Well thanks Arun, it's great to be here. I have the fortune of getting to travel to a lot of universities and interact with students and faculty and I must say this is by far my favorite place to attend. I said the same thing in MIT, no I'm just kidding. This is, you know, the other thing is you can, that was the nicest way anybody said I was old, kind of back to 87, but what does make you feel old is every time you come to university the students are always 18 to 22 and each year I get one year further away from 18 to 22, so, but I'm looking forward to it. I do look forward to talking about really what Arun said which is there's a lot of talk about energy, there's probably more talk about energy today than it has been in a long time. I'm gonna talk, in this talk I'm gonna talk a little bit about the external environment. This is a technology talk, so I'm not gonna spend a lot of time on policy or the other elements. They're obviously very important but I really wanna talk about the role of technology. From an outside perspective first and then bring it back internally and I'll talk a little bit about the work we're doing within our labs at ExxonMobil and talk about the solutions that we're working on which we think are part of the solution. But when you think about energy it is often taken for granted, when you woke up this morning I don't think any of you wondered if the lights would come on when you hit the switch. None of you were worried about a rolling blackout during a football game last night. At least not during the first half. But you know we live in a world where if you have it you take it for granted and if you don't have it it's magic. There's still about a billion people who don't have access to energy largely in the developing world and quite frankly that's the goal. They want the same quality of life we have and while people always think about cars and airplanes the reality is everything in this room is either a direct derivative energy or one step from energy. So whether it's the clothes we're wearing or the upholstery or the carpeting or the computers everything is tied to energy. So it really is quality life. It's simple things like washing machines. It's simple things like medicine and all those have a huge energy component. So it is everywhere. It underpins everything. You know you hear people say energy is essential to life and I certainly believe that. And now we're faced with the challenge of how to continue to grow energy supplies as seven billion people become nine billion people. And as Arun said the challenge now is how do you do that while mitigating emissions while getting on the two degree pathway. Our thesis is that's largely a technology challenge. That we've got to work on technical solutions and one other concept before we get into this is just remember one of the challenges in energy is scale. Scale is almost impossible to explain. So I can wow you with the units of hundreds of millions of barrels a day and gigatons and gigawatts and no one really knows what it, well Stanford students know what a gigawatt is. People know what a gigawatt is thanks to Back to the Future but very few people actually know what a gigawatt is. And so it's trying to explain the scale and how do we get to those scalable solutions which is really the key. So real simple. This is in essence the challenge. So the chart on the left is the y-axis is the human development index which is essentially the UN has criteria, living standards, education, quality of life basically is on the axis and on the right is the energy use per capita and in a different set of units thousands of BTU per person per day. And you can see in general as you move up from the red dots to the blue dots you consume more energy. And so that's simply put and you can see also throughout this talk you'll see the red dots will be the developing nations and the blue dots will be the developed nations. And you can see the disparity between the developing and the developed and obviously the developing nations want to get into that upper right quadrant where they can have the quality of life that we all enjoy and to do that the access to energy is needed. Now the challenge of course is the good news is we have the energy. So for much of my career we were worried about not having enough energy and now we have a lot of energy but as often once you solve one challenge another challenge arises this is the second challenge and that is how to manage the emissions and you can see this data again OECD versus non OECD and you can see the energy related CO2 emissions and you can see the tip where it went from the OECDs to the non OECDs largely driving this and that is essentially you'll hear this phrase often used dual challenge that is the dual challenge how do you do chart one which is easy because we have lots of energy chart two it's easy to control emissions limit demand but you don't want to do that so how do you do the dual challenge how do you solve the dual challenge which is providing affordable scalable energy to a growing middle class to a growing population while reducing the risks of climate change and reducing emissions that is a simple question it's a very difficult question to answer so let's talk about this so how do you do this now many many many years ago you guys can do the math I was a chemical engineering student and I remember the first thing we learned in chemical engineering was when you get a problem the first thing you do is read the problem the second thing you do is reread the problem the third thing you do is draw a picture of the problem which in my world everything was a box and every triangle was a nice little isosceles triangle and the fourth thing you did was listed your assumptions and your pathways so you were four or five steps into it before you even started trying to solve the problem it's not going to spend a little time talking about well how do you define the problem because you could make it a real simple problem nine billion people two degrees that's the problem but the reality is you have to go one you have to go at least one level further and you have to say well where are the emissions coming from and I'm going to call it three sectors it shows us four but I'm going to put buildings in with electricity generation so it's transportation it's power and it's the industrial sector so we've gone from essentially one problem maybe two if you said it was OECD and not OECD and we've gone from two to six because you have three sectors and each sector is going to have a unique suite of solutions so where in the power sector you're really chasing for an electron in the industrial sector if you're trying to make plastic it's really hard to make plastic out of an electron you need to see H bond to make a polymer and so you've got a balance and you've got to get a field of answers across each one of the sectors and then while you could easily say it's OECD and not OECD it's really country specific and in fact in large countries like the US it's often state specific so you can see how a simple one sentence dual challenge problem can expand into fifty hundred plus questions all which have to be solved more or less simultaneously to get to the nine billion people in two degrees so that's the science problem and again it's really instructive to think about this across the sectors and you'll hear you know depending on what you read and what you follow emphasis on one verse they obviously interrelate so if you electrify the the cars that will put uh... more pressure on the power grid and so there is an inner interconnectivity as well not that the problem isn't hard enough you now have codependent dependent variables as well so that's a way to think about this challenge and that's that's certainly the way we think about it we want to come up with robust solutions uh... across the sectors and then ultimately we will talk about carbon capture and things like that because those cut across all sectors if you can just somehow pull the CO2 out that obviously is a changing approach as well I said I was going to spend most of my time on technology this is I think there's only one or two charts here that have anything to do with either policy or some sort of a uh... a model a modeling basis and of course who else better to use than stanford here so this work was done at stanford a few years ago and again this is a very simple chart the y-axis is basically energy efficiency getting more efficient using less higher miles per gallon cars lighter weight plastics etc the x-axis is literally decarbonization pulling CO2 out each dot is five years so the dots begin in nineteen eighty uh... through two thousand fifteen and what you see is you see the uh... the emissions from nineteen eighty two thousand fifteen and then extrapolated out to twenty forty based on public information and he sees things like that and then on the purple blue line there obviously to get to two degrees it's going to be a combination of decarbonization efficiency uh... and so that's a hypothetical two degree line and what you'll see in this shouldn't surprise anyone in this room is over the last twenty five thirty plus years we've really been going down the efficiency axis and we all live it our cars are more efficient the plastics are lighter uh... everything around us has gotten more efficient and so you can see the vertical change now to get to that to the get to the line we want to get to though we have to continue to do everything we can to be more efficient so that continues to be important but ultimately you will have to look for ways to decarbonize to actually pull CO2 out and we'll talk about the technology set there but again this is another way to frame the question in terms of what are we trying to do and what type of urgency, what type of speed do we need to move it at that's not a dramatic pause, I'm just not moving forward, okay so just to put it in perspective if you take that line and say okay just give me some rough estimates for what we have to do so efficiency has to continue to get better so we have to continue 50% more efficient than we are today low greenhouse gas electricity so this includes solar, wind nuclear as well as uh... power with carbon capture so it's all of those there and we have to get uh... you know we have to grow significantly there, we have to get up to 80% and biofuels which today make up about one percent we're gonna have to get to 15% so the amount and by the way that still doesn't quite get you where you want to get so the the challenge is pretty severe it's going to require uh... technologies is going to require the combination of technology policy and infrastructure you can almost think of those in equilibrium that once one is set the other two uh... somewhat become constrained and you know our view is you want to you want to try to let technology you want you want the policies you want things that are as technology agnostic as possible so that the scientists and the technology guys can come up with scalable and affordable solutions so with that I'm now going to switch over to okay so with that is the problem let's start talking about solutions because we spend a lot of time talking about the problem but the real key is how do we solve this