Final Project: Design of an Electric Vehicle
PROJECT
ELECTRICAL VEHICLE DESIGN
AIM:
To create a MATLAB model of an electric car which uses a Battery and DC motor.
DESCRIPTION:
BLOCK DIAGRAM:
Main blocks used to design electric vehicle are vehicle body, DC motor, H-Bridge power converter, Battery, Drive controller and Drive cycle. In this Motor is connected to vehicle body. Instead of battery directly connected to the motor a power controller is connected in between motor and battery to achieve the speed of the vehicle. If we connect battery directly to the motor it will run at rated speed there won’t be any control over the vehicle. We have to control the vehicle that is possible by power converter. To simulate the vehicle we need to have throttle & brake pedal that is given by drive cycle i/p through a driver controller.
MODEL OF ELECTRIC CAR:
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 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.
The permanent magnet DC motor is used to drive the vehicle. Motor shaft is connected to front and rear axel of the vehicle body.
DC Motor Parameters:
Rated load (mechanical power) = 50kW
Rated Voltage = 300V
No Load speed= 6000 RPM
Rated speed = 4500 RPM
Vehicle Body:
Vehicle body is created by using vehicle body block, four tire (Magic Formula) blocks and simple gear block. Simple gear is connected to rear and front axle of vehicle. In vehicle body block Connection 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. Connections V, NF, and NR are physical signal output ports for vehicle velocity and front and rear normal wheel forces, respectively. Wheel forces are considered positive if acting downwards. Connections W and beta are physical signal input ports corresponding to headwind speed and road inclination angle, respectively. If variable mass is modeled, the physical signal input ports CG and M are exposed. CG accepts a two- element vector representing the x and y distance offsets from vehicle CG to additional load mass CG. M represents the additional mass. If both variable mass and pitch dynamics are included, the physical signal port J accepts the inertia of the additional mass about its own CG.
NR is connected to physical signal input port of rear axle that applies the normal force acting on the tire and NF is connected to physical signal input port of front axle that applies the normal force acting on the tire. Wind speed and inclination angle beta inputs are given by using physical constant blocks.
Input is taken from PMC_PORT 2 and vehicle speed output taken out from PMC_PORT 1.
POWER CONTROLLER:
The Motor controller will get input from the longitudinal driver. It is used to control the speed of the motor and drive according to the input of the driver. Acceleration given by driver will be given to PWM of H-bridge controller through controlled PWM voltage block it is used to create pulses. Brake signal is taken from deceleration of the vehicle. We can also use this H-bridge converter as power supply source as selecting the power source as internal.
Parameters of H-bridge converter:
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.
Battery:
The battery is required to power the controller and motor. The controller uses the battery power according to produce the input given by the motor to obtain maximum speed. The battery is also used to power every electrical component in the vehicle. The battery has two stage one is charging and another one is discharging state.
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. Coefficient beta is calculated to satisfy a user-defined data point [AH1, V1].
The battery has a positive and vegative terminal which is given the voltage-controlled source where the battey consumption is controlled by the motor controller and then it is given to the SOC block.
State of charge:
SOC is the percentage or level of battery presents after certain travel or consumption of battery charge by the vehicle. In the designed vehicle battery charge or SOC is calculated by the giving it to the rate transition and then to gain where 1/ (nominal battery capacity) then to a discrete-time integrator and it will get minus from the 1 as it is considered a 100% of battery and it is multiplied with 100 to get percentage of battery present and the entire system is shown below.
The majority of blocks are simscape blocks where physical to simulink converter is used to convert the physical signal from simscape block to simulink signal.
Drive Cycle:
Drive cycle is assumed as the driver's input of a vehicle, it replaced how a driver will drive a vehicle. These drive cycles are standard drive cycle which is used to test the vehicle performances. These drive cycle will have high speed, low speed, braking conditions in it. There are different drive cycles like WOT, FTP75 etc., Here in this model I have used FTP 75 Drive Cycle source.
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 specified speed and time tolerances.
Driver 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.
Drive cycle is connected to a longitudinal driver, it has six ports namely velocity reference, velocity feedback, grade, info, Acceleration, Deceleration.
VelRef is given by the drive cycle data and VelFdbk is given by the output of the motor. These two will get compare and the acceleration or deceleration output will be given to the motor controller. Accelcmd is given the PWM generator block and deccelcmd is given to the regenerative port of the h-bridge which uses to generate regenerative braking. Info is used to get any other data from a longitudinal driver block. The grade is to give the input of gradeability to the driver block. This block helps to generate the driver's conditions of the vehicle using the driver cycle block.
Controlled PWM Voltage source:
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. Duty cycle is set by 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 value equal to the averaged PWM signal.
Results:
Velocity graph:
From the results we can observe that speed of the vehicle is followed the input drive cycle. The blue line shows the reference drive cycle and yellow line shows the velocity of the vehicle. By using the controller, we can get the efficient output for given inputs.
Distance travelled by vehicle:
By integrating the speed of the vehicle we will get the distance travelled by the vehicle.
From display results of the vehicle distance, we observe that the vehicle travelled a distance of 5.4 KM for a given FTP75 drive cycle run over the period of 2474secs.
SOC:
State of charge of the battery is 99.57% at the end of the drive cycle. This we can observe in the display.
