Final Project: Design of an Electric Vehicle

Final Project: Design of an Electric Vehicle

Aim:

Create a MATLAB model of electric car which uses a battery and a DC motor. Choose suitable blocks from Powertrain block set. Prepare a report about your model including following:

Objectives:

1. System level configurations
2. Model parameters
3. Results
4. Conclusion

Electric vehicle:

An electric car is a vehicle that is propelled by one or more electric motors using energy stored in rechargeable battery packs. These are eco friendly and has higher efficiency compared to ICE cars. An electric vehicle is 69-72% efficient when counted against stored chemical energy and around 59-62% efficient when counted against required energy to recharge. They use electric motors for propulsion. The most common types of motors used are permanent magnet synchronous motor (PMSM) and three phase induction motor

In todays world electric vehicles are increasing become a part of modern life. Its eco friendliness and smooth driving have attracted many conscious modern consumers. Electric vehicles are quite different as compared to traditional vehicles with internal combustion engines. Electric vehicles operate with an electric motor instead of an internal combustion engine that generates power by burning a mixture of fuel and gases. The running costs of electric vehicles are low as it has moving parts for maintenance. In order to create awareness of the issue of global warming and to safeguard the environment electric vehicles are seen as a possible replacement for current generation of automobile industry

The main components of an electric vehicle are:

• Battery (auxiliary)
• Electric traction motor
• Onboard charger
• Thermal system (cooling)
• Power electronics controller
• DC/DC converter
• Charge port
• Transmission (electric)
• Traction battery pack

Battery (auxiliary)

The auxiliary battery of the electric vehicle provides electricity to power the accessories of the vehicle

Electric traction motor

Power is taken from the traction battery pack and with this the motor drives the wheels of the vehicle. Some vehicles use motors which serve as drive as well as regeneration

Onboard charger:

Ac electricity supplied the charge port is converted to DC power for charging the traction battery. It also communicates with the charging equipment and monitors battery characteristics such as voltage, current, temperature, and state of charge while charging the pack

Thermal system (cooling):

The thermal system for cooling makes sure that proper operating the temperature range of the engine, power electronics, electric motor and other components are maintained

Power electronics controller:

The flow of electricity which is delivered by the traction battery to the electric motor is controlled and the required speed and torque is produced

DC/DC converter:

The high voltage of the traction battery is stepped down to a low voltage DC power to run the vehicle accessories and recharge the auxiliary battery

Charge port:

The charge port is an external power supply from which the traction battery in the electric vehicle is charged

Transmission (electric):

The transmission converts electric power to mechanical power in order to drive the wheels of the vehicle

Traction battery pack:

The traction battery pack stores electricity for use by the electric traction motor

Drive cycle:

A driving cycle is a series of data points representing the speed of a vehicle versus time. Driving cycles are produced by different countries and organizations to asses the performance of vehicles in various ways as for instance fuel consumption, electric vehicle autonomy and polluting emissions

Driver controller:

The controller transforms the battery’s direct current into alternating current (for AC motors only) and regulates the energy flow from the battery. In the early electric vehicles with DC motors as simple variable resistor type controller controlled the acceleration and speed of the vehicle

Power converter:

In electric engineering a DC to DC converter is a category of power convertors and it is an electric circuit which converts a source of different current (DC) from one voltage level to another by storing the input energy temporarily and then releasing that energy to the output at a different voltage

Motor:

Today, majority of the electric cars are utilizing DC motors (4KW and less power). Induction motor is an exceptionally well known AC motor. A considerable lot of advanced power EV (more than 5KW) utilize Induction motors

Battery:

Most plug-in- hybrids and all electric vehicles use lithium-ion batteries like these. Energy storage systems, usually batteries are essential for hybrid electric vehicles (HEVS), plug -in hybrid electric vehicles (PHEVs) and all electric vehicles (EVs)

Vehicle body:

Car bodies are most often made of steel which is strong and durable but also pretty heavy especially for electric power to move on its own

Explanation of blocks used in model:

• Drive cycle source:

Drive cycle is a data set that contains velocity and time data for the purpose of modelling the motion of vehicle. The drive cycle will be a plot of the velocity against the time and it is made to resemble typical driving conditions that a driver may experience themselves in. for instance they can model high way driving situations driving in urban areas or driving with full power etc. drive cycles are used by automotive companies for various testing procedures such as mileage pollution tests and acceleration and top speed tests. There are various different drive cycles that are industry standard Urban Dynameter Driving schedule (UDDS) FTP 75

In my EV model a drive cycle is used as the reference velocity data for the longitudinal driver block to send acceleration commands according to the drive cycle. There are 3 ways of implementing a drive cycle one method is to create of own drive cycle with sperate sheet of velocity data in one column. An another method is to use a signal builder block and create signals that represent the velocities are to be maintained the last method is to use the industry standard drive cycles which are in build in to the SIMULINK library. In case I have used industry standard WOT drive cycle. This drive cycle stands for wide open throttle and a model the situation where the vehicle is made to accelerate at full power and maintained at a particular speed and made to decelerate back to rest

The drive cycle source block generates a standard or users specified longitudinal drive cycle. The block output is the specified vehicle longitudinal speed which you can use to:

• Predict the engine torque and fuel consumption that a vehicle requires to achieve desired speed and acceleration for a given gear shift reference
• Produce realistic velocity and shift reference for closed loop acceleration and braking commands for vehicle control and plant models
• Study, tune, and optimize vehicle control, system performance, and system robustness over multiple drive cycles

Drive cycles from predefined source. By default the block includes the FTP-75 drive cycle

Multiport:

Pass through the input signals corresponding to the truncated value of the first input the inputs are numbered top to bottom (or left to right). The first input port is the control port. The other input ports are data ports

Motor controller:

H-Bridge:

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 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 voltage at ports PWM, REV and BRK are defined relative to the REF port.

If exposing the power supply connection the block only support PWM mode

Controlled PWM voltage:

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 Right click the block and select Sim scape >Block choices to switch between electrical +ref /-ref ports and PS input u to specify 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 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

Controlled voltage source:

The block represents an ideal voltage source that is power full enough to maintain the specified voltage at its output regardless of the current passing through it. The output voltage is V = Vs where Vs is the numerical value presented at the physical signal port.

Longitudinal driver:

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

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 constant 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

Battery:

This block models a battery. 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

Solver configuration block:

The solver configuration block requires solver setting information for simulation the block specifies the solver parameter that the model requires before running the simulation

Voltage sensor:

The block represents an ideal voltage sensor that is a device that converts voltage measured between any electrical connections into a physical signal proportional to the voltage. Connection + and – are conserving electrical ports through which the sensor is connected to the circuit. Connection V is a physical signal port that outputs voltage value

Current sensor:

The block represents an ideal current sensor that is a device that converts current measured in any electrical branch into a physical signal proportional to the current.

Connections + and – are conserving electrical ports through which the sensor is inserted into the circuit. Connection is a physical signal port that outputs current value.

Controlled current source:

The block represents an ideal current source that is powerful enough to maintain the specified current through it regardless of the voltage across it. The output current is I = IS where is the numerical value presented at the physical signal port

Ps – Simulink and Simulink – Ps converter:

Converts the input physical signal to a Simulink output signal

Converts the Simulink input signal to a physical signal

Mechanical rotational reference:

The block represents it a mechanical rotational reference point that is a frame or a ground. Use it to connect mechanical rotational port that are rigidly affixed to the frame ground

Electrical reference:

Electrical reference port. A model must contain at least one electrical reference port (electrical ground)

Explanation of the motor controller:

