Final Project: Design of an Electric Vehicle

Create a MATLAB model of electric car which uses a battery and a DC motor. Choose suitable blocks from Powertrain block set. Prepare a report about your model including following:

Objectives:

1. System level configurations

2. Model parameters

3. Results

4. Conclusion

Electric vehicle (EV) is defined as a vehicle that uses an electric motor or a traction motor for propulsion unlikely to an internal combustion (IC) engine used by conventional vehicles. Electric vehicles use electric power instead of fuels as conventional vehicles would and because of this difference, electric vehicles do not produce any exhaust gases or pollution(Zero emission). The power needed for the operation of an EV can come from a variety of sources such as batteries, generators, or through a collector system.

MATLAB model of electric car which uses battery and dc motor. Choose suitable blocks from Powertrain block set :

To Model and Simulate an electric vehicle with SIMULINK.

Let us consider a model in this report, an electric vehicle with a dc motor and battery system using the SIMULINK . In modelling this EV for a drive cycle and to check performance parameters : to measure speed, SOC , and total distance travelled by the vehicle.

Primary Components of an EV:

• EVs have no need for the fuel engine and gear transmission, the two of the most crucial components for internal combustion vehicles.
• An electric powered car has three primary components - Battery, motor controller, and the electric motor.

(1) Battery : The battery of an electric car can be charged through the use of ordinary grid electricity at a specialized power station. But aside from the conventional lithium-ion battery technologies, there are also other major battery technologies which can be used for electric cars.

• Lithium-Ion Batteries : This battery technology gives extra performance and range. However, it also carries the highest price tag. Lithium-ion batteries are lighter than Lead acid and Nickel metal. These are also the batteries used in digital cameras and smartphones.
• Lead Acid Batteries : This battery technology is the most popular. It is also the cheapest among the battery technologies. What’s good about it is it’s 97% recyclable.
• Nickel Metal Hydride Batteries : This battery technology provides higher output and better performance but it costs much more than lead-acid batteries.

(2) Motor Controller : The motor controller of an electric car administers its complete operation and the distribution of its power at any given moment. It acts as a floodgate between the motor and batteries. It helps monitor and regulates all key performance indications such as the vehicle’s operator, motor, battery, and accelerator pedal. It has a microprocessor which can limit or redirect current. It is used to either improve the mechanical performance of the car or suit the operator’s driving style. There are also more refined controllers which are capable of greater accuracy and thus, higher efficiency.

(3) Electric Motor : Unlike a gasoline engine with lots of moving parts, a motor only has one moving part. This makes it a very reliable source of motive power. Choosing an electric motor depends on the car’s system voltage. They can be structured to use either AC or DC current. AC motors are less expensive and lighter compared to DC motors. They are also more common and they tend to suffer from less mechanical wear and tear. However, AC technology requires a more refined or sophisticated motor controller.

The detailed model we can see below:

It consists of many components

• Vehicle body subsystem
• DC motor
• motor controller
• Longitudinal driver
• Battery
• Drive cycle
• State of charge

1.Vehicle body subsystem:

This subsystem is consists of 4 tire blocks,vehicle body and simple gear

The vehicle is assumed to be a front axle driven (4 wheels - 2 on each axle).

i)Tire (Magic formula):.

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 the 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 slip of the tire.

• The tires are parameterized by Peak longitudinal force and 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 0.3 m.
• Also, the rolling resistance is given with a constant coefficient of 0.015.

This 2 axle (4 wheel) assebly is now connected to a Velocity Body simscape block.

ii)Vehicle body:

• 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, the connection H is the mechanical translational conserving port hub.
  NF & NR correspond to the output ports for nomral reaction forces on 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 and it is kept as 1m/s (headwind - direction opposite to that of vehicle).
• The gross weight is given to be 1200 kg.
• The geometric parameters of the vehicle are given as default
• 0.05 for proper drag force on the vehicle,Air density is 1.18kg/m^3 and the frontal area is kept as 3m^2
• The pitch dynamics for the vehicle are not considered for this simulation.
  

The input for vehicle body 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 3.73
Here, the rotational direction of the output shaft is kept 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 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 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.
• The rated load is kept as 80kW power and rated DC supply voltage is 300V
  All the other parameters are changed as shown below -
  
  
  
  
• The connection R represents the Rotor (rotational output) while the 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 into 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 :

The H-Bridge circuit along with the controlled PWM voltage together form the motor controller circuit.

i.H-Bridge circuit -

• This block represents an H-bdidge 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 from a Controlled Voltage Source. This will generate emf corresponding to the intensity of brakes applied and fed the power back to the battery.
• 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.

ii)Cotrolled PWM voltage:

• 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 apllied by the driver himself.
• Here, the PWM frequency is 1000 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 3V for 100% duty cycle. Accordingly, the output voltage amplitude becomes 5V.

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 minimise 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 difference 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. Acordingly, the block implements proportional-integral (PI) control with tracking windup and feed-forward gains.
  
  

v)Battery Pack :

• To model the Battery pack, 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 dynaics are disabled.
• The Battery Nominal Voltage is given as 300V.
  The Ampere-hour rating is assumed to be 80Ah.
• voltage V1 when charge is AH1 is kept axs 280V and charge AH1 when no-load voltage is V1 is 10Ah
  The rest all paramaters 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.
  

vi)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.

vii)Battery State of Charge :

• 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 in coulumbs. Now this coulumb value is modified into Ampere hours.
  This value is now subtracted from the charging capacity of the battery of 80Ah
• Finally, the remaining charge is now converted into percentage value of the charging capacity of the battery.

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 time-integration of the vehicle velocity.

Results:

i)Reference speed vs actual speed:-

As we can see from the above picture, the actual velocity of the vehicle differs from the reference drive cycle velocity.

This is because, the chosen battery capacity and motors are not able to propel the speed upto the required extent.

If a battery of higher capacity is chosen, the actual velocity will tend to match with the reference velocity.

but in this case the power rating of the motor also high and battery capacity is also enough if we change the voltage inside the PWM controlled voltage from 3 to 1 then speed will matches and it leads or gear ratio also matters if we lower the ratio from 3.73 to 2 then also the speed leads extremely above reference speed

Also, it may be noted that in certain regions, despite the drive cycle showing small decelerations, the vehicle actually is accelerating with decreasing magnitudes. Reason being the same.

ii)State of charge:-

The State-of-Charge of the battery at the end of simulation run is nearly about 75 %.

This means that the battery is not completely drained at the end and the vehicle can run on the same drive cycle for a 4 more times before the battery SOC becomes 0.

Also, the thing to be noted here is, since we had enabled the regenerative braking for the simulation, the battery SOC increases slightly whenever the vehicle undergoes heavy deceleration.we can see the spikes which are emerging upwards

Again, this depends upon the generating tendency of the motor and the maximum amount of current that the battery can take.

iii)Total distance travelled

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.

The total distance covered by the vehicle is about 20km.

this value is according acual velocity using reference drive cycle and if the speed of the vehicle matches with refrence velocity effectively then distance also increases with respect to the time.

CONCLUSION :

The model was succesfully ran for simulation under the standard FTP75 drive cycle. The results have been properly analyzed.

Also, learnt 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 battery discharge and km per full charge
• different powertrain blocks provided by simulink which can be used to simulate a vehicle model.
• regenerative braking effect on battery(state of charge)
• power rating of the motor and max speed of the vehicle

Using this electric vehicle simulation,changing the motor rating values and checking maximum speed it can generate, changing battery capacity and checking the SOC(%) of the battery and changing many other parameters and how its affected on design is observed.