On connecting renewable energy sources (wind, PV etc) to electric power grids, it is necessary to estimate the grid angle at the point of common coupling so that power electronics converters can be provide decoupled control of active and reactive power. Several techniques are there to estimate the grid angle and frequency. These techniques are different in its speed of response, its accuracy, its ability to deal with harmonic distortion and mostly important their ability to support ride though operation during grid faults. The question is:
How can we establish a benchmark to assess and compare the performance of these different techniques ?
(to clarify the issue: For example in sensorless speed control of drives we can consider that a position and speed sensor can provide a benchmark data for assessing the accuracy of estimated position and speed)
There are indeed many possibilities. However, the question is not what it should be but what you pay for. In low voltage, if you reduce the rms in your own conductors you will need less power. But while using a PFC, you may introduce may be 3% loss and pay for it, it is probably more than the losses in your wires.
In industrial cases one pays for real power and reactive power, in the way the meters measure it, so by 15 minutes averaged.
In fact if you inject harmonic power into the grid, it reduces your energy bill, if you absorb harmonic power you pay for it, it is a shame...
I discussed the problem of harmonics in that paper:
https://www.researchgate.net/publication/224600346_Fundamental_tarification_of_electricity?ev=prf_pub
In fact one rather should pay for the fundamental power, not for the total power you receive....
Also the power factor gets a strange definition when you look at how the electricity is tariffed...
Conference Paper Fundamental tarification of electricity
Thanks professor for the valuable information in your answer, but it would be greatful to elaborate more on the many possibilities especially in case of unbalanced grid faults
Please recall that the grid angle which I mean here is not the displacement angle between the fundamental voltage and current waveform, but the angle which is used to define the three phase fundamental voltages:
Va= Vpeak × sin(theta)
Vb= Vpeak × sin(theta-2*pi/3)
and so on
The concept of phase measuring unit (PMU) is helpful for you.In any fault condition is their then you have to convert the unsymmetrical component to symmetrical component.Like ABC into positive,negative and zero sequence.Generally the negative and zero sequence are neglected in different fault condition(L-L-L,L-L,L-L-L-G). Then you can measure the phase angle of positive sequence component.
Osama,
I agree with Debasis that you will require PMU's rather extensively for your investigations. I would like to add that you may add synchrophasor techniques that are currently being used for state estimation and protection.
But I doubt if a satisfactory benchmark for this will be available anywhere. The reason is that techniques that you mention in your question have case specific problems related to aspects like
So all put together, does a broad benchmark at all exist ? I wonder !
-Sanjay
Thank Sanjay, although grid frequency is cotinuously changing according to the balance between total generation and total load, regulations restrict the window of change to some tight limits. Active control of grid frequency helps maintaining it within limits. In large power grids, can we consider frequency stable enough as a benchmark rather than admitting the fact that no satisfactory benchmark is there anywhere?
Even if we can't accept the hypothesis of constant frequency, we can lean to an instantaneous mean of frequency measurements taken from multiple and scattered locations across the grid. The integration of this signal knowing the initial condition of grid angle at any point of concern ahead of fault occurence or large load disturbance can this provide us with a benchmark for grid angle at the point of concern ?
A bit subjective, Osama.
I guess points like the three already stated by me will decide whether the answer to your last question should be a "YES" or "NO" !!
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