Losses Modeling of the Electric Vehicles Power Chain
Moez Hadj Kacem1, Souhir Tounsi2, Rafik Neji1
1National School of Engineers of Sfax, Sfax University, LETI-Laboratory, Sfax, Tunisia
2National School of Electronics and Telecommunications of Sfax, Sfax University, SETIT Research Unit, Sfax, Tunisia
Moez Hadj Kacem, Souhir Tounsi, Rafik Neji. Losses Modeling of the Electric Vehicles Power Chain. International Journal of Electrical Components and Energy Conversion. Vol. 1, No. 2, 2015, pp. 49-54. doi: 10.11648/j.ijecec.20150102.11
Abstract: In this paper, we present a comparative study of two Electric Vehicle power chain, one in IGBTs and the other with electromagnetic switches (IEs) in order to select the most efficient in point of view of energy economy and production costs. In this context, a model of the total losses of the two power chains is developed an implanted under Matlab-Simulink environnement.
Keywords: Electromagnetic Switches, Electric Vehicle, Converter, IGBT, Losses Model
The major issue of land transport in future years is the economy of energy. The electric vehicle (EV) is part of autonomy as a reliable candidate to solve the problem of energy shortage. The direct drives reinforce this logic power saving by canceling losses in electrical devices and increasing their energy efficiency [1-10].
The static converter is one of the fundamental elements of EV. It is the interface between the battery and the electric motor, its role is to convert the output power of the battery with the consumed by the main engine and to adapted deliver the electrical power to the set of user. So the static converter, driven by the controller, will help to accelerate or decelerate the motor (and the car).
2. Power Chain Structure
A power train of an electrical vehicle is conventionally composed of an electric motor, an electronic system (power source and control) and a mechanical linkage system (gear, differential and wheels), Fig. 1.
The selected power converter is a two-level inverter voltage. This structure is the least expensive compared to others and offers good quality forms of motor power wave voltages and currents, which leads to a good dynamic characteristic of EVs. Two inverter types are studied; the firstwith IGBT and the other electromagnetic switches (IEs). The latter structure has the disadvantage of low switching frequency (Below 150 Hz) , But it is the cheapest and haven’t the problem of the floating potential, since each inverter arm is controlled by a single electromagnet. As against the IGBT structure offers the possibility to achieve a switching frequency of 8000 Hz  which leads to a good quality of the dynamic characteristic of EVs, it raises a lot of disadvantages which can be made, as examples [9-12]:
The Energy losses leading to a reduced range for a fixed energy stored as heat in the transistors and diodes, leading to the incorporation of a cooling system in most cases.
The floating potential,
Thestatic and dynamic Luch-upusually leading to the deterioration of the converter.
3. Losses Modelling
3.1. IGBTs Converter
The relationship of the conduction losses in the transistors is as follows:
Wherer is the duty ratio of the control signals of the transistors, Imis the average current on a half period and Vce is the collector-emitter voltage.
The switching losses in the transistors are also derived by the following equation:
Where fsw is the switching frequency, Udc is the DC bus voltage, Eoff is the energy dissipated in the opening, Eon is the energy dissipated during closing and Ew is the DC voltage after manufacturers testing when determining the energy dissipated at the opening and closing.
Conduction losses in the diodes are also estimated by the following relationship:
The following table provides an overview of results of tests of failures IGBT converters and their genesis . Analysis of these failures, their genesis, their propagation leading to the default setting of the component to characterize its final state, plays an essential role in the development strategies of redundancy and reconfiguration converters IGBT.
