Week-6 Challenge: EV Drivetrain
Aim:
To develop the challenge
1. Which types of power converter circuits are employed in an electric and hybrid electric vehicle?
2. An Electric Vehicle's powertrain with a 72V battery pack is shown in the diagram below. The duty ratio for acceleration operation is 'd1' and for the braking operation the duty ratio is 'd2'. What is EV steady-state speed if the duty cycle is 70%?
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
3. Develop a mathematical model of a DC Motor for the below equation using Simulink.
ω=VKϕ−RaKϕ2.T
4. Refer to the blog on the below topic:
refar tesla
Explain in brief the author’s perspective
Q 1: Types of power converter circuits are employed in electric and hybrid electric vehicle
A converter is an electrical circuit which accepts a DC input and generates a DC output of a different voltage, usually achieved by high frequency switching action employing inductive and capacitive filter elements.
A power converter is an electrical circuit that changes the electric energy from one form into the desired form optimized for the specific load. A converter may do one or more functions and give an output that differs from the input.
It is used to increase or decrease the magnitude of the input voltage, invert polarity, or produce several output voltages of either the same polarity with the input, different polarity, or mixed polarities such as in the computer power supply unit
Types of Power converters
AC to DC Converter ( Rectifier)
DC to DC Converter (DC Chopper)
AC to AC Converter (AC voltage regulator)
DC to AC Converter (Inverter)
AC to DC rectifier.
AC to DC Converters. An AC to DC converter circuit can convert AC
voltage into a DC voltage. The DC output voltage can be controlled by
varying the firing angle of the thyristors.
AC to AC Converters.
AC to AC Converters. This converters can convert from a fixed ac
input voltage into variable AC output voltage. The output voltage is
controlled by varying firing angle of TRIAC
DC to DC chopper
DC to DC Converters. These converters can converter a fixed DC input
voltage into variable DC voltage or vice versa
Dc to AC Inverter
Broadly speaking, an inverter is an electrical device that converts electricity derived from a DC (Direct Current) source to AC (Alternating Current) of the type that can be used to drive a device or appliance. In a solar power system, for example, the power stored by batteries charged by solar panels is converted to standard AC power by the inverter which provides the power to plug-in outlets and other standard 120-volt devices
Q 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'.
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Given that:-
Rated Armature voltage (V)= 72 V
Rated armature current= 400 A
Ra= 0.5Ω,
KΦ= 0.7 Volt second
Chopper Switching frequency= 400 Hz
Duty cycle (dc)= 70% = 0.7
The Average Voltage is given by the product of the battery voltage and the duty cycle,
Vs=V×dcVs=V×dc
Vs=72×0.7Vs=72×0.7
Vs=50.4Vs=50.4
The Average voltage is 50.4 V.
The Vehicle Characteristics are given in the form of the equation,
Tv=24.7+(0.0051)⋅ω2Tv=24.7+(0.0051)⋅ω2---------(1)
The derived formula for the motor speed characteristics
T=Vs×kϕRa−((kϕ)2×ωRa)T=Vs×kϕRa-((kϕ)2×ωRa)
By substituting the Values,
50.4×0.70.5−((0.7)2×ω0.5)50.4×0.70.5-((0.7)2×ω0.5)
T=70.56−0.98⋅ωT=70.56-0.98⋅ω----------(2)
Compare the Equations (1) and (2), we get
70.56−0.98⋅ω=24.7+(0.0051)⋅ω270.56-0.98⋅ω=24.7+(0.0051)⋅ω2
0.0051⋅ω2+0.98⋅ω−45.86=00.0051⋅ω2+0.98⋅ω-45.86=0
By using the Quadratic Equation Formula we get
ω=−b±√b2−4⋅a⋅c2⋅aω=-b±b2-4⋅a⋅c2⋅a
ω=−0.98±√0.982−(4⋅0.0051⋅(−45.86))2⋅0.0051ω=-0.98±0.982-(4⋅0.0051⋅(-45.86))2⋅0.0051
ω=−0.98±1.3770.0102ω=-0.98±1.3770.0102
We get two solutions for this angular speed,
ω=38.92rad.ω=38.92rad./sec.sec. & ω=−231.07rad.ω=-231.07rad./sec.sec.
We can consider only the positive value,
Angular speed = 38.92rad/sec.
Q 3: Develop a mathematical model of a DC Motor for the below equation using Simulink
Ans;
Eq_ω=VKϕ−RaKϕ2.T
Q 4: Refer to the blog on the below topic:
Refar Tesla
DC Brushless Machines:
According to him, the rotor has two or more permanent magnets that generate a DC magnetic field. This magnetic field will enter the stator core which interacts with the currents flowing in the windings to produce an interaction between rotor and stator.
It needs a proper flow of current into the rotor and stator if it’s not connected properly the current will not generate and the torque decreases.
During the Electric and mechanical conversion when the rotor is rotating, the magnitude and polarity of the stator current will continuously vary such that the torque remains constant and optimal efficiency is achieved.
Induction Motor:
The 3-phase induction motor was invented by Nikola Tesla sometime before 1889. 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. The essential difference between the two machines is with the rotor.
Unlike the DC brushless rotor, the induction rotor has no magnets. They have just stacked steel laminations with buried peripheral conductors that form a shorted structure. Currents flowing in the stator windings produce a rotating magnetic field that enters the rotor.
The frequency of this magnetic field as seen by the rotor is equal to the difference between the applied electrical frequency and the rotational frequency of the rotor itself. An induced voltage exists across the shorted structure that is proportionate to this speed difference between the rotor and electrical frequency.
The currents are produced within the rotor conductors that are approximately proportionate to the voltage, hence there’s a speed difference. Finally, these currents interact with the original magnetic field to produce forces.
When a 3-phase induction motor is connected to utility type 3-phase power, torque is produced at the outset. The motor has the ability to start under load. No inverter is needed. The fact that induction motors are directly compatible with conventional utility power is the main reason for their success.
In contrast, a brushless DC motor produces no starting torque when directly connected to fixed frequency utility power. They really need the aid of an inverter whose phase is maintained in step with the angular position of the rotor.
Cost Effectiveness
Permanent magnets are expensive – something like $50 per kilogram. 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.
This means that induction motors will likely retain a cost advantage over PM machines. Also, due to the field weakening capabilities of induction machines, inverter ratings and costs appear to be lower, especially for high performance drives. Since spinning induction machines produce little or no voltage when de-excited, they are easier to protect.
Induction machines are more difficult to control. The control laws are more complex and difficult to understand. Achieving stability over the entire torque-speed range and over temperature is more difficult with induction than with DC brushless. This means added development costs, but likely little or no recurring costs
CONCLUSION /Result:
- 1. Types of power converter circuits are employed in electric and hybrid electric vehicle are explained.
- 2.EV steady state speed is determined at 70% duty cycle.
- 3.Brief explanation of brushless DC motor vs induction motor is done there's completed successfully.
drive details ;
https://drive.google.com/file/d/1OCzg9h4gqkOSaiJME5CTd2-hwa9VD1OB/view?usp=sharing