Final Project: Design of an Electric Vehicle

Aim:- Create a matlab model of electric car which uses a battery and a DC motor.

Apparatus:-

• Tyre’s
• vehicle body
• Simple Gear
• DC Motor
• Current sensor
• Battery
• Controlled current source
• Electrical reference
• H- Bridge
• Controlled PWM voltage
• Solver configuration
• Constant
• Mechanical reference
• Integrator
• Divider
• Longitudinal Driver
• Drive Cycle Source
• Scope
• Display

Theory :-

• Vehicle body:- It is a simple frame of the vehicle which includes components such as wheels, chassis, transmission system, axles etc. Simulink readily has a ‘vehicle body’ block under simscape library where we can feed parameters such as mass of the vehicle, drag, pitch etc. the actual vehicle body also includes wheels which is also available in the simscape library as tires. Other than these components, we can also include simple gear block to simulate the transmission system.
• Motor:- The motor in the electric vehicle is the machine that converts the electrical energy from the battery into mechanical energy so that we could drive the wheels. There are different motors used in the actual EV’s namely induction motor, BLDC motor, Internal Permanent Magnet Synchronous Reactance Motor etc. In our Simulink model, for the sake of simplicity, we use DC Motor for simulation.
• Battery:- Like the petrol or diesel in the IC engine vehicles, the source of fuel for the electric vehicle is the battery. A battery pack in a EV will consist of many individual cells of lower voltages stacked together in series connection to get a larger net voltage battery pack. Many of the EV manufactures like Tesla, Nissan , Audi etc use Lithium Ion batteries in their vehicles. This battery supplies a constant DC voltage and it is connected with a motor controller. 
• Power Converter:- Power converter can be regarded as the brain or processing unit of an electric vehicle. It basically consists of power electronic devices. It is the one which enables the control of an Electric vehicle. Because, the voltage from the battery is a constant DC and if it is given directly to the motor (say BLDC), the motor would always run at constant speed and we could NOT achieve the speed control of the motor. This problem is solved by the power converter which consists of inverter or chopper configurations according to the motor used and it employs various techniques such as Vector Field control, PWM etc to control the speed of the motor.
• Drive Cycle and Longitudinal Driver:- These blocks are specific to the simulation purposes as they act as the reference for the simulation of the model. The drive cycle is simply a velocity vs time plot and this is fed to a driver controller which takes in the input speed and the current output speed and compares both the speeds to get the error. This error is then rectified by doing acceleration or braking in order to satisfy the reference drive cycle.
• 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.
• 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.
• Gear:- A simple gear block is used to connect the motor to the rear axle of the vehicle. It represents the gearbox which connects the input shaft to the base gear and output from the fuller gear.

Observations:-

• Vehicle body connection at (a) input ports:- W- Wind velocity in m/s, beta- Grade angle in radians. (b) Output Ports:- V velocity in m/s , NR- Normal force on rear axle, NF- normal force on front axle
• Tires connections at (a) input port:- N- Normal force acting on tire, positive when force is acting downwards/ towards the contact surface. (b) Output port:- S- Slip value relative to tire and surface of contact. (c) Conserving Ports:- H-represents wheel hub which transmits thrust generated by the wheel to the body of the vehicle. (d) A- represents axle on which the tires are mounted.
• The motor terminals are connected as mentioned below, +ve= electrical signal to the motor positive terminal, -ve= electrical signal to the motor negative terminal, R= casting of the motor connected with the mechanical rotational reference block, C= rotor case connected to the mechanical rotational reference.
• Controlled PWM voltage ports connected at, 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
• Driver model:- the 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 the H-Bridge to maintain the speed according to the drive cycle.

Result:- As we run the simulation on 2474 sec we observe the output at the scope, which was connected on the output of the vehicle subsystem at the velocity port. And we observe the graph of the distance and the velocity the output of the reference velocity also on that scope.

Conclusion:-we came to conclude that the model which have been prepared shows the velocity of the input and output at the given speed it varies from the input source. Our model is working in good manner by making the changes in input we can change the velocity and the braking as per the need. We can also use more blocks as the input source to the longitudinal body but to make it simple we have used the drive cycle block.