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43:22
Transcript
0:12
so I will just go through the
0:15
oldfashioned paper uh syllabus so the
0:20
course is going to be taught on canvas
0:21
so the canvas site has been published uh
0:24
we will for for uh homeworks and things
0:27
like that they'll be handed out and
0:30
turned in on paper but you can download
0:33
them from canvas as
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0:35
well um the classes are going to be here
0:39
Mondays Wednesdays and Thursdays so on
0:41
usual class schedules 1
0:44
pm uh I've mentioned the textbook there
0:47
are some other textbooks that you might
0:49
find Handy and I've listed those in the
0:51
course handout those are completely
0:53
optional you don't have to buy them the
0:55
libraries also have
0:57
copies um the way homeworks will work in
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1:01
this
1:02
class is that will typically be issued
1:05
on a Monday and do the following Monday
1:08
okay and uh for the most part you are
1:12
allowed to collaborate and talk about
1:15
the homework problems so you feel free
1:17
to get together and discuss the problems
1:19
that there it's intended that you do so
1:22
the only constraint we have is that you
1:24
must hand in your own solution right so
1:26
so you can trade ideas but in the end
1:28
the thing you write up it can't be a
1:29
copy your neighbors it has to be your
1:32
solution but you can base it on uh you
1:35
know ideas you've exchanged with others
1:37
okay for those who don't know
1:42
anybody or or don't have access to study
1:45
partners and may have questions first of
1:46
all there will be office hours uh Mon's
1:49
office hours will be Thursdays 4: to 5:
1:52
p.m. and Fridays 4 to 5:00 P p.m. in
1:54
10178 in building 10 okay but there are
1:58
also a number of students students in
2:00
the Le laboratory 1050 who have had this
2:03
class before will be happy to answer any
2:05
questions and a few of those students
2:07
are listed in the uh course
2:12
description we've also decided not to
2:14
have exams this term or in-class exams
2:19
rather we're going to have assessments
2:22
which are essentially take-home mini
2:24
quizzes uh they will generally be uh um
2:31
they'll be generally issued weekly and
2:33
this says they're going to be issued
2:35
starting on March 1st I should check if
2:38
that yeah starting on March 1st they'll
2:40
be issued weekly they'll be issued on a
2:42
Wednesday that will be due the next day
2:44
Thursday and those will be submitted
2:47
through canvas through grade
2:50
scope
2:52
um as for homeworks we can take late
2:55
homeworks if you arrange it ahead of
2:57
time and there's some compelling reason
2:58
why they're late assessments are a
3:00
different
3:01
story also the collaboration policy for
3:04
assessments is different you cannot
3:06
collaborate or discuss the problems at
3:08
all for assessments and and you know we
3:11
can't prove or not prove that you're
3:13
doing so but this is you know this is an
3:15
exam effectively so don't discuss it
3:17
with your neighbors and don't discuss
3:19
anything until the solutions are out
3:20
because there may be people who have
3:22
made some special arrangement for
3:24
because they're traveling or or for
3:26
whatever reason to hand it in late okay
3:28
so we're going to have homework and
3:30
assessments and the goal of the
3:32
assessments really is instead of a you
3:34
sort of very few high stakes
3:37
opportunities to show your abilities the
3:40
assessments are sort of distributed in
3:42
low stakes and focused and gives you a
3:45
better opportunity to show you what you
3:46
really know okay so please complete them
3:50
entirely on your own no consultation the
3:53
only thing you're allowed to do is ask
3:54
the core staff clarifying questions just
3:56
the way you might in an exam okay
4:00
and uh as for the assessments you can
4:03
use any of the course materials you know
4:05
read the book whatever you want
4:09
uh do
4:10
not go outside and try to use the
4:14
worldwide web and for that matter the
4:16
use of Bibles is also prohibited I know
4:18
that there's collections of old 6334
4:22
materials floating around you're not
4:24
supposed to be Consulting those okay
4:27
this just supposed to be a measure of
4:28
what you've learned okay okay so the
4:31
grading will be based on three
4:32
components homeworks are going to be
4:35
40% these assessments will be
4:38
50% and there's also a final project
4:41
which is 10% and the final project
4:44
sounds like it's only 10% but it's the
4:46
last thing we look at when we're going
4:48
to assign a grade to everybody and it
4:50
really is your opportunity to put
4:52
together knowledge that you've learned
4:54
throughout the class into a real it's on
4:57
paper it's not a it's not a phys phical
5:00
converter you will construct but it's a
5:01
paper design but it's really your
5:03
opportunity to show us how you've
5:04
synthesized all this knowledge to be
5:06
able to really design Power Electronics
