[00:12] so I will just go through the
[00:15] oldfashioned paper uh syllabus so the
[00:20] course is going to be taught on canvas
[00:21] so the canvas site has been published uh
[00:24] we will for for uh homeworks and things
[00:27] like that they'll be handed out and
[00:30] turned in on paper but you can download
[00:33] them from canvas as
[00:35] well um the classes are going to be here
[00:39] Mondays Wednesdays and Thursdays so on
[00:41] usual class schedules 1
[00:44] pm uh I've mentioned the textbook there
[00:47] are some other textbooks that you might
[00:49] find Handy and I've listed those in the
[00:51] course handout those are completely
[00:53] optional you don't have to buy them the
[00:55] libraries also have
[00:57] copies um the way homeworks will work in
[01:01] this
[01:02] class is that will typically be issued
[01:05] on a Monday and do the following Monday
[01:08] okay and uh for the most part you are
[01:12] allowed to collaborate and talk about
[01:15] the homework problems so you feel free
[01:17] to get together and discuss the problems
[01:19] that there it's intended that you do so
[01:22] the only constraint we have is that you
[01:24] must hand in your own solution right so
[01:26] so you can trade ideas but in the end
[01:28] the thing you write up it can't be a
[01:29] copy your neighbors it has to be your
[01:32] solution but you can base it on uh you
[01:35] know ideas you've exchanged with others
[01:37] okay for those who don't know
[01:42] anybody or or don't have access to study
[01:45] partners and may have questions first of
[01:46] all there will be office hours uh Mon's
[01:49] office hours will be Thursdays 4: to 5:
[01:52] p.m. and Fridays 4 to 5:00 P p.m. in
[01:54] 10178 in building 10 okay but there are
[01:58] also a number of students students in
[02:00] the Le laboratory 1050 who have had this
[02:03] class before will be happy to answer any
[02:05] questions and a few of those students
[02:07] are listed in the uh course
[02:12] description we've also decided not to
[02:14] have exams this term or in-class exams
[02:19] rather we're going to have assessments
[02:22] which are essentially take-home mini
[02:24] quizzes uh they will generally be uh um
[02:31] they'll be generally issued weekly and
[02:33] this says they're going to be issued
[02:35] starting on March 1st I should check if
[02:38] that yeah starting on March 1st they'll
[02:40] be issued weekly they'll be issued on a
[02:42] Wednesday that will be due the next day
[02:44] Thursday and those will be submitted
[02:47] through canvas through grade
[02:50] scope
[02:52] um as for homeworks we can take late
[02:55] homeworks if you arrange it ahead of
[02:57] time and there's some compelling reason
[02:58] why they're late assessments are a
[03:00] different
[03:01] story also the collaboration policy for
[03:04] assessments is different you cannot
[03:06] collaborate or discuss the problems at
[03:08] all for assessments and and you know we
[03:11] can't prove or not prove that you're
[03:13] doing so but this is you know this is an
[03:15] exam effectively so don't discuss it
[03:17] with your neighbors and don't discuss
[03:19] anything until the solutions are out
[03:20] because there may be people who have
[03:22] made some special arrangement for
[03:24] because they're traveling or or for
[03:26] whatever reason to hand it in late okay
[03:28] so we're going to have homework and
[03:30] assessments and the goal of the
[03:32] assessments really is instead of a you
[03:34] sort of very few high stakes
[03:37] opportunities to show your abilities the
[03:40] assessments are sort of distributed in
[03:42] low stakes and focused and gives you a
[03:45] better opportunity to show you what you
[03:46] really know okay so please complete them
[03:50] entirely on your own no consultation the
[03:53] only thing you're allowed to do is ask
[03:54] the core staff clarifying questions just
[03:56] the way you might in an exam okay
[04:00] and uh as for the assessments you can
[04:03] use any of the course materials you know
[04:05] read the book whatever you want
[04:09] uh do
[04:10] not go outside and try to use the
[04:14] worldwide web and for that matter the
[04:16] use of Bibles is also prohibited I know
[04:18] that there's collections of old 6334
[04:22] materials floating around you're not
[04:24] supposed to be Consulting those okay
[04:27] this just supposed to be a measure of
[04:28] what you've learned okay okay so the
[04:31] grading will be based on three
[04:32] components homeworks are going to be
[04:35] 40% these assessments will be
[04:38] 50% and there's also a final project
[04:41] which is 10% and the final project
[04:44] sounds like it's only 10% but it's the
[04:46] last thing we look at when we're going
[04:48] to assign a grade to everybody and it
[04:50] really is your opportunity to put
[04:52] together knowledge that you've learned
[04:54] throughout the class into a real it's on
[04:57] paper it's not a it's not a phys phical
[05:00] converter you will construct but it's a
[05:01] paper design but it's really your
[05:03] opportunity to show us how you've
[05:04] synthesized all this knowledge to be
[05:06] able to really design Power Electronics
