (EV) powered with batteries.
A battery electric vehicle (BEV) is fully powered by grid electricity stored in a large onboard battery. EV use energy much more efficiently than ICEV; a traditional ICEV fuel efficiency is 15–18%, while a BEV represents a high efficiency about 60–70% [
The viable EV batteries are chemical batteries and ultra-capacitors or supercapacitors. The chemical batteries consist of the lead-acid battery; nickel-based batteries, such as nickel/iron, nickel/cadmium, and nickel-metal hydride (Ni-MH) batteries; and lithium-based batteries such as lithium-polymer (Li-P) and lithium-ion (Li-I) batteries [
An automobile air-conditioning system is an integral member of automotive systems because it is not only responsible for the thermal comfort of a passenger but also for the safety of the passenger, to an extent. The primary purpose of an automobile air-conditioning system is to maintain the vehicle cabin temperature and humidity at comfortable levels for a passenger. It is also responsible for recirculation of air inside the cabin and prevention of stagnation of stale air which will consist of CO2 from the passengers, volatile organic compounds, and other particulate contaminants. This system significantly increases the energy consumption of a vehicle and negatively influences its performance. AC can be considered as the main accessory which extracts the largest quantity of power when it is operating [
The objectives of this work are focused on the modeling and the simulating of an air-conditioning system and analyzing its effect on the power consumption and the autonomy of an electric vehicle powered by a Li-ion battery.
The movement behavior of a vehicle along its moving direction is completely determined by all the forces acting on it in this direction. As shown in Figure
Forces acting on the vehicle.
Under these conditions, the resistive torque
The vehicle considered in this work is two-rear-wheel drive EV destined to urban transportation. Two induction motors are coupled in each of the rear wheels. The energy source of the electric motors comes from the lithium-ion battery [
As shown in Figure
Simplified diagram of the vehicle power system.
As illustrated in Figure
Lithium-ion battery charge/discharge diagram.
During the discharge; the process is reversed where the cathode gains electrons and the lithium ions pass from the anode to the cathode. The overall chemical reaction for the battery is
According to (
A key parameter in the electric vehicle is the state of charge (SOC) of the battery. The SOC is a measure of the residual capacity of a battery. To define it mathematically, consider a completely discharged battery. The battery is charged with a charging current of
The depth of discharge (DOD) is the percentage of battery capacity to which the battery is discharged. The depth of discharge is given by
In our case, the battery must feed the two subsystems: vehicle’s traction motors: (20–47 KW); thermal comfort: (1–5 KW).
Any air-conditioning system design process starts with the calculation of cooling needs. The reason behind carrying out cooling load calculations is to ensure that the cooling and heating equipment designed or selected serves the intended purpose of maintaining the required conditions in the conditioned space. A model was developed to calculate the cooling load of the air-conditioning vehicle compartment during its travel. This model is based on the determination of the AC power as function of the outside temperature which is responsible of the thermal exchanges with the outside environment.
Considering that the interior temperature is constant, the air-conditioning power is proportional to the external temperature. So we have a linear equation: “
AC system is from
Figure
Model of the electric air-conditioning system.
We present in this section the results of our simulations giving the importance to the power consumption, the state of charge, and the depth of discharge for the following cases: air-conditioning system; vehicle without air-conditioning system; vehicle with the air-conditioning system.
The software tool used to realize the all of the simulations is Matlab-Simulink, whose use is very largely widespread in the industrial environment. Also we note that the various studied cases are simulated for an electric vehicle travelling on a straight road and under different climatic conditions as shown in Table
Different climatic conditions.
Phases | Time (s) | Temperature (°C) |
---|---|---|
Phase 1 | 0–2 | 24 |
Phase 2 | 2–4 | 28 |
Phase 3 | 4–6 | 32 |
Phase 4 | 6–8 | 36 |
Phase 5 | 8–10 | 40 |
Phase 6 | 10–12 | 24 |
Figure
Evolution of Li-ion battery power in different climatic conditions.
Figures
Evolution of the SOC in the different phases.
Evolution of the DOD in the different phases.
Concerning the vehicle without air-conditioning system, Figures
Evolution of Li-Ion battery power for the electric vehicle without air-conditioning.
Evolution of the SOC in the different phases.
Evolution of the DOD in the different phases.
Figure
Figures
In this case, the Li-ion battery must be able to supply sufficient power simultaneously to the propulsion system represented by the electric vehicle’s traction motors and the air-conditioning system under the different climatic conditions treated. Figure
Evolution of Li-ion battery power in different climatic conditions.
Evolution of the SOC in the different phases.
Evolution of the DOD in the different phases.
The overview of the simulations is shown in Table
Power consumption comparison.
Vehicle with AC | Vehicle without AC | |||||||
---|---|---|---|---|---|---|---|---|
Phases | Phases | |||||||
2 | 3 | 4 | 5 | 2 | 3 | 4 | 5 | |
Power (KW) | 16.58 | 16.88 | 17.17 | 17.52 | 16.13 |
In this paper, the modeling of an air-conditioning system and the study of its impact on the power consumption of an electric vehicle powered by Li-ion battery were undertaken by way of simulation using Matlab environment. Three simulations carried out in different sunny climatic conditions have been presented. The power necessary to operate the vehicle air-conditioning system is related to the peak cooling load generally related to the outside temperature. This methodology can help the designer to test the effects of the outside temperature variation on the power consumption in order to provide a comfortable climate inside the passenger compartment. It was shown that the Li-ion battery has a good performance and gives good dynamic characteristics simultaneously for the electric vehicle propulsion system and the air-conditioning system.
In addition, it must be mentioned that significant reductions in automotive auxiliary loads are needed, making tomorrow’s vehicles safer and quieter while making passengers comfortable more quickly. A significant benefit could be achieved if the vehicle is equipped by an intelligent power management controller using the present model of the air-conditioned vehicle.