5:09
and I should say just as an aside in
5:11
this class we only have a paper design
5:13
or or but this complements nicely the
5:18
undergraduate Power Electronics class
5:20
which has a lot of really nice lab
5:22
activities and design activities there
5:24
so even if you're a graduate student
5:26
it's it can be a pretty good thing to
5:27
take in terms of of uh rounding out the
5:30
LA your lab skill set in this area
5:34
Okay um if you have any necessary
5:39
technical accommodations don't have
5:41
access to uh iPads or whatever else you
5:44
need for grade scope please let us know
5:46
we'll try to assist uh assist with that
5:53
okay so with that are there any
5:57
questions about anything like associated
5:59
with the course
6:03
mechanics okay so let me um give you a
6:10
sense of what this course is going to be
6:13
about and uh this is one of my favorite
6:17
photos is actually one that uh Nicola
6:20
Tesla mocked up he wasn't really sitting
6:22
next to his Tesla coil when he did this
6:23
or he might have gotten killed um he
6:26
kind of double exposed this but more to
6:28
the point
6:30
uh the quote from him is if we could
6:32
produce electrical effects of the
6:33
required quality this whole planet and
6:35
the conditions of existence on it could
6:37
be transformed and I think the sort of
6:40
the more than a hundred years since he
6:42
he said that or well more than 100 years
6:45
since he said that uh have borne that
6:48
out but it's also true that even
6:51
today uh there's really revolutions
6:55
happening in the way we use energy
6:57
everything's being electrified from
6:59
vehicles to transportation to power
7:02
generation from renewable
7:04
resources and um handling all that
7:08
requires some means of processing
7:10
controlling and converting energy and
7:12
that's really what we're about
7:14
processing controlling converting
7:15
electrical
7:16
energy if you look at what the uh itle e
7:21
the which is sort of the governing body
7:23
of electrical engineering says about
7:25
Power Electronics it says this
7:27
technology encompasses the use of
7:28
electronic components
7:30
the application of circuit Theory and
7:31
design techniques and the development of
7:33
analytical tools towards efficient
7:35
electronic conversion control and
7:37
conditioning of electric power and
7:39
that's what we're really about here so
7:41
we're going to do circuit Theory we're
7:43
going to learn design techniques we're
7:44
going to learn about all the components
7:46
you need to do this we're going to learn
7:47
about controls how do you put it all
7:50
together to make energy conversion
7:52
systems okay so as I mentioned the
7:56
primary function of Power Electronics is
7:58
to take sort of electrical energy in one
8:00
form and convert it into some other form
8:03
you need uh it's really a core
8:06
technology in the electrical
8:07
infrastructure it used to be that the AC
8:09
grid was generators and you'd connect it
8:11
up to things like directly things like
8:13
Motors or lighting or whatever but
8:16
that's pretty much changed at this point
8:18
right lighting is LED lighting you need
8:20
power supplies to go between the grid
8:22
and the lighting same thing heavily
8:24
loads computers Motors everything else
8:27
you need energy tends to flow through
8:30
one or even several layers of power
8:32
conversion circuitry from the principal
8:35
source to the final usage okay and so
8:38
the Power Electronics first of all you
8:41
know the efficiency of that is very
8:42
important but also how you do it impacts
8:45
the quality of the final system so the
8:48
Power Electronics can really be a major
8:50
factor impacting what you can and can't
8:52
do and how well it works
8:56
okay so if you showed up you know
8:59
hundred years
9:01
ago this is what Power Electronics would
9:03
look like right some vacuum tubes and
9:05
some Transformers and that kind of thing
9:09
interestingly of course it's nothing
9:11
like that today but with the techniques
9:14
you're going to learn in this course you
9:15
could actually go back and analyze this
9:17
thing and figure out what it did right
9:19
so some foundational ideas that we're
9:21
going to come back to which can be 100
9:24
years old but there's also elements that
9:26
are extremely new okay and today you
9:29
know this this was fancy 100 years ago
9:32
today Power Electronics is everywhere
9:35
from I say from mowatt to gigawatts and
9:38
and it does actually use switch mode
9:39
power conversion down at those power
9:41
levels this is actually a a multi-watt
9:43
power supply and this is literally at
9:45
the gigawatt scale so if you if you go
9:48
out to S the Sandy Pond terminal there
9:50
is a power converter that takes two gws
9:53
coming down from Canada hydro and
9:55
converts it to AC to power homes and
9:58
everything else around here right so and
10:00
the techniques that we're going to learn
10:01
in this class really span the entire
10:05
range right so some of the details
10:06
change and we'll learn about that but
