 levels should be there, how many different possible configurations in a three level inverter. Before that I will see what are the issues in three level inverter. Each leg of re-inviter, see how many possible combinations are there in two level inverter, conventional three phase two level inverter, eight out of which are two are null and six are active, six states and these six states occupy six what is of an hexagon, there are, are you with me, I do not whether you are, but then it can be proved, it can be proved that, it can be proved that, it can be proved that six hexagons sorry, six active states occupy in the, in the DQ plane, occupy six vertices in the DQ plane, Q axis, V axis, see I do not, see I have three phase voltages V a, V b, V c, are you with me, they are displaced by 120 degrees. Now, what I will do, I will resolve them along x and y axis, are you with me, I will resolve these three voltages along x and y axis, now I call them and call them as D and Q, are you with me, so I have a D and Q, I can get the resultant, come on, I have two voltage components along D, one is along D axis, one is along Q axis, can I get the resultant, square of this plus square of the square root, that is the resultant voltage. So, in one thing is for sure, this six active states, resultant magnitude of that voltage should remain the same, are you able to understand or no, the magnitude of that voltage V, resultant voltage should remain the same, but depending upon the switching positions, the position of the resultant will change, can you got the idea or not, see, see what is the, what are the six states we had, I do not know sometimes, what are the, what are the S 1, S 3, S 5, I said at any given time, three switch, each one switch in each leg is on, three are null, two states are null, remaining six are active, so what are the equivalent circuit, what are the possible combinations, one upper, one upper and two lower or two upper, one lower, six such combinations are there, whatever may be the combination, resultant voltage will remain the same, are you with me, resultant voltage will remain the same, resultant voltage of, what I will do, I had a V a, V b, V c, what I will do, I will resolve those three voltages along X and Y or D and Q, now I have D and Q components, I can get the resultant, square root of that, so resultant will remain the same, but then position of the resultant will change, position of the resultant will change, so it can be proved that, it can be proved that relatively easy, it can be proved that it occupies six vertices of the X again, take it from me, such a, the remaining two null, they are at the origin, so these are six active states two are null, now come to this, now he has asked me a question, I cannot be saying every time, I cannot, I do not occupy, in a three level inverter, how many possible combinations will be there, how many possible combinations are there, how many possible combinations, how 16, how many possible combinations are there, 14, but initially told me 27, now it came to 14, how did it arrive at the 27, total how many possible states, forget about active one, how many, how did you arrive at 27 and that is an answer, I was not satisfied, how many possible states, how did you get that 8 figure, 2 raise to 4, 4, but then how did you arrive at this for, 8 for this, how did you arrive at this, this could be on off, this could be on off, this could be on off, this is 2 to the, this is on off, 2, 2, 2 to the power 3, so 0, 0, 2, 1, 1, 1, 0, 0, 0, 2, 1, 1, 1, forget about it, we will find out, let us not get, work down with this, assume now see there are, there are 3 possible combinations are there, in each leg, each leg, each leg, either upper 2 or lower 2 devices are on, phase A, take for example phase A, these 2 are on, phase B, phase B, these 2 are on, phase C, these 2 are on, it is similar to, similar to 2 level inverter, which up, come on, when this, these 2 are on, A gets connected to, A connected to B D C, lower 2 are on, what is the equivalent circuit, lower 2 are on, what is the equivalent circuit, lower 2 are on, where the B gets connected, B gets, C, A, B, C I have connected, say, connected to the grid or I have connected to a 3 phase load or to a machine, A is connected to this point, B and C are connected to, B and C are connected to ground 9, that is the negative of the DC bus, which is, this equivalent circuit we have studied yesterday, similar to upper 1 device on, lower 2 devices are on, this is the maximum voltage that, one can apply in a 3 level inverter, the moment upper 2 switches are on, what is the voltage applied, what is the voltage applied, B D C, S 2, S 3 on, what is the applied voltage, lower 2, it is, B D C by 2, so definitely to apply a very high voltage or when I am at the top, which one do I need to apply, in a sinusoidal, come on, when I am