In this video, we meet Johannes from Victron Energy at a local distributor 'Midland
Chandlers' and take a look inside a MultiPlus inverter and find out how it works. Well, many people wonder how a MultiPlus
works and actually also how you convert direct current into alternating current, and
how we do that. Well, at Victron Energy, we do that in a specific way, we have a platform of typology,
how we make an AC sine wave converter. And we use that typology throughout the range
that we have, so the inverters, the small ones the larger ones, but also the charging
inverters called 'Multi', but also the large Quattros are actually exactly the same,
they all have the same platform that they operate on to the conversion of direct current to alternating current.
What we do is we turn the inverter into a voltage source, and a voltage source makes the current flow according to the voltage: so we make
a voltage of, let's say 230 volts, and if you connect a load to it, the current will flows automatically, so that's how we do it. So we make a voltage, and then the current." And it does that with a full FET power bridge: this is that full FET power bridge and a FET
all these black components that you see here is actually a switch: a switch
is basically the same as what you have as a light switch: when you push it you can turn the light on, and when you push it the other way, the light goes off again.By changing
the length of the switching of our FETs, can we change the voltage of the output and
also reverse the polarity we can also do it the other way so we
can make a positive sine wave by the length of the switching and also a negative sine wave by the length
of the switching Well that switching is done on a 20 kiloherz signal that means we are switching 20 thousand
times per second from one specific point to another point so the sine wave
is very average very accurate the sine wave of an inverter is eve n accurate or even more
accurate than what comes out of your socket at home, because we have the source
there and we have no noise from other devices or neighbors.
So, the inverter
makes a perfect sine wave, well the perfect sine wave comes from the battery, and
the battery is, well let's say, normally 12 volts, so the sine wave is less than
12 volts, because you can never go higher than that. So the sine wave you're making
at the output of that switching of these FETs is about 8 to 10 volts. So then you have a 10 volt alternating current sine wave. Well, in order to use that, you use a transformer, and
these transformers step up the voltage of that low voltage, from the 8 to 10 volts,
to as high as 230 volts. If you want a 120 volt inverter, we have the same power supply,
but we use a different transformer, because then we go to a different voltage.
So, switching the low voltage and the low transformer for voltage, creates for us a 12
to 230 volt converter.
That's the same across the range. All our inverters work with a full FET bridge and a full FET bridge looks like this:
there are a number of FETs in the FET bridge and a FET is basically the same as a light
switch. If you control the FET you can make it conduct, or you can
stop it from conducting. All these FETs are connected to the controller, at the control panel. The
control panel makes a PVM signal, so with a narrower or a longer signal when
to open the FETs or when to close the FETs. On this side you have the
battery which has a plus and minus, and the plus is connected to the FET bridge on this side
and the minus is connected to the other side. This is the DC input side of the FET
bridge and you also have the AC output side which looks like this. The FETs are
controlled in pairs that means this FET belongs to that FET so initially when you have a PVM signal on this FET so a very small opening signal then
the plus will go through that this side to the other side and it will go back to the
battery.
The next instant, the signal will be a bit longer, meaning the average
voltage on the FET base will go up from here to there to there depending on the length of the PVM signal. So at the end, the PVM signal is so far, and so wide, that the FETs are completely open so you're at the maximum of your sine wave and then of course the signals
get smaller again, which means the average voltage goes down to zero. If you
dare this pair of FETs is stopped being controlled, and then the other two are
controlled, that means the exact same thing happens but with polarity reversed, because if
this and that are controlled, the plus will not go to this one FET, but go
to the other so that the voltage goes through them and then back to the battery.
That means
you have the same thing as in the positive sine wave but then you have the negative sine wave
and then something like this happens. So, you convert a DC voltage from your
battery into an AC voltage at the output of the FET bridge. Well, if this is a 12-volt,
12-volt DC battery, on the other side you have about 8 to 10 volts AC. This is the
principle of making alternating voltage from direct voltage. Of course, this voltage is not useful for home
appliances, so what we do is, we connect a transformer on this side, and that transformer has a ratio between incoming coils and outgoing coils and with that we can raise the voltage
from 12 volts, to let we say 230 volts.
If we should need an inverter to make 110
volts, we simply change the coils in the transformer, so with another transformer we can
also make 120 volts. If you have an inverter like this, you can feed the energy
from your battery through your electronics, through your transformer to the output, but of
course, this can also work the other way around, because you also want to charge the batteries
with the same electronics that you have as the inverter. Well, to do that,
we have an input and that input is connected to this side and you can now connect your power grid
to it, let's say this is 230 volt AC. If you connect that directly to
the output of the inverter, you will most likely have fireworks because the two
don't match, meaning the sine wave coming in on this side isn't exactly
the same as the sine wave the inverter is making.
