Final Project: Design of an Electric Vehicle
Answer :
Introduction
A new study related to Vehicle/Automobile engineering says that by coming 2025, there will be a major transformation in the automobile sector. Many automakers are working to change the vehicle technologies, the major area is to decrease the pollution and use electrification in the upcoming vehicles. The researchers and automakers are continuously working to reduce CO2 emissions.
New technology like high capacity lithium type battery will be a major energy source for the propulsion of electric vehicles.
At present, with the new technologies, some manufacturer has launched its products which are Tesla, Chevy Bolt EV and Nissan leaf which are fully electric battery-based car.
The power and performance of electric vehicles is depending upon the two machines i.e. a brushless DC motor (BLDC) or an induction motor. The DC (direct current) is replaced by DC brushless motors and Induction motors. Also, the lead-acid battery is replaced by lithium-ion batteries for EVs. Because the future of both the components induction or brushless DC motors depends upon their demands and uses.
The most important components of electric vehicle areas:
Traction Battery Pack:
A traction battery pack is also known as Electric Vehicle Battery (EVB) which is used to store the electricity –and to deliver the power to propel the vehicle through motor.
Some examples of traction battery energy storage systems are as given:
- Lithium-Ion
- Nickel-Metal Hydride
- Lead-Acid
- Ultra-Capacitors
Electric Traction Motor:
Another important component is the electric traction motor and this device is used to provide motive power to the wheels.
DC/DC Converter:
Basically, DC/DC converter is an electronic device that is used to convert higher-voltage DC power from the traction battery pack to lower-voltage DC power. The converted power is used to run the vehicle accessories. It is also used to recharge the auxiliary battery.
Onboard charger:
Takes the incoming AC electricity supplied via the charge port and converts it to DC power for charging the traction battery. It monitors battery characteristics such as voltage, current, temperature, and state of charge while charging the pack.
Charge port:
The charge port allows the vehicle to connect to an external power supply in order to charge the traction battery pack.
Power electronics controller:
This unit manages the flow of electrical energy delivered by the traction battery, controlling the speed of the electric traction motor and the torque it produces.
Auxiliary Battery:
In an electric drive vehicle, the auxiliary battery provides electricity to power vehicle accessories.
Thermal system (cooling):
This system maintains a proper operating temperature range of the electric motor, power electronics, and other components.
Transmission (electric):
The transmission transfers mechanical power from the electric traction motor to drive the wheels
BLOCK DAIGRAM OF AN EV :--
MATLAB model of Electric Vehicle;
The electric vehicle is constructed in a manner of four step-by-step processes, so to design of the EV model always starts within the order:
1) construction of vehicle body design
2)Selecting the motor
3)Suitable control unit for motor
4) Source of energy for motors: Battery.
(1) Vehicle Body Subsystem:--
The vehicle is assumed to be front axle driven (4 wheels - 2 on each axle).
The wheels are modeled using simple Tire (Magic formula) Simulink blocks.
The N port of the tire corresponds to the Normal Reaction acting on it.
The A port corresponds to the Mechanical Rotational conserving port for the wheel axle. Thus both the wheels on the same axle should form a connection through their respective A ports.
Connection H corresponds to the Mechanical Translational conserving port for the wheel hub through which the thrust developed by the tire is applied to the vehicle. Thus, all 4 wheels form a connection through their respective H ports and this is in turn connected to the translational hub of the vehicle body.
The connection S represents the output port for a slip of the tire.
The tires are parameterized by Load-dependant –magic formula coefficient - corresponding slip.
The other block parameters such as - rated vertical load, peak longitudinal force at rated load and slip at peak force at rated load - are kept with their default values.
The tire radius is given as 0.32m The tire inertia is kept as 0.5kg/⋅m^2
- Also, the rolling resistance is given with a constant coefficient of 0.015.
Axle :
This 2 axle (4 wheels) assembly is now connected to a Velocity Body simscape block
This block basically represents a two-axle vehicle body in longitudinal motion. The block accounts for -
body mass,
aerodynamic drag,
road incline,
weight distribution between axles due to acceleration
road profile.
