Week-4 Challenge WOT Condition Part-2

WOT CONDITION

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

Mapped Model: The mapped model uses a set of Data’s to calculate Engine performance. The Data’s include mostly “Lookup tables” for calculation of all the parameters inside the engine. For example the mapped CI Engine block implements a mapped compression–ignition (CI) engine model using power, air mass flow, and exhaust temperature, efficiency, and emission performance lookup tables.

Dynamic Model: The dynamic model doesn’t uses any predefined data’s for its calculation, instead that uses the data that are fed by user. This type of model is more accurate than a mapped model. Model decomposes the engine behavior into engine characteristics that are separated into low-level components. By combining components in this way the model capture the dynamic effects.

Mapped Engine: Mapped Engine is default settings in power train block set. It is used to measure performance parameters of the vehicle by using standard look up tables which are preferred to system. This type of model is less accurate, the look up tables value are based on the values of brake torque, commended torque and engine speed. If any other parameter like if input engine temperature selected the look up table values is also a function of temperature parameter.

Dynamic Engine: This type of data uses real time data fed by the user at run time for modeling. It is more accurate than mapped type. The data of subsystem of vehicle is required. We can calculate: Brake torque, fuel flow, gas mass flow.

Mapped Motor: The mapped motor works on the torque control mode. It requires a faster simulation and doesn’t have motor torque, the output torque and reference torque is compared and changes are made. Input torque and speed can be specified electric losses and maximum motor power and torque can be defined.

Dynamic Motor: The dynamic motor a three phase interior permanent magnet synchronous motor (PMSM) used, the block use three phase input voltages to regulate the individual phase current, allowing the control of the motor torque or speed.

Mapped Generator: The mapped generator block is also similar like other blocks. Most of the data required is taken from the look up tables corresponding given input parameters, and simulation time is less.

Dynamic Generator: The dynamic generator involves user entering parameters manually during the run time for their particular applications. The result time take and more accurate.

To switch between Mapped and dynamic model of any given vehicle, follow the following steps:

Open the model of desired vehicle

Click on the ‘passenger car’ block

Under ‘passenger car’ block click the ‘Electric plant/Engine plant’ block

Under that block you will see a ‘Motor’ block (in case of electric vehicle model) right click on that block

After that click on ‘variant’ and select ‘Label mode active choice’ option and select whether the ‘Mapped model’ or ‘Dynamic model’.

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

We can see this calculation in the ‘Visualization block’. This block calculate that how much the vehicle travel per gallon of fuel and in case of purely electric vehicle it calculate the distance travelled by a unit electrical energy consumed.

Above is the image of block that calculate the vehicle performance

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

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

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

HEV reference application with WOT drive cycle:

Use the command ‘autoblkHevstart’ in the command window to open the HEV reference application. The double click on the Drive cycle source block and then change the drive cycle to ‘WOT’ as shown in below figure. Also configure the parameters like time duration, WOT start time, initial speed, final speed, max speed and time to start declaration.

Change the wind speed and grade from the environment block.

From the below graph we can see that,

Following are WOT Analysis

Trace velocity target and actual graph: The yellow line indicates the desired path and blue line indicates the actual path. so it can be seen that battery power is not enough to meet the requirements of trace 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 declaration starts the battery current becomes negative indicating regenerative braking.

Battery SOC: The battery SOC keeps on depleting until regenerative braking starts then increases the SOC.

Engine motor and generator speed: Initially only motor is used to starts 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 overlapped with generator.

Engine motor and generator Torque: Motor torque is high initially (blue line) and then engine kicks in at later stage (yellow line), Generator torque (red line) is negative as its charging the battery.

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

Now simulating the EV vehicle with WOT drive cycle 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 both EV and HEV following conclusions can be drawn:

1.The first graph (Target and actual velocity graph) performance is almost same. The reason could be in that region only motor was operating so the performance in both EV and HEV is similar.

2. The battery current drawn by HEV initially is up to 500A and later decreases the 200A .This can be attributed to the fact that initially only motor takes all the load and later engine kicks in so motor load drops the current drawn by motor reduces. And during the declaration it is seen that negative current (regenerative braking) flows for a longer time HEV as compared to EV. So we can say that, regenerative braking is more aggressive in HEV.
3. SOC improvement of almost 15% is seen in HEV during declaration and only 2%improvement can be see in EV during acceleration. This can be understood by the same reason explained in plot 2.
4. 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 less than the HEV. These differences can attributed to the fact that battery power of EV is more than HEV vehicle.
5. Fuel economy of EV is significantly grater than HEV. This is because the electric motor is more efficient than engine.

Conclusions:

1. Thus all the objectives were achieved successfully.
2. Similar kind of approach can be followed to study similar models in SIMULINK and MATLAB.