Week-6 Challenge: EV Drivetrain
BELONG TO EV LIVE BATCH 17
Which types of power converter circuits are employed in electric and hybrid electric vehicle?
ANSWER:
In Electric and Hybrid Electric Vehicles (EV/HEV), the power electronic converters are considered as the key elements that interface their power sources to the drivetrain of the EVs. In order to design highly efficient converters for the EV's power system, advanced DC/DC 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 (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.(CONVERSION OF VOLTAGE TAKES PLACE INSIDE THE VEHICLE )
An on-board charger, or OBC, serves one main purpose: to convert AC power from the grid to DC power stored in the high-voltage vehicle battery. This conversion is all happening inside the actual vehicle, or on-board.
AC-DC Converter (OFF Board Charger): -
An off-board charging system takes incoming AC power and converts it to the DC power needed to charge the battery system. The term “off-board” refers to charging systems not native to the vehicle itself (e.g., public vehicle charging station). One critical performance aspect of an off-board charger is its ability to quickly recharge the vehicle. For example, some modern fast chargers can recharge 250 miles of range in less than 30 minutes.(CONVERSION OF VOLTAGE TAKES PLACE OUT SIDE THE VEHICLE )
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).(DC TO DC CONVERTER ARE USED TO CONVERT THE VOLTAGE FROM DC TO DC OR TO BOOST VOLTAGE LEVEL .TO SEND VOTAGE FROM BATTERY TO INPUT OF AC CONVERTER )
The different configurations of EV power supply show that at least one DC/DC converter is
necessary to interface the FC, the Battery or the Supercapacitors module to the DC-link.
a DC to DC converter is a category of power converters and it is an
electric circuit which converts a source of direct 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. The storage may be in either magnetic field storage
components (inductors, transformers) or electric field storage components (capacitors).
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.
IAM ATTACHING THE ANOTHER IMAGE FOR BETTER UNDERSTANDING
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).
IF YOU ARE SEEING BELOW DIAGRAM AFTER DC TO DC CONVERTER WE USED THE AC TO DC CONVERTER TO GOVE THE VOLTAGE TO THE MOTOR FOR DRIVING
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'.
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%?
ANSWER :
total voltage Tv=voltage X duty cyle(0.7)
72*0.7=50.4V
TORQUE EQUATION FOR VEHICLE =
in above equation we are putting all values
Tv=(50.4-0.7w)0.7/0.5
Tv=70.56-0.98w.............. eqation 1
............ eqation 2
by solving this 2 equation will get quadratic eqations
0.0051*w`square`+0.98w-46.94=0
after solving this qaudratic eqation in calci will get two values one is positive and second is negative
w=38.85 rad/sec w=-230.95 rad/sec
we take the +ve value so the
steady state speed of vehicle is =38.95 rad/sec
4. Refer to the blog on below topic:
Induction Versus DC brushless motors by Wally Rippel, Tesla
Explain in brief about author’s perspective.
ANSWER:
Explain in brief about author's perspective.
The following points can be concluded from the above topic:
• In the beginning, author describes the dominance of Internal Combustion Engines (ICE) in the world of automobile industry and also discuss different types of engines. He explains that all engines were similar and was up to the user to select according to their requirement. 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.
• 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.