2:31

And finally, at the end of simulation, we call that Tend,

the converter should be in steady state at operating point 3,

and that's the case where we have the power flow in the opposite direction

with the Vbus of 20 volts charging the battery.

On the example template that is provided, we have

those values set to one millisecond, two millisecond, and three millisecond,

but these parameters can be adjusted,

if you find your converter needs more time to get to steady state, that's fine.

Simply adjust the parameter t1 or t2, or Tend.

Your converter will use the switching frequency of your choosing,

and you can define the switching frequency by defining the switching period Ts,

also in the section of simulation commands and parameters.

And then finally, an important box in this section, is the box where we define

the scale factor between the inductor current and the flux density.

5:14

The values associated with the control 1 signal are called Vref1.

And those have one, two,

three different values that corresponds to three operating modes.

So for example, let's suppose you want your converter to be in

steady state at time equal to t1, with five volts at the output.

You can use the value of Vref1_5V as the value that

sets the duty cycle for your converter so that the output

of five volts is produced in steady state, and so on.

So, importantly, in milestone one,

use the control sources that are modeling the behavior

of the power management system as the inputs to the pulse width

modulators that set the switch duty cycles to exactly such

values that the output is equal to the desired operating point.

Now we say, set the duty cycles which really means that you may have

more than one converter in your design,

or you can have one converter that has buck and boost capabilities,

it's your choice.

But you can use up to two of these sources, Vcontrol1 and

Vcontrol2 are available, not more than that but

you can certainly use just one of them, and not do anything with the other.

These control sources have predefined 100-ohm internal resistances,

and they cannot be used to provide any meaningful power in your design.

6:53

Here is an example of how these control sources may be arranged.

So at the beginning, we set Vref1 and Vref2 to the values that

will in our converter produce five volt output, and that lasts up to t1.

Then we have a transition of 0.1 millisecond to Vref1 and

Vref2 that correspond to operation of 20 volts at the output.

And then finally we have the two values defined for

the case where we have the power flow in the opposite direction.

So the sequence of events in milestone one, for

your converter will be first operation at operating point 1,

Then at operating point 2 and finally, operating point 3.

At the end of this, each one of these intervals,

we have a period of time that consists of ten cycles, ten switching cycles.

That period of time is going to be used to measure the average value of

the voltage or to measure the ripple.

So it will be your responsibility to make sure that your converter operates indeed

in steady state

at the end of this time interval, t1,

in steady state at the time interval, t2, and

in steady state at the end of simulation.

All right, now, that is directly related to a number of

commands that are provided to measure performance of your circuit.

You can go through the details of these commands and

in fact you should, to see exactly how different parameters are going to

be measured to verify performance of the circuit.

As an example, let's look at the time t2.

We would like to find out whether the output voltage

of the converter at this time is first of all in steady state,

that should be a visual inspection of the waveforms.

And second, what is the average value of that voltage?

Well, first of all we define this time right here as the beginning of this

OP2 interval,

this time here as the end of the OP2 interval, so

those two times are defined right here.

9:18

There is nothing you need to change in the measurement commands.

Except, if you have more than one inductor, then

you need to include the Bscale factor for the second inductor.

If you have more than two inductors, that's fine but

you need to add additional lines for

the measurement of the flux density in each additional inductor.

The most important point about any of the milestones in the capstone design

is to very carefully review the corresponding

document that spells out the rubrics for grading.

You will be grading the design of other people but the best thing to do first

is to review this grading rubric so you know exactly how to design and

track your converter before you submit your work for grading.

This is just the beginning of that Milestone1.pdf file.

I'm just showing this to emphasize the point that this is perhaps the most

important document to review very carefully.

There are a number of pages that follow with a number of additional rubrics.

11:07

Notice the input port is called in, the output port is called out,

and there is only one control signal used right here.

And that control signal is what sets the duty cycle for

the two switches in the boost converter,

which really means this converter is indeed bi-directional.

The power can flow from input from the battery to the USB or

the other way around,

and so we have a bi-directional power converter in place.

The first rubric associated with grading this design is

a question whether the approach is briefly described and is schematic included.

All right, we have included the schematic right here, but then,

there is a question whether the approach shown is capable of operating at points 1,

2 and 3 described above.

