 Hi, this is Rupesh. I am going to demonstrate you a typical 3 phase photovoltaic to grid connected system. This system is developed under the guidance of professor Vivek Agarwal. So, we have a 2 kilowatt PV installation at the roof. It is a DC supply is coming here. So, this PV installation is in the form of PV modules. So, each module has a 20 volt volt 20 volt DC with a 2.5 ampere current at 1000 watt per meter square. So, as per our requirement of the DC voltage and current, we can configure those panels in series and such a sets in parallel. So, to get to achieve required voltage at the PV output and current from the PV system. So, this I will going to explain you this power circuit of this installation that DC supply as I said is coming here at the input contactor and then followed by the input PV bus DC capacitor, then boost converter, then DC link of voltage source inverter. Then there are the IGBT's voltage source inverter. This is the L C which form LC filter second order LC filter at the output of voltage source inverter. Then through the signal sense circuit then to the grid. So, apart from this power circuit, it has a control circuit. So, that control circuit has a signal sensing board. This control circuit has a signal sensing board which senses the output current and voltages along with that DC link voltage. Then input PV voltage and input PV current and control circuit involves a intelligent controller which is a may be microcontroller or microprocessor or DSP board. This is a DSP processor, XS instrument F2, TMS 320, F2822 board. Then it generates the PWM output followed by the buffer. Then driver circuit which is driving the IGBT modules. Then this is the power circuit and control circuit. So, I will going to explain you. So, this is that system as I just explained is a PV module, PV panels which giving the DC voltage and current. This is very raw power. It depends on the radiation level that is sun status and temperature environmental temperature. Then it is followed by the DC to DC boost converter. So, this boost converter we can operate it at the with the MPPT control technique. Then DC link of the voltage source inverter. This is the voltage source inverter. Then L and C which forms second order filter for the voltage source inverter. Then grid side there is a signal sensing circuit situated which senses the output current and voltage which fits to the processor to microcontroller to the processor and then to the grid. So, this is the power circuit which is developed here. So, this is actually two stage topology. One can develop a single stage topology in single stage topology DC to DC boost converter may not be there. So, this PV modules or PV system can directly fit to the voltage source inverter. This voltage source inverter then will do the two task. One to fit the power into the grid and one to control this DC link voltage at the MPP point of this PV system. So, in that single stage topology boost converter may not be there. So, that may be a high efficient system, but in this two stage topology this voltage source inverter it keeps to regulate this DC bus voltage by voltage source inverter and this DC to DC boost converter it is operating at with the MPPT control algorithm. The MPPT control algorithm may be a perturb and observe algorithm or incremental conductance algorithm. So, here we have developed incremental conductance algorithm for DC to DC boost converter and this voltage source inverter can be operated with the DC link regulation technique. So, this I will just going to now I am going to explain your control block diagram of the system. So, this is the control block diagram of the system. So, as I said the boost converter is operated with the MPPT algorithm. So, MPPT algorithm may be perturb and observe technique or may be incremental conductance system. So, it takes the feedback from PV PV system that is PV voltage PV current. It takes the product of this two which gives the PV power and then it values the duty cycle accordingly to achieve the maximum power point of the system. So, this is the control for the boost converter then there is a voltage source inverter. The voltage source inverter control topology is developed with a reference frame transformation technique. Synchronous rate of reference frame transformation technique is adopted to control the voltage source inverter. In this control technique we transform all AC quantities like grid voltage and grid the current grid current those are in AC. So, we transform this grid voltage and grid current into the rotating reference frame transformation. The advantage of this technique is that the although all original quantities are in AC, but we when we transform it into the synchronously rotating reference frame transformation it gives a DC quantities for the fundamental components. So, let us say if there is a V A V B V C which are route 50 hertz component AC component then we can transform it with a transformation technique like pass transformation class transformation. Then we can achieve the equivalent V D and V Q E component which represents which preserve all information of the AC quantity for fundamental component. So, advantage of this system this control technique is that though original system is AC, but we can control it using DC component. So, it is very it becomes easy to control the system also it gives the good accuracy compared to conventional instantaneous current control instantaneous voltage control technique. So, in this technique we have transformed the current grid current into the I D and I Q E component. Similarly grid voltage into the V D and V Q E component then we are we are using the PLL