|Module||Cycling Type||ΔTj (°C)||Tjmax (°C)||ΔTsemelle (°C)||Tplancher (°C)||Nf (kcycles)||stop test|
|A6||Long (18 s – 43 s)||95||145||60||50||61||Vcesat (+10 %)|
|A7||Long (18 s – 43 s)||95||145||60||50||37||IGBT fault|
|A9||Long (18 s – 43 s)||95||145||60||50||37||IGBT fault|
|GEM 002||Long (18 s – 43 s)||95||145||60||50||39||IGBT fault|
|C1||Long (15 s – 45 s)||60||150||30||90||207||diode fault|
|C2||Long (15 s – 45 s)||60||150||30||90||520||Vcesat (+ 2,3 %)|
|GEM 003||Long (10 s – 30 s)||80||170||40||90||44||IGBT fault|
|GEM 005||Long (10 s – 30 s)||80||170||40||90||56||IGBT fault|
|GEM 006||Long (10 s – 30 s)||80||170||40||90||60||IGBT fault|
|GEM 007||Long (10 s – 30 s)||80||170||40||90||107||diode fault|
|GEM 009||Long (10 s – 30 s)||80||170||40||90||72||IGBT fault|
|GEM 0010||Long (10 s – 30 s)||100||160||40||60||48||IGBT fault|
|GEM 0011||Long (10 s – 30 s)||100||160||40||60||38||IGBTfault|
The global model of the losses in the power chain is implanted under the environment of Matlab/Simulink according to the figure 3 :
3.2. IEs Converter
The converter with electromagnetic switch has the advantage of a good quality of the armature voltage delivered by this type of the inverter and to the absence of power dissipation by conduction and switching.
The structure of a converter arms to electromagnetic switches equipped with the average power control circuit is illustrated by the following figure :
The operating sequences of the power converter to IEs are illustrated by the following figure:
The copper losses dissipated by the control coils are given by the following relationship:
Wherein nm is the number of coils unit for controlling an inverter arm, Rp is the protection resistance of the coil control, Rbob is the resistance of the control coil, I is the excitation current of the control coil and ρ is the duty cycle of the control signals to the converter IEs given by [2-8]:
The power transferred to the movement of the rod is estimated by the following relationship:
Where Vt is the speed of the rod.
Hence the losses in the control coils (Pea) are expressed by the following equation:
Where Tr is the time delay in the closing and opening of the shaft.
The model of the total losses in the static converter IEs is implanted under the environment of Matlab / Simulink according to the following block diagram:
3.3. Model of the Power Converter
The model of the power converter based on the comparison of the reference voltages (the voltage of the motor so that it can develop the necessary torque to the movement of EV), regulator outputs of the phase currents, to a triangular signal with fswfrequency less than the frequency of opening and closing of the electromagnetic switches relies [1-12].
Where nq is the quality factor of supply voltages and fie is the frequency of delay to the opening and closing of the electromagnetic switches:
The output signals of three comparators pulsate to the rhythm of the reference voltages. These signals are attacking three hysteresis of between +Udc and -Udc to reproduce the shape of the supply voltages supplied by the power converter.
The delay in the opening and closing is modeled by a first order transfer function with unity gain and time constant equal to Tr.
4. Simulation Results
Figure 8 shows the evolution of total losses for the power train, the first with IGBT and the other with electromagnetic switch (IEs).
Figure 8 show that the total losses of the IGBT structure are much higher than those of the IEs structure. From these results we deduce that the average efficiency of the IGBT structure is much lower than that of the structure in IEs.
The average yield of the IGBT structure, without considering the losses in the inverter is about RIGBT = 0.92 and R'IGBT = 0.82 while considering the losses in the inverter.
The yield structure of the IEs (RIes = 0.94) is significantly higher than that of the IGBT structure. So we can conclude that the structure IEs is more economical than the one IGBTs.
In this article, we presented a comparative and selective study of twopower chain structures, one with IGBTs and the other with IEs. Indeed, a loss model in the power chainin both cases structuresshowed that the structure with IEs dissipates much less power than in IGBT and this is due mainly to the size of the losses in the converter to IGBTs.
Finally, the power chainwith IEs is chosen to solve the problem the electric traction having less dissipative and cheaper compared to the one IGBT. This power train equipped with the recovery system also modeled on Matlab / Simulink environment therefore present an attractive solution to the problem of electric vehicles drive.