Final Project: Design of an Electric Vehicle

AIM - Create a MATLAB model of electric car which uses lithium ion battery and induction motor. Choose suitable blocks from Powertrain block set.

Introduction - The vehicles which get their driving power source from a Battery are known as Pure Electric Vehicles. Whereas the vehicles which uses 2 power sources such as Battery and IC Engine could also be called as Hybrid Electric Vehicles and so on. There are only a few vehicles in our country which come with the option of HEV such as Toyota Prius, Lexus LS 500h, BMW i8. From all these vehicles we have not seen higher demand as they have a higher initial range and the consumers in India usually fall to purchase the cars in the price bracket of 6 to 12 Lakhs and in that range they do not get an option to experience any Hybrid/Electric options.

Why EV?

There are majorly 5 reasons why one should opt for an EV

1. Low Maintenance
2. Eco Friendly
3. Silent operation
4. Low running cost
5. Incentives from Government

Out of all these 5 reasons the major which should be considered before making the decision for vehicle purchase are that the initial cost for an EV might be higher but when the vehicle is used for subsequent years like 3-4 years the initial cost would surely by compensated as the fuel efficiency nearly falls at 1-2 Rs per km as the charging cost per kW in India ranges nearly to Rs 7-15 which includes as Metro Cities and in this range if the vehicle is set at charging the vehicle usually delivers the efficiency of 6-7km per kW of charging. The battery has a life of nearly 10-12 years and then the batteries could be scrapped for a use of any low energy required resource. This in general is going to account for the overall smart purchase as currently the government is also promoting the purchase of EV at higher levels as the EV are the future. Dependency upon Fossil Fuels could not be cosidered for long duration as we do not have an assurance for the cost to remain constant. Taking an example of our country the cost is booming at highest peak and in the coming years it might change as well. The journeys travelled in an EV are worth the ride as it electrifies all your journeys and gives you the joy while driving.

Components used in an EV -

1. Electric Traction Motor
2. Cooling System
3. Power Electronics Controller
4. Auxiliary Battery
5. Traction Battery Pack
6. Transmission
7. Converter

Together these components when merged with an usual vehicle gives us an EV. There are many system level variations which have to be made and considered for the efficient operations of the vehicle. The vehicle tests has to go through several regions where it is extreme cold and where it is extremely hot. In all these components the major cost contribution is by the Traction Motor and the Batteries everything else does not cost at that higher range.

Block Diagram of an EV

System Level Configuration -

The major components forming the complete system are,

1. Drive Cycle
2. Driver
3. H- Bridge
4. DC Motor
5. Battery Source
6. Controlled PWM Voltage
7. Vehicle and others

Starting with the Drive Cycle, I have chosed the WOT Drive Cycle for the operation of the Cycle. In which the test duration would be 60 seconds.

1. WOT Drive Cycle

2. Driver Model

The Driver Model has the Input and Output Ports which are connected to the following,

Velocity Reference - Drive Cycle

Velocity Feedback - Distance Calculation

Grade - Constant 0

Info - Not Connected

Acceleration Command - Controlled PWM Source

Deceleration Command - Brake in H-Bridge to maintain the speed according to the Drive Cycle.

The parameter inputs are as follows,

PI Control Type is selected (Proportional Integral)

3. H-Bridge

The H-Bridge helps in controlling the power that is input according to the requirement. The output provided are converted voltage as per the controlled parameters.

The Ports for Input and Output are -

PWM - Pulse Width Modulation

REF - Controlling the Reference

REV - Controlling the Reverse

BRK - Controlling the Brake and Regenerative

+ = Controlled Output to the Positive Terminal of the Motor

- = Controlled Output to the Negative Terminal of the Motor

Parameters Considered for the H-Bridge

I have selected the Internal type Power Supply and Enabled the Regenerative Braking.

Rest all others remain the as default.

4. DC Motor

This is the DC Motor which would give the rotational power to the wheels and become the sole power generation source.

The DC Motors terminals are connected as mentioned below,

+ = Electrical signal to the motor Positive Terminal

- = Electrical signal to the motor Negative Terminal

R = Casing of the Motor connected with the Mechanical Rotational Reference Block

C = Rotor Case connected to the Mechanical Rotational reference

The parameter considered are,

The Armature inductance is as default, I have varied the changes in the No-Load Speed @ 8000 rpm, the rated speed @ 5000 rpm, the Rated Load at 50kW, and the Rated DC Supply Voltage @ 300 V. All other parameters are as default.

