sampling frequency = 256/cycle which method is use complex or real fft for 60Hz current, voltage, power harmonics measurement? thanks for any help.
can you help me about reactive power harmonics measurement by FFT
Started by ●February 28, 2008
Reply by ●February 28, 20082008-02-28
On 28 Feb, 12:46, "alpere" <alper...@gmail.com> wrote:> sampling frequency = 256/cycle > which method is use complex or real fft for 60Hz current, voltage, power > harmonics measurement? > thanks for any help.Those are two very different questions: The one in the subject line, mentioning *reactive* powers, and the one in the text not mentioning reactive powers Measuring reactive quantities in 3-phase systems is a specialized task well outside the realms of DSP, so you should try and find a newsgroup where those sorts of questions are discussed. Rune
Reply by ●February 28, 20082008-02-28
Rune Allnor wrote: ...> Measuring reactive quantities in 3-phase systems is a specialized > task well outside the realms of DSP, ...I don't know about that. I built some DSP-based power meters to control circuit breakers (for historical reasons, they're called "relays") when I was with Siemens. The question of this thread is one kind that angers; frustrates; saddens -- pick one -- me: "What code do I use to accomplish X." Never mind the code, what method accomplishes X? In this case, how is real and reactive power measured? There are several options here, (three wattmeters or two in a three-phase system, for one example; separate watt and VAR measurements or both derived from a single set of readings for another) none of which have to do with DSP. We hear so many people saying, "I don't understand what it's all about, but I intend to write a program to do it." Rubbish! Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 28, 20082008-02-28
On Feb 28, 3:46 am, "alpere" <alper...@gmail.com> wrote:> sampling frequency = 256/cycle > which method is use complex or real fft for 60Hz current, voltage, power > harmonics measurement? > thanks for any help.alpere I can't say that I understand precisely what you are looking for or that I could provide it if I did. Your posting illustrates that on comp.dsp an unclear question can make those with some demonstrated technical capabilities appear to be abusive language lawyers. Welcome to usenet. You could try to explain you query a little better, but I couldn't blame you if you didn't. Dale B. Dalrymple http://dbdimages.com
Reply by ●February 28, 20082008-02-28
dbd wrote:> On Feb 28, 3:46 am, "alpere" <alper...@gmail.com> wrote: > >> sampling frequency = 256/cycle >> which method is use complex or real fft for 60Hz current, voltage, power >> harmonics measurement? >> thanks for any help. > > alpere > > I can't say that I understand precisely what you are looking for or > that I could provide it if I did. > > Your posting illustrates that on comp.dsp an unclear question can make > those with some demonstrated technical capabilities appear to be > abusive language lawyers. Welcome to usenet. > > You could try to explain you query a little better, but I couldn't > blame you if you didn't.Dale, You probably think I got up on the wrong side of the bed this morning, and you may be right. Still, do you think that asking which of possibly inappropriate methods is the best way to solve a problem makes sense? Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
Reply by ●February 28, 20082008-02-28
On Feb 28, 1:01 pm, Jerry Avins <j...@ieee.org> wrote:> > Dale, > > You probably think I got up on the wrong side of the bed this morning, > and you may be right. Still, do you think that asking which of possibly > inappropriate methods is the best way to solve a problem makes sense? > > Jerry > --Jerry Given the quality of the original post, I think that picking an interpretation and calling 'Rubbish!' is premature. Even from -your- posts I can't say that I know what -you- mean by 'methods' let alone what the actual purpose for them would be to decide if they were 'inappropriate'. To respond to your question, if you don't know what 'appropriate methods' means, it makes sense to ask questions but not to answer them. Dale B. Dalrymple
Reply by ●February 29, 20082008-02-29
Hi all, thanks for your relevance. I can measure current RMS value, voltage RMS value, active power, reactive power, power factor on three phase systems. But i can't measure current harmonics, voltage harmonics, active power harmonics, reactive power harmonics. For harmonics measurement we must use the DFT. And to do it fastly, we must use the FFT. This subject is realm of DSP. But the question is: What way do I use to measure the harmonics? And i want to know: Why energy analyzer shows only 1., 3., 5., ..., 19. (odd harmonics) harmonics value? I have samplings of current and voltage. Samplings form is array of 16 bits integer that array_current(256), array_voltage(256). And, i have to convert from those arrays to amplitude_1stHarmonic_current, amplitude_3stHarmonic_current etc. with FFT. And, i have to convert for voltage harmonics, current harmonics. Active and reactive power is derived from current and voltage. Thanks for any help.
Reply by ●February 29, 20082008-02-29
Reply by ●February 29, 20082008-02-29
On 29 Feb, 07:31, "alpere" <alper...@gmail.com> wrote:> Hi all, thanks for your relevance. > > I can measure current RMS value, voltage RMS value, active power, reactive > power, power factor on three phase systems. > But i can't measure current harmonics, voltage harmonics, active power > harmonics, reactive power harmonics. > For harmonics measurement we must use the DFT. And to do it fastly, we > must use the FFT. > This subject is realm of DSP. > But the question is: > What way do I use to measure the harmonics?I have seen coherence measurements used to estimate nonlinear distortions/harmonics. However, that technique requires the undistorted input signal as reference. Check out Bendata and Piersol's "Random Data" for details.> And i want to know: > Why energy analyzer shows only 1., 3., 5., ..., 19. (odd harmonics) > harmonics value?That could have to do with the way the nonlinearities distort the fundamental. You would need to check with a physical model of your system or analyze the distorted waveform to see why.> I have samplings of current and voltage. > Samplings form is array of 16 bits integer that array_current(256), > array_voltage(256). > And, i have to convert from those arrays to amplitude_1stHarmonic_current, > amplitude_3stHarmonic_current etc. with FFT. > And, i have to convert for voltage harmonics, current harmonics. Active > and reactive power is derived from current and voltage.That's power electronics; I wouldn't know what to do to get what you want from what you have. Rune
Reply by ●February 29, 20082008-02-29
Rune Allnor wrote:> On 29 Feb, 07:31, "alpere" <alper...@gmail.com> wrote:...>> And i want to know: >> Why energy analyzer shows only 1., 3., 5., ..., 19. (odd harmonics) >> harmonics value? > > That could have to do with the way the nonlinearities distort > the fundamental. You would need to check with a physical > model of your system or analyze the distorted waveform > to see why.Most nonlinearities in power circuits arise from magnetic saturation. In the absence of DC, such nonlinearities are symmetric for positive and negative excursions. Waveforms like that have only odd harmonics. (Consider a square wave.) In balanced three-phase circuits, harmonic currents divisible by three cancel in the neutral leg of wye-connected systems. They cannot exist at all in a delta-connected system. Jerry -- Engineering is the art of making what you want from things you can get. �����������������������������������������������������������������������
