Design of an Electric Vehicle

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

ABSTRACT:-

In this project, we going to build the MATLAB model of ELECTRIC CAR by using a DC motor and a suitable battery for the motor. Before that, we will know about what is Electric vehicle, how it's works and the benefits of EV. Then we make an actual EV model in SIMULINK with suitable blocks from the powertrain block set. My main motto is to check "how my vehicle performs by the difference drive cycle and difference parameters.

OBJECTIVE:

•  To make the simple and low run-time vehicle model using the individual component model.
•  To check out performance parameters: Speed, SOC, current, etc. with various drive cycles.
•  To play with Motor power, vehicle body (Rolling resistance, Air drag, weight) inputs.
•  To know the MATLAB model and their configuration to match with the actual vehicle.

METHODOLOGY:

• The electric vehicle consists of a battery, motors, and controller then it generates propulsion power.
•  For design 1st we have to calculate propulsion power, then the motor is selected.
• Lastly based on the motor rating or operating range and no km/charge we want to depend on everything battery capacity and battery capacity is selected.
• So the Design flow of Electric vehicle engineer has to be like the following:

               1) Identify what amount of propulsion power required 

               2) What is the best suitable motor for that propulsion power.

               3) Then type of battery and range of battery according to the range.

THEORY:-

An Electric Vehicle :

An electric vehicle (EV) is a vehicle that uses one or more electric motor or traction motor 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 first came into existence in the mid-19th century, when electricity was among the preferred methods for motor vehicle propulsion, providing a level of comfort and ease of operation that could not be achieved by the gasoline cars of the time. the term EV is used to refer to an electric car. In the 21st century, EVs have seen a resurgence due to technological developments, and an increased focus on renewable energy, and the potential reduction of transportation's impact on climate change and other environmental issues.

Working of an Electric vehicle :

An electric vehicle works on a basic principle of science: conversion of energy. Electrical energy is converted into mechanical energy. There is a motor used in the electrical system to carry on this duty of conversion. Motors can be of various types. The motor is to an electric vehicle what engine is to the IC vehicle. 

Let’s have a look at different types of motors used in EVs.

There are various types of motors that are used in electric vehicles nowadays:

DC Series Motor:

It was a widely used motor back in the 1990s. This motor is capable of producing high initial torque. The easy speed control and sudden load increase bearing capacity make these motors a good choice. But the high maintenance due to the brushes and commutators is a major drawback in the DC series motor which is also known as Brushed DC Motors. These motors are still in use by the Indian railways. 

                       

Brushless DC Motor (BLDC):

These motors are the technically advanced versions of DC series motors. They don’t use brushes and commutators. Instead, permanent magnets are used. BLDCs have high starting torque, high efficiency and low maintenance. BLDCs are widely used these days either as the hub motor or belt-driven.

                                                      

Permanent Magnet Synchronous Motor (PMSM):

 It is very similar in construction to the BLDCs. But the major difference is in the back emf. PMSM has a sinusoidal back emf whereas BLDC has a trapezoidal one. They have a high power rating and can be used in high-performance applications such as sports cars, buses etc. For eg. Nissan Leaf uses a PMSM for propulsion.

                                                   

Three Phase Induction Motor:

Unlike DC motors, induction motors don’t have a high starting torque. It is cheap as compared to the other available options. But don’t go with the price. It still has very high efficiency and can withstand rugged environmental conditions. Tesla Model S uses this type of motor. Even Tata and TVS are planning to use induction motors in their electric vehicles. Indian Railways have also started using induction motors over DC motors.

                                     

Power source for an electric motor used in EV :

The answer is simple, from a battery. An electric vehicle uses a battery to store electrical energy that is ready to use. A battery pack is made up of a number of cells that are grouped into modules. Once the battery has sufficient energy stored, the vehicle is ready to use.

Battery technology has improved hugely in recent years. Current EV batteries are lithium based. These have a very low rate of discharge. This means an EV should not lose charge if it isn't driven for a few days, or even weeks.

Let’s compare the types on some basic parameters related to batteries.

Parameters	Lithium-ion	Nickel-metal	Lead-acid	Ultracapacitors
Low Cost	YES	NO	YES	NO
Energy efficient	YES	YES	YES	YES
Temp. Performance	YES	NO	NO	YES
Low Weight	YES	YES	YES	YES
Life Cycle	YES	NO	YES	NO

 

Different types of Electric Vehicles:

You must have come across different types of electrics in the market. Some are fully electric while some are electric with ic engines. So what exact categories do they fall into? Electric vehicles are differentiated into three basic categories: Battery Electric Vehicles(BEV), Plug-in Hybrid Electric vehicles (PHEV), and Hybrid Electric vehicles (HEV).

