Final Project: Design of an Electric Vehicle

MATLAB Model Of Electric Car With DC Motor And Battery:

• Block Diagram Of Electric Vehicle.

• Vehicle Body Consists of Wheels and Gears.
• DC Motor is used for vehicle Propulsion.
• Let us Consider a Simple Battery.
• Used 4 Quadrant switches as Power converter.
• Control unit consits of PWM modulation of DC voltage and Lonitudinal Driver

SIMULINK Model Of Electric Vehicle:

PowerTrain Blocks used in Simulink:

1.Vehicle Body: Complete vehicle body is considered as Subsystem as shown below.

• Wheels: This Block represents the physical Wheel properites of a vehicle Specified by tire manufacturer.
• Four Wheel(2 for rear axle and 2 for front axle) Blocks are used and Each one has same specifications.

• Wheel Blocks are considered by default without any changes in all Parameters.
• If wheel parameters are specified then that will certainly effects the vehicle performance.

Ports:

N-Normal Force: This Input Port is used for Force to be applied on Wheel.

• Front Wheels N-Port is connected to NF port of vehicle Body.
• Rear Wheels N-Port is connected to NR port of vehicle Body.

S-Slip:Physical signal output port associated with the relative slip between the tire and road.

A-AXLE: This Mechanical Translational Port gives Mechanical link between two wheels.

• Both Rear and Front Wheels are connected through A-Port.

H-HUB: Mechanical translational port associated with the wheel hub that transmits the thrust generated by the tire to the vehicle body( maintain same speed in all wheels).

• All H-Hub ports of Wheels connected to H-port of Vehicle Body.

2.Vehicle Body: This Block gives the Vehicle Body Parameters to be set measured by Physical Vehicle.

In simulation all Parameters are considered as default to reduce simulation time.

• H,NR and NF ports are connected to Wheels Ports of vehicle.
• beta port gives the vehicle body Inclination to the ground in Radians.
• W-Port Gives the wind velocity applied on front of the Vehicle body(Headwind Speed in m/s).

3.GEAR: Represents a fixed-ratio gear from Base(B) to Follower(F).

• Gear Ratio is specified by manufacturer as of now it is considered as 8.

4.DC Motor: This Block represents the electrical and torque characteristics of DC Motor.

Motor Parameters are set as:

No load speed of vehicle=8000 RPM

Rated Load Speed vehicle=5000 RPM

Rated Voltage =300 V

Rated Load of vehicle =60 KW

• Remaining all other Parameters( Resistance,Inductance,EMF....) are set as Default.
• Blue Part represents electrical Connection to Battery.
• Green part Represents Mechanical Part to be connected to shaft of Gear.
• R-Port is connected to B-Base port of Gear.
• C-Common port is connected to mechanical rotational reference frame.

5.References:

Electrical Reference : Gives the Nuetral Point to the electrical Circuit.

Mechanical Rotational Reference: This Block is considered as a rigid base (ground/frame) point of mechancial body.

Current Sensor: Sense the current taken by DC Motor and gives the feedback to Battery.

Controlled current Source : Maintain required amount of current to flow from the battery which is sensed from current sensor.

Controlled Voltage Source: Maintain Required amount of voltage to be maintain across DC motor which takes voltage level signal from driver.

6.H-Bridge: The H-Bridge block output is a controlled voltage that depends on the input signal at the PWM port.

PWM: If the input signal has a value greater than the Enable threshold voltage parameter value, the H-Bridge block output is on and has a value equal to the value of the Output voltage amplitude parameter.

If it has a value less than the Enable threshold voltage parameter value, the block maintains the load circuit using Freewheeling diode.

• REV and BRK mode are grounded in simulation.

• Output voltage: set to 300v (consider as Motor rated voltage)

• Simulation mode is averaged to reduce the simulation time.

REV: voltage that controls when to reverse the polarity of the H-Bridge block output.

BRK: voltage that controls when to short circuit the H-Bridge block output.

Power supply : Power supply can run in two model Internal and External Mode.

External Mode:

• Gate Pulse is given by external DC source to Semi conductor switches.
• If power supply is internal then Gate pulse is obtain internally(Based on Inductance value of motor) such a way that motor runs continously.

7.Controlled PWM voltage: The Controlled PWM Voltage block represents a pulse-width modulated (PWM) voltage source.

Simulation Mode is AVERAGED to reduce simulation time.

Output voltage: set to 300v (consider as Motor rated voltage)

8. Lonitudinal Driver:(Acts as Driver of vehicle)The block generates normalized acceleration and braking commands that can vary from 0 through 1.

It is Speed Tracking Block which uses a PI controller to reduce the error between Reference velocity and output velocity and gives Accleration and brake commands to Motor through H-bridge.

All Parameters are set as default.

Grade is set as zero so, there is no gradeability in Vehicle.

9.Drive Cycle:The Drive Cycle Source block generates a standard or user-specified longitudinal drive cycle. The block output is the specified vehicle longitudinal speed

FTP75: used to generate velocity across vehicle and evaluate the vehicle performance.

Run Time: 2474sec

10.Battery: This block represents the Physical model of battery.

• Battery voltage=Motor rated voltage =300v
• Amphere-Hr rating =50AH

Calculation Of State of charge (SOC):

• To calculate the SOC from current (I) utlisied by motor is defined as

`SOC(t)=(1/C)int_0^tI(t)dt`

where C= Battery capacitance(AH)

I= current

Simulink model of SOC: Current is Integrated and Divide with battery Ampere hour rating (Gain Block)in seconds then subtracted the obtain result from battery full capacity.

Simulation Results:

1.Ref Velocity Vs Output velocity:

Red : Output Velocity

Blue : Reference Velocity

• Output velocity is almost follows to reference veocity with minor distructions.

• Though Brake is fully applied ,output velocity not becomes zero due to Inertia of motor and vehicle.

• Peak output velocity is greater than reference output veocity due to motor inductance voltage.

SOC:

• Battery is Discharged from 100% (1) to 88% (0.88) throughout drive cycle.
• Battery is also charged during simulation due to Regenerative braking is applied.
• Discharge of Battery Follows the drive cycle pattern.

Accleration and Brake Commands:

Red : Accleration command

Blue : Brake Command

• We can observe whenever brake command is given Battery tries to charge.

Current Flows in DC Motor:

• Peak current is 180A in both Accleration and braking modes.