Week-4 Challenge WOT Condition Part-2

AIM:- 1) To describe the difference between the mapped and dynamic model of engine, motor, and generator & to change the model type.

          2) To describe how the model calculates miles per gallon.

          3) To run the HEV ReferenceApplication with the WOT drive cycle & to change the grade and wind velocity in the environment block for studying the effect on the vehicle. 

          4) To run the pure electric powertrains. 

QUESTIONS:-

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

Mapped Model:-

The mapped model uses preassigned data only in lookup tables means it runs on the data which is predefined for the model and has not real-time considerations. As it runs without considering the real-time parameters, it takes less time for simulation. But the output is not as accurate as of the dynamic model. This type of model is suitable when we do not know the input values on our own. And the outputs we get correspond to given predefined input values.  

In the case of the engine, Mapped engines represent macro engine behavior as a set of lookup tables (brake torque, fuel flow, air mass flow, exhaust temperature, efficiency, and emissions) as functions of commanded load and measured engine speed.          

Dynamic Model:-

The dynamic models generate the final output by combining the output of various subsystems which is fed as an input in real-time for the simulations. The new input values for the simulation changes according to the feedback of the systems from the previous results. The simulation in the dynamic model takes a longer time than the mapped one cause there are many individual simulations that occur at the same time for different data. But the accuracy of these type of models are high as it considers the real-time output of subsystems like engine, motor & generators for the final output of the system.

For Ex, in the case of the engine, Dynamic engines decompose engine behavior into individual component models that account for engine dynamics, most notably intake airflow and turbocharger dynamics.

To change the Model type:-

In the Simulink, Go to Modelling – System Design – Variant Manager.

There are Many Submodels we can see.

Now, In the passenger car, there are submodels called Electric Plat & Engine. In the Electric plant, there are Generator & Motor submodels from which we can change from the mapped model to a dynamic.

As the default setting is the Mapped model. Just right click and click on “ Set as Label Mode Active Choice” to change from the Mapped model to a Dynamic Model & vice-versa. The same method is for Engine Model also.

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

MPG stands for miles per gallon. It is used to give you an indication of the fuel economy of a car or commercial vehicle  i.e. it is used to show how far your car is able to travel for every gallon (or 4.55 liters) of fuel it uses.

To calculate the fuel flow, vehicle speed & battery power are taken into consideration.

HEV model has separate blocks to calculate the miles per gallon which are shown below.

The above MPG calculations are for HEV which means it contains both fuel & battery energy.

First, we get battery power in watt which is converted in kWatt & further convert into energy in kWh.

Then it is converted into US gallon equivalent energy by dividing it by standard value 33.7. Then it is converted into US gallon per second.

It is multiplied by standard value 0.00378541 to get the volume in `m^3` per gallon & it is added to fuel flow for total value as it is an HEV.

Further `m^3`  is converted into US gallon.

On the other hand, the speed of the vehicle is integrated to get distance and the distance which is in the meter is converted into miles by multiplying the standard value 0.000621371.

And finally, MPG is calculated by dividing the US gallon by miles.

Note:-  In the case of pure Electric Vehicle (EV) the term Miles Per Gallon Equivalent (MPGe) is used.

            While the use of MPG and other measures of fuel efficiency work well for liquid fuels, MPG is not a useful measurement for electric, compressed natural gas, liquid natural gas, or hydrogen fuel cell vehicles since those sources of power are not sold by the gallon. This makes it difficult to compare fuel economies of vehicles using alternative fuels. This problem is resolved by introducing a gasoline gallon equivalent (GGE) or diesel gallon equivalent (DGE) - defined to be the amount of an alternative fuel needed to equal the amount of energy in one gallon of gasoline or diesel, respectively. The definitions used by the United States for fuel economy purposes.

            The above table contains the amount of various alternative fuels equal in energy to one gallon of gasoline or one gallon of diesel (GGE or DGE). Units are first given in the official government-defined units and then in SI (metric) units.

            Here the value 33.7 kWh is the battery power required to get the energy equivalent to the energy which is obtained by consuming the 1 gallon of gasoline. It is calculated by the United States Environmental Protection Agency (EPA).  

            A study about electric fuel conversion is provided through the reference mentioned in the report. 

Below are the sample Stickers Provided by EPA for some HEV & EV vehicles:-

1) For HEV: HEV has both MPGe & MPG notations cause it works on both conventional gasoline engine & Battery Electic power as well.