Battery Electric Vehicle (BEV):

These are the ones which you call a fully electric vehicle. This electric vehicle type does not contain any other source of actuation other than motors and batteries. There is zero-emission in these vehicles. The battery is charged through an external source of power such as DC fast charger or AC chargers.
On average, the BEVs take around 8 hours to get fully charged using an AC charger. This time can be reduced to 1 hour using a DC fast charger.
These electric vehicles have a range from 250kms to 500kms depending upon the battery capacity and the motor. Some of the 4-wheeler BEVs in India are Tata Nexon EV, Hyundai Kona Electric, Mahindra eKUV100, MG ZS EV, and more. 2-wheeler BEVs in India include Ather 450, TVS iQube, Bajaj chetck Electric, and many other startups are planning to launch by the end of this year.

Hybrid Electric Vehicle (HEV):

These types of electric vehicles are powered by both, fuel as well as electricity. The electricity is generated by the vehicle’s own braking system. The heat produced by the brakes is converted into electrical energy. This process of conversion is called Regenerative Braking.
The electric motor is used to start off the HEVs. Then the propulsion is taken care of by the IC engine. This ensures better fuel economy. The operation of the engine as well as the motor is controlled by the ECU. Some HEVs in India are Toyota Prius Hybrid, Honda Civic Hybrid, and Toyota Camry Hybrid. Maruti Suzuki recently introduced its hybrid system in few models too.

Plug-in Hybrid Electric Vehicle (PHEV):

These are types of hybrid electric vehicles that can recharge the batteries through regenerative braking or through the external source of power. The HEVs travel about 3-4kms before the engine is switched on, PHEVs can go up to 65kms before the engine provides the required assistance for the propulsion of the vehicle. PHEV options available in India are Mahindra e-Verito, BMW i8, and the Volvo XC90 T8.

PROCEDURE: 

1) Identify what amount of propulsion power required 

2) What is the best suitable motor for that propulsion power.

3) Then type of battery and range of battery according to the range.

Why we should be required to calculate 1st propulsion power?

The final outcome of the vehicle is propulsion power and therefore the start point should be what is propulsion power on the calculation of proper power, therefore, the study must begin with an estimation of propulsion power.

Why we should Disgne 1st instead of directly build the model of EV?

This mathematical model must be build before making an actual hardware design so this model offers great flexibility in conceptual design modification. For example, If I changed the components, you can do it easily in a mathematical model rather than in actual mode and check its parameters.

This model gives the performance idea with reasonable accuracy and avoided repetitive road tests. Models are very helpful in many situations can be realized safely only in analysis and calculation i.e .. thermal.

Yes, there are limitations of mathematical models also it is really difficult to implement all the aspects involves so those models are with certain assumptions with certain inaccuracies. But more and more aspects you covered the more and more benefit and accuracy will get.

* Now we start to design the model from zero like from Wheel, vehicle body, then we get to the motor, battery and it will be full powertrain.

so we divided our model into some part as below:

1) Wheel and vehicle body (mechanical part).

2) Electric system.

3) Battery System and SOC.

4) Controller.

5) Inputs.

 

Wheel and vehicle body:

For wheel and vehicle body we have to consider the following parameters 

Force acting on the vehicle- 1) To bring the vehicle to accelerate. 2) To maintain that speed.  

Where,

1)  `alpha`= Angle 

2)  `Fte`= tractive force.

3)  `Frr`= Rolling resistance force.

4)  `Fad`= Aerodynamic drag force.

5) `Fhc` = Hill climbing force.

6) `Fla`= Linear Acceleration forcre

7) `Fwa` = Angular Acceleration force

 

In the above fig.,

`Fte = Fad+ Fhc + Frr + Fla + Fwa`

Fla & Fwa are acceleration forces experienced by vehicle.

 

Rolling resistance force :-                             

The rolling resistance can be expressed by the generic equation

`Frr = c *m *g ....................................(1)`                  

where,

_Frr = rolling resistance or rolling friction (N)

c = rolling resistance coefficient - dimensionless (coefficient of rolling friction - CRF)

m = mass of body (kg)

g  = acceleration due to gravity  (9.81 m/s²)

 

Note that the rolling resistance coefficient - c - is influenced by different variables like wheel design, rolling surface, wheel dimensions, and more.

The rolling resistance can alternatively be expressed as

`Frr = (c_l * m * g)/r ......................(2)`                   

where,

c_l = rolling resistance coefficient - dimension length (coefficient of rolling friction) (mm)

r = radius of wheel (mm)

Some typical rolling coefficients:

Aerodynamic drag force:-

This force considers the shape drag and skin friction basically for doby of vehicle.