10:08
there's underlying principles that that
10:10
cut across all kinds of electrical
10:12
energy conversion systems
10:16
okay what kind of applications well
10:18
portable Electronics this slightly older
10:20
an iPhone 5 and you think okay iPhones
10:23
got radio transmitters and displays and
10:25
other stuff in it but it turns out that
10:27
a large fraction of the volume and board
10:30
area is actually associated with energy
10:33
conversion in the thing because no
10:34
matter what you're doing you're
10:35
processing energy to process information
10:37
right so something like 40% in this of
10:39
the motherboard in this example was
10:41
associated with power
10:43
conversion likewise you know at some
10:45
point you're going to charge your phone
10:47
or your or your iPad or your computer
10:49
into the wall that's mostly Power
10:52
Electronics too all kinds of computers
10:54
if you're in a data center there's
10:56
several layers of power conversion
10:58
between the AC group GD and the final
11:01
set of
11:02
processors okay this is more of what it
11:05
looks like inside your home computer
11:07
we'll actually learn exactly about those
11:10
kind of converters and about all the
11:12
components that are in them if you're
11:14
going to communicate right the
11:16
transmitters we tend to think of this as
11:19
analog circuits to to make RF
11:21
transmitters but in fact Power
11:22
Electronics are heavily embedded in any
11:25
real communication systems to increase
11:27
the efficiency of transmission
11:31
all kinds of commercial applications
11:33
whether you're you know doing LED
11:35
lighting or this is actually from some
11:38
water
11:39
Purity device but of course it requires
11:42
a power supply right
11:45
so almost any use of energy these days
11:48
requires a power
11:50
supply even in your home I mentioned
11:52
that it used to be that you'd connect
11:54
Motors up to the grid and they'd run and
11:56
maybe You' turn them on and off
11:58
something like that but no longer right
11:59
if you want high performance you need to
12:02
be able to modulate that energy so two
12:04
examples here this is for an air
12:07
conditioning unit and it uses an
12:10
inverter a DC to AC converter inside it
12:12
to drive the motor much more quietly and
12:15
much more modulated for higher overall
12:17
system efficiency even your dishwasher
12:20
these days has power converters in it
12:23
because it's more efficient in this case
12:25
quieter to do it that way okay IDE is
12:30
that you might not think of as power
12:33
converters medical applications this is
12:35
this is actually a uh magnetic
12:39
stimulator generates 5,000 amps pulse
12:41
trains in a transducer coil to throw up
12:43
magnetic fields that can trigger nerves
12:46
this is an interesting one it's actually
12:47
homework zero so the thing you're
12:49
analyzing in the first homework just to
12:51
break the rust off is actually this box
12:53
right here okay scientific applications
12:57
you may not be processing energy but
12:59
even if you just need to generate
13:01
electric High electrical fields for
13:03
whatever reason or magnetic fields as in
13:05
the magnetic stimulator you need energy
13:07
conversion circuits to do it then
13:10
there's the sort of the more maybe the
13:12
applications you might think of
13:14
Transportation right let say that
13:17
electric vehicle or a hybrid vehicle
13:19
right you
13:21
need Power Electronics to drive the
13:23
energy conversion and this is not a
13:24
small thing first of all you need the
13:25
Power Electronics to drive these things
13:28
right secondly in fact as in one
13:31
example they redes they
13:34
redesigned the power converter for a
13:37
Prius the the power train for the Prius
13:40
the fuel economy went up by 5% just by
13:43
redesigning the Power Electronics to be
13:45
better so it has a huge impact on the
13:48
overall application and of course that's
13:52
um electric vehicles but traction right
13:56
trains that's higher power but the same
13:58
issue
13:59
actually even future trains this it's a
14:01
little hard to see behind this railing
14:03
that's a maglev magnetically levitated
14:05
train along the Wayside over in the back
14:08
corner you see this big building here
14:10
inside that big building as these racks
14:12
of Power Electronics now you better have
14:14
pretty reliable Power Electronics if
14:16
your vehicle's flying along at 400 kmers
14:19
an hour floating on you know that far
14:20
off the ground right so not only do you
14:23
need efficiency but you need reliability
14:26
and precision okay even Strang
14:29
things uh this is this is an example of
14:32
a drone just by powered by high voltage
14:37
right you just apply high voltage it
14:38
breaks down the air accelerates ions and
14:41
you can use that for propulsion that's
14:43
the first demonstration of it but it
14:45
actually it's very similar in some
14:47
regards to what people use for space
14:49
propulsion you've heard of ion engines
14:51
right the twin ion engine TIE fighter or
