Week-6 Challenge: EV Drivetrain

Q.

(1).Ans:-

* The power converters used in the electric and hybrid electric vehicles are four types:

(a). A.C to D.C converters

(b). D.C to A.C converters

(c). D.C to D.C converters

(d). A.C to A.C converters

(a). A.C to D.C converters:-

* These type of converters are used to take A.C power supply as input and converted to D.C power supply gives as output.

* An AC power supply has an alternating waveform which repeatedly reverses direction. An AC to DC converter will prevent the current changing direction, so that it only flows unidirectionally.

* In the circuit of an AC to DC converter, there is a step down transformer, a diode, a capacitor and a low dropout voltage regulator.

* The step down transformer takes the high level 230V from the mains supply and steps it down to a lower level e.g. 12 or 13V for our use, but it is still in A.C form.

* Where, a diode or group of diodes is implemented to restrict the current to flow in just one direction.

* In an AC waveform, there will be positive and negative peaks at each half cycle like a sine wave.

* The diode will remove the negative parts of the waveform so that there are positive peaks only,then these process called as rectifing the circuit voltage.

* So, these A.C to D.C converter called as a rectifiers.

* In Electric Vehicle or HybridElectric Vehicles, the battery pack which operates with a DC power supply is charged at home or at a charging station both of which are supplied power in AC form from the electric grid.

* So, these vehicle chargers are an example of the AC to DC power converter.

(b). D.C to A.C converters:-

* These type of converters are used to take D.C power supply as input and converted to A.C power supply gives as output.

* The power generated by solar panels are stored in batteries in the DC form and this can power a house which uses an AC power supply so that we can utilise this power inverts from the mains.

* So, these D.C to A.C converters called as a inverters.

* The DC supply is changed to an AC waveform using an electronic switch, which is basically a set of semiconductor transistors e.g. IGBTs, MOSFETs.

* These switches are controlled by a controller to either be in an open or closed position to direct the flow of current in a circuit.

* In the Electric Vehicles and Hybrid Electric Vehicles, the battery pack will supply its power to the inverter. The inverter contains a transformer which consists of a primary and secondary winding.

* The current from the battery is first supplied to the primary winding where the electronic switches will repeatedly reverse the direction of the current to create an AC waveform.

(c). D.C to D.C converters:-

* This type of converter is similar to a transformer in that it can change the voltage from its current level to another level.

* It can take an input supply of voltage and increase it or do the exact opposite and decrease it similar to a step up or step down transfomer.

* This type of a converters is called a choppers.

* It works by taking the DC supply and passing it through a switching element which converts the waveform to a square wave which is actually AC in nature.

* Then this AC is passed through a filter which will will turn it back in to a DC supply for use in a load.

* In Electric Vehicles and Hybrid Electric Vehicles and conventional vehicles, this type of converter is used for various purposes e.g the car radio may require a stepped down voltage of 12V to operate and would not need the full voltage of the car battery.

* In the case of stepping up the voltage, the motor of a car may require 500V to operate, but the vehicle may need more voltage than the battery pack can provide.

* Here are 2 main types of DC to DC converters which are isolated and non-isolated type.

* The non-isolated type can be subdivided to 5 types:

(i) Buck - to step down the voltage

(ii) Boost - to step up the voltage

(iii) Buck-Boost - this can do both step up and step down operations but is mainly used to reverse polarity.

(iv) Cuk - similar to the Buck/Boost type

(v) Charge Pump - to step up/step down the voltage for low power sources.

* The isolated type can be subdivided in to 2 types:

(i) Flyback converter - similar to the Buck Boost converter except it uses a transformer instead of an inductor to store energy.

(ii) Forward converter - this type will use a transformer to send energy between the input and output in a single step.

(d). A.C to A.C converters:-

* This type of converter takes an input AC waveform with a particular voltage and frequency and outputs a different AC waveform with another voltage and frequency.

* The output voltage or freqency can be changed or maintained depending on the application.

* There are four main types of A.C to A.c converters:

(i) Cycloconverters:-

* The cycloconverters is also known as a frequency changer as it will change the frequency of an input AC waveform and output an AC waveform with another frequency.

* This type of converter does not have any DC linkages and avoids any conversion between AC and DC to prevent losses and save costs.

(ii) A.C to A.C converter with D.C link:-

* These converter includes a DC link along with a rectifier and an inverter. The input AC waveform is first rectified by the rectifier to remove the negative portions of the AC wave and output only the positive portions.