here, what do I need to apply, which vector, come on, when I am here on top, which one do I need to apply, in a 3 level inverter, 3 level inverter, upper 2, upper 2 I need to apply, high on a, suppose when I am in the bottom maximum, which one do I need to apply, lower 2, so this equivalent circuit, it is similar to 2 level inverter, this equivalent circuit is similar to 2 level inverter, wherein one phase is connected to the positive DC bus and 2 are connected to negative DC bus, is not it, here could be S 1, S 2 on, here S 3, S 4, S 3, S 4, this is equivalent to, come on, this is equivalent to phase I connected here, D and C connected here, how many possible combinations are there, how many possible combinations are there, active, 6, null or 2, so here you just see here, point A gets connected to, sorry, one of the phase is connected to positive DC bus, 2 phases are connected to negative or 2 are connected to positive, one is connected to negative, so these are known as, these are known as large voltage vectors, large voltage vectors, entire this one is being connected, these are known as large voltage vectors, so I have 8 possible combinations, this is such similar circuit is possible in 2 level also, I have 8 possible combination out of which, out of which 2 or null, 6 are active, so I get an hexagon, I get an hexagon, those 6 active states occupy at 6 vertices and 2 origin, now consider a case, when can I get this equivalent circuit, when can I think for a while, when can I get this equivalent circuit, 3 level inverter, 3 level inverter, I have 3 lines, this is one leg of an inverter, this is one leg of an inverter, the previous equivalent circuit I showed, S1, S2 are on, S1, S2 are on or S3, S4 are on, the moment I connect S1, S2 are on, A gets connected here, if these are lower on, A gets connected here, something similar will happen to B and C, I showed you at one equivalent circuit, there are 3 lines, there are 3 lines, there are 3 lines, one is connected to positive bus, another one is connected to negative bus and one point is connected to center point, you have to just recall the equivalent circuit, what did I show you, a bit, memory recall is should not take lot of time, one line is up, one line is down in the center, when can I connect this, when this happens, upper 2 are on, when this happens, lower 2 are on, when this happens, middle 2 are on, when point A gets connected to O, S2, S3 are on, depending upon the direction of current whether it will flow through S2 or it will flow through S3, so I have this equivalent circuit, one up, one down, one center, one center, one center, how many possible combinations, this is maximum is 2 top, one down or one top, 2 down, whatever that I said is vice-versa, here is something here, one up, one down, one center, how many possible combinations, he is saying he will take 12 volt supply and use a 3 level inverter, there is a flow in your question, why am I using 3 level, why am I using a 3 level, why did we go to 3 level, as the power level increases, the voltage level increases, stress increases, blah blah blah, 12 volts inverter, one device may not be in turn on, follow what I am saying, to prove the concept, you need to apply at least a sizeable voltage of say 50 to 60 volts, so that some voltage wave you can get, if you are too scared of operating high voltage devices will fail, if you have that fear, apply reasonable voltage of around 60 volts, so that something you will see, 12 volts drop is around 2 volts, 10 volts, now 2 devices will they turn on or off, I do not know, so A, B, C or vice-versa, there are 3 phases, so how many possible combinations will I get, here this how many possible combinations will I get, 6, A, B, C, it could be A or B or C, it could be A or C, it could be, if this is here, this is B or C or A, sorry, yeah and this could be, whatever, one phase A, how many possible combinations, I have only 3 phases, all the time listener mode, not possible, tell me come on, how many possible combinations, I will not buzz an inch if you do not answer, 9 minus 60 that is all, I do not know, there are only 3 phases, there are 3 phases, A, B, C, how many possible combinations, come on, let us electrical engineer 6 or 8, it cannot be, it has a unique answer, how many possible combinations, you have to find out, if A, first combination is A positive, this is 0, then this is negative, second combination is A, continue to remain positive, this is negative, this is 0, is there a third possible combination here, not high enough, now what you do, B you make positive, this could be negative, this is 0 or this is 0, negative, over, so how many possible combinations, 6 possible combinations, 6 possible combinations, is there another way possible, is there any other, for this equivalent circuit, is any other way possible sir, high or not, not sure, for this