So that's what happens then
, the driver, reading the voltage from the incoming current, matches the inverter's current
with the incoming current. And if these two match one hundred percent, so both
in frequency, but also in voltage, then these two will be connected. The connecting is done by a link, that link is placed here. So the converter listens to what's coming in
from the grid, and then synchronizes its own converter, it controls the frequency but
also the voltage of what's coming in and if these two are exactly the same then you can
connect these two together , you can connect the input of your grid to the output
of the inverter. So if you have a generator that turns out to be cold and it's not very
stable, it can take a long time to synchronize and lock in the incoming
power.
Once these two are enclosed the switch will close. So what
you see here is the input and output of the AC power and the input and output of the DC power and you can also control the
terminals if we look at the other side you can see the power supply of the DC power and also
the power supply of the alternating current, that means the device will start up when you have an alternating current but you
don't have a direct current, but it will also start up when you have a direct current but no alternating current. So in both
cases it will work. So even without the battery, the device will start up by itself.
Sure, it will measure the current you get from the AC input, and can also control the
current assist or load according to what is measured here. On this side,
there is the big switch and that is the switch that connects the input and output when
the inverter is synchronized with both of them. So this one gives you the big click when
the device starts charging.
The inverter is controlled in such a way that the switching
of the FETs is done so that the frequency but also the voltage level is exactly
the same as what comes in. If these two are exactly the same, then you can
connect the input and output, which means that the inverter is completely parallel to the incoming current.
When you have done that, you will hear the click: Sometimes it takes ten seconds, sometimes
even twenty seconds before the click is there, because that is the time the inverter needs to be able
to synchronize with the grid. So the further the grid is from the current that the inverter
makes, the longer it takes before you hear that click. If you had a generator
with a not so stable voltage, or a voltage that is much higher, or a frequency that is
further away from the frequency of the inverter, it could also take longer, after
about two minutes at the most you should hear click. Once that click is there you have connected the
current from the input to the current from the output of the inverter, then the inverter is given
a new job, then what happens is that the voltage of the inverter is controlled
to a lower level and if you control it to a lower level that means you have two
voltage sources running in parallel and the energy will flow to the energy source which has the
lowest voltage well in this case then the inverter because the inverter is trying
to lower its voltage of course you can it doesn't because it can't lower the grid voltage,
but it gets a lower potential so the energy will flow from the grid to the inverter
in your batteries, so that's how you charge the batteries.
So the current of charging
is done by regulating the voltage of the inverter so the lower the voltage of the inverter is
the more current of charging you will have to your battery so we control that also by
converting the current . The next step is, of course, that you can also stop charging if you have the
inverter running at exactly the same voltage as the incoming current, charging will simply
stop. The next step is, of course, if you don't have enough power from your grid and
you want to do something extra so you want to help the grid by adding power from your battery
on top of the power you're getting from your grid then you can inverter also raise its own voltage
and if that's the situation then of course the energy from the battery is
added to the energy of your incoming power well that's called "power
assist" so your energy from your battery can help boost the startup power of your air conditioner
or your refrigerator or whatever. That is of course something temporary, because that uses the power of the
battery.
When you've done power assist, the next logical step is to then recharge your
battery, as you'll then top up what you used to power up that power. So you
can with power assist help to overcome your generator's transient so if your
generator isn't powerful enough to start things up the power assist can help but
also in the ports when you have limited power from your port which you want to do if you
want to make a cup of coffee or if you have your microwave on, which is more than your port can provide to you,
is also using the power assist. The Multi's, the inverters and also the Quattro's
use the same typology, which means that the way we do it is exactly the same, and also the
12 volt, 24 volt and also the 48 volt models have the same way they do it.
The difference between
these devices is the models of FETs we use, one FET is made for a 12 volt system,
the other is made for a 24 volt system and so on. A FET is a small component and that
small component can handle about 50 to 100 amps, that means if you want a powerful
inverter you have to have these FETs in parallel: you can't run too many in parallel, because
you also like they must be off in the same time, so the switching of the 20 kilowatts
must be the same on all FETs.
So in our devices, we have 6 FETs in parallel, which is about
the same for all of our inverters and inverters for chargers. If you want a more powerful inverter
than that one, we can also put these devices in parallel, and then what we simply do is
tell the device next to it to do the exact same thing as the main device, so we have double the
current for the inverter, but also the double current for the charge, and also of course the double current for the
transfer, so everything becomes double. The next step for that is also we shift the frequency
between these, and that means you can make a system of 3 phases, so if you have a
120 degree displacement of the phase between the devices, you can have a single device which interacts with
another standalone device, and another standalone device, these 3 together make a 3 phase system.
