Final Project: Design of an Electric Vehicle
AIM:
To crate a MATLAB model of an electric car which uses a battery and a DC motor,by choosing suitable blocks from powertrain block set.
THEORY:
An electric car is a vehicle that is propelled by one or more electric motors,using energy stored in rechargable battery packs.These are eco-friendly and has higher efficiency compared to ICE cars. An electric vehicle is 69-72% efficient when counted against required energy to recharge .They use electric motors for propulsion.The mostt common types of motors used are Permanent Magnet Synchronous Motor.(PMSM)and three phase induction motor.
Motor comparision,
The battery packs are recharged using AC/DC charging technologies.AC charging is slow as it has to be converted to DC.Hence for fast charging DC charges are used.The charging sockets has different standards as shown below,
BLOCK DIAGRAM:
The block diagram for an elecctric vehicle which uses a battery and a DC motor is shown below,
Now let us look at each of the blocks used to create this MATLAB model.
DRIVE CYCLE DATA:
For this we have used Drive cycle source block.
The block parameters for this block is as shown below,
This block will help us in inputting the drive cycle data,Wheather it is built in or custom made by the user.That is we can use custom made drive cycle data in excel sheet using this block.
For this model we have used FTP 75drive cycle,which is built-in this block.
Longitudinal driver:
This block is used to create a longitudinal speed- tracking controller and it is based on reference and feedback velocities,the block generetes normalized acceleration and braking commands that can vary from 0 through 1.we can use this block to model the dynamic response of a driver or to generate the commands necessary to track longitudinaldrive cycle.
The block parameters is as shown below
POWER CONTROL UNIT SUBSYSTEM
This subsystem has the blocks which are used to create the voltage signals to control the motor speed as per the input drive cycle data.
This subsystem is connected to the longitudinsl driver block output ports namely acceleration command and deceleration command.
This subsystem will convert this acceleration and deceleration command into voltage signals using two controlled voltage source block,controled PWM voltage bllock,a H-bridge and a current sensor.
CONTROLLED VOLTAGE SOURCE BLOCK
This block parameters is shown below
Thsi block is used to maintain the specified voltage at its output regardless of the current flowing through the source.
CONTROLLED PWM VOLTAGE BLOCK
The block and its parameters is as shown below.
This block is used to crate the pulse-width modulated (PWM) voltage.
ELECTRICAL INPUT PORTS:
The block calculated the duty cycle based on the reference voltage across its ref +and ref-ports.The modelling variant is the default.
The value of the Output voltage amplitude parameter determines amplitudden of the output voltage.
H-BRIDGE BLOCK
This block is used to change the polarity of the voltage applied across the DC motor so as to run the motor in forwrd and reverse direcion as per the input command.
The block and its parameters shown below,
CURRENT SENSOR BLOCK:
This is used to measur the current flowing through the H-bridge.
The block and its parameters is shown below,
DC MOTOR
To convert the electrical energy to mechanical energy we use motors.In this electric vehicle model we have used DC motor.This motor can act as a generator also in case of regenrative braking.
The motor block and its parameters are shown below.
This block represents the electrical and torque characterstics of a DC motor.
BATTERY SUBSYSTEM
In this subsystem we have a battery block,a controlled current source block and a goto block.
BATTERY BLOCK:
This battery block represents a simple battery model.The block models the battery as a series integral resistance and a constant voltage source.
The block and its parameters are shown below,
All other parameter section are kept at default values.
CONTROLLED CURRENT SOURCE BLOCK
This block gives a constant current output regardless of the voltage across it.
The block and its parameters are shown below,
GOTO BLOCK:
It is used to pass values to the 'From block'so this value can be accessed from anywhere in the simulink diagram.This input can be a real or comples valued signal or vectoe of any data type.This 'From blockand GTO block allows us to pass asignal from one back to another without actually connecting them.
