I have question about a electro motor powered by a frequency regulator. It is the first time I did some test on a frequency regulator on school.
This are the parameters of the motor
The motor is connected in triangle. The frequency regulator is from Schneider. I forgot to write down the specs. But it's a special module for students. It has the schneider frequency regulator, leroy Somer asynchrone motor and a DC motor the can be used as generator to put some load on the asynchrone motor. There is also some special software that came with test bench . With this software we can do test.
So the test I did: I connected a constant load of 5Nm on the motor. After this I regulated the frequency from 10Hz to 50Hz. The following table gives the results of all signals measured.
Where f is the frequency, n the rotation speed, Tu the connected torque, Pm the mechanical power, U voltage output(internal voltage meter of the system, not so accurate), I current, Pe electric power, los. power loss = Pe-Pm , Um.rms is the same as U but with a more accurate voltage meter, Um.1h is the voltage of the first harmonic of the PWM signal, Im.rms current.
Now there are 2 thinks that I don't understand:
the first question: So when I compare Um.rms and Um.1h, with other words the RMS value of the output and the first harmonic of the output there is a difference difference between them. I think this is because, the other harmonics also have a big influence on the RMS value. I read in an technical article (I can't post the article url because reputation isn't high enough yet.) that the 5th and 7th harmonic could have an amplitude of 10% - 40% of the fundamental harmonic. So I think that this is the reason that there is such a big difference between the RMS value of the output and the first harmonic of the output. Is this true?
The second question: When I compare Pe and Pm there is a big difference between them. The motor efficiency is around 50%. Is this because it is powered by a frequency regulator, because the harmonics in the current and voltage? Or those it have another reason. I have no clue why this is. (I can't post the plot because reputation isn't high enough.)