So the device itself does exactly the same as a standalone device, it just listens to what
its neighbor is doing.
Every inverter has passive current, and passive current means it
uses the battery's energy while it's on, so if it's making 230 volts, even if you're
not using 230 volts, it's taking energy from the battery. The current is caused by the
switching of the FETs just like the switching of a light switch it doesn't require much energy
to turn on a light switch but if you have to do it 20 thousand times per second then suddenly it requires
energy to do that So the more you switch it, the more energy is
also lost in the FETs themselves, but also in the transformer, because the transformer always
changes polarity, it changes from plus to minus, so changing polarity in a transformer, requires energy, 20 thousand times per second the FETs switch and therefore a row of FETs
also requires energy.
So, if you want to avoid using a lot of energy while doing nothing
with your energy system, you need to find the right inverter for your load. The bigger your
inverter is, the more loss you will have, because the transformer is bigger and also
the FETs you are switching are more powerful. So you use more energy to run a larger inverter
than to run a smaller inverter. When you make a choice about which inverter to
use, you start by looking at what load you have, you take a look at those loads that you have on board,
and look at what kind of charge they are running out on average, but also what kind of loads they
are on startup/behavior at peak power usage, and what they need to get started.
Well
you take the average of that because normally we don't have everything on at the same time,
about 70 percent of what you have plugged in will need to be covered by your inverter
(that's about the size of your inverter) But also the capacity of your batteries determines
how big your inverter can be because an inverter converts energy from your battery
to AC, but it cannot create energy, so you have to supplement it with energy from your battery.
If your battery is not able to fill the inverter with power well then there is no point
in having a larger inverter as it is all about balance the inverter and your battery
and your loads have to balance with each other. A larger inverter is nice because if
you have an inverter on board, the tendency to use more than what you normally
use makes sense, many people do, but don't overdo it as you
will drain your batteries unnecessarily.
Also, if you are not on board, switch your inverter charger
to "charge only" as you will then be able to charge the batteries, but you will not be unnecessarily
creating 230 volts and draining your battery while you are are not connected to the network. In the inverter,
in all our Multi's and our Quattro's, we have an energy saving mode called AES ("Automatic Energy Saving"), Automatic Energy Saving has two modes: one mode is over voltage mode and over voltage mode
means you get 1 sine wave every second which means that much of that 20 kilohertz switching
of these FETs is avoided because instead of making 50 hertz, you're only making 1, that means you're doing 49 fewer switches. So you do less measurements of your transformer and also less switching
of your FETs. That means you use less power from your battery while in idle mode.
The negative is of course you only have 1 hertz per second which means
devices that do use a frequency to be there like a clock for your microwave and so
on will stop working because they're missing that 49 hertz so that clock will
stop, so it's good for your sleep, it's not so good for your microwave.
The other one
is modified sine wave and modified sine wave even though the word makes it look a bit
different it's not that it's a modified sine wave it's a less accurate sine wave
we switch less which means we have a less accurate way for making our sine wave
so instead of the 20 kilohertz switching we switch less and less switching means
we use less power. Well, for a 3 kilowatt device like this, the idle power when it's fully
on is about 15 watts, when you do a custom sine wave it's about 12 watts, and when you
do search mode it's about 8 watts and at 8 watts, it's mainly the power supply, which runs
the processors in it, and does some of the switching of the FETs.
So you can combine these 3 steps. Well, for a 3 kilowatt device like this, the idle power when it's
fully on is about 15 watts, when you do a custom sine wave it's about 12 watts, and when you do search mode it's about 8 watts and at 8 watts
, it's mainly the power supply, which runs the processors within it, and does some of the switching of the FETs.
So you can combine these 3 steps. It detects when there's power connected to it and of
course when you have them on search mode it looks at it every second so if there's power that second
the device will go full on and here we go again in a custom sine wave
is there is also a level where it goes from the adjusted sine wave to the full sine wave at
a specific level. What we can do with our inverters is you can control them remotely
so you can do that with a panel with a multi control panel, or you can do that a bit more
advanced with a color screen so you also have the screen so you
can see what's going on in your system, but you can also use any potential panel for your
remote switch, if you want to, you can add that to your desktop, you can even do that with
Bluetooth, and nowadays we're able to connecting the device to your phone, and that means you
can change that with your phone too.
On top of that what you can also choose is
to turn off the fan sometimes you want to have the unit on at night because you
need 230 volts but you don't want to hear the fan you want it to be as quiet as possible
so you have the option to turn the fan off at night, or under a specific load if
you wish to do so. So you can put a timer on it to control your fan or
you can do it on the power you use..
