Hi, my name is Ben Hoover. I am a hardware design Engineer at Keysight Technologies,
working in the power analyzer group. Today I am going to talk a little bit about using
the new power analyzer that we just worked on, the PA2203. It is a 3-phase power analyzer.
I am going to talk about how to use it to measure signals on a variable frequency drive.
I've got a block diagram of what I've got wired up here. I've got a 120 volt single
phase line coming into this variable frequency drive. The variable frequency drive is generating
3 phases out; it is in a delta wiring configuration. It is driving a 3-phase AC induction motor,
and then that induction motor is mechanically coupled to a DC generator, and that is connected
to a load. I've got my power analyzer wired both on the front end looking at the 120 volt
single phase line in, measuring it with a 50 amp internal shunt and a voltage measurement.
These are all isolated current and voltage measurements. Then on the output I am measuring
U to V, V to W, W to U as a delta wiring configuration measuring with each one of the voltage inputs
and current inputs 1, 2, and 3. Again, these are 50 amp internal shunts. I will go ahead
and turn this on. This is the motor drive. It turns the variable frequency drive on.
Immediately you can see the voltage waveform, the current waveform, and the power waveform
on the screen. This is the default setup of the instrument. You can actually see that
it is a PWM signal that is trying to generate a sine wave here, and this is just one of
the three phases being driven into the motor. I can zoom in on that and see the PWMs changing
pulse widths, and see that it is running at about – I think – about 8 kilohertz. It's
around 8 kilohertz; it modulates it a little bit. I can zoom out and look at all of the
channels here. Channel 2 is phase 2, or U. Channel 3 is phase 3, or W. I'm measuring
directly across each one of those delta configuration legs and I am measuring the current going
into it. You can see the current is somewhat sinusoidal. I can actually turn filters on
and look at the sinusoid that it is attempting to generate. There, if I bring channel 1 up
to the front, you can actually see the sine wave. I am running it really slow now so the
voltage is relatively low compared to the rails that it is switching to for the PWM,
generating a small waveform. I can actually measure the size of that waveform if I can
get my trigger down there where I can actually measure it. I've got a sinusoid that is 36
volts, but the peak-to-peak on this thing was; on channel 1 the peak-to-peak was 100
volts, but if I look at the peak-to-peak on the actual PWM signal, I can look at channel
2. That's the frequency. Channel 2, peak-to-peak; that is measuring about 700 volts, so that
is the rails of the actual VFD, the DC rails internal to the VFD. I ran this other measurement.
This is our power quality panel. It actually does a different type of measurement than
the on-screen measurements that I was just showing. These measurements are based entirely
what is on-screen right now, where these measurements are actually based on a fixed window and their
continuous whole cycle analysis measurements. That is what we call CWA – Continual Whole
Cycle Analysis, and that is really operating over a time window. During that time window
it operates – the measurement is evaluated only on an integer number of cycles so you
get a very consistent, good measurement that is gapless over time so you can actually data
log that measurement over time and you get a consistent data log over time. Another thing
that I can define here is I can change the window of this analysis. Right now it is at
200 milliseconds. That is okay for a 60 hertz signal. As you go lower and lower in frequency
you need a longer window to get a good measurement, to get a number of cycles so that you average
over a number of cycles. So, I am going to change that to a one second window and that
should get me a very nice, stable measurement there. Right now I am looking at these signals
as individual voltage current measurements. I am not looking at it as a 3-phase delta
wired configuration. That is really what I want to know: If I consider this 3-phase system
what is the total power of the 3-phase system? Now, I am going to go into my wiring diagram
here and actually change my wiring configuration so it is a 3 watt meter, 3-wire measurement
here. This is a diagram showing exactly what I am measuring. I can take that and compare
it to the block diagram and where I've got my wiring set up in my block diagram to see
that I've actually got everything wired up correctly. It is a very convenient way of
showing that. What that allows me to do is now all the channels got filtered. That is
because as soon as we turn that on, the filtering actually controls all channels simultaneously
in that 3-phrase group. I can turn on channel 4 here. That is actually my sine wave input.
That is the 60 hertz, 120 volt line in. You can see it is actually being rectified. You
can see the first thing it does is go directly into a rectifier based on that current pulse
that's probably what is happening inside the device; there is no power factor correction.
We can actually look at the power quality measurement on that channel and look at what
its power factor looks like. I can change my trigger source to channel 4. Now you can
see the power factor is actually quite poor at point 4. The angle doesn't really mean
anything because it's not a sine wave; it's really a very non-linear response. I can actually
turn up the speed of the motor a little bit. Now I can go back and turn on filters and
look at the filtered 3-phase waveforms. That will work. I can turn off channel 4, and now
I am actually looking at each one of these guys – there it is – the filtered version
of each one of those. One other thing that I can look at here is I can turn on a phasor
diagram. The phasor diagram will show the VNI of just a single channel. Or, I can show
the VNI of the entire group. This shows the phase between VNI. Here it shows the magnitude
of the first harmonic. This is really showing us the same angle that you'd get here in the
power quality window. If I go and look at one of the phases here I get 36 degrees there
because I am filtering. If I had turned off the filters, I would not get 36 degrees there
because I am not looking at the fundamental. I would get something completely different
because it is really the full PWM signal that it is looking at there. So, I am going to
turn off the filters and now if I look at the analysis, my power factor is much, much lower and my angle is
72 degrees now, where before it was 36 degrees, and that is because this angle is computed
based on power divided by VA. That is how the power factor is computed and the angle
is the cosine of the power factor, or the inverse cosine of the power factor. There
are other analysis features that we can actually do here. We can turn on – right now it is
looking at power quality – we can also look at the efficiency of the VFD from the input
to the output. I can define my input power as power 4 – because that is my line in
– and my output power as, not power 1, as the grouped 3-phase power. I can see the actual
efficiency that this is running at. I can vary the speed of this thing. It runs at 80
percent efficiency at slow speeds and as I increase the speed the efficiency of this
thing goes up. It's just one of the measures that you can make, is looking at efficiency
input to output on a VFD. Other measures that we could do are we could look at energy over
time. We could look at the harmonics on the waveforms. We have multiple power quality
types of measurements that you could do on this VFD. In conclusion, I walked you through
some of the analysis that you can do using a PA2203 Power Analyzer and how some of the
capability of the PA2203 helps you look at specific signals on a variable frequency drive.