combination it is not possible, so how many possible states, now again this 6 will occupy 6 states of an hexagon, but then voltage, the magnitude of that voltage will be slightly less than the previous one, previous one was 2 top or 1 top, 2 down or vice versa, here it is 1 is in the center, so definitely it will be slightly less, slightly, now what could be the third possibility, this could be the third possibility, this is known as, first one is known as the large voltage vector, these are known as medium, so definitely large medium then next will be small, is it there, here, 2 or top and another one is center, 2 or top, come on, 2 can be on upper 2 and 1 is in the center or 2, 2 center 1 top, in the positive of, sorry in the upper half, I have 2 top, 1 center, can I have 2 down and 1 center, high or not, possible, similarly here I can have down, possible or no, how many possible combinations, how many possible combinations here, how many possible combinations here, remember here, 1 top, 2 down, it can be 2 down, 1 top, how many, quick, 8, how many here, how many possible combinations and what will happen to upper, lower and this one, so what is the total possible combinations, is it 32, I will just quickly say A, B, C, this is the convention 2 level inverter, something similar I can have, 3 level inverter also, so I said A, B and C similarly here, upper 2 or lower 1, lower 2, so I have convention 2, 6 active 2 0, so this is the equivalent circuit, this is what the analysis it does, what am I doing is, this is the equivalent, what is the, what is the, I am determining what is the magnitude of the, what is the magnitude of the voltage applied, the resultant, A, B, C, I know V A 0, V B 0, V C 0, calculates, I am calculating V A 0 is there, V B 0 is there, V C 0 is there, this equation yesterday we derived, not in the matrix form and may not have written in matrix form, but you get this matrix. So, I know V A 0, V B 0, V C 0, I can get V A n, V B n, V C n, 3 voltages are there, so 3 voltages I can, can I get V D and V Q, x, x and y axis, can I, yes this does V D and V Q, this matrix I will derive later, do not worry, this is nothing but resolving along x and y axis, it is as simple as that which might have done in may be in the 9th or 10th, I am telling you, no, no jokes, 9th and 10th, I am getting V D and V Q, if I get V D, V Q I can get V S, resultant, square root of V D and V Q, square root of whatever. So, you will get this x again, this x again, 6 active states, 6 active states, 6 active states and see here I am not, n n means, what it, what it means is n means negative bus, negative bus, p is positive bus, this one is negative bus positive, positive, this one is negative, positive, negative, what you can see, just cover it, what happens, from here how did I go, how can I go here, where n and p, I just did, I changed the conducting state of 1, see n is there, p is there, the second one has become p, see here now, n continues to remain, this p will continue to remain, this p has become n, only one switch is turned on and off, that is all, only one switch is changing its state, only one switch, how did I come here, see p and p and continue to remain, p and this n has become p, only one, one has changed, how did I come here, p, p and will remain, this p became n and so on and so on. So, this is the x again, so magnitude of the voltage is the same, magnitude of voltage is the same and see here, n and p, p, p, n complimentary a phase is on, b and sorry a is positive, b and c are negative, here b and c are positive, a is negative, complimentary, n, p, p, c is negative, b and c are negative, c is negative, c is negative, b and c are positive, here c is positive, b are negative, complimentary, these are c are complimentary, these are large voltage vectors, magnitude is c, now you just see small voltage vectors, two are connected in the same phase, one is to the, one is to the, one is to the, two are should be same, one is this one, so these are the possible combination, these are possible combination, two, any two, a, b, c, this combination, two are to the same point, one is there, is there a difference in opinion, if this happens to the positive bus, it can something similar can happen to the negative bus as well, there also negative difference, so you are here, so how many positive, how many here, 3, 3, 6, 6 plus 6, 12, 12 plus 6, 18, 18, I will just, I will come to this, then this, how many we had, 6, so how many, over, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 20, 24. So, but fortunately what happens is though there are 12 active states, come on there are 12 active states, if you analyze what happens is, what happens is the resultant voltage that I can get resultant and the position, resultant of this position of this vector and correspondingly one here is the same, is the same, what I mean is