and how do we do this I want to talk a little bit about how ExxonMobil approaches this Arun talked about some of the history uh... that Exxon has had in energy but I'm going to talk a little bit more about it and then I'll pivot away pivot into what are we actually doing today in our labs uh... that some of you may have read about uh... but I want to talk about that as well so let's talk about how do we think about this problem and this if you boil this down this is fairly logical okay it's a four pronged approach to progressing solutions the first thing is take care of your own business so mitigate emissions in your own operations so that could be the the goals we've set on reducing methane flaring as we as we continue to explore for oil and gas all the way how do we get more efficient and how we refine to make the fuels that we all use today and make the plastics that we use today so first step mitigate your own second step take care of your customers provide solutions for those in adjacent businesses so that could be the polymers we're making that go into the automotives that make the cars lighter that could be the motor oils mobile one uh... which i'm sure you all use mobile one uh... again makes fuel fuel uh... increases fuel efficiency so it's providing energy options for customers natural gas making that more available as a as a alternative to coal for instance huge emissions reduction if you do that switching step three you got to talk about it you have to engage in the policy you have to engage in places like stanford that has that rare combination of unbelievable science capabilities and unbelievable policy uh... generation and so these these centers here become great places to talk about uh... climate change policy as well as uh... with the various governments that's a that's not my group my group does the research but we have a separate group that really focuses on that and then finally and this is what we're going to pivot to in a minute is with all that said we have a technology gap we have to come up with new affordable and scalable solutions and we have to progress those to where we can get those in the field so they can help us get on the pathway we need to get so that's it it's it's as simple as four steps it's somewhat logical as always it's always the details and how do you execute uh... this plan but that's our approach that's what we've been doing for years and we expect uh... to continue to do that now you need to have a little bit of background to say well what we're doing is what we've been doing so this is a very simple chart that goes back to nineteen forty i could have actually gone back further but as the years get longer powerpoint fonts begin to become the limiting factor here okay so uh... but if i was to show you nineteen nineteen nineteen is when we uh... was the first process to make isopropyl alcohol rubbing alcohol and it was the first petrochemical made and it was made from propylene in a refinery and again propylene plus water with an acid catalyst will give you isopropyl alcohol back in nineteen nineteen you use sulfuric dilute sulfuric acid with propylene to make isopropyl alcohol now the world had rubbing alcohol before then but this was the first time that we made it as a petrochemical and it changed the scalability of isopropyl alcohol so if you move forward and i would just highlight a couple of these so if i'm gonna highlight the first two which uh... technologies that rolled out in the late thirties early forties but actually the research actually began in the academic world twenty years earlier uh... the first one high octane gasoline is actually an offshoot of the fluid catalytic cracker and the concept of fluidization actually goes back to the nineteen tens nineteen twenties uh... in academia and the bottom of course uh... it was all natural rubber back then it was it was rubber plants out of which you you got rubber in our company was the first to develop the process to make synthetic rubber butyl rubber which is still the rubber that's used today predominantly still the same process used predominantly uh... for tires today synthetic the first synthetic catalyst course that was a game changer because that allows you to run reactions at different rates under different conditions to increase yield get more efficient plastic polyethylene polypropylene synthetic lubricants uh... everyone mentioned the lithium-ion battery just to show you that that was nineteen seventy the Nobel Prize was last year just to talk about the time scale uh... for energy and then if you kind of look at nineteen eighty nineteen ninety onward what you'll see is just getting more bigger and faster so deep water becomes ultra deep water thin plastics become ultra thin plastics right horizontal drilling becomes extended reach drilling plastics become specialty plastics and for those of you my age you remember having to change your oil every three thousand miles remember arnold pomeron extractor telling you to change your oil every three thousand miles and now we have mobile one annual protection so this is an innovation cycle where you go from concepts you go to scale and then you continue to push the scale on sometimes called experience curve but you you go down that scale where we are now is we're looking for technologies that can take us to the next uh... to the next uh... generation of solutions and we're going to talk about how we do that a little bit just uh... just real quick we have sites all over the world our core research facility hopefully it's on there isn't right in the middle when it's my chart so it's in the middle okay i'm sure when the guys from houston come here houston is suddenly the center of the universe but clinton for now is the center of the new verse you guys know new jersey everything is an exit so this is exit eighteen on rich seventy eight it's about forty five minutes fifty minutes outside of manhattan and uh... as aroun said it was designed to be an innovation center for energy opened in nineteen eighty three there's actually a science article written on the opening of the building which is a little bit rare for science uh... but it was a concept about driving innovation in energy space and you know it's i started there in eighty seven i still think it's one of the the better places to work and you can see where we are around the world with uh... technology centers a little bit of our people real quick so we do we are a science base we are a technology company uh... you can see the number of engineers and all the other stuff uh... this is uh... off of the patent wall so we have a patent wall in houston that that identifies our people but you know when i come to universities i want to put this chart up because this is a really really important thing to talk about when you talk about challenges that we face the concept of inclusion and diversity and that this is really important so you can see the metrics there i'm gonna channel you know myself a long time ago uh... in a different era where it wasn't talked about as much and i remember my father saying you know that there is the brain has no color so if you if you know science is the ultimate equalizer and so the inclusion diversity challenge we have in the science community is that of thought is we really need to constructively push each other we need to challenge each other but it is one where when you're trying to innovate nothing can stop innovation more than i don't want to hear your idea and so from uh... from an inclusion of diversity thing what we try to do in the r&d community is really really try to drive that uh... the inclusion of thought the inclusion of challenging constructively it is at the end of the end of the essence of academics is the challenge constructively but i think it's important that we continue to uh... to drive inclusion and diversity because i think that is where the innovation is going to come it's going to come from these adjacencies and making sure everybody's comfortable talking about this challenge we have constructively which i think is really really important how are we organized and i give this is just a precursor to to explain why we're working on working so this is essentially how the organization in clinton is set up now if i would have given you guys a pop quiz and it's don't worry about the students are freaking out right now because they think a pop quiz is there's no pop quiz but if i was to give you a pop quiz in the beginning and say well how do you think we're organized the two most common ways people think we're organized are going to be by sector uh... upstream downstream chemicals or by uh... or by application and and the reality is you know our belief is if you want to run a research organization you want to do it by capabilities so you can see that those are somewhat agnostic to the end use but they are the core capabilities from which you you drive energy so you have the physics the computational physics the engineering physics you have the sort of the catalysis and the separations and within the separations you're going to have gas separations you have liquid separations you're going to have gas liquid separations uh... things like that materials materials play such a big role in our world whether it is the actual catalyst or whether it's a membrane or whether it's the final product the polyethylene film the polypropylene film etc so materials are very important and then over on the right you have hydrocarbons and then what we call emerging energy which if this was jeopardy you'd call it the potpourri round right it's the it's the it's the it's the all of the above it's the staying aware of what else is going on because while we're working in our space it is critically important from an r&d standpoint that we know what the adjacent spaces are doing that you don't get the tunnel vision and you're only focused on what you're executing you don't realize that there's a better idea and when you're in a transition as we're in right now it is it is extremely important that you that you're watching around you as you do this and so on the right you see things like organic chemistry climate science aroun mentioned uh... ipcc you know we've been we've been co-authors or authors on many of the reports uh... that come out uh... from their thermodynamics and and more and more bioscience now that that is the newest section in our group we didn't have about actually we had a biosection science in years ago we kind of faded away from it and we've we started back a bioscience section uh... a couple years ago because we see a lot happening in the in the bio conversion in the bio catalysis uh... in trying to understand how biology works and then taking that knowledge and scaling it it's also where the algae program resides because of the biology and the and the capabilities of gene editing and gene sequencing and things like that which are which are huge fundamental enablers for what we're trying to do so that's how we're set up now as good as we are internally we know that we have to collaborate that we have to work outside and so this is just a quick look at how we're working across with uh... these are called energy centers so stanford has one you can see the ones that we're working with across