14:54
what more practically they use to uh to
14:57
reposition satellites those require
14:59
Power Electronics to generate high
15:00
voltages and accelerate ions okay Power
15:05
transmission and generation right that's
15:08
so you're getting your energy from
15:10
somewhere and increasingly we're getting
15:11
it from renewable resources well
15:13
generally the way things are trending
15:16
you take some mechanical or solar or
15:19
other source of energy and you
15:21
transition it not only through a
15:24
generator but through Power Electronics
15:25
to get there and that's true for
15:27
terrestrial things things like this is a
15:30
house rooftop PV system this is a micro
15:33
inverter
15:35
um
15:36
Automotive Systems or even much smaller
15:39
things like uh
15:42
uh Power harvesting energy harvesting
15:45
techniques you need Power Electronics in
15:48
it also all kinds of industrial
15:50
applications whether you're doing uh
15:53
plasma processing for Semiconductor
15:56
processing or you know you want to
15:58
refine metals like a DC Arc furnace you
16:02
need Power Electronics there too okay so
16:04
that's just sort of a way long way of
16:06
saying power electronics are in almost
16:09
everything you care about these days and
16:11
it's only getting more so because we
16:13
have to be better about how we use
16:15
energy
16:19
okay so what's inside a power converter
16:22
and we're going to talk about this in
16:23
much greater detail but if you want to
16:26
think about it what we have
16:30
is typically some kind of energy storage
16:33
elements these could be inductors or
16:35
capacitors or sometimes other things and
16:38
what we're going to do is we're going to
16:40
use semiconductor switches and we're
16:42
going to draw energy from some Source
16:44
we're going to manipulate it somehow so
16:46
we store it in these energy storage
16:48
elements and then we're going to put it
16:49
to the output and we're going to repeat
16:51
that right so draw transform put it to
16:55
the output okay because we do this on a
16:58
cyclic
16:59
basis we generate sort of Ripple and
17:02
potentially noise that could interfere
17:04
with things like television or
17:05
Electronics so you generally need
17:08
filters to do that too we also of course
17:11
need to control that flow of energy
17:13
right we can't be stupid about it we
17:15
have especially for something high
17:16
performance like a microprocessor which
17:18
might be changing its operation very
17:21
very fast we need to control that flow
17:24
so there's control circuitry we're going
17:26
to be learning about all of the aspects
17:27
of Designing
17:29
all of these kinds of elements
17:34
okay
17:36
so we're leveraging sort of everything
17:38
from circuit design semiconductor
17:41
devices passive components and materials
17:43
increasingly packaging and Cooling and
17:46
controls also matter and things have
17:49
been getting better and better and
17:51
better both because the um ways we can
17:55
manufacture things get better and
17:57
because the devices which we have
18:00
our access to in order to implement
18:03
these things get better okay and so
18:05
we're going to look at some of the
18:06
different ways you can do that I'll just
18:09
give you
18:11
uh one example this is what you would
18:14
find something like in a data center
18:16
right so they come in they rectify the
18:18
voltage they get it to sort of 400 Volts
18:21
for reasons we'll go into this converter
18:24
here was designed to take that 400 volts
18:26
and bring it down to 12 volts okay
18:29
that that tiny little thing a little bit
18:31
bigger than a penny there actually can
18:32
handle a kilowatt then you need more
18:35
converters to take it down from there to
18:36
the one VT that the processor uses okay
18:42
so the sort of a long way of saying all
18:45
kinds of things are limited by energy
18:48
and how we can control it right across
18:49
all these applications and what we're
18:52
usually trying to do is how figure out
18:53
how to make them smaller and lighter
18:55
right if you're taking up 40% of your
18:57
iPhone you want
18:59
make that thing smaller so it doesn't
19:00
take that up and you can replace that
19:02
volume either with nothing or with
19:04
things that are more interesting to you
19:06
we need higher efficiency both for the
19:08
converters and the systems how we
19:10
process energy can matter to the not
19:12
only the ultimate efficiency of the
19:14
converter but the efficiency of the
19:15
system how it uses energy can be
19:17
determined by the Power Electronics we
19:19
want higher performance that could mean
19:21
higher bandwidth or other aspects and
19:25
then there's all kinds of means that we
19:28
we can use better electrical processing
19:31
to enable new applications so these are
19:33
the kind of things that we're going to
19:35
learn about this term I'll pause there
19:38
i' I've been going on a while are there
19:39
any questions about any of this before
19:41
we get going this is just to sort of
