1. Introduction
Studies on the design of electric traction vehicles are motivated by the need for radical change in the field of transportation. Indeed, environmental issues and energy consumption are at the heart of our news. This is why a clean means of transport that does not emit greenhouse gases is at stake worldwide [
1].
All-electric vehicles have significant advantages over traditional vehicles, representing the ideal solution to environmental issues. Their advantages include:
No greenhouse gas emissions (electricity production is assumed to be clean);
Efficient traction chain;
Energy recovery;
Smoother and quieter ride; and
Simplified design (elimination of gearboxes, etc.).
However, their disadvantages coincide with the advantages of traditional vehicles. Their on-board energy source, the battery, is characterized by a low energy density, thus resulting in a low-performance vehicle with reduced range.
The complementary nature of traditional and all-electric vehicles emphasizes the need for a compromise that would benefit from their advantages while attempting to eliminate their disadvantages. Vehicles attempting this compromise are called hybrids [
1].
Power devices are very important for power electronic systems because they are closely related to the performance of discrete devices. Their study, their understanding and the improvement of their performance are of major importance for the development of high-performance power electronics equipment. Among the important tools for creating power electronics applications is the development of model semiconductor circuits. The circuit models developed should adequately detail the performance of the terminal in practical situations. In addition, it must be able to adapt to one of the power electronic circuit resolution software. The flared use of these models depends on the adaptation of the model’s accuracy and simplicity [
2]. For a global simulation, the thermal problem is as critical as the electrical operation of the device for the credibility of the system. All semiconductor devices are audible to self-heating since most of the physical parameters of semiconductor materials are temperature related. In addition, the electrical and thermal behavior of the device must be consistently simulated. In this work, we sought to establish the potentiality of the bending models of the behavioral and electrothermal circuits of the diode and the power IGBT applied in static converters dedicated to electric traction. Although the compound electrothermal model developed is not so complex, it is able to give a physical and accurate electrothermal description of the device.
The modeling of an electric power train is largely influenced by the classic models implemented in the SPICE simulator. This simulator uses an equivalent electrical diagram to represent the behavior of the component. The basic idea was therefore the direct resolution of the semiconductor equations in a more or less simplified form, with a method of finite differences or finite elements. Obviously, this would allow a better and more in-depth study of the physics and behavior of the components.
With the exception of the finite element models, which require a complete description of the doping of the structural layers of the components and of the geometric dimensions, and which have significant computation times, there are practically no models which faithfully represent the behavior components. Moreover, even if we have precise models, we must proceed to the identification of their parameters with measurements on the real components, which is not always easy. While our model is based on simple equations that allow us to reduce both the number of parameters and the simulation time, the thermal model of use takes into account the angle of heat propagation [
3]. Thus, our approach is to deal with both electrical and thermal aspects in a single environment in order to solve the problem homogeneously and simultaneously.
In this paper, we present two electric traction systems dedicated to electric vehicles. In addition to the source, these traction models contain a chopper, an inverter controlled by PWM, and an asynchronous motor or a direct current motor. As evident in the following publications, losses in semiconductors have adverse effects on the efficiency of various static converters. The use of the developed models of the diode and the IGBT makes it possible to form an accurate estimate of the losses in the two electric traction systems.
In previous works, the validation of the model of the diode [
3] and of the IGBT [
4] has been carried out from a simple assembly. The next step consists of studying a more complex circuit in order to identify a practical application on a real application assembly. The present study is intended to simulate static converters and machines dedicated to electric traction.
The study of the thermal behavior of power modules has become necessary with regard to the rapid development of power electronics modern. The prediction of the temperature variation is generally carried out using equivalent thermal circuits.
We remain interested in studying the effect of temperature on traction chains. Indeed, in this paper we present the effect of temperature on direct current motors and asynchronous machines.
2. Electrothermal Modeling of a Traction Chain with an Asynchronous Motor
The traction chain, shown in
Figure 1, is composed of a photovoltaic panel, a DC/DC converter, and a direct current motor.