the top and then the y-axis or the column the the three main sections there power transportation industry so this is a great way to stay abreast of what's going on in the state of science and even my discussions today with some of your faculty and some of your students again just reinforces the value of coming out to stanford and talking to the students in the faculty because you guys are right on the cutting edge and you're paying attention to the breakthroughs in in academia and most of what we do in energy started in in academia now just because i know where i am uh... we have a long history with stanford this is a quick chart uh... some of you familiar with g-sept g-sept we were pioneering members of g-sept and it was a very successful area fifteen years of partnership we we put in about a hundred million dollars over those fifteen years but with richard and sally and arounes leadership sanford i think has done a really good thing in moving to the strategic energy alliance to which we were uh... if not the first member one of the first we were the first member we were the first member and that was really exciting and watching just the progress just made since you guys kick that off and you can kind of see the focus areas there and you can see how it's hard to imagine a world of nine billion people where you're mitigating emissions where those four focus areas are not critical and of course the wild card one they're being emerging technology because what a stanford can do is not just develop the dots but can connect the dots and a lot of the solutions and coming from connecting the dots not a single dot uh... that gets there so a lot of good work on on here and we continue to you know we love the relationship we had since oh three and we see this happening for many many years to come so we're excited about being here we also want to talk about the the work we're doing with national labs and also with uh... with smaller companies the rest of the value chain if you will so we signed an agreement with the do we last year a ten year agreement to uh... work with the national labs on developing energy solutions and more and more we're looking with uh... on the right you see two smaller companies synthetic genomics is a partner in algae and fuel cell energy which is a carbonate fuel cell company that we're working on with cap carbon capture and more and more these these uh... what i call smaller companies play a vital role in how we go from lab to scale which i want to talk about now so when you think about the innovation value chain and uh... it looks like i'm photoshopped on that but i'm not okay so this is um that was me uh... and normally i look happy it doesn't look like i'm very happy with my panel right now right uh... i think somebody doctored this picture that uh... so uh... this is an aspen uh... the aspen ideas festival uh... last year and uh... i got to play uh... sort of player coach so i was a panel member and the moderator which i've never done before which is fascinating to do uh... but what we wanted to show was how do you go from lab to scale and what role do we play so with me across there the first one is uh... lin lou and she's head of the anlinger energy center princeton she's on the faculty princeton she leads the energy center and the concept there is universities provide the fundamentals the breakthroughs but more importantly universities have the time and almost the remit to really understand at the basic level what's happening so we want to continue to work with universities martin keller is the director of nrel in golden colorado the national renewable energy lab the national labs have tremendous capabilities to take concepts and do them at the pilot level scale some of the large lab demonstration from which we can then understand some of the modeling and some of the scalability aspects to to the left to your right i guess of oliver that uh... martin is oliver fetzer and he's a ceo synthetic genomics our partner in the algae development so they've got the expertise to do the first demonstration and of course a company like ours then brings the capital the project expertise the engineering expertise to take that and go to scale the key here is we are engaged at all three levels and so instead of doing it from linda martin dolliver what we're trying to do is we're trying to stay in all three of those and so instead of doing it in series do things more and more in parallel and that is one way that you can speed up innovation you can't put a deadline on innovation but you can do things to drive innovation and this concept of this innovation value chain is what we were trying to show there so universities national labs companies and large corporations working together clearly identifying the problem everybody has a role to play and then we try to not only play the role of the final uh... implementer but also the integrator across them and guys like mark disco is sitting here is embedded at stanford to help drive that so we have folks embedded at the universities embedded with the national labs and then working very closely with these companies and we have four five of these types of chains already in place uh... that we're trying to drive let's talk about what we're trying to drive here so i can get to some some questions i'm gonna talk about three areas that were working one for each sector and again they do interconnect so the first one is carbon capture and utilization and i think you all know that today it is practice in fact we've been practicing it for decades uh... it is a liquid chemistry approach so it's an amine uh... liquid amine on the back of a of either a power plant or an industrial uh... facility and as you can see it's power consuming and quite frankly it's complicated it is not modular it's high capital intensive what we're looking for is we're challenging that paradigms and we want lower energy intensive or power generating technology and we'd like it to be modular and so and that's for point source and there we're working on uh... things like a fuel cell uh... different types of uh... capture technologies and then as Arun said and this i'll admit i didn't know if we'd have a direct air capture program a few years ago but again the technology is advancing we see some things that we're liking and uh... so we've we've started looking at direct air capture as well and of course direct air capture and natural sinks are probably the only two ways to really go negative everything else is going to get you at best to net zero but if you have to go negative you need to pull it out of the air either through a you know man-made machine like direct air capture or a natural sink and once you have the co2 you have two options you can sequester it which we've been doing for decades so that's uh... that's one option the other is to somehow take the carbon from the co2 and uh... and reuse it so that's how we're approaching uh... power and to some extent industrial the next one is transportation so while you can electrify uh... cars it is really hard to electrify an airplane uh... in fact i don't see it anytime soon and you know an extension cord from newark to singapore is a really long extension cord okay so batteries electricity is probably going to be hard so you need a c h bond you need it you need a liquid hydrocarbon you need an energy density to do it and of course we get that today from oil but we've been working on biofuels two routes algae and cellulose so the challenge with algae is one of biology so there's two biology steps needed you need uh... photosynthetic efficiency so you need to grow faster and then you need carbon partitioning you want to get the type of oil you want to get the challenge with cellulosic is one of scale so you have to collect the cellulose you have to collect the biomass and then you have to basically break down a very complicated uh... carbon structure to something that you can then turn into a usable oil so we're making progress on both we've had some significant break this analogy we've been working on it since two thousand nine a couple years ago we had some significant publications in in understanding uh... the sequencing enough so we could go in with the crisper cast tools and do some gene editing and drive the carbon partitioning to more lipid uh... we still need uh... you still need improvements in productivity we still need improvements in the carbon partitioning we're making good progress uh... and we've set a target of trying to get to ten thousand barrels a day by twenty twenty five now ten thousand barrels a day when units are usually millions of barrels okay isn't is not a big step but we do believe if you get to that you can then scale from that and so again it's demonstration of a scalable quantity so that we can then go to scale and the cellulose we're still working uh... with several partners and we haven't said that we have not set a target yet so i'll give you some feel for where we are in the development uh... but there is a lot of cellulose and uh... we think that's going to be part of the solution as well on the industrial process last lastly we you know this is steel concrete refining in chemicals and they're all energy intensive and in fact if you look at refining in chemicals at high temperature high pressure for the most part and so how do you do that how do you do separations without using temperature well you could use membranes so advancing membranes with george attack we're working with some other institutes on how to do separations it's a materials game and on the reactor design can you come up with with reactor designs a reactive distillation things like that so you can lower the energy intensity of the reactors again it's a paradigm shift away from where we've been but it's needed if we're going to try to get to the emissions we need an ultimately fuels and chemicals steel concrete those are going to continue to be key key components of our of our society so let me play connect the dots when i left you every little batman episodes where you you had the one episode you didn't know what's going to happen and you had to wait twenty eight minutes or you had to wait a week for the next episode okay so i left you with the dots not quite hitting the line and i said look we got a lot of ideas on efficiency but we don't really see any way to go left we don't have to get the decarbonization so i want to now take those three areas and just show you a hypothetical what what would happen if we did it so we have to continue to be more and more efficient so that is a you know sort of a big big time emerging area at at at the top universities is what's called process intensification so do better heat integration do better better energy management work on better catalyst things like that continue to do process intensification and then as you go to decarbonize two things they can help you get their one is biofuels uh... because algae obviously utilize the c o two uh... and then uh... carbon capture and so that'll turn that'll make you turn left that's what we're working on there's a lot of other science going on there's a lot of other technology what i was trying to do is explain to you how we choose what we work on how we choose who to partner with on what