Week-4 Challenge WOT Condition Part-2

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

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

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

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

Solution:

 

1. Mapped Model (Static model):

 

The mapped model uses a steady-state lookup table (which is nothing but a set of predefined data sets) to characterize the engine/motor and generator's performance. It is generally used for the quasi-steady-state simulations.

 

 

 

 

 

Here the above is an example of a Mapped CI engine model using power, air mass flow, fuel flow, exhaust temperature, efficiency, and emission performance lookup tables (predefined values).

 

Dynamic Model:

 

Here the main model is decomposed into lower-level components. By combining the components this way the model captures the dynamic effects. This actually helps to analyze the individual engine components on the overall performance. This gives real-time data of the vehicle performance on the component level.

 

 

 

To change the model type from mapped to dynamic or vice versa, we need to follow these steps/procedures,

 

 

 

With the selection of the passenger car, then choose any model which needs to changed in this case I have chosen Electric plant

 

 

 

This is followed by choosing the Generator model,

 

 

 

after which we will be getting an additional sub-block,

 

 

 

 

 

By right-clicking the mouse we can change the mapped model or dynamic model using the variant selection.

 

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

 

Fuel Efficiency is an important parameter that helps determine the engine efficiency of the Vehicle. In case of the electric vehicle, Battery capacity (state of charge) is converted into miles per gallon for the Vehicle performance comparison.

 

Miles per gallon is different for every category of Vehicle. Here we are going to look into different categories of vehicles, one is Hybrid Electric Vehicle and the other one is a pure Electric Vehicle.

 

Hybrid Electric Vehicle Model:

 

 

 

The below model is obtained using the path mentioned in the attached image,

 

 

 

Based on the model it is observed that the Miles per Gallon is calculated based on 3 important categories,

 

a) Battery Power 

 

b) Fuel Volume Flow rate

 

c) Vehicle Speed

 

Battery Power: 

 

Based on the observation from the block diagram, the following steps have been carried out to convert the output value in m^3 per gal.

 

i) First the output value is divided by 1000, so that w can be converted into Kw. (product block is used)

 

ii) Kwh/USgal equivalent is obtained by dividing the end result by 33.7. (product block is used)

 

iii) Then Kwh to Kws is obtained by 3600. (product block is used)

 

iv) Finally using the Gain block the obtained result is multiplied with 0.0037 to get the values in m^3 per gal.

 

Fuel Volume Flow rate:

 

i) The value of the Fuel volume flow rate is added along with output obtained from the Battery power (m^3 per gal) using the sum block.

 

ii) The output obtained from the sum block is then using the Integrator block to m^3.

 

iii) The m^3 is converted into L by multiplying 1000 with it. Another output (US Gal) is also obtained by multiplying 264.17. This is followed by connecting it to the "Saturation" block.

 

Vehicle Speed:

 

i) Vehicle Speed is also an important parameter to determine the Fuel efficiency of the vehicle. Here in this block, it is observed that in order to avoid the negative sign in the input Vehicle speed by splitting the values and multiply the same using the product block. The same is taken square root (using root square block) to attain the same value without the negative sign. This is then followed by an integrator block to obtain the distance. This distance (in meters) value is diverted then into 2 routes one is to obtain the km and the other is a mile.

 

In the pure EV, the Miles per gallon is determined only by 2 factors,

 

a) Vehicle Speed

 

b) Battery Power

 

This is shown in the below model. The procedure to calculate the miles per gallon is the same.

 

 

 

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

 

As the question stated the drive cycle is changed from FTP75 to Wide Open Throttle.

 

 

 

The following are the parameters changed in the Wide Open Throttle drive cycle.

 

 

 

 Here I have not changed the Environment factors, the Grade and the Wind are kept zero.

 

 

 

After running the Simulation, the resultant graph is shown below

 

 

 

i) As the drive cycle is WOT and the speed data input is given in a step format, we can notice that the Target velocity increased steeply right after 1 second and ended abruptly after 60 seconds. Whereas the actual velocity is not matched with the target velocity mainly because of the limitations of the Battery capacity (maximum discharge capacity) and IC engine initial torque to propel the vehicle.

 

ii) Based on the graph it is observed the maximum battery capacity is 500 A which makes the Battery to provide more torque at the initial phase when compared to IC engine.

 

iii) After 40 seconds, the Torque from the Motor is reduced and IC engine gets stabilized. This is supported by the Battery discharge as well which is near 200 A

 

iv) During the braking, we can observe the motor speed and Torque is slumped whereas the Engine Torque remains the same. The motor torque and the Battery dropped to negative values indicate the "Regenerative braking" process happening in the HEV vehicle.

 

v) It is also observed that the BMS in this HEV vehicle is designed in such a way that the battery state of charge doesn't go below 58%, below battery get's charged through either IC engine or Plug in. 

 

vi) Maximum fuel efficiency is attained when the vehicle travels at the speed of 60-75 mph (12 MPGe)

 

In the second stage of simulation, I have changed the values of the grade and wind velocity as shown

 

 

 

The simulation results are shown here,

 

 

 

Observations: 

 

i) When compared to the previous result, the actual velocity has drastically reduced this due to the grade and wind velocity values.

 

ii) The fuel efficiency has also dropped significantly from 12 to 7 MPGe.

 

iii) Rest of the parameters are the same.

 

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

 

The below is a comparison of block diagrams used in the HEV and EV,

 

 

 

In the EV (on the right side) there is no IC engine, no separate motor and generator because in the case of EV the Motor itself functions as a generator during the regenerative braking. Hence one set of gear is sufficient for the EV.

 

so for the first case comparison, I have just changed the drive cycle to WOT with the same parameters as given in the HEV.

 

 

 

 

 

i) The first comparison is about the Target and Actual velocity, the graph seems to almost similar to that of HEV this is mainly because of the maximum discharge limit from the Battery, in this case, it is 200 A.

 

ii) Since here the Battery and the Motor are the only driving unit for this vehicle, the maximum Motor speed (RPM) is 12000 which is lesser than the HEV (which had 14000)

 

iii) Motor Torque at the initial level is lesser when compared to HEV [EV - 280Nm (Max) and HEV - 310Nm (Max)] because EV weighs lesser.

 

iv) Here the Fuel economy is higher when compared to HEV.

 

v) The rest are all the same, ie., the Motor Torque goes negative when there is a drop in the velocity and braking by then the motor acts as a generator and converts this mechanical into electrical energy and recharges the battery.

 

Now by changing the parameters of the Environment similar to the HEV model (adjusting the Grade and the wind velocity value)

 

 

 

i) After giving the values for Grade and wind velocity, the Actual velocity dropped much lower than HEV model. This is because HEV is powered by both the Battery and IC Engine whereas the EV mainly relies on the battery.

 

ii) Like in HEV the Motor speed and Fuel efficiency dropped drastically in the EV model because of the grade and the wind velocity values.

 

Conclusion:

a) Mapped system is a block where the simulation is run based on the predefined values (data's taken from the past records) whereas a dynamic system is a block where the simulation is run based on the performance captured from every small component that is coming under the system.

 

b) The difference between HEV and EV model is analyzed and captured based on the simulation results.