Power Generator Conducted Emissions
Power Generator Conducted Emissions
(OP)
I have recently been testing EMI on a permanent magnet generator and observed something I can not explain. I am not extremely familiar with PMGs so I thought I might see if any of you guys have seen anything like this before. I was operating the generator to provide 400Hz output and was monitoring conducted emissions. Of course I saw a large component at 400Hz and then smaller components at a couple of the harmonics. But I also saw a significant component (larger than any of the harmonics) at 350Hz and 450Hz and then another smaller bump at 300Hz and 500Hz. I have not been able to determine what might be causing the noise at +/-50Hz and +/-100Hz of the fundamental. Any ideas?






RE: Power Generator Conducted Emissions
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com
RE: Power Generator Conducted Emissions
Later we did radiated emissions testing with the output at 820Hz and about 70kW resistive load and saw similar noise blips on either side of the fundamental. I only have plots of the results so it is difficult to tell for sure, but it looks like the radiated blips are offset about half as much as they were at 400Hz.
RE: Power Generator Conducted Emissions
Many of us here are familiar with a Permanent Magnet Generator as a small unit on the back end of a much larger generator.
The purpose is to provide energy to the Automatic Voltage Regulator to excite the stationary field of the brushless exciter of the main alternator.
Although PM generators are used with smaller wind turbines to charge batteries, there may be serious voltage control issues if a PMG is used to directly supply a varying load. A 15KW PMG, and an engine speed of 1000 rpm at 400 Hz. seem a little awkward. Not wrong, but begging clarification.
respectfully
RE: Power Generator Conducted Emissions
Yes it is a little bit of a "different" application. We are testing a standalone PMG being driven by a diesel engine. The voltage and frequency output of the generator in the end application are unregulated and we have a fairly wide tolerance to what we can feed to the next stage. Normally we would be operating closer to 800Hz. But for EMI testing the LISNs that were available could only handle 400Hz so we had to slow the generator down. I am including a portion of the plot to better show what we saw.
RE: Power Generator Conducted Emissions
2) What is the number of poles in the rotor?
3) What is your net frequency?
RE: Power Generator Conducted Emissions
RE: Power Generator Conducted Emissions
The question about the frequency of the net or mains voltage was due to the (far fetched?) idea, that the bumps at 350Hz and 450Hz result from some kind of an interference from the mains voltage in the measuring instrument.
RE: Power Generator Conducted Emissions
I have come to about the same conclusion. Something about the generator's construction (magnet strength, location, coil spacing, rotor alignment, etc...) is causing a slight modulation in the output. I was hoping this is something someone might have seen before and could confirm. Thanks for the input.
RE: Power Generator Conducted Emissions
Keith Cress
Flamin Systems, Inc.- http://www.flaminsystems.com