Solar Photovoltaic Generation Part 1: Pulse Width Modulation (PWM) DC/AC Inverter

okay this video is part 1 in this series on understanding solar photovoltaic generation and in particular we're going to talk about some of the electrical electronic components required to connect the DC source of these solar panels solar array to a utilization of alternating current generally the electric utility or some equipment or appliances that require AC to function and we're going to do this using MATLAB and Simulink although you don't need either metal ever seen singly to follow the series we're just going to use it to make it easier to understand and show you the different components and how they interact and how the systems work so we're going to break this into the number of parts this first part is going to be inversion or conversion from the DC of the solar array to AC using pulse width modulation part two we're going to talk about using a phase lock loop to regulate the frequency output of the solar array and then in future video we're going to talk about voltage regulation and also power regulation so using a pulse width modulation scheme to make a DC to AC inverter now first we'll step back and again the the solar panel is basically for our purposes a DC battery now it's kind of nonlinear characteristics but for our purposes we're just going to model it as a simple DC battery DC source so the question becomes how do I connect a simple DC source to a complex alternating current source like a utility system which is a three-phase alternating current system or even a single phase system how do I connect a DC system to a alternating current system well you may be surprised to know that one of the most important components is a single-pole double-throw switch and here I see a show a single-pole double-throw switch and the simple diagram for that switch is shown here where you're basically selecting you've got two inputs and the output is selecting either one of the inputs so it's basically a selector switch with two positions now the reason why this is helpful is because I can connect that up to the battery and select either the plus or the minus of the battery and in doing so I can generate a square wave of plus or minus and it's starting to look like a sine wave and if you switch this at the right time you can generate a 60 Hertz square wave now that's called inversion and the single-pole double-throw switch is called an inverter and the reason why it's called an inverter inverter is because to invert means to put something upside down or in the opposite opposite position order or arrangement which is exactly what we're doing we're taking a fixed plus one DC and we're changing it polarity to plus or minus over time so we are inverting and creating a square wave now if we operate the switch every 8.33 milliseconds we will have generated a 60 Hertz square wave so you can see we're starting to get a little bit closer to a 60 Hertz sinusoidal wave we've got a square wave of 60 Hertz now the question is how do I take that square wave and make it look like a sine wave that we can connect to the AC power system well when you think about it there's only one thing you can vary on the single-pole double-throw switching that is the position over time and what that another term for that is we can vary the timing of the switch or the duty cycle and the duty cycle defines how long you are in each position so to give you an idea here's some graphs of different duty cycles resulting from different positions of the switch over time so for example if I put it in this top position which is on a hundred percent of the time I've got this top wave which is a 100 percent duty cycle always on I have it on 80% of the time and then briefly put it in the off position and then back on I have an 80 percent duty cycle which means the pulse is 80 percent on and 20% of the time off if I have it in equal ly in both positions I've got a 50 percent duty cycle that looks like this and likewise if I am mostly off I've got a 20 percent duty cycle and so on so that that pulse-width is called the duty cycle and what we're doing is modulating the width of that pulse and that's called pulse width modulation or PWM so fancy terminology all it means is I am putting the switch in these two different positions a different amount of time so I can vary that pulse width or the duty cycle over time now if you think about it I can use that duty cycle information or that pulse width information to define the value of a sine wave so how do I do that well if I look here on at the peak of the sine wave and the pulse width is at a maximum it's probably 80 or 90 percent duty cycle here when I'm at a minimum of the sine wave I have a almost zero duty cycle which is it means it's always off or almost always off and in between I've got a maybe a 50 percent duty cycle so in fact I am encoding the value of the sine wave in the duty cycle of this pulse width modulated wave so the duty cycle of the PWM is proportional to the signal value so now you can see how I can use the duty cycle or the pulse width modulation to encode the value of a sine wave okay so now I can take this DC supply using a single pole switch and if I have a controller that tells this switch to operate proportional to value of the sine wave I can generate this PWM waveform that is in code getting some value of the sine wave over time so now I've got a system where I've got this reference which is input to this controller and using this sine wave reference it can generate a PWM wave which is used to control this switch and the output of this system out of this switch is a pulse width modulated waveform that is coming from this high voltage from this solar array okay so now I am using this system to generate a high voltage PWM wave now what am I going to do with this I need to convert this to a high voltage sine wave well I can run this through a low-pass RLC filter and it will filter out this high frequency and just give us this average value information and it will give us a sine wave out of the filter so now I've got