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1. What is the difference between mapped and dynamic model of engine, motor and generator? How can you change model type? The power train block set has two model of combustion engine: a. Mapped Engine b. Dynamic engine Mapped engine is the inbuilt or default setting in the power train blockset. It represents the…
Jiji M
updated on 09 Jun 2022
1. What is the difference between mapped and dynamic model of engine, motor and generator? How can you change model type?
The power train block set has two model of combustion engine:
a. Mapped Engine
b. Dynamic engine
Mapped engine is the inbuilt or default setting in the power train blockset. It represents the macro engine behavior as a set of lookup tables. In this model, the data points are pre-assigned look up tables. The look up table values are based on the values of brake torque, commanded torque and engine speed. Since the performance parameters are measured using the standard values fed in the look up tables, this model is less accurate. However, the model is very fast and takes less time for simuation since there are no real time parameters considered. The engine or motor torque required is sensed and motor (or engine) generates the required torque output, without considering the real-time parameters. The output values are stored with respect to the respective input values.
Dynamic engine splits the engine behavior to individual component or individual subsystems that account for engine dynamics. This model uses the real time data given by the user for modelling. Since the realtme data is used for modelling, the simulation will be time consuming, however the output will be accurate. The required input is taken from the drive cycle and the realtime simulation for each individual subsystem is carried out and summing up all the results will give the output of simulation.
Mapped Motor works in torque control mode. Here, the output torque and reference torque is compared and changes are made. This type is mostly used when we need faster simulation and if there are no known parameters.
Dynamic Motor uses 3 phase input Voltages to regulate individual phase currents, allowing control of motor torque and speed. This type is used when the parameters are known and the output will be more accurate.
Mapped Generator takes the data from the lookup tables corresponding to the given input parameters. It takes less time for simulation.
Dynamic generator will receive the parameters entered by user manually during run time, and this model output will be more accurate even though the simulation is time consuming.
To change the model from dynamic to mapped and vice versa, we need to open the EV model first:
Then open the passenger car block:
Then open the electric plant block:
Then right click on the motor block and we will see an option "Variant", when we click on variant there will be "Label mode active Choice", where we can select either mapped or dynamic model:
Another way to switch the model is through "Variant Manager" in "Modelling" Section:
Open variant manager and there will be all the subsystems listed:
Then right click on the required model and select "Set as Label Mode Active choice":
We can use either way to switch between mapped and dynamic models.
2. How does the model calculate miles per gallon? Which factors are considered to model fuel flow?
Miles per Gallon(MPG) is a measure of fuel economy which determines, how far a vehicle can travel on a gallon of fuel (petrol or Diesel). Miles per Gallon equivalent(MPGe) is the measure of average distance travelled per unit of energy consumed.
Fuel efficiency for Gasoline vehicles are calculated in MPG, where as in Hybrid electric vehicles, the efficiency is calculated in MPGe(miles per gallon equivalent). MPGe is calculated by finding the number of miles a vehicle can go by using gallon of gas. Environmental Protection Agency has calculated that 33.7 KWh of electricity is equivalent to 1 Gallon of gas.
1 Gallon = 33.7 KWh.
Open the performance calculations in the EV reference block, and we can see the MPG calculation in that block.
In this model the inputs considered are:
Vehicle speed, Battery Power and Fuel flow.
The factors considered to model fuel flow can be fuel economy and fuel consumption.
Fuel economy is measured as MPG (Miles Per Gallon). It is a measure of how far a vehcle will travel with a Gallon of fuel. It measures distance travelled per unit of fuel.
Fuel consumption is the amount of fuel used to cover a given distance. It can be the inverse of fuel economy. It is used as a direct measure of volumetric fuel savings and is a fundamental engineering measure.
Vehicle speed in mps is converted to miles by multiplying with 0.000621371.
Fuel in Kilograms is converted to cubic meter by multiplying with 1 / (1000*0.739) and then to Gallons by multiplying with 264.172
Battery power is converted to KWh and then to Gallon equivalent by dividing it with 33.7.
The value is then divided by 3600 (to get the output per second) and multiplied by 0.00378541 to get the cubic meter per Gallons.
3. Run the HEV ReferenceApplication with WOT drive cycle. Change the grade and wind velocity in the environment block. Comment on the results.
Here, we are using the HEV Multimode Reference Application with WOT drive cycle for the study.
First, the drive cycle block is opened and the drive cycle source has been changed to WOT drive cycle along with changes in parameters, like nominal reference speed, deceleration time, etc.
Now changing the wind speed and grade to 10, from the environment block.
The following graph has been plotted according to the changes made.
From the first graph, it can be seen that the battery power is not meeting the desired changes that was made to the wind speed and grade. From the battery current graph, we can see that the current increases, when the vehicle starts accelarating and when the vehicle is at constant speed, the current remains constant as well. However, when the vehicle is decelerating the current drops and that indicates the point of regenerative braking. When the vehicle is decelerating the current value drops to negative. When the vehicle starts decelerating, the regenerative braking starts, after which the battery SOC will increase. Battery SOC graph shows that it is depleting till regenerative braking starts. Engine speed, motor speed and generator speed graph shows that the motor is used to start the vehicle as it has high initial torque. After a certain point, the battery SOC shows a gradual drop, at that point, the generator starts to work and charge the battery, which is the reason of the drop in Battery SOC. The torque of the motor is initiall high and then generator starts to work, after which the motor torque is decreased and this is shown in the torqur graph of engine, motor and generator.
4. Keeping all other parameters same, compare the simulated results of hybrid and pure electric powertrains.
Here, we are using the HEV Multimode Reference Application with WOT drive cycle and EV Reference Application with WOT drive cycle, with wind speed and grade 10.
EV Reference Application with WOT drive cycle:
Changing wind speed and grade:
The following graph has been plotted for EV with the changes made:
Comparing both graphs, it can be seen that the trace velocity and actual velocity graph for both HEV and EV appears to be similar as both works on motor initially. The battery current in both EV and HEV drops to negative value in regerative braking, however, in HEV the negatove current flows for more time after regenerative braking compared to EV. From the Battery SOC graph of both, it can be seen that the Battery SOC improvement after regenerative braking is higher in HEV than EV, since the battery current in EV remains negative only for small amount of time. The SOC improvement in EV is only for 2% or 3%, whereas in HEV, it is almost 15% or 20%. Since the battery power in EV is more than that of HEV, the motor speed is almost stable and not too much fluctuating, however, in HEV, the motor speed is too much varying from the start. And the peak value of RPM in EV is nearly 6000 rpm, whereas in HEV it is nearly 800 rpm. Since the electic motor is more efficient than engine, the fuel economy seems to be high in EV than in HEV.
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