2.1. Photovoltaic Panels
In recent years, photovoltaic panels have garnered increasing interest in power generation for both stationary and onboard applications.
The photovoltaic module is based on a number of cells connected in series and in parallel. This last circuit is based on an ideal current source, which models the photo current Iph, associated in parallel with the diode, which represents the PN junction, to determine the voltage source. Two resistors (Rs and Rp) are added to represent the cell losses [
5], as shown in
Figure 2.
2.2. Chopper
As mentioned above, photovoltaic panels have garnered increasing interest for their potential in the generation of power for applications such as the electric vehicle. However, some questions are pending, particularly the low voltage produced at the output of the panels. Consequently, a DC/DC converter is essential to raise this voltage to the voltage level of the DC bus. In order to be optimal, DC/DC converters must meet many requirements in electric vehicle applications, namely [
6]:
Low mass and small volume;
High energy efficiency;
High power density;
Low cost;
Low electromagnetic disturbance; and
Reduced current ripple to extend fuel cell life.
In addition, the reliability and continuity of service of traction chains is crucial for electric vehicles to access the general public automotive market. Indeed, the presence of faults in the traction chains can lead to malfunctions in the vehicles and thus reducing their performance leveling comparison to conventional vehicles.
In the event that electrical faults do occur, electric vehicle drivelines should include fault-tolerant topologies and/or controls for the DC/DC converter.
This aspect of research focuses on the study of two intertwined DC/DC converter topologies in terms of fault tolerance. The two most critical components in DC/DC converters are aluminum electrolytic capacitors and power switches. Indeed, 60% of malfunctions and breakdowns are due to failures of electrolytic capacitors, while 31% are due to failures of power switches [
7].
In [
8], Mohamed Kabalo proposes a four-phase floating interleaved boost converter (FIBC). As the same work for [
9,
10,
11], Christopher D. Lute et al. provide an experimental evaluation of a four-phase floating interleaved boost converter for a photovoltaic power system application. However, the principle switches of the proposed converter have a higher voltage stress; therefore, it influences negatively in the output voltage response.
Thus, this study emphasizes the losses of power switches. The electric vehicle uses a photovoltaic panel as the main power source and an auxiliary power source (batteries or super capacitors) to assist the propulsion of the vehicle.
The first topology is an interlaced DC/DC boost converter, known as the interleaved boost converter (IBC), consisting in which connecting connects N boost converters in parallel sharing a common DC bus. The number of phases results from a compromise between the values of the inductors, efficiency, input current ripple, and cost. On the other hand, the second topology is an interlaced floating DC/DC boost converter, commonly called “floating interleaving boost converter”(FIBC) [
12]. The latter has certain advantages, for example interlacing and high voltage gain. To respect the equilibrium of the floating bus, the number of interleaves of the FIBC converter must always be even. The choice of the number of phases of this converter results from a compromise between the input current ripple, the volume of inductors, and energy efficiency [
13]. The electrical diagrams of the two interlaced topologies are shown on in
Figure 3.
2.3. DC Motor
The direct current (DC) motor is a device that has been used in many applications such as electric traction to convert electrical energy into mechanical energy. In most applications, efficiency is very important. For example, if we have a direct current motor in our car, we always try to get the most out of it. Therefore, it is important to study and seek to improve the performance as to continuously maintain the desired performance level [
13].
The electrical characteristics of the synthetic winding motor are modeled as an RL series circuit representing the inductance and resistance of the armature. The mechanical part of the motor is modeled as a parallel RC circuit. The electrical and mechanical parts are connected using controlled sources. The rear CEM is also modeled and included in the series with the motor winding so that it opposes the input voltage [
14].
2.4. Simulation Results
Figure 4 represents the complete model of the traction chain of the electric vehicle and is composedof a photovoltaic panel, a chopper, and the direct current motor.
The phenomenon of self-heating is characterized by the fact that the production of heat is faster than its dissipation. This then results in a rise in temperature of the system (
Figure 5).