a system where I put in a reference sine wave it generates a pulse width modulated waveform that's used to operate the switch it's also called a gating signal that used to operate the switch in proportion to this duty cycle and the output is a pulse width modulated waveform proportional to this high voltage and high power out of the solar array and I run that through a filter and now I've got a high voltage sinusoidal waveform proportional to this output of the solar array so now the question is how does this pulp pulse width modulation controller convert from a sine wave to this proportional PWM signal well here I've got this modulating a sine wave going into the controller and what I'm gonna do is I'm going to expand I'm going to blow up this little section here of the sine wave and it's this reference signal in red so it's the reference or modulating signal from the sine wave so what I'm going to do is I'm going to compare at every point in time that reference for modulating sine waves with a linear triangle wave shown here and it's called the carrier okay so at any point if this sine wave is greater than the value of the carrier then I will output a 1 if the triangle wave is greater than the sine wave I will output a 0 so you can see when the I'm at the maximum of the sine wave I'm generating a 1 and a minimum of the sine wave on generating 0 because I'm just checking it I'm comparing it to this triangle wave and outputting the 1 or 0 based on the position of the two ways so if you look at that a little clearer I've got my sinusoidal input comparing it to this triangle wave and here I've got a sinusoid is greater in value than the triangle way so I'm going to plot and it's this little point right here the triangle is a head of the sine wave so it goes to 0 now down at the minimum of the sine wave the sine wave is less than the carrier wave so I'm in here oh so you can say using this I have generated a pulse width modulated waveform whose value whose average value is proportional to the value of the sine wave so now you can see where I can use this reference to generate a pulse width modulated wave that has information about the sine wave and use that as a gating signal and then that will output as a out of the filter as a high voltage sinusoidal waveform so what I can do now is I can go into MATLAB and Simulink and develop a system like that so we can actually generate using pulse width modulation we can generate generate an AC waveform a four-element Simulink and what I've done is I've taken one of the examples that's provided in the power system tool box and I've modified it quite a bit but if you want to follow along you can load the if you look down here power underscore PWM generator two-level example and what I've done is I've gone through and modified that very heavily to make a more simplified single-phase solar inverter system so let me go through and show you what I've done here we'll start up top here I've got a mod a single-phase modulating 60 Hertz square wave so this is just a regular block of a sine wave and I'll go to amplitude one by zero frequency in radians per second two times five times 60 and zero things and it comes with a modulating index that you can use and we'll talk about that later on but we'll just leave it where it is here I've got a pulse width modulated generator and I've changed it to a single phase half bridge two pulses and I try left it unsynchronized and frequency 33 times 60 and that is the frequency and hearth of the triangle wave that we talked about and I think the rest of this is less come from the standard so what this does we'll film in here this pulse width modulated waveform generator will take the input sine wave and compare it to this triangle wave called the carrier and it's at 33 times 60 or 1980 Hertz and it will generate based on whether the sine wave is greater than or less than the triangle wave it will generate this PWM signal and it will send it out this pulse of output and here's the PWM signal and it will feed that into the gate of this Universal bridge now the universal bridge I've modified it a bit and I I've changed it to one bridge arm so a single-phase lifted it ID BT diodes and I believe all the rest is the same and it will give you just a single-phase output and then here we've got the solar arrays modeled as batteries this you need to change instead of a neutral change it to ground so we'll connect to the AC ground so basically this is a single-pole double-throw switch and it's sending out the resulting pwm waveform to this a phase and we'll run it through this filter which is basically an RLC low-pass filter and that will give us the output single phase AC measured by this HC meter and those the two signals the gating signal and the AC voltage will go into this scope now one thing I've done this this gives you two signals coming out of this pulse output of the PWM generator so I've set up a deluxe demultiplexer so take pull two outputs from this signal line and I'm using the the first one which is the gate signal going in to the scope so really that's all it is and if I run it you can see here is on the top here's the gate signal and here's the output AC waveform and like I do I can zoom in to a section here and you can see I'm at the peak of the AC and I'm at the peak of the duty cycle and if I go down here I'm at a minimum of the duty cycle it's maybe 10 or 20 percent duty cycle at the minimum and it's proportional to the sine wave value so that's basically what a simple PWM does now you can basically multiply this time free for three-phase system but here I've just made it simple with a single phase so that's basically a pulseless module a system for a solar array so I hope it helps take care and have a good day

Channel: EETechStuff

Views: 32,157

Rating: 4.8790321 out of 5

Keywords: photovoltaic, PV, solar, solar array, phase locked loop, pll, voltage controlled oscillator, VCO, simulink, matlab, renewable, pulse width modulation, pwm, dc inverter, inverter, dc to ac

Id: OztKg7EV-Dk

Length: 15min 42sec (942 seconds)

Published: Sun Mar 12 2017