we work on and then how we think it's all part of putting our corporation in a position to compete as the uh... energy transition continues and we get to the point where we can have nine billion people with the emissions targets we want real quick uh... hopefully without being too alarming the current technology sets insufficient this is a research problem this is a technology problem and that's what we're that's how we're addressing it we have a long history of solving these types of problems of being part of the solution at the only solution but part of the solution and so we think we understand how to go from lab to scale we think we understand the types of capabilities we have and how they could apply to the solutions we need so we want to work on that and then we're taking that long history of science and engineering and that commitment to r&d that our corporation has and looking on developing the next generation solutions so that's a quick tour of what's going on outside how we think about it inside and then what we're doing to operationalize our capabilities to address the dual challenge again thanks so much for coming out on a on a on a monday afternoon and i've got a few minutes if uh... if there's any questions thanks very much for jay i think we're all impressed by the depth and breadth of your approach to the problem students first students first that's our well that's actually one of my questions how many of you here because you have to be because there's a tendency to take it okay i mean that's always the humbling part of these talks right you realize it eighty percent don't want to be okay so you mentioned developing countries and affordable energy i'm from a developing country and in addition to all the challenges you mentioned we also have what i would call like a democratic challenge because we we are improving our sustainable energy but our low-income communities they don't have access to it because clean energy simply does not exist to them because they live far away from big cities or from industry zones how do you think technology can address this democratic problem yeah i think i think uh... so again i'm biased i turn everything into a technical problem okay and that's that's i'll just admit my biases here so even that to me boils down to an insufficient set of technologies so even though we have expected mass urbanization to occur over the next twenty thirty years uh... there's still going to be the mix of rural and urban and so a solution for a mega city you know a city of ten million people the type of grid you're going to need the types of solution isn't very different than if you're in a rural area where you might be able to get by with a more distributed uh... solution you might be able to that might be a place depending again on other aspects of the country where solar panels uh... combining with uh... small-scale storage uh... could fit and then for the larger cities where you need the mass quantities of energy might have to have a bigger grid and have different sources so i think it's it comes back to understanding what the problem is and defining the problem and then developing a suite of solutions uh... of which we're developing some and others are developing others uh... but then bring it all those solutions together and figure out which ones you are right now uh... i can draw whatever analogy want i mean i i go back to you know kind of academic things we have the you have on one set you have solutions in a one-set you have problems and right now we have more problems than we have solutions so we've really got to build up our arsenal of options such that your community or any other community can look at those options like a what fits best and that comes back to that equilibrium between technology policy infrastructure because i think we've got to get the technology weight up a little bit and understand a little more what the technical options are as we as we determine what else we need to do it's a really good question it's it's the essence of the challenge it isn't a singular uh... solution it's really focusing on what the problem is that was a good fake-out because it looked like he was asking the question and it's just very good uh... so you gave us some kind of concrete projects you're excited about in carbon capture and biofuels and i was wondering as a non-expert if you could give a project or an example something you're especially excited about in that industrial and adjacent sector so um... so in carbon capture i'm gonna and again if you if you look me up you'll probably see some me talking about these various things but i'm going to talk about the carbonate fuel cell and what what do i like about the carbonate fuel cell and what excites us about that is it is as far as i can tell the only material that can concentrate co2 and generate power so it basically accepts co2 and then as the co2 goes across the film it it concentrates the co2 on the other side and it generates power so that that is a paradigm shift it's modular it's it's it's it's a battery right it's a fuel cell and so the power it the power sector should be comfortable with something that's modular and looks like something they're comfortable with versus having a chemical plant on the back of a power plant so so that's pretty exciting and and uh... you know we've set some targets out to try to uh... advance that technology to where we can understand whether or not it can actually work the challenge with uh... some of these things is okay to work in an industrial setting you have different sets of impurities the problem in in industry is not the the core concept of the chemistry it's the stuff that happens in the real world it's the impurities it's that it's not always you know in a lab it's always the same temperature in the same pressure and everything is ideal and then you go outside and life happens so it's really understanding the robustness of some of these technologies so that would be on carbon capture and then on the on the on the biofield side i'm going to go back to the two things we're very excited about algae again when it comes back to algae algae is an organism that is pretty well understood with the breakthroughs you know that the breakthrough we had an algae we started in oh nine the breakthrough in seventeen was actually enabled by two things that weren't even invented in oh nine uh... the first was a supercomputer so you just sequenced that much faster because there is a bit of trial and error to this and the other is the gene editing tools so part of this challenge that we have is one of the patients so while we could have given up by saying there's no way we can manipulate because we don't know how to actually uh... uh... engineer the the algae here universities like berkeley and mit we're coming up with gene editing tools and that became a huge enabler so so both of those and and again why am i excited because they're modular they're scalable algae is fantastic it doesn't compete for water or food it's brackish water and it typically wants to be around the equator so you're not really competing for for land or for or for water again because to to some of the other things have been said one problem solved another problem open since you try to anticipate as many of these can is as as you can and again last comment on why i like this it's our core capabilities fit well with advancing those technologies so that that's kind of a quick one uh... thank you uh... so i really love the what the work you guys are doing but let's zoom out a little bit so you guys have been in the industry for more than like five six decades and uh... the problem is why would we as a society trust you guys to spearhead the innovations that will actually be both affordable and at the same time solve the climate change issue because the clock is ticking and you guys really need to stay in business to be honest yeah well that's true i mean we we we have shareholders we have uh... interest but again one of the reasons why i wanted to show you a look back was not to not to say that it's it's a guarantee that happens going forward but to show that it's always been this is this is an incredibly technical industry in fact it's underappreciated how hard energy is and i'll just give you a quick example and i'll answer your question if you want to be a pharmacist what do you study you probably study pharmacy if you want to be a chemist you study chemistry if you want to be an energy what do you study and in fact energy may be the only discipline the only industry that requires every sector of engineering and every sector of science so while others may hire a geologist they're hiring a geologist because the geologist is smart we're hiring a geologist because we need to understand rocks we understand how to do we need to understand how to do sequestrations safely so what to solve this problem requires that interdisciplinary approach it also requires to your point project expertise because of the scale and so you need corporations that understand how to uh... put out very complicated chemistry is very complicated engineering solutions at a scale uh... the matters and that's what the energy sector does and now with the challenges do what you've been doing do it with a different set of technologies that we can get on the pathway and uh... you know our our belief is not believe this personally that you've got to be fundamentally sound you've got to understand the fundamentals you've got to have the pathway to scale and then how do you go faster well you can't put a deadline on innovation that's really hard to do but what you can do is you can change up the way you do things and that's what that slide on the innovation pipeline was meant to show that instead of doing things in series and center at Stanford you guys go spend the next ten years and develop your ideas we'll just watch and read the papers and then we'll come back to you no we had active discussions this afternoon saying okay if that's what you're seeing why don't you guys think about this because that's what's going to stop it from being scalable get in there you know sweat equity have people in the lab collaborating at the national labs and then the newest link in this value chain are these small companies i must admit in 87 when i started there weren't many small companies like synthetic genomics like fuel cell energy uh... there are more and more of those popping up and so find the ones that that compliment our capabilities and then try to understand how to cross-pollinate and add capability so that we can get there faster that that to us is the most logical and probably the most probable way to be able to come up with solutions that can be scalable that can get us where we want to go it's a really good question though and i think it's one that quite frankly we ought to challenge ourselves on is how do we do this more efficiently a lot of it is communication a lot of it is how we work together to get this done hi thanks for your uh... overview uh... i'm really interested in your in your assertion that the problems are essentially technology problems i did research myself when i was here and i'm really excited about exxon's continuing engagement it's really important and at the same time