How Do I Verify The Output Power Of Inverter Drive.

Easy. Shove a friction brake on the motor shaft, measure the heat produced, and compare it to the manufacturer's efficiency graph, Mildred.

Perhaps it doesn't have any load on it at the moment. An unloaded motor, when spinning, has a low Power Factor.

The power output of the inverter can be established using the motor manufacturer's published perfomance data, given the indicated voltage, current and frequency at any moment.

WHY do you doubt it?

Have you tried to estimate the power absorbed by the machine it is driving? I suppose you could install a torque measuring coupling on the shaft.

Do what knowledgeable power engineers do, rent a modern 3 phase PQM (Power Quality Meter/Monitor) and record the data for at least a week, though longer is better if the process conditions are highly variable.

Most PQMs come with software for analyzing and plotting the data without doing all the complex math involved when the frequency and/or waveform is highly variable/non-sinusoidal.

PWSlack has it. It appears you may be equivocating current and power, but to do so you are ignoring power factor and the effect that has based on mechanical load on the motor shaft.

As to redfred's point, my personal rule on that is that if your metering equipment was purchased for less than $3000 USD, it's inability to correctly interpret the complex waveforms on the output of a VFD are going to mean the data is of no real value. However, the circuits and algorithms necessary to accomplish this are the same as the circuits and algorithms used to make a VFD into a VFD. So you ALREADY have the necessary metering built-in. You just don't seem to trust it.

Which of course is bigg's point.

Exactly the golden lane I was hoping our OP was going to realize for themselves. If they do not trust the data their VFD is telling them then only sophisticated, calibrated test instrumentation with some proper analysis calculations will do. Fortunately many $20,000 oscilloscopes with active current probes will come with the power analysis and digital filtering capability built in.

I have not performed this test on a 7.4 hp three phase induction(?) motor using either a VFD or inverter. I have performed this type of test with a stepping motor that change the gap between permanent magnets attracting each other with a few Tesla field strength. It was fun showing that motors were slightly exceeding their designed torque specification when they were skipping steps. There were some odd looks from people when I asked for an expected kinematic load analysis and they couldn't produce one.

You'd be surprised, or maybe not, at how many of our process skid customers want to trust the reading of a $400 clamp on meter and $25 VOM over the reading on the VFD. (the logic - they've been calibrated - they must be right - the VFD has not) I have tried to explain the non-sinusoidal nature of the output to no avail. I had one rather large pharmaceutical company make me change the circuit breaker on the input to the VFD to handle what they thought the output was doing based on the above mentioned clamp on meter.

If you get paid to do it, so much the better I guess, but if not, that's tough to swallow. It's frustrating to bang your head against obstinate ignorance, I know. I do it almost every day... I try to educate, usually to little avail.

Put a clamp on Ammeter and do some math based on voltage, amps, speed and frequency.

"we know that the output power of inverter is non-sinusoidal"

why?

have you compared your mains voltage and inverter output on a scope?