5. Battery Source

The battery is connected as the power source to the model so that the power could be generated and the same power is transmitted accordingly to all the operating sources.

The terminals connected are to,

+ = The positive terminal of the operating sources

- = The negative terminal of the operating sources.

The complete Battery Block

The complete battery block is as mentioned above it includes the Controlled Current Source, the Electrical Reference, the Power Source to Simulink Converters, the Scope and the SOC Estimate.

SOC Estimate Block

The SOC Estimate Block is connected with the Rate transition, the Gain considered at (1/80*3600), the Sum Block, the Discrete Time Integrator and the Constant Block. This gives us the Battery SOC Estimate. The more the usage of the operating sources the more the Battery SOC goes down in the specified interval.

The paramters considered of the battery are -

The battery Nominal Voltage is rated as per 300 Volts, the internal resistance is as per 0.5 Ohms and rest all others are as default.

6. Controlled PWM Voltage

The Controlled PWM Voltage Block helps in keeping the Modulated Pulses as per the required pulses. So that the operations happens smooth and higher variations are not observed.

The Ports are connected as follows,

ref+ = Reference Positive connected with the Acceleration Commands from the Driver Model

ref- = Reference Negative connected with the Deceleration Commands from the Driver Model

PWM = PWM connected directly to the H-Block

REF = REF connected directly to the H-Block

The parameters are as default, no variations are made.

7. Vehicle

Vehicle Block defines the condition, mass and the tyres been used. The rotational velocity, capacity is been taken care by the vehicle. Yes it comes accross many types of loads and drag during operation all that could be altered as required.

Inside the block

The components in the block are the

1. Simple Gear - For engaging the correct gear at the right duration where required
2. Tyre - 4 Tyre and the Operational wheels are the Rear, as the vehicle represented here are Rear Wheel Drive
3. Vehicle Block - Specifications of the same are mentioned below
4. Angle - The angle could be as per the road conditions the slope at which the car is running
5. Wind - The wind could be specified as per the condition where the vehicle has to be driven
6. Velocity - The Speed of the car
7. NF - The Front wheel connection
8. NR - The Rear wheel connection

The detailed parameters are as follows,

These are the model details which would be simulated and the results are as follows,

Scope 1 - The Velocity Feedback and the Drive Cycle Source

As represented on the plot given above the yellow curve shows the drive cycle data, as we know that the WOT (Wide Open Throttle) Drive cycle operates on the full throttle for some seconds and then the drive cycle is turned to 0 this in case operates the vehicle and accelerates the car at the top speed for the initial stage and throttles the car at the maximum, though the vehicle is unable to match the speed of the vehicle with the drive cycle but it is running at its peak and then comes the phase where the acceleration is left now the vehicle is operated on the free wheeling mode, the vehicle is not powered and the vehicle runs on the speed which is sustained. The important point to note here is the vehicle does not come to rest in 60 seconds, the vehicles speed is reduced but it does not come to 0.

The vehicle is operated as per the battery specifications as mentioned above on the specifications, the battery voltage supplied as the major source is 300 V and the motor used is the DC Motor in the overall operation the efficiency is been measured and as the operation of the cycle is operated at a specified duration of the WOT the same is been experienced.

The overall distance travelled by the vehicle is 0.6 kms in a duration of 60 seconds.

Battery SOC Scope

It is noted that the the Charge of the battery started from 100% at the initial level and during the operation of the vehicle for 60 seconds using the WOT Drive Cycle which has its peak throttle after the initial range the discharge occured/noted from the battery are until the high throttle was applied and it was been accelerated the battery got dishcharged at 97% and after the acceleration was been released the battery started recharging as the regenerative energy comes into action. The regenerative braking effectively charges the battery by 1% in the same duration where the vehicles acceleration pedal was been taken off and free wheeling.

Conclusion

It is clearly visible that the vehicle could be simulated in the same manner and indifferent such simulations could be made to analyze the efficiency of the vehicle by keeping in consideration of the various parameters. These same simulations could be carried out before deciding the overall specification that the vehicle should achieve. In this manner the Motor, Battery and other components could be chosen and then the actual model could be manufactured. There are chance of variation in the results which would be obtained in comparison of the Actual and Matlab Simulations as atual conditions would vary the results.

All components could be customized as per the test which has to be carried out, like the vehicle mass, the vehicle battery specification the battery Motor and all others.

As we analyzed in the test carried out above the vehicle has successfully achived the speed of 25 m/s and the vehicle covered a distance of 0.6 kms the same would differ once the vehicle parameters are varied.

Note - The .slx file of the model is attached with the submission