Accurate Harmonic Analysis
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From: Jerry Avins on 4 Mar 2010 09:07 steveu wrote: ... > It still tends to be efficient solutions that get the volume sales. Many > utilities are interested in charging based on fundamental power energy > consumption, rather than the active energy consumption they use today. > They'll put really detailed harmonic analysis into every consumer > electricity meter if its cheap enough. You'd better make the cost delta > over a simply electricity meter close to zero, though, if you don't want to > be confined to a niche. Interesting! The utilities supplie all the power. Why do they want to be paid for only part of it? Jerry -- Everyone is entitled to an opinion; not all opinions deserve respect. ���������������������������������������������������������������������
From: steveu on 4 Mar 2010 09:31 >steveu wrote: > > ... > >> It still tends to be efficient solutions that get the volume sales. Many >> utilities are interested in charging based on fundamental power energy >> consumption, rather than the active energy consumption they use today. >> They'll put really detailed harmonic analysis into every consumer >> electricity meter if its cheap enough. You'd better make the cost delta >> over a simply electricity meter close to zero, though, if you don't want to >> be confined to a niche. > >Interesting! The utilities supplie all the power. Why do they want to be >paid for only part of it? There are a number of questions about the rights and wrong of charging. The distortion in the voltage signal is mostly the fault of the utility, though a little is be due to resistive drop in the consumer's own wiring, due to the consumer's load current. The distortion in the current signal is mostly the fault of the consumer. However, for a simple resistive load, distortion in the current waveform is a direct result of distortion in the voltage waveform. How should all this play out in the bill? There is an increasing urge to punish poor power factors and highly distorted loads. They do cause a lot of grief for the utility. Steve
From: Manny on 5 Mar 2010 06:07 On Mar 2, 2:33 pm, Vladimir Vassilevsky <nos...(a)nowhere.com> wrote: > steveu wrote: > > Why take a roundabout approach to finding the THD (finding all the > > harmonics with an FFT and summing them), rather than go straight for your > > goal? What about: > > > - Phase lock a synthesised pure sine wave to your signal. > > - Tune the amplitude of your sine wave, so that > > original.pure == pure.pure > > I wouldn't recommend this for beginners. > > > Now, sqrt(original.original) is your harmonic polluted RMS value, and > > sqrt(pure.pure) is the fundamental RMS value. The difference is the > > harmonic content. > > Not quite. The difference is THD + N + numeric artifacts. > > > Calculate those dot products in a leaky manner, and you can perform a > > continuous measurement, tuning the phase lock and amplitude as you go. > > I've heard that some digital scopes adjust their sample rate so the > period of fundamental falls exactly in the FFT bin. Just too follow on Vlad's idea, if you want this offline, I see no reason why you can not search for a resampling rate that minimizes your THD. This would be your true THD. If you want this in realtime, you can in theory do so adaptively. And I could be missing the point here and this could all be rubbish :). -Momo
From: evilzucchini on 5 Mar 2010 15:39
Thanks for all the input directly applicable to my question. The rest was also quite interesting. It is kind of nice to hear a discussion of DSP related to something I already have a decent understanding of. |