technique because this transformation is possible with the it is actually synchronously rotating reference frame transformation. So, for that purpose we need the information of the grid frequency. So, here is the PLL which takes the feedback of the grid voltages V A V B V C there is a transformation. So, it transforms A B C quantity into the V D V Q E quantities and then from that V Q E component can be used to develop this PLL technique. So, that PLL technique is also based on the reference frame transformation synchronous reference frame transformation technique. So, other way to develop the PLL is based on the instantaneous power theory proposed by Akaki in that we take the feedback of V A V B V C rather than transforming those quantities into the reference frame transformation there is a control strategy which gives directly V sin theta and cos theta which has the information of frequency grid frequency that instantaneous power the PLL based on instantaneous power theory is very rigid to the unbalances to the harmonics. So, it gives the good result for sin theta and cos theta for the fundamental components. So, this sin theta and cos theta obtained from the PLL can be used to transform the A B C into D component and Q component. So, once we achieve the I D that is I D and I Q E which has a information of A B C I A I B I C grid current that can be used for the further control. So, as I said the voltage source inverter is controlled using DC bus voltage regulation. So, we takes the feedback of DC actual DC voltage DC link voltage we compare with the reference then through the PI regulator it gives the equivalent quantity of the active power. So, this it gives the I D star that is reference current for the direct axis component of current. So, this direct axis component of current is in fact proportional to the active power available at the PV source. So, because that as I said this DC to DC boost converter is operating with the MPPT control algorithm. So, it dumps all available power with at the PV into the DC link. So, this DC link voltage may tends to put up. So, during that process this PI regulator comes into action and it develop the active the reference current for the direct axis component of current. So, this direct axis component of current is proportional to the active power and the react quadrature axis of current that is I Q E star it depends on the reactive power. So, by controlling this I D star that is active power component and I Q star that is reactive power component we can control the power injection that is active power and reactive power. So, by regulating the DC link voltage in fact we are controlling the active power which is coming from the PV panel and then we are controlling and then we are actually controlling this I D star to make that actual current I D equal to the I D star the obtained reference current. We are keeping I Q E star that is a quadrature axis component of current which decides the reactive power equals to 0. So, at the output of PI regulator it gives the V Q E star and V D star. So, this V D star and V Q E star are then again it is a it is this are actually a component to control the voltage source inverter. So, again we have to convert it back to the original AC forms. So, as I said we have transform original quantities into the DQ reference frame transformation into the DQ reference frame which is synchronously rotating reference frame transformation technique. Then we have done the control then again we have to come back to our original system that is AC quantities. So, again this V D star and V Q star which is the references for the voltage source inverter control we are transform it into again written back to ABC quantities. So, DQ to ABC it is a inverse of class and pass transformation. So, it gives the reference quantities V A, V B, V C for voltage source inverter. Then one can adapt sinusoidal PWM technique for voltage source inverter control or may be space vector modulation technique for voltage source inverter control. So, we have used here sinusoidal PWM technique for voltage source inverter control. So, in that way by controlling this voltage source inverter by this reference V D star V Q star obtained from this control it actually regulates it actually controls the active power component of current and the reactive power component of current flow into the grid. As I said I am keeping reactive power component of current at 0. So, this system is operated at unity power factor control unity power factor as I said. So, one can give the some reference to I Q star here may be some 10 percent or 20 percent of the equivalent to the active power then we can even control the reactive power feed into the grid if required. So, this is a typical control circuit of this two stage topology. In the single stage topology what we will do rather than using a boost converter there will be no boost converter. So, we will regulate the DC link voltage of the voltage source inverter at the MPP of the PV panel. So, there we need to control the DC link voltage of the voltage source inverter may be with the control algorithm like perturb and observe or incremental conductance technique. So, that to achieve that DC link voltage equal to the MPP point of the PV panel. So, it is actually a real time control which controls the DC link voltage equal to the MPP voltage of the PV panel. So, as to achieve MPP power from the PV installation. So, as I explained the power circuit it is a control circuit then this system. So, this system is developed using discrete component only in this lab. So, discrete component may be a single IGBTs or may be a pair of IGBTs which form a link of