 Last one is the battery charging. This is the various topic that I intend to cover. For power level above 1 kilowatt lead acid batteries, there are one other type of nickel cadmium batteries as well. Comparison, long life, high energy density, high capacity even for fast discharging rate, deep discharge is possible, but here it is a low cost. This is a bit expensive. So, these are the battery characteristics. This is the battery characteristics. If you see here, can I expand this? Available capacity versus storage time. In the sense if I charge the battery and keep it as it is without connecting a load, battery does discharge. This one, nickel cadmium, this is for lead acid. So, lead acid seems to be having an edge over nickel cadmium battery. Coming to depth of discharge, depth of this is the number of cycles and the depth of discharge. See here, nickel cadmium battery seems to having an edge over the lead acid battery. Say for 70 percent depth of discharge, see the number of cycles. This is the life of the battery. And see here for 70 percent depth of discharge, see the number of hours. And here the operating temperature. In India, when the ambient temperature is, when we are in this range, there is no much, nothing to choose. Otherwise, at a very high temperature, sorry, at low temperature looks like nickel lead acid. This is available capacity versus operating temperature. Upper one is the nickel cadmium. This one is the lead acid battery. And this difference goes on reducing as the temperature increases. These are terminologies. Battery capacity n into I n, where n is the discharging hours. I n is the discharging current. Charge coefficient rho is defined as ampere R per charge, but ampere R discharge. And battery efficiency is 1 over rho. And this efficiency is slightly higher for lead acid. Lead acid seems to be having an edge. Gassing voltage is the maximum voltage that has to be, that above which the battery should not be allowed. Gassing voltage is the maximum voltage the battery can attain. One should not allow the voltage to increase above gas in voltage. This is around 2.4 volts per cell in lead acid. 1.5 to 1.65 volts per cell in nickel cadmium. So, battery charging. What do I do? This is how I represent the battery. Voltage behind or resistance. This is the internal resistance. This voltage is also changing. Either I can connect a current source or I can connect a voltage source, which is the most optimal method. See, there are various apologies. Charging battery current, constant current, constant current, constant voltage and a constant power, power remaining constant. So, these are basically three control strategies, which is preferred. So, these are the derived. Can I have two values of constant current? C C C C. Or can I have a constant power? These are the four different powers. Constant one value of power here as the battery charges, battery charges reduce the or go for a different value of current. See here, constant current. When the battery is completely discharged, when the battery is completely discharged, supply more current as the battery is getting fully charged, reduce the current, reduce the current. Similarly here, what happens if I keep the same power, if I make only, if I charge the battery under constant power, what will happen? We will see. I will discuss each and every case. Similarly here, constant current and constant voltage. And finally, constant current in the beginning, constant voltage in between, when the voltage is equal to the gas in voltage, charge it is a very small value of current, see here, very small value of current. When the battery voltage has attained its gas in voltage requirement, see before choosing the type of, before deciding on the method of charging, we will see what are the precaution that we need to take. Limit the charging current at gas in voltage that you need to do. You have to limit the current at the gas in voltage, option constant power. If the power is, if the, see I said only one slope if I use, if I use only one value of constant power. And I say here, the current has to be limited to, sorry, when the, when the battery voltage is equal to the gas in voltage, I have to limit the current. And I am doing it a constant power throughout. So, I will take this as the current. So, battery is being charged at a, a very small value of current. It takes a very longer time to charge and it is not good for parallel batteries. In the sense, large number of batteries are connected in series, one value of current going and that current may not be distributed equally to all the remaining batteries. Constant power and constant power, something like this, two values of current. As the battery voltage increases, I will reduce the current. When the battery voltage is low, I will use some of the current. This is slightly a faster method, faster alternative to constant power. But then same limitation, one value of current, the large number of batteries that current may not flow in all the batteries, it will be difficult to distribute. Constant current, 5 to 8 for the low charging. Why? This current, this corresponds to the voltage at the gas in voltage. If I use only one slope, constant current. And I told you here that a battery current has to be limited, a charging current has to be limited when it at the gas in voltage. So, I have to choose this value of current. So, it is very slow. CCCC, if high value of current initially as it charges, reduce the current. Same, not good for parallel, something similar. Now, constant current, constant voltage and constant, again constant current, which is very popular, fast charging is possible. A high current initially, when you charge at constant voltage, when the voltage is reached to gas in voltage, go in for constant current. Finally, constant current and constant, parallel battery charging, good charging rate. However, C by 10 or C by 8, whatever that you want to choose, you can see, C by is the capacity. So, there is the value of reference current that you can pump in there. So, implementing the batch recharging here, here is the constant current and constant voltage. This is the reference voltage, actual voltage, V I regulator. If the error is large, I go to current controller. This, the limiter saturates, I do the current control. When the voltage is increasing, this error decreases. V I regulator is out of saturation. I am in the linear region, we are in the constant current mode. This error is compared with this strangler for a constant to maintain a constant switching frequency. That is all. What are the various types of charging methods? These are the various charging methods, diode rectifier, the peaky current using a off control bridge, change alpha to maintain the current here. Here, power factor is very poor. In order to improve the power factor, use switch mode rectification. If you do not know, it is a fully controlled IGBT. This is a full bridge inverter. Unity power factor, you can have bidirection. I think I will stop here. There are other topics also, because since so long it has already come, I will just take 5 more minutes, for that you can take till 11.10 or so. If there are any questions, please feel free to ask. Sir, regarding the electrical equivalent model of a battery, the resistance that is in series, that is a function of the charged level in the battery. Is it correct? That is what I said that. That is what I showed you as a variable resistor there. So, while when we are using it for our simulation purposes, so we have to write an equation that corresponds to that term. Yeah, see there are various models are available and literature is also there. How to represent a battery during simulation? Thank you, sir. Any other question? Quick. The question says, in case of sensitive load, will there be any change in load power factor while injecting a voltage from inverter into the line during voltage disturbance like voltage sag swell? Let us first try to understand the theory behind grid connection, feed the power to the grid, then we will worry about voltage sag and swell. Is there any possibility to increase the lifetime of the battery or dump load? Now, why do you use dump load? Dump load is a sense in that the generation is more and storage is less or demand is less. So, it is better to use in the sense, use the conventional standard practice to charge the battery just because there is high insulation increase is generally what we do is either C by 10 or C by 8, the value of reference current just because at high power level, there is no demand increasing C 5, the increasing the charging rate will affect or will reduce the life of the battery. Do not do that. Last question, I told you NITC, which type of battery charging is good for life? Constant current, constant voltage, constant current, CC, CV, CC. I did tell you in my during my lecture. Anyway, thank you.