Week-4 Challenge WOT Condition Part-2

1. Difference between mapped and dynamic model of Engine, Motor and Generator and steps to change model type:

Mapped Engine Model:

The term "Mapped" model basically refers to a model with a precalculated dataset for which the ouput values are readily available for the corresponding inputs. In simple words, the mapped models provide constant output values for constant input values. The values are mapped and stored as data points that are calculated using an actual dynamic model in practice. Mapped engine is a block in powertrain blockset. It is used to measure performance parameters of the vehicle by using standard lookup tables which are prefered to the system. This type of modelling is less accurate. The lookup table values are based on the values of brake torque, overall torque, fuel flow rate, engine-out exhaust emission, etc. This data is used to find out other parameters which are needed by the user. This blocks are used when we have engine data from a dynamometer or a design tool like GT-POWER and for quasi steady-state engine simulations. Below attachment provides the figure of mapped engine block.

Dynamic Engine Model:

A "Dynamic" model performs a real-time simulation of components that actually takes place in an original system to generate an output, depending upon random input situations. In otherwords, both the mapped and dynamic models take in the same input variables and give out same output variables but only difference is that the way on how the output data is generated in each case. Dynamic model decomposes the engine behavior into engine characteristics that are separated into lower-level components. By combining components in this way, the models capture the dynamic effects. This model is more accurate than mapped engine model. This type of models are used when the data of subsystems of a vehicle is required. If we need a more detailed dynamic model and have component-level data and to analyze the impact of individual engine components on the overall performance, we use the dynamic engine model.

Mapped Motor:

The mapped motor block is component in the powertrain blocksets and implements a mapped motor and drive electronics operating in torque-control mode. The output torque tracks the torque reference demand and includes a motor-response and drive-response time constant. The mapped motor block is used for fast system-level simulations when we do not know details of motor parameters for example, for motor power and torque tradeoff studies. The block assumes that the speed fluctuations due to mechanical load do not affect the motor torque tracking. we can specify input torque or speed which are the port configuration, electrical torque range which is the torque speed envelope or maximum motor power and torque, electrical loss. Below attachment is the mapped motor block.

Dynamic Motor:

In the dynamic motor, a three phase interior permanent magnet synchronous motor (PMSM) is used. The block uses three phase input voltage 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:

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

Dynamic Generator:

The dynamic generator involves user entered parameters manually during the run time for their particular applications.

Steps for changing model types:

We can use the variant manager in the modelling tab to find the variant systems available. Then right click on the model we want to use and select "Set as Label Model Active Choice" to select modes i.e., mapped or dynamic model or follow the steps below:

i) Open the powertrain module blockset for the required vehicle.

ii) Click on passenger car/vehicle block and select electric plant or engine.

iii) Right click on Engine/EV motor/generator based on vehicle model and select variant.

iv) Under variant, scroll to label model active choice and choose mapped or dynamic for the required calculation.

Below attachments are the respective figures representing the above steps.

2. To determine how the model calculate miles per gallon and factors considered to model fuel flow:

Miles Per Gallon(mpg):

Miles per gallon or mpg, is the distance measured in miles, that a car or a vehicle can travel per gallon of fuel. Miles per gallon is also the primary measurement of a car's fuel efficiency: The higher a vehicle's mpg, the more fuel efficient it is. As an example, if we have a vehicle that can return 50 mpg and its fuel tank only has one gallon of petrol or diesel in it, we should be able to drive 50 miles before the car runs out of fuel. Here, we have taken the "Hybrid Electrical Vehicle Input Power-Split Reference Application" is used for addressing the problem statement. Now, to find out how the fuel economy is calculated here is by the following path: HevipsReferenceApplication-Visualization-PerformanceCalculations. First a complete diagram is given then a graphical explanation is ahown to have a brief idea about the calculations with parameters and units. From the figures in the attachment, we can see that with the help of three inputs we are getting our only output which is the mileage, but in two different units. The inputs are Vehicle speed, fuel flow and battery power, the output we seek is the fuel economy. Since we have used the model of a HEV, both the fuel and battery contribute to its capability of covering distances, that is, its mileage or fuel economy. The battery power is converted from Watts to Kg/s of equivalent California Phase II US gasoline, which when burned gives the same power as the battery input. Both these sources of power are added in kg/s and integrated to find out the entire equivalent fuel consumed in kg which is converted to volume consumed. The entire distance travelled is further divided by the volume consumed for that distance. Factors that are required to model fuel flow are battery power, conversions from watt to cubic meter per gallon because it is a hybrid vehicle like Toyota Prius. The unit miles per gallon is a US standard unit and L/100 km is used by most European countries and in other countries like China, Australia, etc,.

Let us consider an example: A battery propells the vehicle for 3.125 miles per kwh capacity of battery. So,

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

So, therefore, 1 gallon of gas = 33.7 kwh of electricity.

So, as said above, battery power is first converted into kW (W/1000) then it is divided 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.

