Week-4 Challenge WOT Condition Part-2

Aim:

1. What is the difference between mapped and dynamic model of engine, motor and generator? How can you change model type?

2. How does the model calculate miles per gallon? Which factors are considered to model fuel flow?

3. Run the HEV ReferenceApplication with WOT drive cycle. Change the grade and wind velocity in the environment block. Comment on the results.

4. Keeping all other parameters same, compare the simulated results of hybrid and pure electric powertrains.

Problem #1

What is the difference between mapped and dynamic model of engine, motor and generator? How can you change model type?

Mapped models are basically models which has a dataset of outputs mapped corresponding to the given inputs. These data sets or lookup tables are mapped or generated in real world experiments whose outputs are calculated and stored to form these datasets corresponding to different inputs given during the experiments.

Dynamic models on the other hand are real-time simulation models and does not have datasets of outputs stored corresponding to the given inputs. Random inputs are fed and model simulates to give results based on the inputs. It simulates using real world scenarios in form of subsystems and blocks to give the output.

To demonstrate an example, below you can see that mapped model and dynamic model both co-exist together in the motor block with mapped model(above) being active and dynamic model(below) being inactive for the given simulation.

Now, on clicking on the mapped model, we can see as shown below, that different inputs such as Battery voltage, Motor speed and torque command is taken as input and fed into the lookup table to give outputs such as, Battery current and motor torque.

While on the other hand, in case of dynamic model when clicked shows model as below.

As you can see in above model, number of inputs have increased and instead of feeding the input to the lookup tables, these inputs are used to calculate the same outputs as received from the mapped model but in this case, calculated under real- time simulation.

To change the model type, go the motor model blockset, Right-click, Go to Variant, Click on Label Model Active case and then click on Mapped or Dynamic model as per requirement. A picture depicitng the same is shown below.

Here we took the example of motor. But the same implies to engine and generator since both comprises of mapped and dynamic models.

Problem #2

How does the model calculate miles per gallon? Which factors are considered to model fuel flow?

For this problem I have taken model Hybrid Electric Vehicle Input Power Split Reference and to understand how model calculates miles per gallon follow the path as shown in the figure given below

HevIpsReferenceApplication-->Visualization-->Performance Calculations

To understand how miles per gallon is calculated, see the picture below

There are 3 inputs which give outputs in 2 forms i.e. miles/gallon and km/L

The 3 inputs are as follows,

1. Vehicle Speed(m/s)

2. Fuel flow(kg/s)

3. Battery Power(W)

Now, vehicle speed is converted into miles and divided by volume obtained by dividing the kg of fuel(California PhaseII Gasoline) with its density and then converted into gallons to obtain miles/gallon.

Secondly, W is converted into equivalent kg/s of fuel and then added to actual fuel flow to obtain km/L.

Factors that are considered for fuel flow includes vehicle velocity, fuel flow and battery power. Battery power is converted into equivalent gasoline flow and then the fuel flow is calculated.

Problem #3

Run the HEV ReferenceApplication with WOT drive cycle. Change the grade and wind velocity in the environment block. Comment on the results.

For this problem, Hybrid Electric Vehicle Multimode reference application is taken with WOT Drive Cylce as shown in the figure.

Now the simulation is run with first case

i) Grade = 0; ii) Wind Velocity = 0

The results are as follows

From the above figure we can see that, since no grade or wind velocity is present, vehicle is able to achieve its maximum speed with battery power itself. We can see that, the yellow line in Trace velocity curve represents wide open throttle but the velocity curve does not correspond to the curve and instead takes time to reach maximum speed. This is due to maximum motor power. Had the motor power been more, with more Ampere, maximum velocity would have been reached earlier.

Now for the second case

i) Grade = 10 ; ii) Wind Velocity = 10

The results are as follows,

From the above figure we conclude that desired velocity is not achieved and power of the battery is not sufficient enough to run the vehicle. This is the time when engine plays its role during which the battery is charged. Also during braking, current goes to negative which indicates regenerative braking. All this charge the battery which can now run extra miles which would have been difficult in the absence of engine. As the velocity is increasing, i.e. acceleration, Battery current increases and decreases during decceleration and even goes to negative implying that the battery is recharging.

To understand what happens, here I take two points 1 and 2 as shown below,

As velocity decreases from 1 to 2 current decreases and goes below zero that shows regenerative braking i.e. charging the battery. Also as engines runs during this period, battery SOC is increasing, i.e. battering is charging and battery current is also negative implying the same.

Problem #4

Keeping all other parameters same, compare the simulated results of hybrid and pure electric powertrains.

For this problem, Electric Vehicle reference application is taken with WOT Drive Cylce as shown in the figure.

Now, after running the simulation the result comes out to be as shown below.

Case 1:

Grade = 0 and Wind Velocity = 0

From both the figure, we can see that both take approximately same speed to accelerate to maximum speed.

It can be noted from the above that in case of HEV, the Battery current has a curve that runs between 500A and -100A where as in case of EV the battery current curve runs between 250A and -150A. This is because initially motor takes the load and later engine supports due to which maximum speed in case of HEV achieved is more than that in the case of pure EV.

Grade = 10 and Wind Velocity = 10

From the figure we can see that the current is negative for more amount of time in case of HEV which shows better regenerative braking and battery charging than in the case of Pure Electric Vehicle which concludes that the regenerative braking is better in case of HEV.

Conclusion: Differences between Mapped and Dynamic models have been explained and difference between Pure EV and HEV have been explained and supported with graphs.