Week-6 Challenge: EV Drivetrain

1. Which types of power converter circuits are employed in electric and hybrid electric vehicle?

Ans:- As we know, the basic differences between the Electric vehicle and Hybrid electric vehicle are

• Electric vehicle operated by one source of energy i.e:-Electric supply where as the hybrid electric vehicle is operated by two source of energy i.e:- electric supply and conventional energy source like petrol,diesel,gasoline etc.
• storage element inside electric vehicle is Battery where inside the hybrid electric vehicle,the storage elements are fuel tanks and battery.
• CO2 emission by the Electric vehicle is less than Hybrid electric vehicle.

So,to operate an Electric vehicle and Hybrid electric vehicle,electricity is needed. and we also know that there are many components inside the vehicle which are operated by DC voltage or Dc supply but we have only AC supply at the charging station.

We have two type of sorces such as:-

• AC source
• DC source

so,there are 4 possible conversion between these two sources i.e:-

1. AC - DC convertes
2. DC - AC converters
3. AC - AC converters
4. DC - DC converters

In an electric vehicle, the basic diagram is

Electric supply-------->Battery----------->Motor---------->Transmission System------->Axels & Wheels

1. As we have electric supply at the charging station to charge the Traction Battery but the battery will store the DC voltages. so there is an AC -DC converters named as Rectifire is used to convert the AC supply to DC voltages which is stored in the trection battery.
2. then we know,the Motor connected to the transmission systen is an induction motor which requires AC voltage to operate or to work, so again, we used a DC - AC converter named as Inverter which converts DC supply from the traction battery into AC supply which turn on the induction motor and the indution motor run thr transmission system.
3. there are some components such as Horn,Head light,Music system,wiper etc which require low DC voltage like 5V,9V,12V etc to operate. but our traction battery can supply high DC voltage like 120V. if we direct connect these component to the traction baterry then these component will burn or damage. so in order to protect these componemt we use DC - DC converters to convert high DC supply to low DC supply(Buck converters) which is stored in auxillary battery.then the auxillary battery will provide voltage to the components which are operated on low voltage.

there is no need of AC - AC converters in an Electric vehicle.

IN an Hybrid electric vehicle, the basic diagram is

Electric supply + Conventional Energy source-------->Fuel tank & Battery-------->Engine + Motor-------->Transmission System-------->Axels & wheels

In Hybrid electric vehicle,Same power converters which are used in electric vehicle are also used in this vehicle.

1. In hybrid electric vehicle, traction battery can be charged by two ways:- by charging station,by regerative braking, by the power supplied by generator which is operated by IC engine. the generator produce AC supply so we use AC - DC converter named as rectifire which converts AC supply to DC supply. then the battery will able to store the DC voltage.
2. then we know,the Motor connected to the transmission systen is an induction motor which requires AC voltage to operate or to work, so again, we used a DC - AC converter named as Inverter which converts DC supply from the traction battery into AC supply which turn on the induction motor and the indution motor run thr transmission system.
3. there are some components such as Horn,Head light,Music system,wiper etc which require low DC voltage like 5V,9V,12V etc to operate. but our traction battery can supply high DC voltage like 120V. if we direct connect these component to the traction baterry then these component will burn or damage. so in order to protect these componemt we use DC - DC converters to convert high DC supply to low DC supply(Buck converters) which is stored in auxillary battery.then the auxillary battery will provide voltage to the components which are operated on low voltage.

there is no need of AC - AC converter in this Hybrid electric vehicle.

Difference between electric vehicle and hybrid electric vehicle:

Specifications	Hybrid Cars	Electric Cars
Power/Fuel Source	Electricity and Fossil Fuel (Petrol and Diesel)	Electricity Through Battery Pack (DC)
Engine	Internal Combustion Engine (ICE) and Electric Motor(s)	Electric Motor(s)
Fuel Efficiency	Combination of ICE and Battery Range	Depends on Battery Range
Emission Levels	Higher Compared to Electric Cars	Lower Compared to ICE and Hybrid Cars
Price Range	Similar to Conventional ICE Cars	High
Charging	Not Needed	Needed

Power Converter:

Types of Power converter:

There are four main types of power converter circuits , which are used in electric and hybrid electric vehicles...There are ,,

AC to DC Converter:

• AC to DC Converters are one of the most important in power electronics because there are lot of real applications are based on this conversions..
• The AC current DC current conversion process is known as Rectification. The Rectifier convert AC supply into the DC supply at loaad end connection..
• Normally Transformers are used to adjust the AC source to get step down transformer to reduce the volatge level to have better operation range for DC supply.Noramlly AC to DC converter converts low voltage values..
• In most of the countries , the electrical power generation and transmission are purely based on alternating current .DIfferent types of eleectrical power stations use alternators to generate electricity.
• Most of the electrical appliance which use DC current for their operation such as Television,computers,mobiles etc..
• In the case of EVs and HEVs the battery pack which operates with a DC power supply is charged at home or at a charging station both of which are supplied power inAC form from the electric grid ,, so the charges for these vehicles are an example of the AC to DC power converter..