And those are points of 5 volts, 20 volts, and 20 volts charging.

When you grade someone else's work, you choose one of these two answers.

It’s either Yes or No.

Yes is worth 70 points, No is worth 0 points.

So what do you say for this design?

We have a boost converter from battery to the bus.

There is no way that boost converter can step down the voltage to five volts,

and so we're now going to be able to operate at operating point 1.

So, operating point 1 is not available.

In this case here, it would earn 0 points for the design.

15:46

and that's great.

You can see for example this start of the five

volt operating point is 0.9 milliseconds.

The end of that is 1 millisecond.

And that for the converter that is switching at 100 kilohertz is exactly 10 periods.

And we have such time start and end defined for

the operating point two and the operating point three.

Right, let's look at the results.

The vout_5v, that is supposed to be the average value of the bus voltage at

the operating point one, it should be 5V +/- 0.1V but

our result is far from that because we have a boost converter

that's not enable to produce or reduce the voltage to 5 volts.

And so this is not good, and here we will earn 0 points.

Now the second operating point,

we want to be between 20 +/- 0.1,

and our result of 20.0082 is great.

And so, we're going to earn 5 points right here.

Now we also check ripples over the same steady state time intervals,

but we do that only at the operating point two.

And so we have the input voltage ripple, that's right here,

it's supposed to be less than 0.1 volt.

What is it?

Well we have 0.112, so it is greater than what is allowed.

And so, we would earn 0 points here as well.

That simply means our input capacitor is too small.

On the output side, however, our ripple meets the requirement and

so we will earn five points for that.

Now, the next line checks the maximum flux density through the inductor.

In this case here, we have just one inductor and so

there is just one measurement line.

If you had more inductors, you need to have multiple measurement lines, one for

each inductor.

The maximum flux density in steady state operation

at operating point two is found to be about 0.2 Tesla,

that meets the requirement of less than 0.33 Tesla,

and so we earn five points for that rubric.

And finally, that is a calculation of efficiency.

It's automated.

So efficiency is calculated as output power over input power, at

the operating point 2.

And the result obtained is 96% for

the boost example; that 96% is a good result,

and that will actually earn full 10 points in the rubric.

You will see the rubric for efficiency actually has several different values.

The higher the efficiency you have, the larger number of points you will earn.

The final point is the check whether the charging current

from the USB bus at the operating point 3 is 3 amps plus minus 0.1 amp.

If you look at the measurement result and you see that's okay and

you earn points for that rubric.

So this is just an example of how the grading is going to go,

but again, this is also a very good guide of how you can

check your design before you submit your work for grading.

And finally, a couple of important notes on submission of your work and

for peer grading.

An important point is, you will be allowed to submit your work only once.

So, make sure that everything is correct and

complete before you click the submit button.

Why is that?

Well, it is related to the fact that these works are going to be peer graded

so there has to be a point where the submission is available to other

learners to look at, and you cannot make updates after that,

after someone has already started looking at your design.

So bear in mind that you will only be allowed to submit once.

And again, make sure that everything is fine and

correct before you click on the submission button.

As I already mentioned, it is very important to very carefully

review the rubrics in the Milestone1 document.

Rubric can be used through the entire design process to make sure that

you're meeting all the design requirements,

and you can actually score yourself, and

have a good expectation of what scores you should expect from your peers.

You will be asked to submit your work and

simulation files to be evaluated by peer graders.

When you prepare your simulation files for submission,

make sure that you include all necessary simulation files.

This is very important.

Do not assume the grader has a library or doesn't have a library.

Include everything that is necessary to run your simulation.

It is also your responsibility to make sure that simulation converges and

completes without errors.

Do not include any raw files.

And do not include your results in the submission because the raw

files are very large in size and they really are not going to matter at all.

The grader will have to reproduce your simulation anyway and so

the raw files are not going to be necessary.

You will collect all the files you need into a very clean folder,

zip the folder and upload the zipped file.

And that's going to be the submission of the simulation of work.

Upon submission of your work,

you'll be required to grade submissions by three other students.

Many students choose to grade more and

you will be offered opportunities to grade more than three if you wish to do so.