Here, connection H is the mechanical translational conserving port hub.
NF & NR correspond to the output ports for normal reaction forces on the front axle and rear axle wheels respectively.
Connection V represents the actual output translational velocity of the vehicle.
beta is the road inclination angle & W corresponds to the headwind speed (headwind - direction opposite to that of the vehicle).
The gross weight is given to be
800kg.
The geometric parameters of the vehicle are given as –
to account for proper drag force on the vehicle, the related parameters are kept as above.
The pitch dynamics for the vehicle are not considered for this simulation.
The complete subsystem is shown below –
The input for this subsystem is taken as the Rotational speed of the motor. This input is fed to the front axle through a Simple Gear representing the Final Drive Ratio of 3.7
Here, the rotational direction of the output shaft is kep the same as that of the input shaft. Also, no meshing losses are considered for the simulation.
2) DC Motor :--
Simulink provides an inbuilt model block for a DC motor which converts electrical input into mechanical rotational output.
Note: Here, the blue colour corresponds to the electrical side of the motor and the green colour corresponds to the mechanical side.
Here, the motor field type is kept as a Permanent magnet and the model parameterization is done by rated load and speed.
The armature inductance and the mechanical parameters are given their default values.
All the other parameters are changed as shown below –
Mechanical Part parameters have been kept default values
Connection R represents the Rotor (rotational output) while connection C is for the Casing (stationary). Thus, the R port is connected to the input of the vehicle subsystem created earlier. The C port is connected to a mechanical rotational reference.
The + and - terminals of the motor are connected to the motor controller. If these terminals are directly connected to a battery, the required DC motor will run on the rated capacity of the battery. This will eventually result in no control over the DC motor and the vehicle will run at top speed throughout the simulation.
Thus, a motor controller is very much needed.
(3) Motor Controller:--
H-Bridge circuit –
This block represents an H-bridge motor drive. The block can be driven by the Controlled PWM Voltage block in PWM or Averaged mode.
In PWM mode, the motor is powered if the PWM port voltage is above the enabled threshold voltage.
In Averaged mode, the PWM port voltage divided by the PWM signal amplitude parameter defines the ratio of the on-time to the PWM period.
Connection REF is for the reference input. This combined with the PWM connected will form the pulse input for the H-Bridge.
Here, the REF input is connected to the Electrical Reference (ground).
Connection REV corresponds to the reverse motion of the motor which essentially means, the backward motion of the vehicle.
Here, the backward motion of the vehicle is not accounted for and so, the port is connected to the electrical reference.
Connection BRK is for the braking of the vehicle.
Since, the PWM mode results in a huge amount of simulation time, Averaged mode is selected for this simulation
Load current characteristics are considered to be smoothed here.
Also, the regenerative braking is enabled for the simulation. This means, when the vehicle starts decelerating, corresponding amount of charge will be fed back to the battery.
Accordingly, the BRK input is connected to a Controlled Voltage Source. This will generate emf corresponding to the intensity of brakes applied and feed the power back to the battery.
H-Bridge parameters
The Input Threshold parameters are left with their default values.
The Output Voltage Amplitude of the H-Bridge circuit is given the same value as the rated DC supply voltage of the DC motor.
PVM voltage Block:
Simulink provides an inbuilt Controlled PWM Voltage block. This block is used for providing the proper pulse inputs to the H-Brdige circuit.
The PWM & REF connections are for the corresponding ports on the H-Bridge circuit.
The 2 reference inputs correspond to the throttle inputs given by the driver. The block generates corresponding pulse width as per the accelerations and brakes applied by the driver himself.
Here, the PWM frequency is 4000 Hz. Also, the simulation mode is Averaged as that in the H-Bridge circuit.
the input scaling parameters given are -
0V for 0% duty cycle and 5V for 100% duty cycle.
Accordingly, the output voltage amplitude becomes 5V.