The block diagram of the subsystem is as shown below,
STATE OF CHARGE CALCULATION SUBSYSTEM
The block diagram of the subsystem is as shown below,
Now this is connected to the rate transition block.This handles the transfer of data between blocks operating at different rates.The block and its parameters are shown below,
Then a gain is connected to it.This gain will multiply the value of
k=1/A*sec
where A*sec is the ampere second value of the battery.
In this case the battery capacity is in A*hr
which is ampere hour.
To convert
A*sec =A*hr*(3600)
Then to add all these values with respect to time,we have used a Discrete-time integrator.This block will accumulate the parameters are shown below,
Now this summed value is subtracted from 1, which will give us the remaining State of charge.To convert this to percentage,we have multiplied by 100 using another gain block.
Also Goto block is used here to get SOC values.
The output from this subsystem is connected to a a displaye block,which will display the Battery Percentage as shown below
VEHICLE BODY SUBSYSTEM
This subsystem represents the body of a vehicle.The block diagram for this subsystem is shown below,
The input to this subsystem is the mechanical rotational conserving port of the DC motor block.
This is connected to th single speed gear box of gear ratio 3.7.This block and its parameters are shown below.
The inertia acting on the shafts is given using a inertia block.This block and its parameters are shown below,
Now the simple gear is connected to all four wheels,representing an all wheel Drive vehicle.The tires are represented using tire(magic formula)blocks.This block and its parameters are shown below,
The simple gear is connected to the axle port of the tire block.
Now to represent the vehicle body we have used the vehicle body block.This block and its parameters are shown below,
Now to the front and rear normal forces ports represented by NF&NR and two at NR ports.This represents the front 2 tires and the rear 2 tires.
Also the mechanical translational conserving port for the wheel hub represented by H in tire block is connected to the port 'H' in the vehicle body block which represents the machanical translational conserving port associated with the horizontal motion of the vechile body.
To the gradient and wind speed ports of the vwhicle body block.we have conncted physical signal constant block.
The output from the vehicle body is the velocity of the vehicle m/s.This output is connected to the Goto block with tag'vfd'.
Now coming back to the longitudinal driver block,the VelFdbk input to this block is given using the 'From block' with tag'vfd'.This is the output from the vehicle body block.
RESULT
The results section of this EV model is shown below,
Her the first scope is input vs output velocity graph.This scope has two inputs one is FTP 75drive cycle an the other one is the velocity feedback.This two is combinned using a bus and connected to a Goto block with tag'result'and the corresponding 'From block' is connected to the scope to get this graph.
The resulting graph for this scope is shown below.
The next scope is used to get the change in SOC value with respect to time.The input for this scope is'From block'with tag'SOC'.
The resulting graph is shown below,
The third scope is used to get the current value with respect to time.its input is 'From block'with tag'current'the resulting graph is shown below,
The last result displays the distance covered by the vechicle in km.It is calculated by integrating the velocity feedback value and dividing it by 1000 to convert it to km.
CONCLUSION:
The MATLAB model of an electric car which uses a battery and a DC motor has been successfully made by choosing suitable blocks from powertrain block set and following connections has been drawn from the results.
From the Input vs output Velocity graph we can see that the EV model that we designed have traced the FTP 75 drive cycle very closely.Only when the speed suddenly drops to 0 in the FTP75 drive cycle very closely.Only when the speed suddenly drops to 0 in the FTP 75 drive cycle,the model takes time to catch up. On all other occasions the model traced the drive cycle closely.
Now looking at the SOC graph we can see that almost 50% of the battery capacity is used for completing this drive cycle.And also we can see sudden spikes in that graph,these spikes represents the regenerative braking region.During which the SOC value increases.
And from the Current variation graph,we can see that the maximum current value during normal driving is around 300A and during regenerative braking the maximum current value reached is near to 150A.
The Distance covered is 25km which is higher than the drive cycle data.For FTP75 the total distance is 17.77km.But still the value is closer to that FTP75 value,showing that the model is quite accurate in following the drive cycle data.