19:43
Orient you as to what we're going to
19:44
focus the term
19:49
on I can put the slides on canvas
19:53
sure any other
19:57
questions okay
20:01
okay I will just give
20:05
you a slight
20:07
notion okay just and this is a
20:11
favorite thing I like to bring in just
20:13
to show you the kind of things we're
20:16
going to look at this
20:17
term this is a piece of commercial
20:20
Hardware from a company called MKS
20:22
instruments that I just happen to have
20:23
in my
20:24
office this input piece is a filter so
20:27
you don't create electrom magnetic
20:29
interference and you don't generate
20:30
noise you don't
20:31
want then this piece here takes energy
20:35
from the 60 HZ grid and generates DC
20:37
from it and it has to do it while making
20:40
the whole thing look like a resistor to
20:42
the grid so you don't mess up the grid
20:44
okay that's what this part does then it
20:46
has these isolated dcdc converters that
20:49
can take that DC voltage and generate
20:51
other DC voltages referenced in other
20:54
ways and without worrying about uh sort
20:58
of currents going back to ground okay
21:00
it's galvanically isolated and then it
21:04
takes that energy and goes back DC to AC
21:07
okay now in some systems you might go DC
21:09
to AC for 60 hertz to to generate into
21:11
the Grid or for a motor or something
21:13
else this particular one has these
21:15
outputs that are at 13 megahertz for
21:17
driving plasmas to process
21:20
semiconductors okay but you get all
21:22
these kind of functions AC to DC DC to
21:25
DC DC to AC and we're going to learn the
21:28
first of all the
21:29
underlying uh principles of doing all
21:31
these things and how to design them okay
21:34
so the the the real goal
21:38
is by the time you walk out of here you
21:41
should have all the tools to go off and
21:43
design Power
21:44
Electronics for all kinds of
21:47
applications and and in fact graduates
21:49
of this
21:50
class have worked on electric vehicles
21:53
Char battery charger
21:55
solar
21:57
uh communication
21:59
systems data
22:01
centers the in fact the the power supply
22:04
I usually use for my laptop and the in
22:06
fact the wireless charger for my
22:08
eyewatch were all designed or the teams
22:11
were led by graduates of this class
22:13
right so this the goal is to give you
22:15
the tools you need to go do these things
22:18
okay so with
22:21
that um let me
22:25
start by just giving you a sense
22:29
of
22:31
um what goes on inside Power
22:40
Electronics so let's think of the
22:43
simplest case I have some DC input
22:46
voltage and I'd like some other DC
22:49
voltage so suppose I have some
22:54
input that's you know maybe it's 9 volts
22:58
to 6 16
22:59
Vols I'm making that up arbitrarily but
23:02
that's roughly what you might get in a
23:04
typical vehicle right out of the
23:06
cigarette lighter
23:09
okay and suppose I want and I'll call
23:11
this
23:13
VN and suppose I want here's some load
23:16
that I'm going to represent with a
23:18
resistor I'm going to call that V out
23:21
okay and suppose I want EG 5
23:25
volts right to power something that
23:27
takes five volts
23:29
right what's the most obvious and simple
23:33
way to get 5 volts at my output from
23:36
some higher
23:41
voltage voltage divider precisely right
23:44
I could come up here I could say okay
23:47
let me put
23:50
in some volt variable
23:53
resistor and I'll drop down this voltage
23:56
to give me the voltage I want and I'm
23:58
done and in fact a lot of systems that's
24:02
exactly more or less what they have
24:03
inside them in fact inside most
24:07
integrated circuits there's lots of
24:09
these things going on okay well okay
24:12
they don't do it quite this way what do
24:14
they really do
24:18
they will take VN and what they will do
24:21
is they'll use some kind of transistor a
24:24
mosfet or a bipolar
24:26
transistor and they will treat that
24:31
essentially as a variable resistor right
24:34
so I implement the variable resistor
24:35
with a controlled transistor and I will
24:38
come and I'll have some feedback loop
24:40
I'll Fe feed in a reference
24:43
voltage and I'll measure the output
24:45
voltage and I'll control the Gate of
24:47
this transistor and essentially make
24:49
that transistor look like a variable
24:51
resistor and control the voltage
24:53
division so that even if this voltage
24:55
varies between 9 and 16 volts I always
24:58
get my 5 Vols output
25:01
Okay and like I said that's very
25:05
common but what's the problem with this
25:07
well there's a whole lot of problems
25:08
with this right why why wouldn't you
25:10
want to do this uh
25:13
in typical
25:15
operation efficiency terrible efficiency
25:19
yes
25:20
exactly so let's think about this if I
25:25
accept the fact let me call this current
25:27
I in
25:33
okay and this current I
25:37
out
25:38
okay if this thing does act exactly like
25:42
a variable resistor the input currents
25:45
equal to the output current now this
25:47
actually a real system might have some
25:49