The H-Bridge circuit along with the PWM input, together form the motor controller circuit
(4) Longitudinal Driver:--
Longitudinal Driver is an inbuilt block provided by the powertrain blockset.
it is a parametric longitudinal speed tracking controller for generating normalized Acceleration and Braking commands based on reference and feedback velocities.
The VelRef port is the reference velocity port where the input drive cycle data is fed.
The VelFdbk port corresponds to the feedback velocity. The actual velocity output given by the vehicle body is connected here. By comparing the actual (feedback) velocity with the reference velocity, the driver block generates acceleration and braking signals in order to minimize the error between the two concerned velocities.
Grade corresponds to the grade angle. For this simulation, no inclination is considered, and hence, a constant block with value 0 is connected.
Info gives the output for the bus signal for different block calculations like differences in reference vehicle speed and vehicle speed, etc.
AccelCmd & DecelCmd correspond to the acceleration and deceleration commands generated respectively and are connected to the corresponding ports of the Controlled PWM Voltage block.
Here, the selected control type is PI. Accordingly, the block implements proportional-integral (PI) control with tracking windup and feed-forward gains.
(5) Battery Pack :--
To model the Battery pak, a simple Battery block is used. This is because, if the generic battery block is used instead, the simulation will run for a much longer time.
Here, the selected option for Battery Charge Capacity is Finite. Accordingly, the block models the battery as a series internal resistance plus a charge-dependent voltage source.
If the chosen option had been Infinite, the voltage source would have been constant.
Also, the self-discharging of the battery and the battery dynamics are disabled.
The Battery Nominal Voltage is given as 330V.
The Ampere-hour rating is assumed to be 10
The rest the parameters are left with their default values.
To ensure the battery supplies current as per the requirements of the motor controller and not the rated current, a Current Sensor & Controlled Current Source pair is connected.
(6) Reference Velocity (Drive Cycle) :--
The Drive Cycle Source block is used to provide the reference speed for the simulation.
It generates a standard or user-specified longitudinal drive cycle
Here, the selected drive cycle is the standard FTP75
The plot of the drive cycle is shown below;
(7) Battery State of Charge:--S.O.C
A small subsystem is created to calculate the State of Charge of the battery.
This subsystem takes the battery current as the input.
The essential process to calculate the SOC is by subtracting the charge from the rated capacity of the battery.
Accordingly, the current is integrated w.r.t. time to get the charge through rate- transition block. Now this value is modified into Ampere hours. This value is now subtracted from the charging capacity of the battery i.e. 50 Ah. Finally, the remaining charge is now converted into a percentage value of the charging capacity of the battery. BY connecting a multiplication block for a value of 100 this can be modeled.
SIMULATION:--
The system is ran for simulation for 2474 s which is the total time for which the input drive cycle is defined.
A Solver Configuration is added to ensure proper solving of the mathematical equations by the model.
Scopes are connected to analyze different outputs such as the SOC of the battery, the reference velocity & the actual velocity of the vehicle, and the distance covered by the vehicle during the total run.
The 2 velocities are first converted from m/s to kmph values. For this, simple Gain blocks are used.
The distance is calculated by simply the time-integration of the vehicle velocity.
OUTPUTS:--
Battery-operated Dc drive – scopes
FTP75--Velocity:
Drive cycle:
SOC:
CURRENT
Distance Covered:--
It may be noted that, since the reference velocity of the drive cycle never becomes negative (i.e. there is no backward motion of the vehicle), the distance is increasing throughout. through the output block connected below -- we can get the readings at the end of running the model.
The total distance covered by the vehicle is about 5.201km.
CONCLUSION:--
The model was successfully run for simulation under the standard FTP75 drive cycle. The results have been properly analyzed.
Also, learned quite a lot of interesting things like -
- how to model an EV and carry out a real-time simulation
- how a motor controller works and what role it plays in the control of the electric motor
- how to calculate the SOC of the battery in terms of % .
- different powertrain blocks provided by Simulink which can be used to simulate a vehicle model.
REFERENCE:--
https://afdc.energy.gov/vehicles/how-do-all-electric-cars-work