Calculating Energy consumption{Software simulation in Scilab and Xcos} Part 1 - swapnilmankame1995/EV-course GitHub Wiki

The battery of an electric vehicle (EV) is one of the most important components since it dictates the dynamic performance, range and charging time of the vehicle. In order to calculate the size of the battery, we need two main inputs: the average energy consumption and the range of the vehicle.

1. Energy Consumption of a vehicle

There are two ways in which we can calculate the energy consumption of a vehicle

  • NEDC Testing
  • WLTP Testing

While the NEDC test determines test values based on a theoretical driving profile, the WLTP cycle was developed using real-driving data, gathered from around the world. WLTP, therefore, better represents everyday driving profiles.

WLTC drive cycle

The average energy consumption of the vehicle E-avg [Wh/km] will be calculated on a homologation cycle.

For our example, we are going to use the WLTC drive cycle. The test procedure WLTP (Worldwide harmonized Light vehicles Test Procedure) contains several driving cycles:

  • Class 1 – low power vehicles with PWr <= 22
  • Class 2 – vehicles with 22 < PWr <= 34
  • Class 3 – high-power vehicles with PWr > 34

Where PWr [kW/Tonne] is the power-to-weight ratio, defined as the ratio between the rated engine power and kerb weight.

CodeCogsEqn.png

Our target is to convert the Hyundai i10 vehicle into a battery electric vehicle (BEV). Therefore we need to understand what is the current energy consumption of the vehicle.

From the previous task, we can extract the maximum power and kerb weight from the spec table and calculate the power-to-weight ratio:

CodeCogsEqn (1).png

Since the vehicle’s PWr is bigger than 34, we are going to use the WLTC Class 3 driving cycle to calculate the energy consumption.

Speed-profile-for-WLTC-Class-3-driving-cycle.pngImage: Speed profile for WLTC Class 3 driving cycle

The parameters of the WLTC Class 3 cycle are summarised in the table below:

Low Medium High Extra High Total
Duration, s 589 433 455 323 1800
Stop duration, s 150 49 31 8 235
Distance, m 3095 4756 7162 8254 23266
% of stops 26.5% 11.1% 6.8% 2.2% 13.4%
Maximum speed, km/h 56.5 76.6 97.4 131.3
Average speed without stops, km/h 25.3 44.5 60.7 94.0 53.5
Average speed with stops, km/h 18.9 39.4 56.5 91.7 46.5
Minimum acceleration, m/s2 -1.5 -1.5 -1.5 -1.44
Maximum acceleration, m/s2 1.611 1.611 1.666 1.055

The method to calculate the energy consumption is straight forward and it makes use of the Scilab/Xcos simulation environment.

1. Setting up the Simulation Envionment

We will now need to install and Setup Scilab, Follow the steps below to install and set it up.

Step 1. Download Scilab

Click here to go to Scilab website, under the Download section and choose your installation package. For windows operating systems the are two versions: 32 and 64-bit. Download the one matching your operating system.

When the download is complete you’ll have on your disk drive a *.exe file (e.g. Scilab-5.4.0.exe)

Step 2: Run *.exe file

1_install_Scilab_Windows.png

Execute the downloaded *.exe file. Make sure that you have administrator rights on your operating system.

Click on the “Run” button.

Step 3: Select the language to be used during the installation process

Use the drop down list to select English

After the language selection, click on the “OK” button.

Step 4: Launch the Scilab Setup Wizard

3_install_Scilab_Windows.png

Click “Next” button.

Step 5: Read the License Agreement

select “I accept the agreement” and click on the “Next” button.

4_install_Scilab_Windows.png

If you press the “Back” button you’ll go to the previous installation step. Clicking on the “Cancel” button will abort the installation process.

Step 6: Review all installation settings

Click next till installation starts

Step 7: Launch Scilab

At the end of the installation, if you check the box for “Launch Scilab”, when you click the “Finish” button, Scilab will be launched.

Click the “Finish” button to exit the Setup Wizard.