* This creates a DC waveform which is stored in the DC link and is then converted back to an AC waveform using the inverter.

(iii) Matrix converters:-

* The Matrix converters , converts from AC to AC directly without using a DC linkage to reduce costs and losses that would otherwise be incurred with a DC link storage element.

* Matrix converters use bidirectional switches i.e IGBTs to conduct current and block voltages of both polarities.

(iv) Hybrid matrix converters:-

* These hybrid matrix type is very similar to the matrix converter in that they combine the AC-DC-AC design with the matrix design.

* It uses unidirectional switches and 2 converter stages, without the DC link to reduce the size and weight of the converter.

* These are the main four main types of power converters used in the electric and hybrid electric vehicles.

(2).Ans:-

Given data:-

Motor and Controller Parameters:

Rated Armature voltage= 72 V

Rated armature current= 400 A

Armture resistance Ra= 0.5Ω

constant K*pi= 0.7 Volt second

Chopper Switching frequency= 400 Hz

The vehicle speed-torque characteristics are given by the below equation:

Tv= 24.7 + (0.0051)w^2 ....eq(1)

* To find the EV steady state speed if duty cycle is 70%?

* we know the torque-speed relation for a motor, we are provided the armature resistance, voltage and kphi values. We also know the duty cycle is 70%.

* So the average voltage is given by the product of the battery voltage and the duty cycle:

Vo= V * dc

Vo= 72 * 0.7

The average voltage i= 50.4 V.

We know that torque-speed is given bye the equation,

Tm= [(Vo*(k*pi)/Ra] - [(w * (k*pi^2))/Ra]

where,

Tm= torque

V=Armature voltage

Ra=resistance

w=speed rad/sec

Tm = [(72*(0.7)/0.5] - [(w*(0.7)^2)/0.5]

by simplifing the above equation we get,

Tm = 70.56 - 0.98w

* In order to find the roots,

* Now we have 2 expressions for the torque that are both in terms of the angular speed. The first expression is the torque of the vehicle, whereas the second one is for the motor.

* Equating the 2 expresssions, we will get a quadratic equation which can be solved to find the angular speed.

Tm = Tv

70.56 -0.98w = 0.0051w^2 + 24.7

by using formula ax^2 + bx + c

0.0051w^2 + 0.98w -45.89 = 0

we get,

x=( -0.98 + or - 1.377) /0.0102

here we got two solutions for the x

w= 38.92 rad/s or w= -231.08 rad/s

so,

* here we consider only positive value for the result of speed.

* The forward direction is the positive and that the vehicle is in steady speed moving in the forward direction.

* Here we consider first solution and reject the second solution.

(3).Ans:-

To Develop a mathematical model of a DC Motor for the below equation using Simulink:-

w = [V/(k*pi) - Ra/(k*pi)^2] * T

V= 50.4 at 70% of EV steady state speed if duty cycle .

Ra= 0.5

K= 0.7

* By using above parameters we develop a simulink model.

OUTPUT RESULTS:-

(4).Ans:-

* In the referel artical summary about the brushless DC and induction motor by the words of Wally Rippel, Principal Power Electronics Engineer.

* He also worked in jet propulsion laboratory on electric vehicle battery research ,among other projects proponent means someone who is in favor of something.

* He said the lead acid battery is replaced by lithium and brush DC motor with brushless DC motor or induction motor,Next he talk a closer look of the brushless DC motor and induction motor there technologies.

* He said that induction motor not require inverter and the motor has ability to start under the load with the fixed utility power dc brushless motor produces no starting torque it needs inverter.

* The wally ripple studied and compared the difference between the brushless d.c motor and the induction motor.

* And finally he didnt get the answer which one is best for the electrical vehicle both are same in characterstics and parameters.

* Both DC brushless and induction drives use motors having similar stators.

* Both drives use 3-phase modulating inverters. The only differences are the rotors and the inverter controls. And with digital controllers, the only control differences are with control code.

* One of the main differences is that much less rotor heat is generated with the DC brushless drive.

* Rotor cooling is easier and peak point efficiency is generally higher for this drive.

* The DC brushless drive can also operate at unity power factor, whereas the best power factor for the induction drive is about 85 percent.

* In an ideal brushless drive, the strength of the magnetic field produced by the permanent magnets would be adjustable.

* 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.

* Finally, by the above artical walley ripple was found that both the motors are useful as per required parameters.

* He conclude that Dc brushless drives alre using mostly in electric vehicles.