the voltage source inverter. So, this IGBT this single IGBT has gate collector and emitter one can use a 2 IGBT which form a link of voltage source inverter. People used to prefer this thing with this special construction one can keep the distance between collector of the upper IGBT and emitter of the lower IGBT very near to each other by this special technique. One can reduce the distance between those two that is collector of the upper IGBT and emitter of the lower IGBT. So, that to reduce the path inductance. So, path inductance causes voltage pipe across the IGBT there. So, one has that one is always target to reduce that such a inductances path inductances. So, one can connect a snubber circuit across these two points. So, it is collector of the upper IGBT and emitter of the lower IGBT. So, it is very convenient to connect the snubber capacitor across these two points. So, it is a leg type IGBT it has two IGBT in this module. So, see in that way we need a three IGBT leg type three IGBT modules. So, it will give the six IGBT's for voltage source inverter. So, this is major component of this system. Then as I said there is LC filter. So, inductor and then capacitor at the output of voltage source inverter it forms a second order filter which gives the minus 40 dB slope at the of the gain. So, it gives the good performance for damping the or reducing the harmonics higher order harmonics. So, voltage source converter switching technique take care of the lower order harmonics and this LC filter take care for the higher order harmonics. So, these are the other two elements of this system. So, this is another element of this system it is Texas instrument TMS 320 F 2812 DSP board. So, it has a resources like PWM it has resources like ADC then IO pins. So, these are the essential requirement from this controller from this DSP processor. So, whatever control strategy I have explained earlier which was based on reference frame transformation technique and then boost converter algorithm that is MPPT tracking algorithms which is may be a part of an observe or incremental conductors algorithm those can be coded into this processor. So, during development process which one can use such a processor then after development one can shift over the chip processor which is available in market. So, I will give you example of such a processor or controller this is Piccolo controller provided by Texas instrument TMS 320 F 280 27. So, this is a Piccolo controller then. So, there are other controllers available in the market like this is micro chip DSP 30 F 3011 micro controller. So, this controller also has the features like PWM ADCs and IO pins. The only thing for selection of the such a controller is that it should provide the speed that is whatever control strategy we are coding into this processor it should provide enough speed to execute such a all statement within the stipulated sampling time of the control strategy. I will explain that control strategy and instruction set which I have adopted to controls this system. The next component is the driver IC for this IGBTs. So, just I have explained that the micro controller speed to PWM we have to provide it to the voltage source inverter. But those PWM is not enough to drive the or their capacity is not enough to drive the IGBTs. So, we have to buffer those signals then after buffering we have to boost up the voltage level and the current kind current capacity of the PWM. So, that it successfully drive the IGBTs. So, this is the one of the IC available in market it is A3120 driver IC. So, one can use this driver IC. So, to drive the IGBT modules. So, we have developed a driver circuit using this 3120 driver IC. So, for that purpose we have to we have to obtain isolated supplies there are 7 isolated supplies for the in the driver circuit 6 for the IGBT modules of the voltage source inverter 1 for the driver 1 for the IGBT of the boost converter in market in market such a IGBT modules are available such a driver for IGBT modules are available. So, this is very highly sophisticated driver it drives the 2 IGBTs of a leg. So, that PWM pins PWM signals can be given to the input port of this driver PCB. So, we have to buffer that PWM signal up to 15 volt and then we can provide it at this port and it gives the signal for the or PWM for the IGBT modules. So, such a IGBT sorry driver circuit for the IGBTs are available in market. So, it has some features like protection which it provides the protection against in a shoot through current for the IGBT modules. This is another element used in this system it is Hall effect current sensor. So, the line current is transformed into the signals using this Hall effect sensors and then that signal is conditioned and then one can feed into the processor. So, it provides the isolation from the power circuit from the between the control circuit and the power circuit. So, this is another element used in this system it is for the voltage measurement. So, it takes the feedback of grid voltage it provides the isolation from at the output signal then it can be provided to the microcontrollers. So, all these quantities are in AC. So, and the processor adopt only DC signals from 0 to 3 volt. So, we have to transform those AC signals at the output like current may be up to 3 ampere RMS AC then voltage may be 230 volt AC those signals can be we have to condition it we have to step down those signals then we have to use the some filters to further condition to reduce the noise and then we have to shift those AC signals. So, that it the output signal can be gets can be obtained in between 0 to 3 volt range. So, that we can give it to the processor. So, these