[05:09] and I should say just as an aside in
[05:11] this class we only have a paper design
[05:13] or or but this complements nicely the
[05:18] undergraduate Power Electronics class
[05:20] which has a lot of really nice lab
[05:22] activities and design activities there
[05:24] so even if you're a graduate student
[05:26] it's it can be a pretty good thing to
[05:27] take in terms of of uh rounding out the
[05:30] LA your lab skill set in this area
[05:34] Okay um if you have any necessary
[05:39] technical accommodations don't have
[05:41] access to uh iPads or whatever else you
[05:44] need for grade scope please let us know
[05:46] we'll try to assist uh assist with that
[05:53] okay so with that are there any
[05:57] questions about anything like associated
[05:59] with the course
[06:03] mechanics okay so let me um give you a
[06:10] sense of what this course is going to be
[06:13] about and uh this is one of my favorite
[06:17] photos is actually one that uh Nicola
[06:20] Tesla mocked up he wasn't really sitting
[06:22] next to his Tesla coil when he did this
[06:23] or he might have gotten killed um he
[06:26] kind of double exposed this but more to
[06:28] the point
[06:30] uh the quote from him is if we could
[06:32] produce electrical effects of the
[06:33] required quality this whole planet and
[06:35] the conditions of existence on it could
[06:37] be transformed and I think the sort of
[06:40] the more than a hundred years since he
[06:42] he said that or well more than 100 years
[06:45] since he said that uh have borne that
[06:48] out but it's also true that even
[06:51] today uh there's really revolutions
[06:55] happening in the way we use energy
[06:57] everything's being electrified from
[06:59] vehicles to transportation to power
[07:02] generation from renewable
[07:04] resources and um handling all that
[07:08] requires some means of processing
[07:10] controlling and converting energy and
[07:12] that's really what we're about
[07:14] processing controlling converting
[07:15] electrical
[07:16] energy if you look at what the uh itle e
[07:21] the which is sort of the governing body
[07:23] of electrical engineering says about
[07:25] Power Electronics it says this
[07:27] technology encompasses the use of
[07:28] electronic components
[07:30] the application of circuit Theory and
[07:31] design techniques and the development of
[07:33] analytical tools towards efficient
[07:35] electronic conversion control and
[07:37] conditioning of electric power and
[07:39] that's what we're really about here so
[07:41] we're going to do circuit Theory we're
[07:43] going to learn design techniques we're
[07:44] going to learn about all the components
[07:46] you need to do this we're going to learn
[07:47] about controls how do you put it all
[07:50] together to make energy conversion
[07:52] systems okay so as I mentioned the
[07:56] primary function of Power Electronics is
[07:58] to take sort of electrical energy in one
[08:00] form and convert it into some other form
[08:03] you need uh it's really a core
[08:06] technology in the electrical
[08:07] infrastructure it used to be that the AC
[08:09] grid was generators and you'd connect it
[08:11] up to things like directly things like
[08:13] Motors or lighting or whatever but
[08:16] that's pretty much changed at this point
[08:18] right lighting is LED lighting you need
[08:20] power supplies to go between the grid
[08:22] and the lighting same thing heavily
[08:24] loads computers Motors everything else
[08:27] you need energy tends to flow through
[08:30] one or even several layers of power
[08:32] conversion circuitry from the principal
[08:35] source to the final usage okay and so
[08:38] the Power Electronics first of all you
[08:41] know the efficiency of that is very
[08:42] important but also how you do it impacts
[08:45] the quality of the final system so the
[08:48] Power Electronics can really be a major
[08:50] factor impacting what you can and can't
[08:52] do and how well it works
[08:56] okay so if you showed up you know
[08:59] hundred years
[09:01] ago this is what Power Electronics would
[09:03] look like right some vacuum tubes and
[09:05] some Transformers and that kind of thing
[09:09] interestingly of course it's nothing
[09:11] like that today but with the techniques
[09:14] you're going to learn in this course you
[09:15] could actually go back and analyze this
[09:17] thing and figure out what it did right
[09:19] so some foundational ideas that we're
[09:21] going to come back to which can be 100
[09:24] years old but there's also elements that
[09:26] are extremely new okay and today you
[09:29] know this this was fancy 100 years ago
[09:32] today Power Electronics is everywhere
[09:35] from I say from mowatt to gigawatts and
[09:38] and it does actually use switch mode
[09:39] power conversion down at those power
[09:41] levels this is actually a a multi-watt
[09:43] power supply and this is literally at
[09:45] the gigawatt scale so if you if you go
[09:48] out to S the Sandy Pond terminal there
[09:50] is a power converter that takes two gws
[09:53] coming down from Canada hydro and
[09:55] converts it to AC to power homes and
[09:58] 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