DC to AC converter:

• A power inverter is a power electronic device or circuitry that changes direct current to alternating current .The input voltage ,output voltage and frequency ,and overall power handling depend on the design of the specific device .The inverter does not produce any power , the power is provided by the DC source ..
• A power inverters can be entirely electronic or may be a combination of mechanical effects and electronic circuitry.Static inverters do not use moving parts in the conversion process
• An inverter is a device that converts DC power to the AC power uesd in an electric vehicle motor .The inverter can change the speed at which the motor rotates by adjusting the frequency of the alternating current ..

DC to DC converter :

• In electric engineering , a DC to DC converter is a category of power converters and it is an eletric circuit which converts a source of direct current from one voltage level to another , by storing the input energy temporarily and then releasing that energy to the output at a different voltage ..
• DC/DC converters can be designed to transfer power in only one direction, from the input to the output. However, almost all DC/DC converter topologies can be made bi-directional. A bi-directional converter can move power in either direction, which is useful in applications requiring regenerative braking.

1. Non-isolated converters:

The non-isolated converters type is generally used where the voltage needs to be stepped up or down by a relatively small ratio (less than 4:1). And when there is no problem with the output and input having no dielectric isolation. There are five main types of converter in this non-isolated group, usually called the buck, boost, buck-boost, Cuk and charge-pump converters. The buck converter is used for voltage step-down, while the boost converter is used for voltage step-up. The buck-boost and Cuk converters can be used for either step-down or step-up. The charge-pump converter is used for either voltage step-up or voltage inversion, but only in relatively low power applications.

2. Isolated converters:

Usually, in this type of converters a high frequency transformer is used. In the applications where the output needs to be completely isolated from the input, an isolated converter is necessary. There are many types of converters in this group such as Half-Bridge, Full-Bridge, Fly-back, Forward and Push-Pull DC/DC converters . All of these converters can be used as bi-directional converters and the ratio of stepping down or stepping up the voltage is high.

AC to AC converter:

• Ac to Ac converters is used for converting the AC waveforms with one particular frequency and magnitude to AC waveform with another frequency at another magnituide .This conversion is mainly required in case of speed controlling of machines ,for low frequency and variable voltage magnitude applications as well.
• We know that there are different types of loads that work with different types of power supplies like single phase ,three phase supply ,and the supplies can be differentiated based on the voltage and frequency range also..
• We require a paricular voltage and particular frequency for operating some special devices or machines ..for speed control of induction motors ,, AC to AC converters is used majorly for obtaining a desired AC power supply from the actual power supply ,we need some converters called AC to AC converters

2. An Electric Vehicle's powertrain with 72V battery pack in shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is 'd2'.

Answer:

Given:

The other parameters of the electric vehicle is given below,

Motor and Controller Parameters:

Rated Armature voltage= 72 V

Rated armature current= 400 A

Ra= 0.5Ω, KΦ= 0.7 Volt second

Chopper Switching frequency= 400 Hz

The vehicle speed-torque characteristics are given by the below equation

What is EV steady state speed if duty cycle is 70%?

As the torque formula is given ,we need to find the speed in rad\sec;

T=((v*k)/R)-((k^2*w)/R)

T= torque

v=Armature voltage

R=resistance

w=speed rad/sec

24.7+0.0051*w^2 = ((v*k)/R)-((k^2*w)/R)

24.7+0.0051*w^2=(72*0.7)/0.5-(0.7^2/0.5)*w

70.56-0.98*w=24.7+0.0051*w^2

w^2+192.15*w-8992.5=0

n order to find the roots use following formula for a quadratic equation of the form ax^2+bx+c=0 the solution are

As the speed values can be negative

w=38.95 rad\sec

or

clear all
close all
clc
%% input paramater 
fprintf("Input Parameter \n")

Va = input("Enter the Va battery or Armature voltage(volt) = ") ; 
Ia = input("Enter the Ia Armature current (Ampere) = ") ; 
Ra = input("Enter the Ra resistance (ohm) = ") ; 
Kphi = input("Enter the Kphi motor constant(volt sec) = ") ; 
d = input("Enter the d duty cycle (in percentage) = ") ; 

f = 400; % chopper switching frequency (Hz)

%% duty cycle (d),Vo output voltage , Va battery voltage
d1 = d/100  ;% 70 percent
Vo = Va * d1 ;

%% Tm torque for motor and O omega angular speed
syms('Tm','O')
eqn = Tm == ((Vo - (O.*Kphi)).*Kphi)./Ra ;
s1 = solve(eqn);

fprintf("\n")
fprintf("Equation of motor Tm = %s \n",s1)

%% Tv torque for vehicle 
% Tv = 24.7 +(0.0051*(O.^2));
eqn1 =  24.7 +(0.0051*(O.^2));
% at steady state Tm = Tv
syms('O')
eqn2 = s1 == eqn1 ;
s2 = vpasolve(eqn2,[O]);
s2rpm =(s2(2)*60)./(2*3.14);

fprintf("\n")
fprintf(" EV steady state speed \n if duty cycle is 70 percentage = %f radian/sec %f RPM",s2(2),s2rpm)
 
challange_objective2.m
Displaying challange_objective2.m.

ans:

3. Develop a mathematical model of a DC Motor for the below equation using Simulink.

ω

= V/Kϕ -Ra/Kϕ

^2 .T

Result:

4. Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

Explain in brief about author’s perspective.

