Week-6 Challenge: EV Drivetrain

EV Drivetrain

AIM:

1. types of power converter circuits employed in electric and hybrid electric vehicle.
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'. Rated Armature voltage= 72 V. Rated armature current= 400 A. Ra= 0.5Ω, KΦ= 0.7 Volt second. Chopper Switching frequency= 400 Hz.Vehicle speed torque characteristics T_v = 24.7+(0.0051)w . What is EV steady state speed if duty cycle is 70%?
3. Develop a mathematical model of a DC Motor for the below equation using Simulink.

ω= V/Kϕ -Ra/Kϕ^2 .T

4. Refer to the blog on below topic: Explain in brief about author’s perspective.

SOLUTION:

1.

There are three major power electronic units in the general configuration

• DC-DC converter
• DC-AC inverter
• AC-DC Rectifier

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 chose the voltage variation of the devices and the power of each device can be controlled. The different configurations of EV power supply show that at least one DC/DC converter is necessary to interface the Battery or the Supercapacitors module to the DC-link. The amount of power flow between the input and the output can be controlled by adjusting the duty cycle.

DC-AC inverter: Converts direct current (DC) from the battery to alternating current (AC) to be used by other devices such as the traction motor and coolant pump.

AC-DC Rectifier: Electric cars have batteries that run on direct current (DC) power. So the AC power which we use for charging batteries is converted to DC using a rectifier which feeds DC power to the battery .

2.

GIVEN:

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

Duty cycle=70% , V_bat = 72V

SOLUTION:

We know that

Ω = V_t/Kϕ -Ra/Kϕ^2 .T_t

V_t = V_bat * Duty cycle.

= 72 * 0.70

V_t = 50.4

Ω= (50.4/0.7) - (0.5/(0.7) 2). T_t

T_t = (72- Ω)/1.020

T_t = 70.58-0.98 Ω

But we know that,

Tv=24.7+0.0051 Ω²

Comparing T_v and T_t

24.7+0.0051 Ω² = 70.58-0.98 Ω

0.0051 Ω²+0.98 Ω-45.88 = 0

(Ω-38.92)( Ω+231.08) = 0

Ω=38.92, -231.08

speed cannot be a negative, hence consider only the positive value

Therefore EV steady state speed = 38.92 rad/sec.

3.

4.

Wally Rippel’s perspectives are

• All engines are alike and its up to the user to select one according to his/her requirements. Due to the improvising technology, there has been alternatives found now and then such as lead-acid batteries, DC brush motors and contact controllers have been replaced by lithium batteries, brushless DC or induction motors and inverters.
• Though there has been various replacements, brushless DC and induction motors are playing a major role till this date.
• The construction and working of the brushless motors and induction motors are being discussed. 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. Both drives use 3-phase modulating inverters. The only differences are the rotors and the inverter controls.
• The pros and cons of both brushless DC motors and induction motors are being discussed. The advantages of brushless dc motors are: much less rotor heat is generated. the peak point efficiency will only be a few % higher than an induction motor. The disadvantages are: as the machine size grows, the magnetic losses increase proportionately and part load efficiency drops. permanent magnet (PM) rotors are also difficult to handle due to very large forces that come into play when anything ferromagnetic gets close to them.
• Induction motor has some advantages: the motor has no magnets. the motor can start under no-load conditions. the disadvantages are: they cannot operate in DC. When operated with utility power, they have limited starting torque and limited running peak torque capabilities when compared to DC type machines.
• The author’s conclusion is 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.
• The fact that so much of the hardware is common for both drives could mean that we will see induction and DC brushless live and work side by side during the coming golden era of hybrid and electric vehicles.