However, a sharp rise in temperature can damage or even destroy the electronic component.
The thermal behavior and electrical operation of a component or an electronic system are linked. This connection is due on the one hand to the electrical properties of semiconductors, which are affected by the temperature variation, and on the other hand to the junction temperature which varies depending on the power dissipated and the cooling environment. Thus, in order to increase the reliability of electronic systems and to optimize their thermal design (boxes, operating conditions, location of components on printed circuits, etc.), it is necessary to form a good estimate of the electrothermal behavior of circuits and components. The necessary steps for carrying out the electrothermal coupling of the electronic components are explained in [
15].
In the first step we created an electrical model of the electronic component (IGBT, Diode…). Then we defined all the parameters of the electrical model which are affected by temperature (mobility, carrier concentration, lifespan, etc.).
Finally, we developed the thermal model of the entire structure, constituted of the component, its casing, and its cooling to establish communication between these two models [
14] (
Figure 6).
In
Figure 7 and
Figure 8, we illustrate the different output voltages and currents of the chopper in the DC motor.
The output voltage of the chopper for T = 45 °C and T = 90 °C.
The output current of the chopper for T = 45 °C and T = 90 °C.
As shown in
Figure 7,
Figure 8,
Figure 9 and
Figure 10 the ripple of the output voltage of the chopper is very important for the temperature T = 90 °C. This ripple causes adverse effects on the system performance.
Figure 11 and
Figure 12 show the motor output voltage and current for a temperature equal to 45 °C.
Vs and Is for T = 90 °C.
Figure 13 shows the motor output voltage and current for a temperature of 90 °C.
Figure 12 and
Figure 13 show the effect of temperature on DC motor voltage and current. It can be concluded that these ripples have adverse effects on the efficiency of the system. This makes the addition of a cooling system for the semiconductors mandatory.
Figure 7,
Figure 8,
Figure 9,
Figure 10,
Figure 11 and
Figure 12 presented previously show the outputs of the chopper and the outputs of the motor for two temperature values from these curves and we notice that when the temperature increases the ripples become very interesting which influences negatively on system performance.
In the figures below we first show the validation of our model of the interlaced chopper by comparing it to the work published in [
16]. The converter efficiency curve as a function of power shows a good compromise between our simulated converters with the semiconductor models developed in [
17].
Figure 14 shows the efficiency with and without a semiconductor cooling system. In addition,
Figure 15 shows the voltages gain of our interlaced DC/DC converter with and without a cooling system. From these two figures we can see that a semiconductor cooling system would improve the results of the studied system.
4. Conclusions
In this article, simplified electrothermal models of two electric traction chains have been developed. This simple and effective representation requires a relatively low calculation time, certainly reducing the simulation time of a complete electrothermal analysis of the module. The support we used for the implementation of this model is the Pspice software, which is an important simulation tool where several types of physical phenomena can be described. The flexibility of this tool encouraged its use as the developed model would be used to study a complete electrothermal model. The user can implement the electrothermal model in any simulation tool with a description language.
The study of power semiconductor components is a discipline in its own right. Our goal in this article is not to deal with details of the physics of semiconductors or their manufacturing technology. We have considered keeping it to the minimum necessary to present the basics of semiconductor physics in a simple way. We have confirmed the simulation results obtained by the electrothermal model by comparing them with the results obtained experimentally. We found a very good correlation between the different thermal responses. In addition, we have added a cooling system for the semiconductors, this system improves the performance of the asynchronous motor and the DC motor.
The comparison shows that these models are simple, tunable with the electric circuit software simulator. They benefit from a better ability to predict the main circuit parameters necessary for power electronics design. The results obtained show that these models have adapted to complete electrothermal simulations of power electronic circuits.
The results obtained are satisfactory and make it possible to open a path to several lines of research with the aim of improving the performance of power electronic systems dedicated to electric vehicles and better improving the electrothermal modeling of these systems.