current that actually also goes to
25:50
ground let's take the best case where
25:52
the output current is equal to the input
25:54
current okay what would be the
25:56
efficiency of this Beast well the
26:05
efficiency the efficiency is equal to
26:07
the output power over the input power
26:11
right I'm drawing energy maybe from my
26:13
car battery or whatever my battery
26:15
source is and I'm delivering it to the
26:17
output but not all of it's getting to
26:19
the output so the output power is V out
26:23
time I
26:24
out and my input power is VN time I in
26:30
and I just told you that I out was equal
26:33
to I in in the best case so that's V out
26:36
over
26:37
VN right so if I'm coming in from 15
26:41
volts and I'm getting five
26:44
volts that's 33% efficiency right I've
26:47
taken 2/3 of my energy and thrown it
26:50
away
26:52
now if I got lots of energy floating
26:54
around and I'm processing a microwatt
26:58
maybe maybe I don't care maybe I'll live
26:59
with that because this thing's pretty
27:01
simple right it's a transistor it's a
27:03
power transistor and some controls and
27:05
they can often put all that on one
27:06
integrated circuit or even as a subblock
27:09
on an integrated circuit I might still
27:11
need some filtering it's not it's not
27:13
quite as easy as it sounds but um pretty
27:17
much it's relatively simple but my
27:21
efficiency is miserable now if I thought
27:23
about in your in your
27:24
computer right your desktop computer
27:27
typically the intermediate Supply that
27:29
you're getting after it's sort of come
27:31
in from the grid and been transformed
27:33
down you get 12 volts right and let's
27:35
say your computer is it sort of it
27:37
depends on what it's doing but say it's
27:40
operating at a volt right so then you're
27:42
less than 10% efficient right and if you
27:45
think that you know you can have a
27:47
microprocessor that's taking 200 amps at
27:49
a volt or few hundred Watts suddenly if
27:53
I've got less than 10% efficiency on 200
27:55
Watts that means I need to put in a few
27:58
kilowatts well you can't even plug that
27:59
into the wall never mind the fact you've
28:01
just made a massive room heater right
28:03
that's that's like that'd be great for
28:06
heating your dorm room um but pretty
28:10
terrible for the overall system okay so
28:13
the number one reason we don't like this
28:17
solution is
28:19
efficiency good thing it's simple bad
28:21
thing it's terrible efficiency this
28:24
technique I should have noted
28:28
is what's known for historical reasons
28:30
as a quote unquote
28:33
linear power
28:35
supply why linear I think only because
28:40
analog circuits kind of a category of
28:43
them became known as quote unquote
28:45
linear circuits there's nothing really
28:47
that linear about it but this would be
28:49
called a linear power converter or or
28:51
some sometimes a linear regulator is
28:54
what it would be called
28:56
okay for obvious reasons I hate throwing
28:59
away energy we're not going to talk
29:01
about linear Regulators at all in this
29:03
class and there's plenty of classes
29:04
where you can learn about that we want
29:06
to do things some better way that's not
29:09
going to burn lots of energy okay so
29:13
ideally you know in my world the goal is
29:18
to take as much of the input energy in
29:22
and put it to the output right and
29:24
that's important because think about it
29:26
this way I I showed you a photo graph of
29:29
something that was you know really tiny
29:31
maybe that big right and that thick and
29:35
was processing a kilowatt right if I
29:38
don't do that at really high efficiency
29:40
that thing will burn up right so in
29:42
order to make something small I need to
29:45
make it efficient all right so we want
29:48
almost all of the energy at the input to
29:50
get to the output well how can we do
29:52
that let's think of a completely
29:55
different way we might achieve this same
29:57
function function all right and here's
30:00
the idea here's my
30:09
input I'm going to create a switch here
30:12
single pole double throw switch now
30:15
we're not going to go get physical
30:16
switches we're probably going to get
30:17
semiconductor devices and make it do
30:19
something like this but we could use
30:22
anything any technology that was
30:24
practical as a switch okay and let me
30:27
just Define if I'm going to define a
30:29
switching function that I'm going to
30:30
call Q of T if Q of T is
30:33
one I'll connect the switch to the input
30:37
if Q of T is
30:41
zero I'll connect the switch to the
30:43
ground okay so this notion this voltage
30:47
okay maybe I'll call this voltage
30:54
VX all right so one thing I could do is
30:57
I could say okay let me just hook this
30:59
up to my load here's my resistive
31:02
load whatever it is and I'll call this V
31:06
out all right well all right what would
31:10
that look like well let me Define my
31:12
switching
31:22
function I'm going to put the switch in
31:25
the up position for a little while then
31:28