here, see here, I did the same analysis I will do, I can get one voltage position of the result, see this is the resultant of the magnitude of the resultant, I can get this, I can get this using two different voltage vectors, I can get this using two different voltage vectors, should I prove it, simple nothing else, what am I doing, see this position what is V a 0, V a 0 is V dc by 2, what is V b 0, V c 0, 0. So, I know V a 0, V b 0, V c 0, can I get V a n, V b n, V c n from that matrix, I get V a n, V b n, V c n, I can get V d n, V q. So, if I can V d, V q I can get V s that is all, as simple as that. So, I can get V d f by 3, V b n by 3, I can get, therefore I can get the space vector V s. So, you can prove that, you know that OOP will give you same thing, what is OOP, what is OOP, two center one positive, I can get same as two negative and one similarly. So, there were 12 active states, but I can get only 6, there are 12 active states, but then magnitude and resultant get only 6. So, they occupy again 6 vertices of the x square, but then magnitude of the voltage is low, magnitude of the space vector here is V dc, magnitude of the resultant is V dc by 2, magnitude of the resultant is V dc by 2 and in the previous case magnitude of the resultant, magnitude of the resultant is V dc of the voltage and third last one is medium, magnitude of the resultant is root 3 by 2, root 3 by 2, root 3 by 2, root 3 by 2, root 3 by 2, see the advantage that we get now, this is the hexagon, do not get nervous, sorry do not get intimidated, do not get intimidated, that is the right word. See here, large, large, large, large hexagon, outer hexagon, inner hexagon, N and P OOP, inner hexagon, if this is V dc, this is V dc by 2 centre point, another one was root 3 by 2, now you tell me, see this side is this side is the same, is an isosceles triangle, are you with me? So, what is this isosceles triangle, what will be the height of this, root 3 by 2, root 3 by 2 and position, see one thing, one difference is, these are large vectors occupy the, what is of the outer hexagon, these are small voltage vectors, again occupy the inner hexagon, inner hexagon, magnitude is only the difference, but then they are in, they are in same phase, same phase, but then medium voltage vector is, magnitude is root 3 by 2, but then they are in whatever 30 degrees. So, they occupy analysis I have given, if you have time go through it, by the way any questions here, any questions, why are we doing all this, that question you should have asked me, why you have to do this, for what, why the hexagon, that is, at the end of the day, why pulse width modulation are you doing, why are you doing, let me talk about only about grid connection or something like that, output voltage is between motor, inductor, this is a, this is V 1, V 2, X into sin delta, this is power is V 1, V 2, X into sin delta, V 1, V 2 divided by X into, now if you want to control the output voltage V 1, you want to change V 1, why do you want to, if you want to change V 1, what will you do, in any inverter, if I want to change the output, I want to change this output voltage, what can be done, say do not go to pulse width modulation, it is just not obvious to me in that, to change the output voltage, I need to do pulse width modulation, no see, I do not trust, that was, that is the problem, let us not straight away jump, see half bridge inverter, the moment I close S 1, what is the voltage applied, V dc by 2, I want to change voltage applied to that load, what do I do, what do I do, I have to change V dc by 2 itself, come on, if this is 100 volts, this is 100 volts, I can get V in the, when S 1 is closed, I get 100, when S 2 is closed, I get minus 100, now I want to change it to 50, what do I do, what do I do, I will make it 50 and this 50, so in other words, I have to change the DC link voltage to change the output voltage, makes sense, fine, in the sense, I will do that, but then here while I am doing, what is happening is, I get something like this, I have a square wave, and if I take the Fourier series, what all components will be there, it has a fundamental component and what is the predominant harmonic, 3rd, 5th, 7th, all odd harmonics are there, in a three phase system, this third harmonic will get cancelled out, then you will get 5th and 7th, so if I am using this inverter to feed the power to the grid, and if I use this, what will happen, there is a 5th and 7th harmonic predominant harmonics, fine. So, to change the output voltage, I need to change the DC link itself, then another thing is, and here since each device is conducting for 180 degrees, predominant harmonic is, predominant harmonic is 5th, in here it is 3rd and whatever. Now, instead what I will do is, I will keep this DC link voltage constant, I will not change it, instead of allowing this device to conduct for 180 degrees, I