Learners will design a DC-DC converter that powers USB-C devices (20 V at 3 A) from a dc input voltage source such as a lithium-ion battery pack or a desktop computer power bus. Aspects of the project will include: ● Design of converter power stage and magnetics. Requires mastery of courses 1, 2, and 5. ● Simulation to verify correct steady-state operation. Requires mastery of courses 1, 2 and 4. ● Design of converter control system. Requires mastery of courses 3 and 4. ● Simulation to verify correct control system operation. Requires mastery of courses 3 and 4. ● Preparation of milestone reports documenting the design and its performance The reports will be peer graded.
Milestones for Weeks 3-4
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來自 University of Colorado Boulder 的課程
Capstone Design Project in Power Electronics
55 個評分
從本節課中
Preliminary Controller Design
Develop an averaged model of your power converter. Select a control approach (voltage mode, peak current mode, or average current mode control), and begin the design of the control loop(s) to meet requirements on crossover frequency and maximum closed-loop output impedance. Begin development of LTspice averaged simulation of your controller design.
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Dr. Robert EricksonProfessor
Electrical, Computer, and Energy Engineering
Dr. Dragan MaksimovicCharles V. Schelke Endowed Professor
Electrical, Computer and Energy Engineering
Dr. Khurram AfridiAssistant Professor
Electrical, Computer and Energy Engineering
In this lecture we briefly review Milestone 2 requirements.
In Weeks 3 and 4, you're going to do a preliminary
design of the control loops around your converter
and you will verify the control loop operation by simulations of
an averaged model of your converter with control loops included.
As in Milestone 1, we rely on a header template
that we call milestone2 schematic.
And that milestone2 schematic includes, again, model of the battery,
model of the USB, the power management control signals, simulation commands and
parameters, and importantly the measurement commands for,
in this case, transient and AC simulations.
The template must be included in the schematic
file that you submit for grading.
So the file that you submit for grading will look like this.
It will have the template in the top, and it'll have your circuit at the bottom.
Notice that we use standard node names.
The input is in, that's the battery side.
The output, or the USB side, is out.
Both the input and
the output must share the same ground, that's the ground in SPICE.
And there are up to two control signals available as piecewise linear
sources that can, in this case here, be used to set
appropriate references for your control loops.
The simulation commands and parameters have
several parameters that you should adjust according to your design.
Parameter t1 is the time when the converter should be in steady state at
operating point 2 delivering 20 volt at USB at 3 amps,
and parameter Tend is the end of simulation where the converter should
be in steady state at operating point 1,
delivering 5 volts at 2 amps at the output.
So in this case here, we have the reverse, right?
So we are first at operating point 2 at 20 volts,
because this is the operating point, we will do AC simulation at.
And then second after that we go on to operating point 1 and
show that we can produce 5 volt at the output.
You again define your switching period or your switching periods.
If you use more than one converter,
you may have different switching frequencies in the two.
And in this case here, since there is going to be an AC simulation
that is based on the SPICE ability to solve for an operating point first,
that can have convergence problems, especially if the circuit is complex and
includes a number of control loops around.
What may help in the process of going around convergence problems
is to set the voltage values to something that is known.
There is a command that's called .nodeset that can be used to
set node voltages to known values.
In this example here, we have set the output voltage to 20 volts,
and the input to 9.3 volts,
but you can add additional voltages, depending on the type of your circuit.
Typically, the voltages across capacitors or
other voltages that you know the steady state value of.
And then finally, at the bottom are the commands that control simulation.
You should not change those except that you should have activated
either the transient simulation or the AC simulation.
There's going to be two simulation runs performed to verify your design.
The control signals look exactly the same as in Milestone 1.
Again, those are the control signals that, in this case since you have control
loops designed, you're operating the converter in closed loop,
you can use these control signals to set the references for your control loops.
The measurement commands, there's no need to change those.
They're set up to measure the values that are going to be checked in the rubrics for
Milestone 2.
Here's an example of a simulation, a Milestone 2 simulation of a design.
An example of a transient simulation that shows
that indeed at t1, that's going to be right here,
our converter is at the operating point 2 and
producing 20 volt at 3 amps.
At time Tend, the converter is at operating point 1,
and is producing 5 volts at 2 amps.
So the converter is capable, in this case, to produce both the 20 volt and
the 5 volt,
and this is done in the average circuit model.
The transient simulation is going to compute the average values
at the time interval around t1 and the time interval around Tend,
and the values obtained by simulation
are at t1, 19.98 volt.
That's very, very close to 20.
It certainly meets the requirement, and so the rubric would receive full credit.
At operating point 2, the measured value of the voltage is 4.98,
and that's operating point 1, and
that certainly is a well-regulated voltage as it should be at 5 volts.
Then for the same design, we perform AC simulation.
And you see now we have commented out the transient simulation,
and we have the AC simulation active.
The template is set up to have an AC source at the output port,
at the USB port, an AC current source of value 1.
And so measurement of the output voltage is going to actually
give us the output impedance.
A test source is given in the template.
And you plot V(out) to observe the output impedance of the converter.
The rubric is based on the maximum value of the output impedance.
That's the value that is important for
the quality of load transient responses, for example.
And in this case here, we find that the maximum value of the output impedance
occurs somewhere between 10 and 11 kilohertz, and
it has a value of about -12 dBohm.
In the measurement lines that you obtain in the SPICE error log,
you will see that dB value here is -12.468 dB.
But we would like to check that value in ohms.
And so, the measurement template also includes conversion of that
value back to ohms, and the value that is obtained right here is in fact in ohms.
Ignore the dB next to it.
We obtain the output impedance, the maximum value,
is around 0.24 ohms which is less
than 0.5 ohms required.
And so we again earn credit for this particular rubric.
Finally, I would like to remind you that it is really important to review
carefully the Milestone2 document that has details of the rubrics for the Milestone 2.
And do your design based on the rubrics, and
grade other students' work based on the rubrics.