I'll put it in the down
31:29
position by setting the switching
31:31
function to zero and then I'll just
31:33
repeat that so I said we're going to
31:35
operate in some kind of repetitive
31:36
fashion here and so
31:39
forth let me operate with some period
31:43
T okay that's mean my switching period
31:46
in this example I'm showing you is a
31:47
fixed switching period okay and I will
31:50
keep the switch in the up position some
31:52
fraction of the time that I'll call DT
31:56
so D is a fraction zero is less than D
31:59
is less than
32:01
one
32:03
okay so if I do that then what do I get
32:07
for VX VX is going to look something
32:09
like
32:11
this okay um when the switch is in the
32:15
up position VX equals
32:21
VN so this is VX when the switch is in
32:24
the down position VX is equal to zero
32:31
okay and I rinse and repeat and I get
32:34
this now now I have this pulsating
32:36
voltage VX okay what's the average value
32:40
of that voltage
32:42
VX right I can take you know simple
32:45
integration right one over T the
32:47
integral of VX of T over a period
32:50
T okay and what I would
32:53
find is the average voltage of VX
32:58
is equal to D *
33:01
VN all right so I can create a waveform
33:05
here whose average value is something
33:08
different than VN just by controlling
33:11
this timing
33:13
D all right so now if my load resistor
33:19
here was a space heater you know maybe
33:22
this is some load resistance RL and I
33:25
wanted to modulate the power to that
33:27
load resistance by controlling the
33:29
average voltage on the load resistance
33:32
then this technique would work
33:35
great if on the other hand my load was a
33:38
microprocessor and I start you know
33:40
pulsing 12 volts between 12 volts and
33:43
zero on it I'm probably going to blow it
33:44
up right so that's no good all right but
33:47
this notion is at least that I can
33:49
control an average voltage by pulsing a
33:52
set a switch okay and this would be
33:55
known as pwm or pulse width modulation
33:58
because I control the average volage by
34:01
the fraction of the time the switch is
34:02
in one position versus the
34:05
other okay so that's that's the basic
34:08
concept we're going to be using how do I
34:11
fix this
34:12
little problem of in practice right what
34:16
I wanted was a DC voltage what I got was
34:19
a pulsating voltage that just happened
34:21
to have the right average value well I
34:23
could go do something like this maybe
34:25
I'll go back and say okay let me throw
34:28
in a
34:30
filter and extract out the component I
34:33
want right I want the average value of
34:36
VX so maybe I'll come back here and say
34:39
okay let me throw in a filter and I'll
34:43
use an inductor
34:47
here an l and if I want optionally I can
34:50
put a capacitor here
34:53
C okay and you know I think people can
34:57
look at
34:59
this filter block and recognize that as
35:02
a low pass filter the DC component of VX
35:07
passes through the filter to the
35:09
output and the AC component of VX gets
35:13
rejected by the filter and doesn't get
35:15
to the output so in this case I might
35:17
get an output voltage V out that looks
35:19
something like this I'm going to sort of
35:22
make this up but you know I'm amplifying
35:24
the Ripple but eventually it's going to
35:27
filter
35:28
the energy content of that and the
35:30
fundamental and higher harmonic terms of
35:33
VX are going to go away and the DC terms
35:35
going to go through and I get an output
35:37
voltage V out that's very close to
35:40
whatever value I want and if I'm
35:43
basically make the filter cut off hard
35:46
enough I can't distinguish between V out
35:49
and the average value of VX and I get
35:51
exactly what I wanted Okay so we've
35:55
essentially now created
36:00
a voltage
36:04
converter that lets me use this
36:07
pulsewidth modulation by controlling
36:09
this duty cycle D to regulate the output
36:13
just the way I wanted so instead of you
36:15
know here I'm just changing the gate
36:17
voltage on my transistor to control the
36:19
output here I'm changing timing I'm
36:21
going to control
36:23
timing okay and by controlling timing I
36:26
control average value and then I get
36:27
what I want right any questions about
36:31
that what's what's the
36:33
efficiency that is an excellent question
36:37
the answer is
36:42
um ideally theoretically the efficiency
36:46
can be
36:47
100% in reality it can't be why do I say
36:51
the efficiency can ideally be
36:54
100% well how would I implement
36:58
this box in the real world usually I I
37:02
don't get semiconductor single pole
37:04
double throw switches the way I would
37:06
usually build this Beast is like
37:08
this okay I would usually have a first
37:11
switch and a second switch implemented
37:14
like this so I close this when Q of T is
37:17
equal to
37:18
one and I close this one when Q of T is
37:21
equal to
37:22
zero okay and then I build my filter
37:30
and then I put my load on here okay
37:35
so what would be the efficiency of this
37:37