This force is the function of the frontal area, shape, side mirror, ducts, air passage, etc.

 `Fad = 1/2 * rho*A* Cd*V^2`

Where,

`rho`= Air density.

A =Frontal area.

Cd= drag coefficient 

V= velocity m/s

 

Hill climbing force:-

`Fhc = m*g*sin(alpha)`

where,

`alpha` is in radians.

 

This hill climbing force is also represented by using GRADEABILITY. Gradeability can overcome by vehicle constant speed.

There are two ways

1) Degree       

2) Percentage

 

The power output by the car's engine goes into the force-directed up the slope. This force is actually static friction exerted on the drive wheels by the road - the road exerts this force F because the engine causes the drive wheels to rotate. 

By considering all parameters we can know the design of the vehicle body and Wheel of the car.

So we selected the following block for tire and vehicle body:

In the above body and tire model following blocks are used:

1) Tire (Magic Formula):-

Represents the longitudinal behavior of a highway tire characterized by the tire Magic Formula. The block is built from Tire-Road Interaction (Magic Formula) and Simscape Foundation Library Wheel and Axle blocks. Optionally, the effects of tire inertia, stiffness, and damping can be included.

A is the mechanical rotational conserving port for the wheel axle

H is the mechanical translational conserving port for the wheel hub through which the thrust developed by the tire is applied to the vehicle.

N is a physical signal input port that applies the normal force acting on the tire.

S is a physical signal output port that reports the tire slip. 

So this is a car we need 4 wheel and this tire ports connected to the appropriate signal as mention above.

Following parameters considered for tire:

Now we just take the default values to check how they perform but we can take parameters of the currently present car model.  

 

2) Vehicle Body:-

 Represents a two-axle vehicle body in longitudinal motion. The block accounts for body mass, aerodynamic drag, road incline, and weight distribution between axles due to acceleration and road profile. The vehicle can have the same or a different number of wheels on each axle. Optionally include pitch and suspension dynamics or additional variable mass and inertia.

H is the mechanical translational conserving port associated with the horizontal motion of the vehicle body. The resulting traction motion developed by tires should be connected to this port.

V, NF, and NR are physical signal output ports for vehicle velocity and front and rear normal wheel forces, respectively.

W and beta are physical signal input ports corresponding to headwind speed and road inclination angle, respectively.

Following parameters considered for vehicle body:

 

3) PS constant:-

This block creates a physical signal constant:

y = constant

The Constant parameter accepts both positive and negative values. The block output is a physical signal port.

This PS constant is connected to the Vehicle body port W and delt for we can change the value of angel and wind velocity but we kept this value now zero.

 

 

4) Simple gear:-

Represents a fixed-ratio gear or gearbox. No inertia or compliance is modeled in this block. You can optionally include gear meshing and viscous bearing losses.

B (base) and F (follower) are mechanical rotational conserving ports.

Specify the relation between base and follower rotation directions with the Output shaft rotates parameter. Optionally include thermal effects and expose thermal conserving port H by setting the Friction model to a temperature-dependent setting.

Here we selected a gear ratio is 5.

 

 

Electric system:-

Depending upon the tractive force, Environmental conditions, type of vehicle application we choose the motor for the vehicle. For that motor we will decide the controller 

In Electric system Included the Motor, H-Bridge, controlled  PWM voltage.

As per our Aim, we using the DC motor and for that motor, we used DC to Dc converter which is H-bridge. Following is my Electric model used in this EV model:

To build this model we used the following blocks and parameters changed in it:

 

1)DC motor:-

This block represents the electrical and torque characteristics of a DC motor.The block assumes that no electromagnetic energy is lost, and hence the back-emf and torque constants have the same numerical value when in SI units. Motor parameters can either be specified directly, or derived from the no-load speed and stall torque. If no information is available on armature inductance, this parameter can be set to some small non-zero value. 

When a positive current flows from the electrical + to - ports, a positive torque acts from the mechanical C to R ports. Motor torque direction can be changed by altering the sign of the back-emf or torque constants.

Following parameters, we used for this Ev model:

This DC motor is Mechanically coupled with Simple gear Which having a gear ratio is 5.

For this DC motor, our rated DC voltage is 80v so we require an 80-volt battery this battery connected to the motor through H-bridge.

To change the speed and reverse the direction of the rotor we h-bridge in this model.