uh... i can think of and i'm sure many others can think of maturing technologies that are having a hard time getting a foothold in their respective markets which has a lot to do with market structure and business incentives and so i i guess i want to offer a friendly addition that the technology is is absolutely necessary and sometimes so too are the business incentive structures and the market structure uh... and so and i was particularly interested in when you were showing the four stages uh... that by which exxon engages uh... these questions the first that you had was uh... optimizing exxon's own internal process so uh... so with the broader question in mind of what is driving these from the market perspective i was interested to hear if you can share any insights on what is it what is the internal exxon mobile business case for doing things like reducing methane leakage or for process intensification uh... how does how does that look to the was the investment case for those to the business managers and to sign off the necessary so let's first start with the most logical thing which is um... you'd much rather capture the methane and sell it than not okay so there's obviously an incentive to being as efficient as you can be uh... so it starts there there's never a downside to efficiency and i think what what has happened is is as we understand the various components of efficiency and our analytics get better and our ability to understand where we have value leakage is what we call it uh... you want to try to close those value leakage is a huge business proposition to being more efficient the second part was okay yeah so that's the business case and and then yeah yeah i think it comes down to just that there's there's never rarely is being more efficient to bad thing and it's just how you define more efficient and so we're now looking at that efficiency along those axes which is how do we mitigate emissions and our operations i will say the other thing where i thought you were headed which is look technology and policy have to go together i'm the technology guy so i'm going to talk about technology if we'd have brought my policy the policy guy with us he'd have talked about policy in fact we often give a talk where we go back and forth because it is important and and my belief is the technology guys have to really talk about what is possible and what we're doing to get there to be possible see you after really we're in a pen shirt at stanford i don't see many forty-niners shirts you kind of touched upon a bit but when it comes to carbon sequestration it throws a lot of criticism for being for being too costly and too complex as well as potentially a temporary solution and you kind of uh... went over a bit with the whole carbon so i was wondering what potential avenues do you see in the future solve those problems and what role do you see carbon sequestration carbon capture and sequestration playing in the future yes i actually encourage you to read some of the papers out of stanford uh... that have been written on sequestration because a lot of the pioneering work on understanding how co2 can be sequestered safely and for pick your unit of time but for a long long long time has actually been done at stanford has been done by the department of energy and has also been done by you know and companies like ours have experiential uh... uh... experience with uh... with sequestration so uh... yeah i think uh... co2 sequestration is a is a very good thing to do it's obviously an expertise we have because it's it's kind of reversing what we've done which is instead of taking it out you put it back in and so it is geology it's engineering it's it's moving gas at at pressures and temperatures so it is something that we feel comfortable doing it now it's a question again of getting the other components that are needed for co2 sequestration like infrastructure because if you if you capture co2 on a power plant that's great now you've got it captured it's unlikely that you can sequester right where you capture so you then have to move the co2 that comes in infrastructure that comes in policy and all the other things you said but to me it still starts with uh... i think there's better ways we can't be satisfied with the solutions we have today for carbon capture uh... so we got to get better at co2 capture the rest is more or less straightforward how you move co2 in pipelines is fairly well understood and then there's plenty plenty plenty of studies on where you can safely uh... store uh... co2 and it's been validated a lot by stanford but as well as not just the u.s. government but but governments around the world so i think if we can come up with a scalable reliable affordable way to do carbon capture the other two pieces will come in line thank you so much for your time


I'm an engineer, turned psychologist. And I was an undergraduate, I got interested in control systems. And I realized that the brain is the most sophisticated control system in the known universe. Just consider a simple reaching movement. You've got 37 muscles in your arm, 17 in your hand, not to mention 600 muscles in your body. Your brain needs to learn to control that. It has to deal with the real physics, the real equations of motion, of how to move the limb. And we've yet to crack the code on how we do this. Robots can be made to do very specific tasks very well, but they lack the flexibility to do common everyday tasks that we take for granted. Why do they fail so miserably? Well, they maybe lack our remarkable ability to learn and also use our semantic knowledge about the world to contextualize the task. As an engineer, you can write out nice adaptive neural network control systems that can refine action execution over time, such as making movements smoother, but it lacks a psychological aspect of motor control. How do we come up with novel cognitive strategies to solve a motor task, such as opening a wine bottle with your shoe? Useful trick tonight if you lose your corkscrew. Okay, it works. A great example comes from the sport of high jumping. At the turn of the century, people were going over the bar using the scissors technique, basically hurtling sideways. By the end of the century, everybody was going over backwards. This is Dick Fosbury doing the Fosbury flop. How did this change in strategy happen? It really led to a breakthrough in how many feet someone can clear the bar. I went to look at the world records and they actually look quite gradual. Like a nice little progression of heights that you could achieve. But if you actually look closer, you see that there's four different strategies that are used. Each time a new strategy was invented in an arrow here, it gave way to a new wave of record breaking. Just consider the last two of this era, the parallel straddle and the Fosbury flop. As you can see, they're diametrically opposed to one another. With the parallel straddle, you're going over with your chest first. With the Fosbury flop, you're going over with your back first. It wouldn't be the gradual refinement of action execution, of practicing the parallel straddle that would ever have given rise to the Fosbury flop. You need a whole new strategy. How does this come about? Well, the classic theory says that it starts off in a cognitive stage. You think about what the strategy is explicitly, and that then gives way to an associative learning process that you then slowly get better at. And much of research is focused on the latter phase. But all the action, 80% of your learning is happening in this cognitive stage. How can we get at that? In my lab, we try to do this. And while we love this study of high jumping, it's a bit unpractical. So what we have people do is make reaching movements while they hold on to robotic manipulantum and move in a virtual environment, and this robot knocks them off their path, and they have to learn these new forces that are put on their limb. And as you can see here, they can learn overall in purple, but we can actually measure two dissociable learning processes. In blue are strategies that they use in the beginning a lot, and it kind of peters out a little bit towards the end, and then a slow gradual rise, and that's something implicit that they don't know about accumulates over time. But both are kind of always operating, and they're there at the end of learning. And this is very different from the classic theory that posits a unitary process of strategies into skill. And we actually know that these are dissociable things in the brain by looking at people with neurological damage. This is an individual that has lost her hippocampus due to viral encephalitis. She cannot remember anything for more than about five minutes. So if she met you, she'd quickly forget your name, who you were, or ever having a memory of meeting you before. But she can learn new motor skills. She can learn something like drawing a figure while looking through a mirror and retain that across days. Okay, and very different from an explicit thing that she would know like your name. The problem is that she actually learns much slower than anybody else. She always does much worse. And we think this is because she can't use strategies. She can't remember them, and she can't employ them. So she's stuck with just action refinement. She can't come up with a new way to solve this trick. So it got us to think, can we actually get her to learn a motor test as a one-shot strategy that's not very apparent? This is just a little cute parlor trick that I'd like to show you called Jacob's Revenge. And the goal is to get the ball to the neck of the bottle. The problem when you try to tilt it is that dowel gets in the way. It blocks the ball. And you have to actually spin the bottle to get it to work. You use centrifugal force to move that ball down to the neck of the bottle. So what you're going to see here is a video. I've already explained to her how to do this. You don't hear the audio, but she's telling me back how to solve the task. I'm doing it for her. I'm going to then spin the bottle. She knows how to solve it. She just told me how to do it. And then we're going to have her perform it. But again, she can't remember anything more than about five minutes. She learns in that permanent present. This is just 15 minutes later after doing a different task, distracting her. And now I ask her again if she can solve this task. And she says that she can't. She doesn't know what to do. She looks at the bottle, and she tries to solve it in that direct way. Kind of tipping, trying to get the ball down. She's lost the memory of how to spin. So in this one-shot strategy task, motor skill task, she's unable to do it. She's committed at just following that kind of orange trace of doing this action refinement. She can't use strategies over time, that blue trace, that allow us to achieve high levels of performance. And an analogy back to the Fosbury flop is that she would be committed to doing the scissors technique, the direct approach to getting over that high jump bar. She'd never come up with Fosbury flop. And the strategies are an integral part of our learning process. It isn't just through practice and refinement that we can ever achieve top levels of performance. Thanks.