thing well let's think about
37:40
this um this is voltage Vex and this is
37:44
voltage
37:46
vout all
37:50
right what power is theoretically
37:54
dissipated in my switch if I have an
37:56
ideal switch has zero resistance when
37:59
it's on and has infinite resistance when
38:01
it's
38:02
off what's that zero power why because
38:06
the power dissipated the power that goes
38:08
into this box let me call this V
38:12
switch let me call this I switch okay
38:17
well P switch the power going into the
38:19
switch the power being dissipated in the
38:22
switch is going to be V switch time I
38:25
switch
38:28
okay well if it's an ideal switch then
38:32
if the switch is on V switch is
38:35
zero right it's ideal so it has no
38:37
voltage drop when it's on so the power
38:40
when it's on is
38:42
zero when the switch is off it has
38:44
infinite resistance so the switch is
38:46
current zero so basically the power
38:50
going into the switch if it's an ideal
38:52
switch
38:54
um is ideally zero so these these
38:57
elements this ideal switch is a lossless
39:01
element
39:02
right
39:05
likewise I wasn't I didn't just randomly
39:07
choose any filter here right I chose an
39:10
LC filter why did I choose an LC filter
39:14
I choose an LC filter because inductors
39:16
and capacitors are energy storage
39:17
elements if they're ideal then they
39:19
store energy but they don't dissipate
39:21
energy right so basically
39:25
everything in the box here everything
39:28
between the input and the output is a
39:30
lossless element so then one would
39:33
assume that if every element's lossless
39:36
any energy walking in to the left comes
39:39
out to the right right and that's how
39:42
that that kilowatt little 400 volt to
39:44
12vt converter I showed you um in the
39:48
photo is about 97% efficient it's not
39:51
100% because you know the wires have
39:54
some resistance and the switches have
39:55
some on-state resistance a whole bunch
39:57
of things that contribute to loss and
39:58
we'll talk about that um but I can make
40:02
it really close to 100% even though I
40:05
might be doing a huge step down right so
40:08
if I tried to build a linear regulator
40:09
that was going from 400 to 12 volts
40:11
that' be about 2 and a half% efficient
40:13
right so if I want to generate a
40:14
kilowatt at 2 and a half% efficiency
40:16
what is that 40 kilowatt input and
40:19
instead what I get is sort of like 1.03
40:24
kilowatt input to generate a kilowatt
40:26
output right
40:27
so the whole Magic that we're going to
40:30
talk about this term is how can I use
40:33
sort of perfectly lossless elements draw
40:36
energy in process it and put it out the
40:38
other side okay and by the way I should
40:41
say not only did I say oh inductors and
40:43
capacitors are lossless in principle
40:45
lossless elements uh it wasn't an
40:50
accident that we put an inductor
40:54
here right because think about it when
40:57
this switch is
40:59
closed right I have V in on this side of
41:03
the inductor and V out on this side of
41:04
the inductor and I have current flowing
41:07
this way right well what's happening
41:10
when this switch is closed basically
41:13
there's voltage across this inductor and
41:15
current going through it we are storing
41:17
energy in that inductor so the
41:19
difference in voltage between the input
41:21
and the output is basically putting
41:22
energy in the
41:24
inductor in this the other part of the
41:26
cycle
41:28
when I turn this switch off and this
41:30
switch
41:31
on basically I'm taking now I have a
41:34
negative voltage across the inductor I'm
41:36
taking energy out of the inductor and
41:38
put it in the output so essentially I'm
41:40
using this inductor as a filter but it's
41:43
also an intermediate store of energy
41:45
that lets me kind of take energy from
41:48
the input and transfer to the output
41:50
with a voltage conversion without losing
41:52
any of the
41:54
energy excellent question long answer to
41:57
a short question any other
42:04
questions okay so as I said um my goal
42:09
is to sort of first of all teach you a
42:12
lot of the underlying principles this is
42:14
the this is the world's if you will
42:16
simplest switching power converter so
42:18
the when we use this technique we also
42:20
often say we're switched
42:24
mode all right with the notion that
42:26
we're going to use
42:27
switches and energy storage elements to
42:29
process energy and that's sort of what
42:31
sits at the core of Power
42:33
Electronics okay and as I said we're
42:35
going to look at all of the aspects how
42:38
do you design these things how do you
42:39
control them how do you design the
42:41
components and by the time we're done
42:43
you should be able to put it all
42:44
together and and start designing Power
42:46
Electronics of your own and you will for
42:49
the final project
42:52
okay so any final questions
42:59
okay we'll wrap up today and I will see
43:01
everybody on Wednesday
— end of transcript —
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