We’re going to be looking at power inverters to understand the basics of how they work and where we use them remember electricity is dangerous and can be fatal you should be qualified and competent to carry out any electrical work

A typical inverter looks something like this it has some red and black DC terminals on the back end and on the front end we find some AEC electrical outlets that’s because there are two types of electricity there is AC and there is DC an inverter is used to convert DC or direct current into AC alternating current we can also convert AC into DC with the use of a rectifier but we’ll cover that in a separate video and I’ll leave some links in the video description down below for that the appliances in our homes are designed to run off of an AC supply and they get that from the electrical outlets which all provide AC electricity however electricity produced by things such as solar panels and batteries produce DC electricity so if we want to power our electrical devices from renewable sources battery banks or even our car then we need to convert DC electricity into AC electricity and we do that with an inverter where have you seen inverters used or where would you like to use one let me know your thoughts and your project ideas in the comment section down below to understand how an inverter works we first need to understand some fundamentals of electricity

Inside a copper wire we find copper atoms these have electrons which can move to other atoms these are known as free electrons because they are free to move around they will randomly move in all directions but this isn’t of any use to us we need lots of electrons to move in the same direction and we do that by applying a voltage difference across the wire the voltage is like pressure and will push the electrons when we connect a wire to the positive and the negative terminals of a battery we complete the circuit and electrons begin to flow we call this flow of electrons current the electrons always try to get back to their source so if we place things such as lamps in the path of the electrons they will have to pass through this and they will therefore do work for us such as illuminating this lamp the electricity from solar panels and batteries is known as DC electricity and that’s because this type of electricity flows in just one single direction it flows from one terminal directly to the other terminal

if we reverse the battery the electrons flow in the opposite direction you can think of DC electricity like a river with the current of water flowing in just a single direction now in these animations I use electron flow which is from negative to positive but you might be used to seeing conventional current which is from positive to negative electron flow is what’s actually occurring conventional current was the original theory and it’s still widely taught today just be aware of the two and which one we’re using when we use in the scylla scope to look at the electrical waveform for DC we get this flat line at the maximum voltage in the positive region if we were to cut the power then the line will drop to zero if we turn the power on and off repeatedly then we get a square wave pattern between zero and maximum but if we were to post the switch to open and close over different lengths of time then we would get a pulsating pattern with AC electricity the electrons Oktay by flowing forwards and backwards constantly that’s how it gets its name because the current of electrons alternates in direction you can think of this type of electricity let the tide of the sea it constantly flows in and out between the maximums of high tide and low tide if we followed the copper wires back to the generator the wires are connected to some coils of wire which sit within the generator inside a basic generator we also find a magnet at the center which is rotating the magnet has a north and south pole or you can think of it as a positive and a negative half the electrons in the wire are negatively charged as you might already know magnets push or pull depending on the polarity so as the magnets rotate past the coils the positive and the negative half are going to therefore push and pull the electrons within the copper coils and also through the connected copper wires the magnetic field of the magnet varies in intensity so as the magnet rotates past the coil the coil will experience a change in intensity of the magnetic field this will be from 0 up to its maximum intensity and then as it passes the coil

it will decrease again back to 0 then the negative half comes in and pulls the electrons backwards with the same change in intensity each full rotation of the magnet will therefore produce this wave pattern known as a sine wave the voltage is not constant in this type of electricity instead it repeatedly moves from zero up to its peak back to zero then to the negative peak and then finally back to zero again frequency refers to how many times this AC sine wave repeats per second in North America and a few other parts of the world we find 60 Hertz electricity which means the sine wave repeats 60 times per second and as each wave has a positive and a negative half this means its polarity will therefore reverse 120 times per second in the rest of the world we mostly find 50 Hertz electricity so the sine wave repeats 50 times per second and therefore the current reverses 100 times per second the inverter consists of a number of electronic switches known as IGBTs the opening and closing of the switches is controlled by a controller these can open and close superfast in pairs to control the flow of electricity by controlling the path which the electricity takes and how long it flows in the different paths we can produce AC electricity from the DC source I’m going to animate these using some simple switches to make them easier to visualize