Flying and shooting targets from the air just makes it that much better. Soldiers with the 1189th General Support Aviation Battalion conducted helicopter aerial gunnery March 28 through 31 at the Orchard Combat Training Center. We're doing what's called HAG, it's helicopter aerial gunnery. We're here qualifying all of the back seaters on firing and shooting out of the CH-47 or the UH-60 depending on who you're here with. Crews learn how to defend an aircraft should they be attacked. From crew coordination and target identification to understanding the limitations of the weapon system and the aircraft. Being with your unit, it's kind of a bonding experience for us. It's always fun to shoot machine guns out of a helicopter. It's something that a lot of people don't get to do. You kind of feel pretty cool when you get to do that.


Hey Kevin! This is Megan with Oxmore Toyota. I just want to send this quick video greeting just to personally introduce myself. It has come to my attention that you're interested in training in your 2014 Toyota Camry. When you can, go ahead and give me a call. You can reach me at<PHONE_NUMBER> and I look forward to hearing from you soon. Bye!


Welcome to class 24 in Topics in Power Electronics and Distributed Generation. In the last class, we talked about transfer of power between two sources and we looked at a efficient way of transferring power from one source to the other with one side being a voltage source and the other side being a current source. And efficient switch arrangement to transfer power in such a condition can be modeled as a single pole double throw switch. And we saw how it can then be extended to a DC to AC inverter which is commonly required for a distributed generation or a power quality or any inverter application. And we looked at the simple case of it where we are looking at it on a single phase basis one leg at a time. And it can also then be generalized to include the actual diodes and transistors to form a real realization of such a converter circuit using transistors and diodes to implement the single pole double throw configuration. So one can then look at what is the output voltage that can be generated in such a system and we looked at the average output voltage that can be obtained. So we looked at the average voltage from the output to the neutral midpoint of the DC bus and this was V DC by 2 T on minus V DC by 2 T off and this is average over duration of T SW which is a switching duration. And we know that the T on can be related to the duty cycle as T on is equal to D times T SW and T off. So it gives the time T on is a time duration of the top switch being on. And we saw that we could actually get a relationship between the duty cycle and the output voltage on an average switching cycle basis. So if your duty cycle is varying between 0 and 1 your output voltage can have a value of minus V DC by 2 at a value of 0 and plus V DC by 2 when duty cycle has a value of 1. So if you look at the grid voltage that or the voltage that gets connected to power converter at the output you would like to get a relationship between what is the actual output voltage at your load or at the terminal of the inverter and the DC bus voltage that is available to you.  A common voltage that we have in a single phase system in India is 230 volts. So A V is 230 square root of 2 would be the amplitude of your voltage that is being applied. And for the positive half cycle your T on max can be as much as your. So in the positive half cycle your T on max can be as much as T SW. So you can apply as much a voltage as V DC by 2. In the negative half cycle T off can be as large as T SW. So you can as apply as much as minus V DC by 2. So you can get a relationship between what is the output voltage that you are applying and what is your DC bus your T on max is T SW when duty cycle is equal to 1. And so you get your average V ON that is being applied can have maximum value of V DC by 2. And if you take V ON average to be equal to the peak of the voltage that you are applying you are talking about 230 root 2 is equal to V DC by 2. So this is about 230 root 2 is about 325 volts. So you are talking ideally of about 650 volts as your DC bus voltage when your input voltage is about 230 volts. We will see that you have to add additional factors over and above this particular DC voltage in an actual application. So before we do that we will actually look at what it means to say you are building a inverter of a given specification. So a typical power converter that will be built you first need to know what power rating it is going to handle. So whether it is 100 watts a kilowatt 10 kilowatt megawatt. So a basic quantity of that is specified when you design a power converter is the power rating. So once you know the power rating the next important quantity is what is the voltage rating especially the AC voltage rating which is what gets connected out of the terminals of your power converter. And common AC voltages are can be 110 volts 220 230 volts 480 volts 560 690 there can be a range of voltages depending on different geographical locations etc. A common voltage for a single phase system is 230 volts for us. So it is not just the voltage rating we also want to know what is the range around the nominal voltage because ideally you get the exact voltage but we know that there is going to be a range around the nominal voltage you might have a positive value above the range and negative value below the range you might have 10 plus 5 percent voltage over the nominal minus 10 percent. So depending on the range around the nominal we also have to know to actually design the specification of the power converter ok. So you are talking about in terms of power rating you are talking about of range of watts could be even as large as mega watts depending on the application. So voltage rating you are talking about your AC voltage rating so you are talking about 110 230 480 volts 690 etc. All these voltages are below 1000 volts so what is typically considered low voltage systems. The frequency rating is also a important factor though it might not directly affect your power semiconductors it might affect your speed of cooling fans etc. Nominal frequency in our case would be 50 hertz. Again the electrical interface required is also a important consideration by electrical interface it is the most basic aspect of it is whether it is a three phase system single phase system whether you have three wires four wires. So the number of AC connections coming into your power converter is a important aspect of the design. So what we have been considering in our basic design is a single phase power converter. Other important factors which are important are environmental specifications. So when we talk about environmental specification the number of factors one is what is the ambient temperature. So higher ambient temperature would be more challenging design for a power converter. Also whether your power converter is designed for indoor or outdoor application the environmental degradation experienced by a converter meant for outdoor can be more severe compared to indoor. So you will have to pay attention to where exactly is the location of your power converter. You also have what people refer to as the ingress protection of your power converter. So people talk about IP rating of your converter cabinets. IP ratings like IP 00 means that there is no protection you can put your hand in and you will potentially get a shock. There is no water proofing whereas a larger number like IP 66 means that it is fully sealed and your dust will not enter the cabinet. Also you can have water jet sprays under which some of these cabinets can be immersed and you won't have damage to the electronics. The electronics would function even when the ingress protection number is at the higher side. Again the cost of equipment goes up with higher IP numbers ingress protection numbers. So if you have a enclosure which is very tightly sealed it means thermally cooling it is more challenging whereas something which is open frame is easier to cool but there is more risk that some dirt might fall on it might get damaged. So there is always a risk between how you handle your IP ratings. Typically when we develop something in an academic lab we might develop things in an open frame basis but finally when you have to send it to a customer aspects such as IP protection is important. Also there are other important factors such as vibration or whether your equipment will survive an earthquake depending on what level of impact or shock is being experienced in the cabinets whether there are capacitors in the cabinet which might fall off from your mounting. These are important aspects of specifying a power converter. We will start with the basic single phase power converter and if we take a single phase power converter and assume that it is going to be operating is going to be operating as a distributed generation unit will assume that it is going to be at unity power factor. We will assume that there is unity power factor operation sinusoidal AC voltages and currents. So your power is VRMS IRMS and so your I rated is P rated divided by your V and one thing that we just mentioned is the V depends on what range around the nominal you want to actually operate. So for example if you have a range around the nominal as plus 5% minus 10% it means that for a given power rated if your voltage is 10% lower it means that your current has to be rated higher which means that your component costs are going to be higher. If you have a system which is now going to be used in an application where the power quality is going to be poorer it means that your voltage range may be wider it has impact on the cost because it means that you have to have higher current ratings. So you need to make sure that there is a trade off between how much power quality situation you are willing to encounter and to what specification you want to maintain your power requirement. So a larger voltage range would imply that greater current rating or the components given P rated. So we will again look at what is the voltage that we would we need to have on your DC bus given AC voltage and