are all about the major elements used in this system apart from that there may be other small elements. I had explained you control strategy which was based on the reference frame transformation technique and then for boost converter there was a part of an observer or incremental conductors algorithm for the control of the boost converter. So, these are these are the control strategies. So, we have to code it into the micro processor I have used TMS 320 F 2812 DSP processor it is Texas instrument processor. So, this control we have to code it we have to discretize it first then we have to code it into the processor. So, there is software provided by Texas instrument that I am going to explain you this is code composed studio provided by Texas instrument for the debugging for development of our code. So, our code our control strategy was on continuous time domain. So, we have to discretize it into the digital domain. So, there are discretization methods like forward ellipse method backward ellipse method trapezoidal method and there are many other methods. So, I have adopted trapezoidal discretization method for converting or continuous time domain signals into the discrete time domain signals like then like controls of the P I then filters then some other signals. So, this code composed studio is a C language platform which helps to develop our code for the system control. So, as you can see the main start from this one there are system controls like that specific to the processor there is a configuration for the system clock then GPIO then pi control that is address of the sub routines then there is pi vector table the same then event manager for PWM then for ADC configuration then CPU timers then one can use our user defined functions then there are some special instruction for the system preparation. So, I am using two sub routine CPU timer sub routine which provide me interrupt sub routine of 30 microsecond and one for 1000 microsecond. So, this sub routine out of the sub routine 30 microsecond is our critical sub routine there is a code just I have explained the control strategy those are discretized and coded into that 30 microsecond sub routine that 1000 microsecond sub routine is our monitor loop. So, at the beginning I am start turning on 1000 microsecond sub routine at the beginning which check the complete system parameters whether DC bus voltage is available or not it forms the communication if anything is there between this system and the some outside system again it provides the interface from by the user to the system like emergency off like start signal then it provides the monitoring signal. So, this is outer monitoring sub routine which is 1000 microsecond the essential thing in such a system development is that we should have enough we should have a enough resources for the debugging also during development stages we need to have a information of all variables which is running in the into the system. So, such a debugging thing the such a resources like debugging for the variable signals like DAC operation that processor do not have a digital to analog converter, but we can check the variable or we can check the signals by putting those signals into the PWM pins of the processor and then by filtering out those PWM pins we can take out the signal which is carrying by the self variables. So, this is one of the debugging for in this process apart from that this code composes studio provides a debugging tool like graph. So, we can see signals available assigned to the variables apart from that this software provide the debugging tools like watch window there we can check the actual variable or the value assigned to the available in the variable or registers. So, there are registers like PWM registers ADC registers we can check online our values available in that registers. So, this is code composes studio there we can develop our code. So, I will just explain a critical code in that code composes in this software. So, at the beginning CPU timer 1 is start then it is actually a CPU timer 1 is a monitoring loop it start first then if the user provides on signal to the system it turn on the CPU timer 0. So, this is a CPU timer 0 sub routine which is a critical sub routine where our code control where our control strategy is coded. So, it takes the signal from system like it is reading the ADC like output current voltage then DC link voltage then PV voltage current after again shifting back into the AC signal because I had converted those AC signal into the 0 to 3 volt range then again I have to convert it back to the AC signals. So, these are the ABC voltage of the grid similarly for current line currents then DC link voltage then there are filters for the voltages then current there is a PLL which gives the system frequency sin and cos theta sin theta and cos theta belongs to the fundamental system frequency belongs to the fundamental component that is belongs to the 50er system frequency then there is a transformation from ABC to DQ which is used for the further control here is the DC bus voltage regulation. As you can see those PI is transforming into the discrete form. So, I have used tapasodal approximation technique for transforming those filters and PI into the discrete form. So, here is the PI over ID reference component PI over IQ reference component that is active power and reactive power control then again transform those DQ component to ABC component for voltage source converter control. So, this is all about the system development the code composer studio provides a very strong debugging tool like watch window graph then we can use a DAC operation through PWM and we can develop