Week-6 Challenge: EV Drivetrain

AC to DC converter

DC or direct current is a electricity flowing in a constant direction. It has posetive (+Ve) and negetive (-Ve) terminals. DC is the kind of electricity that made by converting alternative current or AC, from battery or rubbing some specific materials each other.

Some motors, dynamos or electro mechanical generator can naturally produce voltage. But in this case they are alternate their polarity. Maybe by a voltage switching or as a current switching back and forth. It is called AC. As polarity changes it creates frequency.

First of all you need a transformer which transform 220v and make it a low voltage AC wave. Remember Transformer only work on AC, Transformer size depends on core material, voltage rating, current, and copper quality.

After step down to a smaller voltage you need to stop polarity changes and also stop those frequency as DC pass in one direction and has 0 frequency.

How to do it?

Rectifires

(A rectifier is an electrical device that converts alternating current, which periodically reverses direction, to direct current, which flows in only one direction. The process is known as rectification, since it "straightens" the direction of current. )

For this you need diodes. Diode is a component which allows Electrons to pass in one direction by his anode cathode combination. It acts as a valve. Back to 1960-70 vaccum tubes are used insted of diodes.

In the extreme left ac wave changing its direction. Up down up down. When you connect 4 diodes as same as the picture those lower waves are lifted and make the wave as one directional. Now it is DC. But not purely. This wave is not smooth.

Then what to do?

Here is a very good way to rectify this wave. Lets add a electolitic capacitor with a higher value. Capacitor work as a tank. It’s has a ability to store charge.

What is going on in this circuit?

When those first round of DC wave comes up capacitor get cherged wave comes to zero instantly but capacitor discharge slowly, so inthe output line voltage always presented. Filter capacitor fills those gaps as the don't get discharge very fast. It’s smoothly generates DC.

Now if you want to make it more streight then add a voltage regulator. This can be achieved by a zener diode too. Zener diode is a type of diode that act as same as diode but has a condition. It has limitation at a specific voltage (this voltage is a rating of zener diode). If the voltage reach the limitation it will pass the flow in bi directional. It will not act as diode in this time. Best way to use regulator. This regulator is IC inbuilt with those zeners and many components. It will regulate the voltage and block unwanted spikes.

AC to AC converter

AC to AC converters is used for converting the AC waveforms with one particular frequency and magnitude to AC waveform with another frequency at another magnitude. This conversion is mainly required in case of speed controlling of machines, for low frequency and variable voltage magnitude applications as well. We know that there are different types of loads that work with different types of powersupplies like single-phase, three-phase supply, and the supplies can be differentiated based on the voltage and frequency range also.

The AC to AC converters can be classified into different types:

• Cycl converters
• AC to AC Converters with DC link
• Matrix Converters
• Hybrid Matrix Converters

1. Cycloconverters

Cycloconverters are majorly called as frequency changers that convert the AC power with one input frequency to AC power with a different output frequency and can be used for changing the magnitude of the AC power also. Cycloconverters are preferred for avoiding DC links and to avoid many stages like AC to DC to AC which is not economical and causes more losses. The cost of the DC link required will vary according to the ratings of the supply power being used.The input wave frequency changed by changing the firing angle applied to the thyristors. By switching the positive and negative limb thyristors, we can get variable output frequency that can be step-up or step-down frequency compared to the input frequency.

2. AC to AC Converters with a DC Link

AC to AC converters with a DC link generally consists of a rectifier, DC link and inverter as in this process the AC is converted into DC by using the rectifier. After being converted into DC, the DC link is used to store DC power, and then again it is converted into AC by using the inverter.

3. Matrix Converters

Matrix converters are used for converting AC to AC directly without using any DC link for increasing the reliability and efficiency of the system by reducing the cost and losses of the DC-link storage element.
Matrix converter consists of the bidirectional switches that practically don’t exist at present but can be realized by using the IGBTs, and these are capable of conducting current and blocking voltage of both polarities.

4 .Hybrid Matrix Converter

DC to DC converter

A DC-DC converter is a type of electronic circuit that takes the DC source and then converts it from the current voltage into another voltage. In some instances, one may have to increase or decrease the voltage. This is actually very common when it comes to automobiles. Some devices you might use in your vehicle, such as a portable DVD player for the kids, require a certain amount of power to run.

Two of the terms commonly found around DC-DC converters are non-isolated and isolated converters. The non-isolated converters are often used when the change in voltage is small. Five different types of converters fall into this group.

Buck: The buck converter is used whenever one needs to reduce the amount of voltage.

Boost: A boost converter does the opposite of the buck converter. It steps up the voltage level.

Buck-Boost: This type of converter can work as either bucking or boosting the voltage. The most common usage for the converter is to reverse polarity.

Cuk: This type of converter is similar to buck-boost converters. The biggest difference is really the name. The Cuk was named after Slobodan Cuk, the man who created it.

Charge-Pump: This converter is used for stepping the voltage up or down in applications that have low power.

2.

Known parameters:

Rated Armature voltage= 72 V

Rated armature current= 400 A

Ra= 0.5Ω, KΦ= 0.7 V-s

Chopper Switching frequency= 400 Hz

The vehicle characteristics are given by the equation

TTR=24.7+0.0051w2

EV steady state speed if duty cycle is 70%

`T = V*Km/Ra - Km*phi^2/Ra*w`

There motor volatge = 0.7*72

= 50.4 volts

On substituting the values

`T = 50.4*0.7/0.5 - 0.7^2/0.5*w`...........1

We know that

TTR=24.7+0.0051w2 ...............2

On substuting 1&2

`24.7+0.0051w2 = 50.4*0.7/0.5 - 0.7^2/0.5*w`

Solving this equation we get

w= 38.82rad/s or w =-230.9 rad/s

As -ve value is unrealistic we we get 38.82rad/s

3 Induction Versus DC brushless motors by Wally Rippel, Tesla

The author basically conveys that there is no hard and fast rule that one is better than the other ,discussing working of both the motors and explaining both of their pros and cons author comes to a conclusion that both of them have their own uniqueness and depending on the requirement and skill availablity preffered motor can be chosen

some key diffrences for consideration include

• One of the main differences is that much less rotor heat is generated with the DC brushless 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.
• Induction machines have no magnets and B fields are “adjustable,” since B is proportionate to V/f (voltage to frequency). This means that at light loads the inverter can reduce voltage such that magnetic losses are reduced and efficiency is maximized. Thus, the induction machine when operated with a smart inverter has an advantage over a DC brushless machine
• With induction, as machine size grows, losses do not necessarily grow. Thus, induction drives may be the favored approach where high-performance is desired; peak efficiency will be a little less than with DC brushless, but average efficiency may actually be better.
• Induction motors will likely retain a cost advantage over PM machines.
• Induction machines are more difficult to control.
• Final conclusion accourding to author 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.

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