these voltages are related to your nominal AC voltage variation. So if you think about the grid voltage as a phaser V grid you can have a number of factors one thing that we mentioned is that the grid voltage might have some tolerance which might increase the value of the actual Vg. The other factors that can actually affect us between the power converter and the your output voltage and your inverter you have a filter inductor. So you might end up with a drop on the filter inductor. So you need to also incorporate how much drop you might expect on that particular filter inductor drop. So depending on the power factor if your I out is going to be lagging for some reason if you want to actually provide capacity watts you might end up with further increase in value in your terminal voltage that is required by your power converter. If you take a typical filter starting assumption might be your filter inductance might be 10 percent. So you are talking about here a AC voltage variation of say 5 percent addition over here you might be talking about a 10 percent addition over here. You also have factors such as dead band which is will explain what the dead band is. Typically when you have a leg of a power converter we saw that to the one of the condition is that we cannot short both the tops and the bottom together or you will cause a shoot through across the voltage source. The other is that your current always has a path. So to prevent the positive and negative being shorted you always have a duration where both S plus and S minus is simultaneously kept off for a short duration called the dead time. Now if you look at the effect of this particular dead time the effect of the dead time depends on the polarity of the current. So if you look at an ideal sine triangle modulation whenever your duty cycle is greater than the triangle V TRI your S plus is on and S minus is on whenever S plus goes low. But in the actual signal that is provided to the gate of the devices your S plus and S minus your starting edge of your signal is always delayed a little bit. So as to prevent both top and bottom switches from shooting through and this delayed duration is called the dead time. Now if your current polarity is positive turning off S1 will automatically cause the complementary diode to turn on. So there is no error being caused during the positive polarity current when your when your current is in the positive polarity but when you are trying to actually turn on the top switch any delay in the turn on of the top switch will increase the amount of time for which the bottom diode is still conducting which leads to an error in voltage and this error in voltage depends on the ratio of your the average value of this particular error in voltage depends on your DC bus voltage in this particular case the error is negative it depends on your dead time it depends on your switching duration TSW and you can think of it as a voltage which is like a square wave and if you want to convert it back to a sine wave of some particular fundamental it will you can add a factor of 4 by pi to get the fundamental effect of the dead time and this gives you an additional factor which you need to have in your AC voltage output to generate your your required PWM output. So, we will assume that this is also having a factor of plus 0.5 percent. So, overall if you then look at the relationship between your DC bus voltage and your AC output you will end up with now your 230 times root 2 plus a factor for your dead time plus a factor for your delta Vg your Vg variation and you might have a factor for filter drops some of these factors might be not exactly in phase for example, the filter drop might be 90 degrees lagging whereas your dead time might be in phase, but we also need to consider that you have a margin between what is the actual dynamic voltage available to control your output and the actual voltage that is there at the terminals of the inverter. So, overall keeping in mind factors such as this we will see that the actual DC bus voltage required is not just 325 it might has it would have or 650 volts it has to be greater than 650 volts a common voltage you might end up requiring maybe you multiply these factors you might be getting a voltage close to 800 volt. So, you can see that these factors do add up and you have to actually get adequate margin between your actual DC bus voltage and your operating voltage for your AC side of your system. Also keep in mind that we are assuming basic single phase sine triangle modulation for your pulse width modulation of the switches this voltage now has an implication on your selection of components within your power converter two parts are there to at one is we know that in the actual power converter your DC bus is which is over here shown as 2 voltage sources of V DC by 2 is actually built with capacitors. So, the first implication is on the rating of the capacitors that are used in your DC bus. So, if you have to have a DC bus voltage of 800 volts it means that your electrolytic capacitors have to be maybe 850 900 volts etc. and because it is not very common to have high voltage capacitors greater than 500 volts you might have to end up now having series connected capacitors in a power electronic application where you are having to have say 230 volts AC. So, in this particular case maybe because your DC bus voltage is 800 volts you might use two capacitors each capacitor having 450 volts. Another important implication of this particular relationship of AC voltage with the DC voltage is the rating of the switches and the diodes. So, the switches that you would typically use it might be some transistor to some extent maybe you could even find a FET which can operate at that voltage commonly people might use IGBTs which are insulated gate bipolar transistors. And again the voltage ratings of these components these transistors are not continuously varying you might have say FETs at 100 volts 200 volts 400 volts 600 volts then it may jump to 1200 volts there may be a few components which are available at 1000 volts. So, quite often you might end up selecting the voltage rating of your switches to be 1200 volts commonly when you deal with a 230 volt system because it now directly links your AC side voltage to what is required on your DC and we will see that you also need adequate margin in your transistors because there is large di-dt's during switching of the transistors and you need adequate margin between your actual voltage rating of your DC bus and your voltage rating of your transistor devices. So, now that we have a feel for what would be the preliminary voltage rating required by some of the components we can then take a look at what could be some of the currents that are flowing through this particular circuit especially on the DC bus. And we will look at the capacitor currents closely and there are actually in a circuit such as this different frequency components of currents that can actually flow through the circuit. The first component that we will look at is the fundamental component of the capacitor current because this is a single phase system your I out is actually a 50 hertz AC quantity and we saw how I out is related to your P rating and your AC voltage rating. So, your I out in this particular case can flow through your source which is your AC grid, but then it has to flow back through your neutral and come back into your DC bus. And if you take your current I out to be AI cos omega naught t your your IRMS is AI by root 2 taking the output current to be a sinusoidal quantity which is well filtered. We also know that you can relate your grid we had taken it as A v cos omega naught t where the instantaneous grid voltage is related to the amplitude and it is a sinusoidal function. So, you can relate your power rating your P rated is A v AI by root 2 root 2. So, you know what your your AI has to be in terms of your power rating and your terminal voltage rating. And so, you know what your current is that is actually flowing into your neutral point. So, this neutral point current is actually a 50 hertz current and we are assuming that the switches S plus and S minus are being modulated in a symmetric manner. So, during the positive half cycle what is happening to S plus it is identical to what is happening in the negative half cycle to S minus. So, there is symmetry between the operation of the top and the bottom leg of the switches in this particular power converter ok. So, whatever current is flowing in splits between the capacitor C dc C dc as i cap going in one direction into your top bank and i cap going into the bottom direction in the bottom bank. And one thing that you could immediately note about this current. So, if there is a current flowing into the bottom bank this is actually charging this bottom capacitor whereas, the same current which is flowing out into your top bank is actually discharging the top capacitor. So, the current is actually a common mode current it does not affect the differential voltage between your positive and negative dc bus. Even though it affects the individual capacitor voltage the total voltage between your positive and negative is not affected by this common mode current because one is charging when the other is discharging and the other way around depending on the instant at which the current is flowing. So, the next component of the current that can flow through this capacitor bank is we will see that it is has a dc and a 100 hertz component. And for this again we are assuming your the voltage to be a V cos omega t. So, V o n is a V and we can we can look at what is the power going out of your part of the ac leg and the power coming in. And we will make some assumptions we will assume that the inverter is very efficient which means it is a lossless and the filter is purely inductive. So, this again no losses in the inductor. So, we will also assume that the voltage at the input V dc is quite stiff typically by design you will try to maintain that voltage to be a constant.  