Week-6 Challenge: EV Drivetrain

1.Types of power converter circuits are employed in electric and hybrid electric vehicle

Depending on the type of function performed, power electronic converters are categorized into following types.

• AC to DC = Rectifier: It converts AC to unipolar (DC) current
• DC to AC = Inverter: It converts DC to AC of desired frequency and voltage
• DC to DC = Chopper: It converts constant to variable DC or variable DC to constant DC
• AC to AC = Cycloconverter, Matrix converter: It converts AC of desired frequency and/or desired voltage magnitude from a line AC supply.

The 3 types of converters which are widely used in an Electric Vehicle are:

1. AC – DC Converter (On Board Charger): -

AC to DC converters are most commonly used in Plug-in Hybrid Electric Vehicles (PHEV) & Plug-in Electric Vehicles (PEV). These vehicles get their propulsion power from an external electricity source (charging stations) which is alternating current. The battery needs to be charged using a direct current source. For this purpose, AC to DC converter is employed in a PHEV & PEV.

2.DC – DC Converter: -

DC-DC converters can be used to interface the elements in the electric power train by boosting or chopping the voltage levels. By introducing DC/DC converters one can choose the voltage variation of the devices and the power of each device can be controlled. The power of the DC/DC converter depends on the characteristics of the vehicle such as top speed, acceleration time from 0 to 100 Km/h, weight, maximum torque, and power profile (peak power, continuous power).

3.DC – AC Converter (Inverter): -

The DC/AC converter is required to convert the dc power to a suitable ac power for the electrical machine. The power output from battery pack (DC current) is converted using inverter to be used in electric motor (AC current).

2 . Given parameters

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

Duty cycle = 70% = 0.7

Solution:-

Vehicle Output Voltage = Battery Voltage(V)*Duty Cycle

= 72*0.70

= 50.4 V

The motor torque is given as

T = (V/KΦ)/Ra - (KΦ^2/Ra)*w

By substituting values in above equation ,

T = 70.56 - 0.98w

but when vehicle is steady state the motor torque = vehicle torque so,

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

0.0051*w^2+0.98*w−45.86=0

by solving this by quadratic equation we get, we get two w values as but we select positive one i.r 38.915

So, the EV steady state speed if duty cycle is 70% = 38.915 rad/sec or 371 RPM

3. Mathematical model of a DC Motor

I prefer Q.2 values for simulink as

V = 50.4 V

R = 0.5 0hm

k = 0.7

and for torque I choose ramp as increasing signal

Model :

Result :

4. Refer to the blog on below topic:

Induction Versus DC brushless motors by Wally Rippel, Tesla

The following points can be concluded from the above topic:

Firstly author introduce varios types of the IC engines which are avilable in the markets. also its user wish to choose whcih types of engine they will prefer on the basics of the price and performance.He also speaks about induction motor and brushless DC motors and presents his view that these two technologies will be widely used for the coming years and he also said that how technologics changed rapidliy like brushed DC motor changed to brushless DC motor and lead battery to Lithium.

Then he explains the working of both 3-phase induction motor and a brushless DC motor.Now the author has done comparison between these two technologies and stated some advantages and disadvantages of each.

Induction motor have some advantages like: it has no magnets. The motor has the ability to start under load. No inverter is needed. Some disadvantages of Induction motors are: They cannot operate from DC; AC is a must. Shaft speed is proportionate to line frequency. Hence, when used with utility power, they are constant speed machines. When operated from utility power, they have limited starting torque and somewhat limited running peak torque capabilities, when compared to DC type machines.

Brushless DC motor have some advantages like: much less rotor heat is generated with the DC brushless drive. The peak point energy efficiency for a DC brushless drive will typically be a few percentage points higher than for an induction drive. Some disadvantages of Brushless DC motor are: as machine size grows, the magnetic losses increase proportionately and part load efficiency drops. Permanent magnets are expensive and difficult to handle due to very large forces that come into play when anything ferromagnetic gets close to them.

Finally the author couldn’t choose which drive is better than the other but makes it clear that DC brushless drives will likely continue to dominate in the hybrid and coming plug-in hybrid markets, and that induction drives will likely maintain dominance for the high-performance pure electrics.