Ans:- In the above article, author Wally Rippel who is principal power electronics engineering & has worked for Jet propulsion laboratory on electric vehicle battery research, discussed about the comparision between Induction motor & Brushless DC motor according to their construction,working principle,losses in these devices etc.

He said in that article that, there are various types of shape of engine such as Hemis, straight, opposed,V configurations,Flat heads & so on.we can't choice one engine for every situation & every operation as they all have their different specific feature indivisually. when he started to design various types of projects at that type they had used lead acid batteries,brushed DC motor & contactor controllers. but now a days,lead has replaced by lithium,DC has replaced by DC brushless or Induction & contactor has been replaced by modulating inverters. he questioned that will each of these element can be replaced by some other more efficiencible elements in the future?

Working principle of these two Motors:-

• Brushless DC motor:- According to Wally, rotor consist of 2 to 3 permanent magnet which produce DC magnetic field & this magnetic field interacts with the current flowing in the windings on stotor due to which torque is produced between the stotor and rotor.When the rotor rotates due to this torque, it is necessary that the magnitude and polarity of the stator currents be continuously varied in such a righjt way that the torque remains constant.the device which control polarity of current is called as inverters.Without inverter, brushless motor is useless motor.

• Induction motor:- In an induction motor,rotor has no magnets but has stacked with steel laminations with buried peripheral structure taht is short circuited called as Endrings. when 3 phase supply is connected to the stator winding then a rotating magnetic field is produced which enters into the rotor & the frequency of this rotating magnetic field at the rotor is equal to the difference between the supllied electrical frequency and rotational frequency of rotor. them a voltage is produced at the endrings which is propertional to the the speed difference between the rotor and electrical frequency.so current is produced within the rotor conductor which is propertional to the voltage at endrings as well as the speed difference.finnally these current interacts with the origonal magnetic field to produce desied force component i.e;- rotor torque. and these rotor torque rotate the rotor and coversion of electrical energy to mechanical energy takes place.

Comparision between Brushless DC & Induction motor:-

1. the stators for the 3-phase induction motor and the DC brushless motor are virtually identical. Both have three sets of “distributed windings” that are inserted within the stator core but the rotors are different like Brushless DC motor has the rotor which consist of 2 to 3 permanent magnets but Induction motor has stacked steel laminated rotor with buried peripheral short circuited structured.
2. When induction motor is connected with utility type 3-phase power then torque is produced & the motor is capable to start underload condition without inverter. But in case of Brushless DC motor, no starting torque will produced when motor is connected to fixed frequency utility factor & they need the aid of an inverter whose “phase” is maintained in step with the angular position of the rotor.
3. in the basis of control method for speed of rotor, Brushless DC motor requires position sensor where as the Induction motor require speed sensor.
4. Brushless DC drive can be operated at unity power factor where as the best power factor for the Indution power factor is 85% i.e;- 0.85 .for which the peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive.
5. Rotor heat is less in Brushless DC motor as compared to Induction motor.
6. when we consider about an ideal Brushless drive, then the magnetic field produced by the permanent magnet can be adjuctable so at rquirement of high torque( at low speed condition) then the strength of magnetic field should be maximum so the inverter & motor currents should be low for which I^2*R loss will be minimum * efficiency will be high. in case of low torque requirement ( at high speed condition) the strength of magnetic field should be minimum so that hysteresis loss and eddy current loss will be less and efficiency will be maximum. but this the the case for ideal brudhless DC drive. Unfortunately, there is no easy way of changing strength of magnetic field with permanent magnets. but in case of Induction motor,there is no permanent magnet so magnetic field strength(B) can be adjustable. so at high torque requirement,inverter current and motor current is low and I^2*R loss is very less & in case of low torque requirement,the hystersis & eddy current losses is traded in such a way that that overall losess i.e:-I^2*R loss, hysteresis losses & eddy current losses are low for which Induction motor can provide higher efficiency as compared to Brushless DC motor by using a smart inverter
7. Peak efficieny is low of an Induction motor as compared to Brushless DC motor but average frequency is much better than Brushless DC motor.
8. Cost of permanent magnet is very high such as $50 per kg. & when ferromagnet element comes in contact or placed near to brushless DC motor then it is difficult to handle the rotor due to large ammount of force is produced. so the cost advantage induction motor is less tha Brushless DC motor.
9. Induction machine are also difficult to handle due to it's camplexity control laws.Achieving stability over the entire torque-speed range and over temperature is more difficult with induction than with DC brushless.

At last he concluded that, Brushless DC motors are used in a dominating range in Hybrid & plug-in hybrid market where as the Induction motors are used in pure Electric vehicle in a wide range.he thought that if the Hybrid vehicle become more electrically intensive & as their performance level increases ? then he said that as the hardware construction of both drives are same likely so in future we can see both Induction drive & Brushless DC drive will work side by side during the upcoming golden era of Hybrid & Electric vehicle.