Week-4 Challenge WOT Condition Part-2

Question 1.

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

Mapped Engine:

Mapped Engine is the default settings in powertrain blockset. It is used to measure to measure performance parameters of the vehicle by using standard lookup tables which are prefed to the system. This type of modelling is less accurate. The lookup tables value are based on the values of brake torque, commanded torque and engine speed. If any other parameter like Input engine temperature is selected then lookup table values are also a function of the temperature parameter. The data extracted from lookup tables are: air mass flow, fuel flow, emission data, exhaust temperature and efficiency. This data is used to find out other parameters which are needed by the end user.

Dynamic Engine:

This type of model uses real time data fed by the user at run time for modelling. This model is more accurate than mapped engine model. This type of model is used when the data of subsystems of a vehicle is required. We can calculate : Brake torque, fuel flow, port gas mass flow, exhaust temperature, exhaust mass flow rate and exhaust emissions.

Mapped Motor:

The mapped motor works in torque control mode. This type of motor is used when the user requires a faster simulation and doesn't have the knowledge of motor parameters. The output torque and reference torque is compared and changes are made. Input torque or speed can be specified, electrical losses and maximum motor power and torque can be defined.

Dynamic Motor:

In the dynamic motor a three phase interior permanent magnet synchronous motor (PMSM) is used. The block uses three phase input voltages to regulate the individual phase currents, allowing control of the motor torque or speed. This block is used when the user knows what parameters are to be used in that particular simulation. This motor is more accurate.

Mapped Generator:

The mapped generator block is also similar like other blocks. Most of the data required is taken from the lookup tables corresponding to the given input parameters. Its simulation time is less.

Dynamic Generator:

The dynamic generator involves user entering the parameters manually during the run time for their particular applications. The results take time and are more accurate.

To change the model from mapped to dynamic:

Go to Modelling then Variant Manager.

Suppose we plan to change the generator block from mapped to dynamic. Select GenDynamic then right click, then select 'Set as Label Model Active Choice'. Then double click 'GenDynamic'.

This process can be repeated for motor and engine.

Question 2.

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

MPGe:

In the US to compare the efficiency of gasoline vehicle with the BEVs, PHEVs or FCEVs MPGe unit was formulated. MPGe stands for Miles Per Gallon Equivalent. It has been found that 1 gallon of gas has the same amount of energy as 33.7 kwh of electricity.

Eg. A battery propells the vehicle for 3.125 miles per kwh capacity of battery. So,

3.125 miles/kwh * 33.7 kwh/gallon = 105 MPGe

In the model it is calculated by this block:

The inputs are vehicle speed, fuel volume flow and battery power.

The above image has two fuels electricity and fuel. As discussed earlier 1 gallon of gas equal to 33.7 kwh of electricity.

So battery power is first converted into KW (W/1000) then its divides by 33.7 kwh. The fuel equivalent of battery is added to the fuel flow. Using the vehicle speed and time the distance of travel is calculated. Then distance is converted into miles by conversions. Then as we have the fuel flow in m^3 and distance in miles. We can calculate the fuel efficiency.

Question 3.

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

HEV ReferenceApplication with WOT drive cycle:

Use the command 'autoblkHevStart ' in the command window to open the HEV reference application. Then double click Drive cycle source block and then change the drive cycle to 'WOT' as shown in the below image. Also configure the parameters like time duration, WOT start time, initial speed, final speed, max speed and time to start deceleration.

Change the wind speed and grade from the Environment block.

The following graphs are obtained for WOT analysis.

From the above graphs we can see that,

• Trace Velocity target and actual graph: The yellow line indicates the desired path and blue line is the actual path. So it can be seen that battery power is not enough to meet the requirements of the grade and wind velocity.
• Battery Current Graph: When the vehicle is accelerating the battery current is also increasing. When the velocity is constant the current requirement also becomes constant. When the deceleration starts the battery current becomes negative indicating regenerative braking.
• Battery SOC: The battery SOC keeps on depleting until regenerative braking starts. This increases the SOC.
• Engine, Motor and Generator Speed: Initially only motor is used to start the vehicle as motor has high initial torque. Later generator (red graph) kicks in charging the battery when SOC drops below 70%. Engine graph can't be seen as it may have overlaped with generator.
• Engine, Motor and Generator Torque: Motor torque is high initially (blue line) and then engine kicks in at a later stage (yellow line). Generator torque (red line) is negative as its charging the battery.

Question 4.

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

Now simulating the EV with WOT drivecylce, wind velocity as 5m/s, grade as 5 degree and keeping the rest of the parameters same as above HEV case.

We get the following performance graphs:

After comparing the graphs of both EV and HEV following conclusions can be drawn:

• The first graph (target and actual velocity graph) performance is almost same. the reason could be that in that region only motor was operating so the performance in both EV and HEV is similar.
• The battery current drawn by HEV initially is upto 500 A and later decreases to 200 A. This can be attributed to the fact that initially only motor takes all the load and later engine kicks in so motor load drops thus current drawn by motor reduces. And during the deceleration it is seen that negative current (regenerative braking) flows for a longer time in HEV as compared to EV. So we can say that, regenerative braking is more aggressive in HEV.
• SOC improvement of almost 15% is seen in HEV during deceleration and only 2% improvement can be seen in EV during deceleration. This can be understood by the same reason explained in point 2.
• Motor torque and motor speed are stable in EV and they keep fluctuating a lot in HEV during the starting. Also the peak RPM of the motor in EV is less than HEV. These differences can attributed to the fact that battery power of EV is more than HEV.
• Fuel economy of EV is significantly greater than HEV. This is because electric motor is more efficient than engine.