12_install_Scilab_Windows.png

When you launch Scilab you’ll get the start screen as in the image above

2. Building an Environment

Create a folder Named "Electric vehicles" on the desktop, or where-ever you like.

This will be the folder where all our project files are stored.

Important note! unless all the required files are stored in the same folder, the simulation wont work.

3. Acquiring the WLTC Test cycle Data

Click on the link below to Download the data, Make sure you store it in the Electric vehicles folder created in the previous step.

Download WLTP-DHC-12-07e.xls

4. Importing xls (Excel) data into Scilab and Xcos.

There is a predefined Scilab function which can read the content of *.xls files. The Scilab function xls_read() reads a sheet from an Excel file and saves the data in the Scilab workspace.

The xls_read() function reads an Excel sheet given a logical unit on an Excel stream and the position of the beginning of the sheet within this stream. It returns the numerical data and the strings contained by the Excel cells.

The read_xls() function can be used to read all sheets from an Excel file in one function with a single function call.

The function can be called as:

[Value,TextInd] = xls_read(fd,Sheetpos)

where:

  • fd – a number: the logical unit on the Excel stream returned by xls_open() Scilab function
  • Sheetpos – a number: the position of the beginning of the sheet in the Excel stream. This position is one of those returned by xls_open()
  • Value – a matrix of numbers: the numerical data found in the sheet. The cells without numerical data are represented by NaN values
  • TextInd – a matrix of indices with the same size as Value. The 0 indices indicates that no string exists in the corresponding Excel cell. A positive index i points to the string SST(i) where SST is given by xls_open()

Dont worry, You dont have to type your own code! it will be given to you in the coming steps! this is just to make you understand what the code does

Important note: Only Excel file version (2003) are handled.

Let’s import the data describing the WLTP speed profile. The file can be found here:

The data will be first imported into Scilab, stored into a variable, and used later in Xcos for simulation purposes.

Step 1. Save the *.xls file after downloading, in the current Scilab working folder, i.e "Electric vehicles"

Step 2. Open the *.xls file and examine the data you want to import.

xls.jpg

In this example, the data is located in the second sheet, named WLTC_class_3. We will import the WLTP speed profile, which consist of time values and speed values.

  • The time values, in s, begin in the 8th row and 3rd column (C), with value 0.

  • The speed values, in kph, begin in the 8th row and 5th column (E), with value 0.0. If you scroll down towards the end of the table, you’ll see that the last data points are in the row 1808.

Step 3. Open SciNotes (Applications>Scinotes) and create a script file with the following content:

clear()
clc()
//Decode ole file, extract and open Excel stream
[fd,SST,Sheetnames,Sheetpos] = xls_open('WLTP-DHC-12-07e.xls');
//Read second data sheet
[Value,TextInd] = xls_read(fd,Sheetpos(2));
//close the spreadsheet stream
mclose(fd);
//load WLTP time and speed values in structure
WLTP.time = Value(8:1808,3);
WLTP.values = Value(8:1808,5);
//plot WLTP speed profile
plot(WLTP.time,WLTP.values)
xgrid()
xlabel("Time [s]")
ylabel("Vehicle speed [kph]")
title("Pupilfirst")

The file is opened with the Scilab function xls_open(). The data from the second sheet, Sheetpos(2), is read by the xls_read() function and assigned to the Value variable. Further, the WLTP time and speed values are assigned to the WLTP structure.

Notice that from the variable Value we extracted the data between rows 8 and 1808 and columns 3 and 5, as described in Step 2.

Save the Scilab script as *.sce file in the same Scilab folder ("Eectric vehicles" folder).

Step 4. Run the Scilab script and visualise the data.

After running the script we’ll get the following graphical image:

Graphic window number 0.png

As you can see, the data has been correctly imported, all 1800 time and speed values being plotted.

Now that we have our Simulation environment up and running! lets move on to simulating our energy consumption in our vehicle in the next chapter

Click here to continue to the next part