3. Run and observe the HEV Reference Application with WOT drive cycle and changing grade and velocity of the vehicle:

To perform the task and get output results of "HEV Reference Application" is simulated from the Matlab Powertrain block. We can either obtain the model from the help option or by using the command "autoblkHevStart" in the command window and open the model. Below figure is the model of HEV Reference Application. In the model, double click Drive cycle source block and then change the drive cycle to 'WOT' as shown in the figure. Also, configure the parameters like time duration, WOT start time, initial time, final speed, max speed and time to start deceleration. Now, by editing the grade and wind velocity values, we got following different results shown and also briefly explained. We can change the grade and velocity of the vehicle by double clicking the environment block in the model.

The parameters which are to be altered: Grade and Wind Velocity.

Observation:

From the simulations, a total of six types of data are monitored which are velocity of the vehicle with the desired velocity, speed of engine-motor-generator, torque production, battery current, battery SOC (State Of Charge) and fuel economy.

From the figure (a), velocity achieved the desired value well enough due to the absence of both grade and wind velocity values (both zero). But when two factors are present, like in figure (b), it can be seen from the graph that battery power is not enough to meet the requirements of the grade and wind velocity. So, the engine kicks in to provide extra power for the vehicle to maintain its speed. When the vehicle is accelerating the battery current is also increasing. When the velocity is constant the current requirement also become constant. This is because when the driver is applying the accelerator at the beginning itself, more power is utilised from the battery, that is, current drawn from the battery will be increased at this time. The opposite takes place during deceleration. During deceleration, the battery current becomes negative. This is because, during deceleration or braking, the power is fed back to the battery. The motor acts as generator and supplies or recharges the battery. This regerative braking is indicated by the negative value of battery current. The battery SOC keeps on depleting until the regenerative operation kicks in. When the vehicle is started, it is in the electric mode. So, when we (the driver) accelerates, more current is drawn from the battery hence the battery SOC reduces. When the vehicle is going to decelerate or in simple words, when the driver slows down or stops accelerating the vehicle and applies brakes, the vehicle decelerates and hence the traction motor acts as a generator and hence supplies power to the battery that is charges the battery. Hence at this time, as the battery is not supplying to the system, the depletion of battery SOC is increased during regenerative braking. Also, it can be seen that fuel economy is increasing of the vehicle because of this regenerative braking and charging of battery which ultimately gives us the ability to cover more miles.

Initially, only a motor is used to start the vehicle as the motor has high initial torque. Later generator kicks in charging the battery when SOC drops below about 70%. The engine graph cannot be seen as always because it has overlapped with the generator most of the time. From figure (c) and (d), we can see the motor torque is high initially and then the engine kicks in at a later stage. Generator torque is negative as it is charging the battery. These are present because the grade and wind velocity values demand more power from the vehicle. Higher the grade and wind velocity values, the more power is demanded from the vehicle and as a result, it becomes more difficult for the vehicle to keep up with its desired velocity. From the graphs, it is seen that higher values of these parameters, give the vehicle greater challenge and so the vehicle ends up not achieving the desired speed even with the full-throttle applied. The main observation we can see that grade value is dominant here because a change in this value slightly can give us a different result. From figures (c) and (d), grade value is same (15) but different wind velocities (10m/s and 15m/s). As we increased the wind velocity value to about 50m/s, in figure (e), the clear difference in the highest velocity achieved by the vehicle during the simulation which is way less that from figure (d).

In short, we can conclude the following:

i) Trace Velocity and actual graph: The yellow line in the graph 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 the grade and wind velocity.

ii) 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 regenrative braking.

iii) Battery SOC: The battery SOC keeps on depleting until regenrative braking starts. This increases the SOC.

iv) Engine, Motor and Generator Speed: Initially, only motor is used to start the vehicle as motor has high initial torque. Later generator kicks in charging the battery when the SOC drops below about 70%. Engine graph cannot be seen as it may have overlapped with generator.

iv) Engine, Motor and Generator Torque: Motor torque is high initially and then the engine kicks in at a later stage. Generator torque is neagtive as it is charging the battery.

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

A Hybrid Electric Vehicle (HEV) is a type of hybrid vehicle that combines a conventional internal combustion engine (ICE) system with an electric propulsion system (hybrid vehicle drivetrain). The presence of the electric powertrain is intended to achieve either better fuel economy than a conventional vehicle or better performance. There is a variety of HEV types and the degree to which each function as an electric vehicle (EV) also varies. The most common form of HEV is the hybrid electric car, although hybrid electric trucks(pickups and tractors) and buses also exist.

An Electric Vehicle (EV), also called electrics is a vehicle that uses one or more electric motors or traction motors for propulsion. An electric vehicle may be powered through a collector system by electricity from off-vehicle sources or may be self-contained with a battery, solar panels, fuel cells, or an electric generator to convert fuel to electricity. EVs include, but are not limited to road and rail vehicles, surface and underwater vessels, electric aircraft and electric spacecraft. Here in this case, we are going to simulate the EV with WOT drivecycle, wind velocity as 5m/s , grade as 5 degree and keeping the rest of the parameters same as above HEV case. Below figure shows about the model of the EV drivecycle and selecting WOT drivecycle and the performance graphs for various grade and wind velocity.

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

1. The first graph ( target and actual velocity graph) performance is almost same, the reason is that 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 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.

3. 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 above point.

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 is less than HEV. These differences can attributedto the fact that battery power of EV is more than HEV.

5. Fuel economy of EV is significantly greater than HEV. This is because electric motor is more efficient than engine.