8/10/2019 report_HV

1/8

Simulation of an electric vehicleEMR and IBC MATLAB/SIMULNIK

Abstract:

In this report we will present the the modeling and simulation results of an electrical vehicle

using the Energetic Macroscopic Representation (EMR) and its Inversed Based Control(IBC).

Introduction

The studied electric vehicle (EV) has a traction system that consists of the following

elements:

Batteries (NiMH 9.6kW module)

Power converter (4 Quadrant DC/DC converter)

Electrical machine (DC permanent magnet machine)

Shaft Gearbox

Differential with the wheels

Chasis

Sources:

The energy sources in this study are NiMH batteries used for powering the DC machine.

Environment:

The environment of the vehicle is considered as a mechanical source. This source yields a

resistant force which consists of three components defined as:

Other elements are represented with their mathematical equivalents:

Shaft:

Because we work with the assumtion that all rotating masses have a negligable inertia, there

will be no need to model the shaft.

Gearbox:

Where

8/10/2019 report_HV

2/8

Differential :

Wheels :

If we assume that the vehicle will drive only in a straight direction we can represent the

wheels of the wehicle with only one equvalent wheel and therefore we have :

4-quadrant converter :

Permanent Magnet DC machine :

Chasis :

8/10/2019 report_HV

3/8

The used values for the parameters in this case are:

The obtained EMR with its full IBC structure is obtained and represented in the following

figure (Figure 1):

Figure 1

Analysis of the obtained results:

In the first case we will consider only the implemented EMR model without the IBC. In order

to observe the behavior of the model we will consider a step change of the modulation factor

of the converter where the initial value is 0.8 (this will provide us a positive current andtherefore the acceleration of the vehicle in one direction) and after 100 sec the step change

will occur and set a new value being 0.4 (this will provide us a negative current and the

movement of the vehicle in the opposite direction). The obtained results are presented in

figure 2 where different areas are identified and will be explained.

The violet curve in the figure represents the speed profile which has to be followed. Because

we havent implemented the IBC this is right now not achieved. In the first 100 sec of the

simulation, because of the modulation factor, we have the positive speed which is represented

in the figure with the yellow curve. Because we have obtained a certain speed the distance of

the vehicle from its initial point will linearly increase during time, this is shown in the same

figure. After a certain distance our vehicle has arrived to a positive slope which is alsopresented, but in this case as a step function. This can be validated by analyzing the speed in

the area marked as A. In this zone we can observe that our speed has decreased which is

logical if we take into account the fact that our vehicle is on the positive slope and therefore

the gravity will slow down the speed of the studied vehicle. By analyzing the distance we see

that our vehicle is still moving.

8/10/2019 report_HV

4/8

Figure 2

At the time t=100 sec our simulation takes the step change into account and the modulation

factor gets the value 0.4 which corresponds to a negative current and therefore the change of

direction for the vehicle. This can be observed in the marked zone B where the speed has a

negative value as well as in the distance profile where the distance decreases (the reference is

the initial starting point). We can also observe that after a while our speed slightly decreases

which corresponds to the moment when we are no longer on the slope and therefore there is

no additional speed due to the gravity. Afterwards we have a constant negative speed and that

means that our vehicle is going backwards which again is seen from the distance profile.

8/10/2019 report_HV

5/8

The second analysis of our simulation will be done according to the measured voltage and

current of the vehicles battery and its state of charge (SOC). This is shown in figure 3 where

again some characteristic areas are identified and will be explained.

Figure 3

From the previous figure we identify the zone C which corresponds to the condition where

our vehicle starts accelerating in one (positive) direction while still not reaching the slope. As

expected the SOC is decreasing and therefore we are extracting energy from our battery.

Looking at the marked areas C and C which corresponds to the battery voltage and current

respectively we see that at the very beginning there is a sudden increase of the current and at

the same time a decrease of the voltage. This has a physical meaning due to the start of the

vehicle. During the time where we do not reach the slope (C and C) the voltage and currentstabilize to a certain value. At the moment we reach the slope (D and D) we see that

8/10/2019 report_HV

6/8

discharge current increases and the battery voltage decreases. Also we see from the SOC

(zone D) that our battery discharges faster which is the consequence of demanding more

energy from the battery in order to climb up the slope. At the moment where we suddenly

change the modulation factor and force our vehicle to go backwards we see that there is a

peak change in the battery current and voltage (the unnamed zone between D and E as well

between D and E). In the zone E we observe a negative current which actually representsthe charging current of the battery (regenerative braking mode). This has as a consequence

the increase of the battery voltage (E) as well as the charging of the battery. This is seen in

zone E where the SOC increases. After reaching the flat ground (the vehicle is no longer on

the slope) we see that again the battery is discharging in order to move the vehicle in the

opposite direction as well that the current again has a positive value.

From the previous analysis we conclude that our implemented model responds to the

environment in an expected way according to the physical limitations and therefore we

conclude that it is valid. In the next step we proceed to the definition and implementation of

the IBC.

Design of the IBC structure

From the EMR we can identify one tuning parameter which is the modulation factor of the

converter. The corresponding tuning path is:

The speed profile of the vehicle will be our reference quantity and it is defined as a look-up

table. The implemented SIMULINK block diagram with the IBC is presented in figure 4.

Figure 4

By analyzing the given EMR we identify two energy storage elements (armature windings of

the PM DC machine and the chassis of the vehicle) which in the IBC are represented with

two conventional PI controllers. All the other elements are direct inversion elements. In the

first approach we set the gains of the PI controllers arbitrary to see how our simulation will

perform. After some trial and error we derived some values for the parameters and the

simulation result which is given in the figure 5.

We can observe that after implementing the IBC the speed obtained from the vehicle matches

the given reference. By having a better look at the given speed profile and the obtained one

we see that there is a small mismatch (due to the response speed of the controller) but still inthe global view we can say that the designed IBC fulfils its role in an appropriate way. Also it

8/10/2019 report_HV

7/8

is clear that the distance profile behaves as expected (no change of distance when there is no

speed).

Figure 5

Figure 6

8/10/2019 report_HV

8/8

If we analyse now the battery SOC, voltage and current we can obtain the following results

which are represented in figure 7.

Figure 7

From the previous figure we see the changes in the voltage and current profile which indeed

correspond to the obtained speed profile. The relatively high changes (peaks) of the battery

current correspond to the sudden change of the speed (this is plausible because in order to

maintain the desired speed). We also observe the change of the current due to the presence of

the slope after a certain distance. The current has a constant value only during the time where

a constant speed has to be maintained. We note also some time periods where the current has

a negative value which is a direct consequence when the vehicle decreases its speed or when

it is on the negative slope. Again, this negative current represents the charging current of the

battery which is also shown in the SOC profile. By analyzing the voltage profile we see that it

corresponds to the battery current and in fact its shape is similar to the current profile. Thevoltage changes can be explained due the internal resistance of the battery.