• The motor controller subsystem contains mainly of H- bridge and a controlled PWM voltage block
• A controller is needed to control the motor according to the needs which is why a controller block is used which is the H- bridge
• H- bridge is used to supply power from the battery to the DC motor H- bridges has four switches that give the controlled DC voltage supply to the DC motor that can control the supply of voltage
• In H – bridge block parameters there are two option for simulation mode to chooses from either averaged or PWM but averaged mode is choose sine the simulation time is in mins or hours and it is faster as compared to PWM mode
• The output voltage amplitude of the H- bridge block is same as the rated DC supply voltage to the motor
• In the H – bridge block there is a PWM signal input port where PWM input can be given to this port the REF and REV ports are grounded using electrical reference block. This is done to prevent reverse operation of the motor. BRK port is connected to a controlled voltage source which helps in carrying out regenerative braking.
• PWM signal is given to the H- bridge block using controlled voltage block. This block helps in creating PWM signals which are generated according to the variable voltage
• The PWM and REF port of the controlled PWM voltage is connected to PWM and REF port of the H-bridge. The ref-port is grounded since we don’t need negative voltage. The ref+ port is connected to controlled voltage block so that the input voltage is the same always
• Controlled PWM voltage block is connected to the input PWM port in the H- bridge block
• This block will apply pulses and based on these pulses from the fixed battery voltage variable output voltage will be available to the motor and the motor torque and motor speed are changed
• Finally the subsystem is created with the following blocks and the subsystem will control the power supply to the DC motor

simple gear:

Represents a fixed-ratio gear or gear box. No inertia or compliance is modeled in this block. You can optionally include gear meshing and viscous bearing losses.

Connections B (base) and F (follower) are mechanical rotational conserving ports. Specify the relation between base and follower rotation directions with the Output shaft rotates parameter. Optionally include thermal effects and expose thermal conserving port H by setting Friction model to a temperature-dependent setting.

Tire:

Represents the longitudinal behavior of a highway tire characterized by the tire Magic Formula. The block is built from Tire-Road Interaction (Magic Formula) and Simscape Foundation Library Wheel and Axle blocks. Optionally, the effects of tire inertia, stiffness, and damping can be included.

N- this port stands for nominal and is the physical signal input port for the normal force acting on the tire and is considered positive in the downwards direction

S- this port stands far slip and is the physical signal output port is that reports the slip acting on the tire

A – this port stands for axle and is the mechanical rotational conserving port for the wheel axle

H- this port stands for hub and is the mechanical translational conserving port for the wheel hub through which the thrust developed by the tires is applied to the vehicle body

Vehicle body:

The six ports are used to model various characteristics of the vehicle body

• H- this stands for HUB and is used to connect the hubs of the wheels to the main body of the vehicle
• V- this is a physical signal output port which stands for velocity and is used to output the speed/ velocity at which the vehicle is moving at
• W- this is a physical signal input port and allows us to model a headwind acting on the vehicle by giving a speed for it
• NR- this is a physical signal output port model the rear wheel normal forces
• Beta- this is a physical signal input port and allows us to model the vehicle on an inclination angle to create the effect of hill climbing force

Ps constant:

This block creates a physical signal constant parameter accept both positive and negative values. The block output is a physical signal port

Sate of charge (SOC);

State of charge is defined as the measurement of available charge in the battery when the battery is fully charged it is considered to have 100% and when it is 0% it is said to be discharged. After the simulation is run we get an estimate of the current and S.O.C of the battery with respect to time as there are two scopes connected one to the current sensor and other to the subsystem of SOC estimate. In order for the current to be measured a Ps Simulink converter block is used because the current signal is physical

Explanation of the SOC sub system:

• To measure the state of charge of the battery a subsystem as create with various block such as integrator block, gain block and sum block
• Integrator block outputs the value of integral of its input with respect to time and then it is connected to the gain block
• Gain block divides the current signal with the ampere rating of the battery which is taken as 80AH multiplied by 3600 seconds in an hour
• Constant block is used to represent the initial state of charge of the battery when performing the simulation and assuming the battery charge is full the constant block can be altered with the value representing 100% charge
• Sum block is used to perform addition and subtraction operation
• The signal form the gain block will be subtracted from the constant block representing 100% charge
• Finally the three blocks are made into a subsystem which is the state of charge estimate and it is linked with the battery circuit using PS Simulink converter two scopes are connected one at the junction of the PS Simulink convert (to plot the output signal of the current from the battery) and other at the SOC sub system (to get an estimate of the battery charge after the simulation is run)