our continuous control strategy into discrete control strategy after discretization. So, this is all about the code development. Now, I will start the system and I will show you the grid current voltage and unit to power factor operation for this 3 phase PV 2 grid current system. So, I am going to demonstrate you the output current and output voltage from the grid side. So, this control technique is very similar to the STATCOM control technique where we are regulating the DC bus voltage, but rather than regulating DC bus voltage here we can control the DC link voltage such that it up it achieves that MPP point of the PV PV system. If it is a if it is configured for the single stage topology in case of two stage topology we are we are using a boost converter with the MPP control algorithm. So, I am turning on the system. So, this blue wave form is showing the grid voltage you can see it has some harmonics at the top of this wave form you can see the wave form is very tapered it is because of a non-linear loads using this premises. So, this one is a grid voltage the one is a grid current that is current injection from this system right now system is in the off state. So, it is taking a current like small peaky current at the peak of the AC voltage. So, so you can see it is also drawing harmonics or it is also injecting harmonics into the grid. So, this is a peaky current it is because of the anti-parallel diodes across across every IGBT of the voltage source inverter. So, for demonstration purpose I have intentionally connected a resistance across the DC link to demonstrate that during a sun is not when the sun is not available or radiation enough radiation is not available that time the system takes some small amount of power from the grid to link to regular the DC link voltage. So, this operation is almost like similar to the STATCOM operation when sun is there, radiation is there. So, while regulated DC bus voltage or while controlling the DC link voltage that active power of the PV is injecting into the grid. So, as I have intentionally connected resistance across the DC link voltage it must take active power from the grid to regulate the DC link voltage. So, I will turn on the system and I will show you that operation. So, you can see the blue one is the grid voltage and yellow one is the grid current that is current injection into the system from injection into the grid from this system as it is 180 degree out of phase. So, it means that right now this system is taking power or absorbing power from the grid to regulate the DC link voltage as I said I have intentionally connected resistance across the DC link. So, now I am turning on the PV emulated PV over the system and to demonstrate you the active power injection into the system. Right now there is no PV input at the system. So, it is drawing power from the grid to regulate the DC link voltage. Now, I am going to turning on the PV input and to demonstrate you the active power injection into the grid. For demonstration purpose instead of the PV panels I am using a DC source which will give you a source which will be a variable source and after by controlling this source I can inlet a PV power emulated PV power into the system. I am slowly increasing this voltage just look at those waveform. So, initially status was system is this PV to grid current system is taking power from the grid. Now, I am inletting PV power into the grid as you said you can see when PV power is not there that time this yellow waveform and the blue waveform those are current and the voltage those were out of phase that it means that that time it was delivering power from the grid. Now, these are in phase it means that this system like PV is injecting power into the grid. You can see though grid voltage is very very dirty like it has some harmonics I show you the harmonic spectrum of the grid it is it has some fifth harmonic and seventh harmonic because of that the waveform is tapered at the peak. The yellow one is the grid current which is almost very sinusoidal I show you it is a THD. So, as you can see this is fundamental bar and THD is around 1.6 1.7 percent though grid voltage THD is around 3 percent. So, you can see it is injecting very high quality power into the grid. This is fundamental bar you can see these are other harmonics second third fourth fifth sixth seventh those are the harmonics those are almost sitting at the bottom. So, this was the grid voltage this is the grid current from the from the PV system emulated PV system when now I am going to turn off the PV system again as I have deliberately connected resistance across the DC link it is delivering power from the grid to regulate the DC link voltage. Once we turn on the PV injection into the system it delivers the power into the grid. So, now I have disconnected from DC source which was emulating the PV from this system now I connected a physical PV panel to this system to demonstrate you actual physical PV panel power in injection into the grid. This waveform is showing blue one is showing the grid voltage and yellow one is showing the grid current. Right now radiation level is not enough to inject a full current now it is delivering whatever power available with the PV into the grid. So, yellow one is showing the grid current injection into the grid current which is injecting from this system into the grid. So, it has small distortion into the grid current because the system is not delivering full rated current into the system when radiation level is good enough then that time it will definitely show a good THD into the current. So, this is all about 3 phase photoalty to grid current system. Thank you.