So, you can write what your I p of t is a V a i by V dc cos square omega t. So, you can see that by looking at the power balance between your input and your output you can see that there is a dc quantity that is flowing through your dc bus which you would naturally expect because you are exchanging power from one source to the other. But in addition to that now you see that you have a 100 hertz component which is coming in the dc bus and has a value of a V a i by 2 V dc and then there is a second harmonic component and its amplitude is also a V a i by 2 V dc. So, if you then look at where is the this particular second harmonic this particular current flowing this current is actually flowing through this particular circuit back through this particular loop and this is actually a component which is circulating in the dc bus. So, it shows up as a differential voltage across your dc bus. So, this component will so, if you actually measure the voltage across the dc bus the 50 hertz would not show up across the dc bus as a total across the total voltage whereas, the 100 hertz component will actually be measured across the dc bus. And some part of it because if you are thinking about say an application like a photovoltaic inverter you might have a prime source which might be your your PV panels it might be your batteries if it is a storage system it might be a fuel cell stack depending on whether what application it is. So, one thing that a 100 hertz component can actually do is it will split between your capacitor c dc and your prime source depending on the impedance of these two sources at that particular 100 hertz. So, if you have a higher impedance for c dc it means that most of your 100 hertz might flow through the prime source and many times the effects of this 100 hertz ripple in the prime source is actually negative in the sense that in a photovoltaic system the 100 hertz component would just cause heating of the elements not any real generation of power also the 100 hertz voltage which would mean that your actual operating point is deviating from your MPPT point. So, in multiple ways you are actually losing out on power if you are taking a battery your effective capacitance of the battery can be quite large which means that a fair amount of 100 hertz can actually flow into it and this will cause losses in the electrolyte the electrodes etcetera again in things like a fuel cell it is it will cause cause heating of the stack etcetera. So, these are undesirable components to some extent that people might even think about adding a power converter over here to prevent that 100 hertz ripple from actually flowing into the prime source and affecting the performance of the prime source. The other item of interest when we are looking at the 100 hertz component is that if you look at the path for the 100 hertz component the output current I out consists of largely the fundamental. So, this is 50 hertz it might have some switching frequency ripple, but you are assuming that your filtering is being designed in a efficient manner that it is largely 50 hertz and you are not having much of switching ripple and also your controls are ensuring that you are not having low frequency harmonic distortions in your output voltage. So, if you look at where is the path for the 100 hertz component it is flowing through the DC bus it is flowing through the switches. So, it is an interesting path that even though we as we know that the both the switches do not say conducts simultaneously because of the modulation effect of the power converter the non-linearity involved in modulation you end up with a 100 hertz current through the switches through your DC bus and you could actually explicitly look at these waveforms in a time domain simulation to convince yourself that the path for this 100 hertz component is actually through the inverter. The third component of the current through a power converter such as what we have just discussed is now the high frequency component. So, we looked at the DC 50 hertz 100 hertz. So, you also have because of the PWM switching action a high frequency component of the current flowing through the switches and to determine what these high frequency currents are in the switch we can look at the switching functions that are being generated by the power converter. So, if you look at the power converter we have essentially we had the switching function of the stop switch being S plus. So, whenever S plus is on your current in IP gets connected to I out. So, there is a you can make use of the switching function to relate IP to I out we also make can make use of the switching functions to relate your output voltage to your DC bus voltage which was what we did to look at what the average output voltages. We will assume that all the switching frequency effects occur at the switching frequency rather than spread around a range of band around the nominal switching frequency. We will also assume that the ripple in AC current is small and we can make use of the switching functions to obtain your voltage relationship we saw that VON is S plus VDC by 2 plus S minus minus VDC by 2. So, this is O with respect to the neutral if you look at voltage O with respect to the negative bus you would have S plus VDC to be directly giving your V O with respect to your negative DC bus. Similarly, you can write an expression for what is your positive DC bus current is S plus your times I out of T. So, this gives the relationship between your actual current that is flowing in your positive DC bus to your AC output current and the AC output current you know what it is based on the specification of the inverter and we saw how the specification of the inverter is linked to the power rating voltage rating etcetera. So, what is plotted over here is this black waveform over here is I out what is shown over here in red is your V O with respect to your I P of T this is I out of T and we can actually then calculate what the average value of I P is in the different durations. So, if you look at over one switching period interval say from one peak to the next peak we will take that your current is not changing by much because you have about 200 switching cycles when you are talking about a 20 hertz I mean 50 hertz fundamental and 10 kilohertz switching frequency. So, I out times D because D is the duration D times T SW is your on duration. So, if you look at your I out your on duration over here is D times T SW. Now, if you look at the I P average over and what we have averaged it is over the duration of T SW the actual if you look at it over multiple such cycles you will see an average which has a 50 hertz buried in it it has 100 hertz buried in it has DC. So, it is not just a flat quantity it is a it is something which is changing slowly on a cycle by cycle basis ok. You could also then look at what is a RMS value of this I P current which is flowing on a flowing in your positive DC bus. So, the RMS. So, you can calculate what your I P RMS is and we know that I P square of T can be written as it is on only during the T on duration. So, it is T on divided by T SW into I P square. So, T on by T SW is your duty cycle. So, you can write your I P RMS to be equal to the magnitude of I P times square root of D ok. So, if you look at the RMS component of the switching frequency in I P during this particular T S duration the RMS switching frequency component because I P average contained also the low frequency 50 hertz 100 hertz effect. We want to then calculate what is the switching frequency effect component we will get we can get it as. So, you can take the I P RMS square minus the I P average square and take the square root of that we will get the I P switching frequency component during that particular duration T SW. So, this is equal to I P I out of T times square root of D minus D square where T the D term is because of the RMS and the D square is because of the average effect and we know that your D belongs to the interval 0 to 1. So, D minus D square will always have the appropriate sign. Now, we know that this is on per switching cycle basis. So, if you will want to look at the switching frequency effect over the whole fundamental cycle then you need to take this individual high frequency harmonics and sum it up appropriately on a sum of square basis over the longer time frame ok. We have N times T SW is 1 by F naught W is 1 by F naught F naught is your fundamental frequency. So, using that we can get a relationship for your output for your output if you are for your RMS current as I P FSW RMS is 1 by N summation K is equal to 1 to N over the N points I out of K T S. So, it depends depending on what your AC output is at the particular instant square. So, you do the RMS calculation over the number of cycles. So, if you will look at. So, if this is duration say K is equal to 1 K is equal to 1 to N over the N points I out of K T S. So, it depends depending on what your AC output is at the particular instant square. So, you do the RMS calculation over the number of cycles. So, if you look at. So, if this is duration say K is equal to 2 K is equal to 3 and you know what your I P values are at these different instance. You can go through a fairly simple calculation just a summing over say 200 points for fundamental frequency of 50 hertz and a switching frequency of 10 kilo hertz. So, you will be able to calculate what your high frequency current is going to be through your capacitor bank. Now, once you have the value of the currents calculated at the different components frequency components then we have to make a decision about what type of capacitor we would actually be using in the DC bus and that the type of capacitor depends on many factors of one important factor is the type of dielectric that is being used. And depending on the type of dielectric you can have ceramic capacitors, mica capacitors, paper capacitors these are high frequency type of capacitors. You could have tantalum type capacitors or electrolytics you can have poly propylene or polyester if it is AC application. And in the DC bus of a voltage source converter a common capacitor that is be that would be used is a electrolytic capacitor. And we will see that now once you have this effects how next can we actually go in and see what would be the appropriate electrolytic capacitor that can be used in the DC bus of power converter. Thank you.