H-bridge:-

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 Enable 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. Using this ratio and assumptions about the load, the block applies an average voltage to the load that achieves the correct average load current. The Simulation mode parameter value must be the same for the Controlled PWM Voltage and H-Bridge blocks.

If the REV port voltage is greater than the Reverse threshold voltage, then the output voltage polarity is reversed. If the BRK port voltage is greater than the Braking threshold voltage, then the output terminals are short-circuited via one bridge arm in series with the parallel combination of a second bridge arm and a freewheeling diode. Voltages at ports PWM, REV, and BRK are defined relative to the REF port.

The following parameters are selected for H-bridge:

Controlled PWM voltage:-

This block creates a Pulse-Width Modulated (PWM) voltage across the PWM and REF ports. The output voltage is zero when the pulse is low and is equal to the Output voltage amplitude parameter when high. The duty cycle is set by the input value. Right-click the block and select Simscape->Block choices to switch between electrical +ref/-ref ports and PS input u to specify the input value. At time zero, the pulse is initialized as high unless the duty cycle is set to zero or the Pulse delay time is greater than zero. 

The Simulation mode can be set to PWM or Averaged. In PWM mode, the output is a PWM signal. In Averaged mode, the output is constant with a value equal to the averaged PWM signal. 

Electrical input ports — The block calculates the duty cycle based on the reference voltage across its ref+ and ref- ports. This modeling variant is the default. 

PS input — Specify the duty cycle value directly by using an input physical signal port.

Following parameters used in H-bridge:

 

 

Controlled voltage source:-

The block represents an ideal voltage source that is powerful enough to maintain the specified voltage at its output regardless of the current passing through it. The output voltage is V = Vs, where Vs is the numerical value presented at the physical signal port.

 

Electrical Reference:- 

Electrical reference port. A model must contain at least one electrical reference port (electrical ground).

 

Current sensor:-

The block represents an ideal current sensor, that is, a device that converts current measured in any electrical branch into a physical signal proportional to the current.

Connections + and - are conserving electrical ports through which the sensor is inserted into the circuit. Connection I is a physical signal port that outputs the current value.

 

Battery System and SOC:-

To give electric power to the EV model we need a battery set. 

 

Battery:-

This block models a battery. If you select Infinite for the Battery charge capacity parameter, the block models the battery as a series internal resistance and a constant voltage source. If you select Finite for the Battery charge capacity parameter, the block models the battery as a series internal resistance plus a charge-dependent voltage source defined by:

V = Vnom*SOC/(1-beta*(1-SOC))

where SOC is the state of charge and Vnom is the nominal voltage. The coefficient beta is calculated to satisfy a user-defined data point [AH1, V1].

(SOC)  the state of charge estimator:

This estimator includes the above block which explained below:

Rate Transition: Handle data transfer between different rates and tasks.

Gain: Element-wise gain (y = K.*u) or matrix gain (y = K*u or y = u*K). Where we used 80v battery so our formula is like 1/(80*3600)

Discrete-time Integrator: Discrete-time integration or accumulation of the input signal.

Scope: to get the result of SOC, Current.

PS Simulink converter: Converts the input Physical Signal to a Simulink output signal.

Controller: 

 

We use Longitudinal Driver as a controller 

A parametric longitudinal speed tracking controller for generating normalized acceleration and braking commands based on reference and feedback velocities.

Use the external actions to input signals that can disable, hold, or override the closed-loop commands determined by the block. The block uses this priority for the input commands: disable, hold, override.

Parameters:

 

Inputs:-

For the Control hole EV model we give input which is Drive cycle, Signal Bilder, etc.

To select the one from these 3 we used the multiport switch 

Drive cycle:-

generates a standard or user-specified longitudinal drive cycle. The block output is the vehicle longitudinal speed. You can import drive cycles from:

- Predefined sources

- Workspace variables, including arrays and time series objects

- mat, Xls, xlsx, or txt files

Use the fault tracking parameters to identify drive cycle faults within the specified speed and time tolerances.

We used Drive cycle is FTP75. According to the drive cycle, we have to change Simulink time.

Now run our model and get the result run time will be 2474.

EV model:

Result: 

1) let check our model will follow the input drive cycle :

 

As seen in the graph our model follows the drive cycle.

2) Now we check the Battery state (SOC);

2) check the current Follw :

Input acceleration:

The vehicle traveled distance:

So for the drive cycle, our model covered 6.031 distance.

Conclusion:

1) EV model Covers the 6.031m/s distance.

2) My Ev model followed the reference drive cycle. As we saw in the result our top speed is 22km/h and the maximum difference is 2 km/h.

3) When we completed 6.031m/s distance SOC is 53.7%.