will turn on of several times, follow what I am saying, what did I do, what you told me to change this output voltage, this madam told me that, you change the DC link itself, it is which is looks very obvious to me as, to change this magnitude, I will change this, fine, very easy, I have to change the DC link voltage, but fine, in that trigger, but then this has a lower odd harmonics, 3rd, 5th, 7th, all other things. Second option I have is, I will keep this at, I will keep this constant at a very high value, if I want to change the voltage, I will not allow it to remain on for the entire period, I will on of, on of, on of I will do. So, pulse width modulation you do for voltage control, not to eliminate harmonics, it is so happen that, if you switch at proper instance, you will eliminate harmonics, remember, remember, you do pulse width modulation for voltage control and you suitably, switch them, you can eliminate harmonics. So, that is what we are doing, we are doing pulse width modulation to eliminate the harmonics, otherwise to eliminate 5th and 7th is going to be, you have to order 2nd order filter, size increases, what not. So, henceforth we will be doing only pulse width modulation, we will not do anything to the DC link. Now, there are various pulse width modulations, sinusoidal Vino and very popular is asked any power system engineer, he will talk about space vector feed volume technique, space vector feed volume technique. So, let me not, so if you see here, see the magnitude of the voltage changes, I want to change the, so I may be anywhere between in this hexagon, are you with me, if I want to increase, so very high voltage, maybe I will use this vector, if I want a low voltage, what will I do, I am, I am in a hexagon, take any hexagon, see here, I have taken, I have taken 1 sector, 60 degrees, 60 degrees, whatever is there I have copied, same thing whatever, NNP, NPP, NOP and those 3, these are null vectors, all are on, all are off or all are, see NNP, NPP whatever, this is the resultant voltage that you want, are you with me, come on, this is the capability of, capability of the inverter, like capability curve of synchronous machine, you have heard or no, have you heard about capability curve of synchronous machine, electrical engineering, you have heard, so these are the possible vectors of the, of the, of the inverter and magnitude of voltage you want to control now, are you with me, magnitude of voltage vector, so this could be the magnitude of the voltage that you want or it could be, I may be here, if the length of the vector, I may be in this triangle, I may be in this triangle or I may be in this, may be in this smaller triangle as well, you take any triangle, see the size of those 3 triangles, what do you find, T here, equivalent to, other than that what you can find out, what you can infer, now you can, you should be able to find out, be any triangle what you can find out from those, not triangle, outer triangles, smaller triangles, what you can infer, you can, that observation I have, we have already made, is that same observation is valid here, you be anywhere, see here, if you are here, it is over P, suppose see I can get this using over P or N and O, assuming that I am in N and O, I can come here, I can come here by making N to O, if I am, if I, if I immolate this by using over P, I can come here by making O, P P, suppose I am here, see now, it is the same thing, anywhere or if you are in this vector, N N P, here I will come to N O P and here, from here to here you just see this triangle, N N P, N O P, here, N N P or N N O, N N P, O 2 P, here N 2 O, here O, if I add O O P, no N N O, N N O P, N O P, yeah. So, every time one, I can go from one vector to another vector by change the conducting set of only one device. So, the problem in, is that ok, any questions, feel free please, easy, you are saying not easy. Now, what stand will I take? What stand will I take? In life which you think which is easy, logically it is difficult to implement, conventional two level inverter, phase vector P DLM technique is so popular, if you see the expressions, they become very simple to implement and there are DSP processors have a dedicated pins, which give the output signals. Are you with me? If you derive, I do not, if you are so popular should have told me, I would have come prepared, I would have brought that lecture, phase vector P DLM technique, what is that P DLM technique? The expressions, time for which, time for which I should be here, time for which I should be here, if you see expressions are very simple, very simple to implement, very simple to implement. There is a reason there are dedicated, there are process of dedicated pins. Now, you may, you will find bit time to understand this P DLM technique, but then I do not think you took time to understand this P DLM technique, which