Hi, I'm Bryan Boswell with Keysight Technologies. I am a design engineer, and I will be describing
a PV inverter test set using the Keysight Technologies N8937 APV photovoltaic array
simulator and the PA2203A IntegraVision Power Analyzer. The device under test that we will
be talking about today is a 12 KVA transformerless 480 volt 3-phase inverter. The input is normally
supplied by a solar array. We will be simulating that with the N8937 APV, which is sourced
by a 208 volt 3-phase input which then generates the DC input to the inverter. The output is
connected to 480 volt 3-phase, and I will be measuring the output of the inverter using
channels 1, 2, and 3 on the three phases connected to neutral. On the input I will be using channel
4 to measure the voltage and current of the DC input to the inverter. These are wired
into the power analyzer. That's our configuration. I will now talk about how it is actually wired.
Our 208 3-phase input comes into our power supply, which does the 3-phase AC to DC conversion.
The output of the power supply then supplies the input to the inverter mounted here. The
inverter output is then connected to 480 volt 3-phase, which then goes out to the 3-phase
power of our building. Power is being transferred from the 208 through back out to the 480 volt
3-phase. One thing I might note here on my wiring conventions is – because I am using
a standard breakout box here – I've defined the power as being delivered from the wall.
So, positive power would be coming out of the wall. Because the power flow through our
test system is from the 208 to the 480, I should expect to see negative power as measured
on our input group. We will see that once we power up.
With that, I will go ahead and get set up. For consistency, I like to store all of my
setups on my USB stick and then just recall them when I want to use them. We'll put that
in and recall our setup. There's my setup. I've now got the power analyzer configured.
I've preconfigured the PV simulator and what I've got it doing is tracking to a solar simulation
curve which we program with the short circuit current and the open circuit voltage and then
the maximum power point voltage and current. This is the output characteristic which corresponds
to the following power curve, and you will notice what we expect the inverter to do is
start the open circuit voltage, increase power until it reaches the maximum, and that is
where it is going to track to that maximum power. Once we power on the system, we will
actually see that works. With that, let me go ahead and apply the 480
volt input to the system. We now see I've got input voltage that we're measuring that
is coming into the inverter. I haven't actually turned on the array simulator, so nothing
is actually being converted yet. But, we can go into the system and actually look at the
voltages being measured; 280 volts lined to neutral, which of course is 480 volt 3-phase.
Our voltage is there, and if you look at the power, very little power being developed at
this point. To kick things off, what I'll do – we can see that the array simulator
is in the curve mode. It is set up for 200 volts at 20 amps, which would be 12 KVA. It
is exactly the maximum power of our inverter. So, we'll go ahead and start that. If you
notice, the power supply went to 750 volts just like it is supposed to. We are now sitting
right at this point waiting for the inverter to actually turn on. In a few seconds you
will hear the inverter start to turn on and it will start converting power. Give it just
a second. Now we can hear the inverter starting to kick on and as you watch the power supply
you will actually see when it starts to sense the power and do some conversion. There you
are starting to see some current flow. I actually like to click this over and watch the power
buildup. This is the output voltage and this is the output DC power being delivered by
the N8937 APV. We are up to 5 KW, and if you look at the front of the power analyzer
you see we've now got current being built up as well as the power waveforms being displayed.
More and more power is being converted by the inverter from the DC out to the 480 volt.
Voltage waveforms are at the top; the current waveforms are in the center, and I am displaying
power waveforms here on the bottom. We've pretty much reached our maximum power point
of 12 KVA. Things are pretty stable right now. If we're looking at the grouping here
on the output power, again, the voltage is still 280 volts. I now have 13.8 amps flowing,
which converts to 11.65 kilowatts. Notice the sine – negative power being driven out
back onto our 480 volt grid. So, the system is now fully up and running. The next thing
we might want to look at is: What is the efficiency of the system. If we look at our CWA analysis,
one of our options here is efficiency. I have predefined a couple of different efficiencies
that we will be looking at, efficiency 1 being the power being delivered from channel 4;
that's the DC input to the inverter, and the output being the group A, or the output of
the inverter. If you look at that setup, it is showing an input power of 11.9 kilowatts,
an output power of -11.65, for a total efficiency of -97.4 percent. This particular inverter,
the manufacturer specifies efficiency of greater than 97 percent, so it appears to be doing
what the manufacturer said it would do. I also set up a second efficiency set to look
at. In this case, I am looking at the input being the group A total power, and the output
being one of the phases of the power. We will see how well the power is being converted
on a phase-by-phase basis. If you look at this case, -11.6, -3.9 for an efficiency of
33.45. You can see it is being split fairly equally between the three phases. You can
look at each of the phases if you would like by scrolling through them. Again, just about
exactly 33 percent on each one of those. Another test that you might want to look at would
be the harmonics of some of the signals. In this case I am looking at the harmonics of
one of the phase currents. In this case phase current 1 which is displayed, has a total
harmonic distortion of about 4 percent, and each one of the harmonics of that are shown
here. You can also display that in a table format and see the various sizes of each of
the harmonics there. You can look at the same thing for maybe one of the voltage channels.
In that case, a significantly lower THD, higher signal integrity. The voltage is actually
measured at about 1 percent in this case. Another type of measurement you might want
to be making on inverters would be the phasor diagram. In this case we are going to look
at it for group A, that being the output. The phasor diagram in this case is very close
to ideal, with each one of the voltage waveforms being 120 degrees out of phase and the current
being nearly identical to 180 degrees out of phase. We can verify that. If you come
back to the power quality panel and look at the power factor you see the power factor
on group A at .993; very, very efficient inverter at a very high power factor. As I was putting
together this little demonstration, one of the things that I noticed about this setup
that surprised me was when I looked at this current waveform I noticed that there was
a small signal on the input power – that being channel 4 – signal. I was interested
because the input is actually DC but I can see that there is a waveform on there. The
PA2203 has the ability to zoom in on that signal and investigate it. So, one of the
things that I did was take a look at that current signal. The best way to do that would
be to be AC coupled on it. We are now AC coupled. We will center the waveform. We will
turn on auto-ranging and we will expand that waveform such that we can actually look at it. We will do the
same thing with the voltage waveform, increase the resolution on that waveform. We'll do
the same thing on the power waveform. We've now got them AC coupled, autoranged, and
zoomed in to the point where we should be able to see some signal. I notice that it
is a high frequency signal. I increase my sweep speed and I can now see the signal come
over to my power analysis, switch over to channel 4, and I can see that the frequency of the current waveform is switching
as an AC signal at 32 KHz, which I suspect is actually the switching frequency of the
inverter itself. My AC coupling on the waveform – we're able to remove the DC offset, zoom
in on the signal, and actually see the switching waveform. The other thing that you may notice
as you are watching the waveform here is occasionally I am seeing an increase in the power waveform.
That might be a second thing we could zoom in and look for. One of the things that the
PA2203A has is the ability not only to see the power waveform, but you can trigger on
the power waveform. Let's change our triggering from voltage 1 – which was the nice stable
channel – to the power 4 waveform. Once we do that we can adjust our trigger level
to then see the intermittent power levels that are occurring there. We know it is an
event that is happening fairly seldom, so I decrease my sweep speed to the point where
I can actually see this intermittent event and trigger on it. What we see is occasionally
there is an adjustment to the voltage waveform. By triggering on this power signal we can
zoom in and see that. This is just an example of some of the measurements that you could
make with the PA2203 and find information in those signals that can add insight into
the design that you are trying to analyze. With that, I am going to call the video to
a conclusion. Hopefully you have enjoyed the information presented. Thank you.