2) For pure EV: Pure EV has only MPGe notation cause it works on Battery alone.

                  All the notations are discussed through the references mentioned in the report below.                    

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

HEV Reference Application Model with WOT:-

Simulink Model for HEV:-

WOT conditions:-

Environment Conditions:- Grade = 5; & Wind Velocity = 10 m/s

Result:- Below results can be seen through the scope in the Visualization block.

1) HEV with WOT with default Environment conditions.

2) HEV with WOT with Environment conditions.

From the above results;

Graph 1:- Trace velocity – Target vs Actual

                  The yellow indication is the target path and the blue indication is the actual vehicle speed. Here it is seen that vehicles requited around 20 sec to attend the maximum speed toward the target path by using battery power own. After that vehicle starts to decelerates.

Graph 2:- Engine, Motor & Generator Speed.

                  As the battery is fully charged,  at initial condition, only motor speed (blue indication) is used which high at starting because of resistance due to slope & wind velocity. The engine speed (yellow indication) is overlapped with generator speed (orange indication) indicating both running at on the same rpm. Initial there is no need for engine  & generator speed as the motor is fulfilling the requirement to achieve the maximum speed of the vehicle. Therefore they are at 0 rpm. But when the battery will discharging Or when the State of Charge (SOC) becomes below 70% then only Engine will start to rotate to provide & maintain the speed of the vehicle & so far generator will also start to charge the battery at the same time. Hence their rpm are the same.

Graph 3:- Engine Torque, Motor Torque & Generator torque

                  As the battery is being used at the start, so torque will also maximum for the motor in this case until the vehicle acquires its maximum speed. Once the vehicle reached at a constant speed, the torque requirement will reduce. Here also when there is deceleration, the torque value becomes negative indicating no need of toque. Also, it becomes constant once the battery goes into charging state cause now, here Engine torque is being used due below 70% SOC. Also, generator torque will be negative indicating that Electric Motor is charging & in this period Engine has overcome the torque requirement of the vehicle successfully.

                  Blue indication – Motor Torque

                  Yellow indication – Engine Torque

                  Orange indication – Generator Torque

Graph 4: - Battery Current

                  Battery current is a simple term. When a vehicle uses Electric Motor then only it is used to generate power for the Motor. When the vehicle decelerates, then no current is extracted to produce power for the motor. From the graph also you can see, the current requirement becomes stable while charging the mode of the battery.

Graph 5:- SOC

                   Sate of Charge (SOC) is important for battery-driven vehicles. From the graph, it can be seen that when the battery used is bellowed 70%, it goes in charging mode & hence SOC is also increased due to charging of the battery through the generator. Hence it can be used further once it gets fully charged.

Graph 6:- MPGe

                 The graph shows the miles per gallon equivalent require to run the vehicle.

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

EV Reference Application Model with WOT:-

Simulink Model for EV:-

WOT conditions:-

Environment Conditions:- Grade = 5; & Wind Velocity = 10 m/s

Result:- Below results can be seen through the scope in the Visualization block.

From the above graphs:-

Pure EV can achieve less velocity than that of HEV. HEV can attend velocity above 60 mph but in pure EV velocity is less than 60 mph.

Motor speed in rpm is also less than that of HEV. But path tracing is the same as that of HEV.

But Motor torque of pure EV is almost the same as that of HEV.

Battery current uses is almost half in pure EV to produce power as that of HEV.

Also as battery use is less, battery draining is low & it can be seen from the SOC graph. From the SOC graph, it can be seen that for the same parameters battery uses is 5 times more in the case of HEV than that of pure EV, battery drains fast in the case of HEV.

Fuel economy is also almost double in the case of pure EV than that of HEV.

CONCLUSIONS:-

                    In this report, we have successfully studied HEV & Pure EV Vehicle models along with a change in output w.r.t change in input conditions. And also benefits of EV at some extend are known over the traditional gasoline engines.

REFERENCES:-

https://www.mathworks.com/help/autoblks/ug/explore-the-electric-vehicle-reference-application.html 

https://www.mathworks.com/help/autoblks/ug/explore-the-hybrid-electric-vehicle-multimode-reference-application.html 

https://www.edmunds.com/fuel-economy/decoding-electric-car-mpg.html 

https://www.epa.gov/fueleconomy/plug-hybrid-electric-vehicle-learn-more-about-new-label 

https://www.epa.gov/fueleconomy/interactive-version-electric-vehicle-label