one? Sine versus triangular, I am asking you to implement on a microcontroller. You are nodding your head, have you implemented? How did you derive? What did you do? What you had, 99 percent what you have done is, you have generated a sine wave, you have generated a sine wave, you have generated a triangular wave using a, using a functional IC, you everything in a microprocessor? No, look up table in sine wave, ok, but how did you implement this P DLM technique? This P DLM technique is sine versus triangle, compare, compare and here you get pulses. Are you with me? To get this pulses in space vector P DLM technique, I have to implement very simple equations, very simple equations, very simple equations, very simple equations. Now, I want you to do and you say that it is difficult because it is not and whereas sine versus triangle is very simple to understand, are you with me? Very simple to understand. I am asking you, have you implemented this sine triangle in a DSP, in a, in a processor or microcontroller? I want the pulses, have you implemented? What you have to do is, you have to generate a sine, you have to generate a triangle inside, compare it inside, not outside. Why sine wave is so popular is, there are dedicated chips which generate sine, which generates triangular, you compare it using opamp and get the pulses. If you have to do everything inside, this is extremely difficult, extremely difficult. Generating PWM signals using sine triangle, in a microcontroller is more difficult than generating PWM signals using space vector. There are dedicated DSP processor, TMS 320 F 240, there are dedicated, which are there is for drives application, they have dedicated, dedicated pins. You have to just give the modulation index, on the time it will give. See there is no unique answer for it, you have to do some cost-benefit analysis, then you have to decide and you have to justify. Someone may, can challenge me, I may be wrong, I may be wrong, I accept. In engineering, I do not think you have an unique answer. No, no, no, there are, literature is available, Japanese have, Japanese have installed, they have gone up to 31 or 33 levels, they are there. See in three level itself, there are lot of problems, we have not come, I have not come to that level. There are drives, three level ABBs using, any other question? I have VABBBC, what is the locus of, locus of BS? I have VABBBC, I will get D and Q, are you with me? Then I will get VS, I want the locus of VS, if VABBBC are sinusoidal, what is the locus of VS, for 360 degrees? VABBBC are pure sinusoid, pure sinusoid, VABBBC circle, is this circle? Now, what is the diameter, what is the radius of the circle? What is the radius of the incirculating circle for this hexagon? BDC curve, incirculating circle, this is the radius, beyond, if you go, if you try to increase the modulation, beyond that, I am going out of the circle. So, my voltages are no longer sinusoid, VABBBC. You are asking a question, you are going to answer, it may not be possible to answer. First of all, you need to find out. So, incirculating circle diameter or radius, if I am, if my modulation index within that, it is sinusoid. If I am trying to go outside, my voltage VABBBC are, may not be sinusoid, they are not sinusoidal, feel free, quick, quick. See, the problem in multi-level is not PWM technique, the problem in multi-level is, now you need to tell me, I want to discuss only this in multi-level, since you have asked, I came here, otherwise I will not have discussed. What you can infer? Now, you need to tell me, see this equivalent circuit, see this equivalent circuit, this equivalent circuit and this equivalent circuit, is there a problem? Three equivalent circuit, observe please, this is an equivalent circuit, this is another one, equivalent circuit. These are a large voltage vectors, the medium voltage vectors, these are small voltage vectors, I have to divide this and I will find out, what you can observe, what you can observe? Magnitude is varying that you want, that is you want to model, you want to change the output voltage, what you can incur, you see here, you are, see the problem here, capacitor is connected across the load, both C1 and C2, you are charging and this is the discharge path. So, here also is the same. Now, you see here, see here, this is the external source charging the capacitor, this is discharging, this is also discharging. Now, you see here, when I am in this mode, one capacitor is just charging, another capacitor is both. So, it will so happen that capacitor voltages may be, may be, may be unbalanced, they voltage may not be the same, may not be the same. See here, this is continuously charged, but only this is discharging, only discharging. So, capacitor voltage balancing is an issue in three phase, in a multi-level inverter, capacitor voltage balancing. Now, you have