remember AC is where the current reverses direction we saw earlier in the video we can reverse the direction of current by reversing the battery we could very quickly reverse the battery to produce a rough AC supply but an easier way would be to connect four switches or IGBTs across our load such as a lamp if we open and close these in pairs then we can produce AC electricity so if we were to close which is one and four then the current flows in one direction and if we then open these and close which is two and three we get current flowing in the other direction so we can use the controller to automatically do this again and again and again if we did that 120 times per second then we would get 60 Hertz electricity and if we did that 100 times per second and we would get 50 Hertz electricity as we have a low voltage input we’re going to get a low voltage output to reach the 120 volts or 230 volts required to power our appliances we will also need a transformer to step up the voltage to a useful level when we look at this through an oscilloscope we get a square wave in the positive and the negative regions this is theoretically AC

because it reverses direction but it doesn’t really look much like an AC sine wave so how can we improve this do you remember earlier in the video when I said we can open and close the switch at different speeds and durations to change the waveform well we can do that for this too what we do is to use a controller to rapidly open and close the switches multiple times per cycle in a pulsating pattern each pulse varying in width

this is known as pulse width modulation the cycle is broken up into multiple smaller segments each segment has a total amount of current that could flow but by rapidly pulsating the switches we control the amount of flow occurring per segment this will result in an average current per segment which we see increases and decreases thus giving us a wave the load will therefore experience a sine wave the more segments we have than the closer

it mimics a smooth wave we can control the output voltage by controlling how long the switches are closed for so we could for example output 240 volts or 120 volts just by trimming the opening and closing times

we can also control the frequency by controlling the timing of the switches so we could for example output 60 Hertz 50 Hertz or 30 Hertz whatever is needed for the application so that’s how we can take a 12-volt DC battery and convert this into a 120 volts or 230 volts ac supply by using some IGBTs pulse width modulation and a transformer but what if we needed more power we also have single-phase as well as three-phase AC electricity most homes around the world use single-phase electricity large commercial buildings as well as some homes especially in Europe will use three-phase electricity homes in North America use split-phase electricity where a center tap transformer splits a single phase into two which provides two hot wires and a neutral we’ve covered how split phase electricity works in detail in our previous video do check that out links down below with single-phase we have a connection to just a single-phase from a generator so we have just one sine wave but with three-phase electricity we have a connection to each of the three phases the phases are coils of wire which were inserted into the generator 120 degrees apart from the previous this means the coils experience the peak of the rotating magnetic field at different times and it’s this that gives us our three phases each with a different sine wave that is slightly out of sync from the previous remember electricity wants to get back to its source in a complete circuit as the current is flowing forwards and backwards at different times in each of the phases we can essentially connect the phases together and the current will move between the different phases as the polarity of each phase moves forwards and backwards at different times any excess will flow in the neutral back to the source if needed but that’s only if the load on any of the phases is unbalanced with single phase

we have these large gaps between the peaks but with three-phase these can be combined to fill in the gaps and therefore deliver more power larger applications require a three-phase inverter for example to run the compressors in a large cooling system the DC supply in this case will be a rectified three-phase AC supply that means that three AC sine waves are combined together and pass through some diodes which prevent the electrons from flowing backwards this turns it into a ripple DC waveform we then use a capacitor to smooth the ripple out into a constant DC supply now we have covered this in great detail previously do check that out links down below to turn the clean DC into three-phase AC we use a three-phase inverter for this we use 6i gbts again I’ll animate these as simple switches for simplicity and also number these as follows to get our three phases we need to open and close witches in pairs to direct the flow of current form our supply and return paths that way the connected motor will experience alternating current for the three-phase supply we time the switches to simulate the three phases let’s see how this works first we close which is one and six this will give us phase 1 to phase 2 then we close which is one and two this will give us phase 1 to phase 3 then we close which is three and two this will give us phase two and phase three then we close which is three and four this will give us phase two and phase one then we close which is five and four this will give us phase 3 and phase one then we close which is five and six and this will give us phase 3 and phase two this cycle repeats again and again like so if we check this with an oscilloscope we now have a wave pattern that looks something like AC except it’s still a little bit square this will work fine for some applications but not all so again we need to use pulse width modulation to create the sine wave so we’re going to use a controller to rapidly open and close the switches to vary the output frequency and voltage and that way we get our three-phase AC supply.


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