Week-6 Challenge: EV Drivetrain

1.Power electronic converters:

In electric and hybrid electric vehicles, the power electronic converters are considered as the key elements that interface their power source to the drivetrain of the EVs.In order to design highly efficient converters for the EVs power system, advanced DC/AC and DC/AC converters are required to adapt the output voltage and current levels with high power quality.

the 3 types of converters which are widely used in an electric vehicle are:

AC-DC converter(on board charger)

AC to DC converters are most commonly used in plug-in hybrid electric vehicles and plug in electric vehicles. these vehicles get their propulsion power from an external electricity source which is alternating current. the battery need to be charged using a direct current source. for this purpose, AC to DC converter is employed in a PHEV and PEV.

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 characterstics of the vehicle such as top speed,acceleration time from 0 to 100lm/h, weight, maximum torque, and power file.

DC-AC converter:

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

2.given data:

battey pack voltage(v)=72v

rated armature current=400 A

armature resistance(Ra)=0.5 ohms

motor constant(k)=0.7

chopper switching frequency= 400 Hz

duty cycle=70%

calculations:

vehicle output voltage is given by(Vv):-

Vv=battery voltage*duty cycle

Vv=72*0.70

vehicle voltage(Vv)=50.4v

now, equation for vehicle torque is given by:-

Tv=((Vv-w*K)*K)/Ra

where:

Tv= vehicle torque(N-m)

Vv=vehicle voltage(volts)

w=steady speed of vehicle(rps)

K=motor constant

Ra= armature resistance

substituting all these values in equation, we get:

Tv=((50.04-7.7*w)*0.7)/0.5

Tv=70.56-0.98w

Tv=24.7+0.0051*w^2

solving these equations:

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

0.0051*w^2+0.98*w-46.94=0

solving the equation:

w=38.85 rad/sec and w=-230.95 rad/s

taking the positive value:

steady state speed of vehicle==38.85 rad/s

3.The mathematical model of the given equation is:

4.Induction versus DC brushless motors by wally rippel, tesla:

the following points can be concluded from the above topic:

• In the beginning, author describes the dominance of internal combustion engines in the world of automobile industry and also discuss different types of engine.he explains that all engines were similar and it was up to the user to select according to thier requirement. he also speaks about induction motor and brushless adca motors and presents his view that these two technologies will be widely used for the coming years.
• then he explains the working of both 3-phase induction motor and a brushless dc motor.
• now the author has done comparision between these two technologies and stated some advantages and disadvantages of each.
• induction motor have some disadvantages 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 proportinate to the 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 advantages 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.