to monitor the capacitor link voltages, if this is getting over charged, remove the charge and dump it in this. Come on, it will so, if I am applying low voltages when I am in this, so what happens? It will so happen that this will complete discharge and this will charge. You cannot, now what will happen? Capacitor voltages are unbalanced, that will affect your output voltage waveform. Come on, what is the magnitude of the voltage applied here now? It depends on this voltage, is not it? This is no longer VDC by 2, this is no longer VDC by 2, it could be anything because this is VDC, high enough. So, this voltage you are applying, this appears at the output, now I may not get a symmetrical waveform, the positive half and negative half. So, what you need to do is, you have to continuously monitor the voltages, if this is getting over charged, what do I need to do? Extract the charge and give it to the other capacitor. Now, I cannot, if you have one capacitor is charging, another one is discharging, what do you do? What do you do? Now, how to do? I am not asking here, what do you do? I have two capacitors connected in there, one is getting charged, another one is getting discharged, what is to be done? One is charging, one was, one the voltage across the capacitor higher than another one, I want to make it equal, what do I do? Extract the charge from the capacitor which is over charged and give it to the capacitor which voltage is low. How to do? Do not worry, do not worry how to do it? This should be done, cascaded multilevel, just 5 minutes or there I will wind up and down, cascaded multilevel, just see. What was the problem in diode clamp? As the number of level increases, power circuit configuration has also changed, as the power circuit, as the number of levels change, what will happen? Power circuit configuration has changed, connecting the diode across the capacitor becomes a problem. Now, what do you do? See here, what is this? Single phase, the full bridge, full bridge, full bridge, full bridge, there is a connection. So, I need to have 4 full bridges for one leg, are you with me? Now, what this could be, this voltage, what are the possible ways, what voltage I can have? Full bridge, what voltage I can have? Full bridge in motor, what this voltage could be man? When S1, these two are on, it is VDC, if these two are on, either 0, if this is on and this is on, this voltage is here, this is here, what is the voltage? VDC, if this is also on and this is also on, what is that voltage? 0, that is all, there is only two possibilities, no more, VDC 0, VDC 0, VDC 0, VDC 0. So, if this is VDC, VDC, VDC, VDC, what is the output voltage? 4 VDC, so here, here, 4 VDC, see the phase shift, VC 4, this could be VC 4, for this period it is on, after some time, so during this period VC 3 is 0, this is also 0 and here it is VDC, 4 in this zone, output voltage of VC 2 is 0, in this zone it is VDC and here in this zone 0, in this zone, small zone it is VDC, add the map, what do you get? 4 VDC, a strapped wave, a strapped wave, cascaded multilevel, cascaded multilevel, inventory low, everything is low, could be a solution for solar, any question? Instead of that 2 level, 3 level is possible for each one. 2 level, 3 level means? Instead of 2 switches only 4 switches, like that. What is 4 switches? This is a single phase inverter, this is a what says box, full bridge, what are the voltage levels? Full bridge, now we did 3 phase, 3 phase, what is that? 3 level, 4 level, now I mean single phase bridge, what is the possible output voltage 0 or? VDC. Magnitude VDC, I can get plus or minus VDC, because if this is on and this is of this point gets positive and whatever, are you with me? So, this voltage it can be in the magnitude is VDC or 0, that is all. This is also VDC or 0, VDC or 0, VDC or 0, all are 0, only this is VDC, now these 2 VDC, VDC, these are 0s. Sir, instead of 4 set of configurations, 2 sets, 3 level you can. That I do not know, now that you invent, no problem, he is saying you want to use only 2 bridges and you want how many levels? I do not know, take a paper and a pencil and you take a, you have a paper and a pencil, now you have only 2 bridges, you know how it works, this voltage called VDC, this is also VDC, VDC 0, VDC 0, how many you can get? You may be having only this 2, VDC, VDC, right, you have to add up only this 2, see these questions, you need not ask me, you need to, I have only this 2 waveforms, how do I do, add them up, what you will get, what you will get, what you will get? Colom, you have to add this 2, what do you get? He is talking only this. He is talking only this, I know, is not it, this what he is talking about, what he wants, using 2 he wants more level, that is what your question, that I do not know, going against the law of nature, I do not know, I do not know, that you have to find out.