Microcontrollers > Microcontrollers/General
Dynamic demand project(s)
DamonHD:
Right, I've started *another* project (I have too many going):
https://sourceforge.net/projects/dhddd/
The aim is to build prototypes that will make individual houses/appliances more grid-friendly by reducing instantaneous power demand when (a) grid frequency drops and/or (b) the house is not exporting from local grid-tied microgeneration.
This should basically help make the house import less from the grid especially when the grid is stressed.
But this could also help with big off-grid systems by avoiding them tripping if too much load goes on at once and/or the microgen drops, eg the sun briefly goes behind a cloud.
In particular I want first to try with an ordinary electric (tea)kettle, then may also try with my dishwasher.
I may build it with PICAXE or AVR/Arduino for the microcontroller element, and it'll have a radio module, transformer for power (and crude voltage/phase sensing with current clamp at consumer unit), and meaty zero-crossing SSR for appliance control.
Nothing to see yet, but a great chunk of the design will be cut-n-paste from elsewhere!
Rgds
Damon
SparWeb:
Frequency-dependent load shedding? Cool idea. Stop giving them away before you start the patent applications.
What's wrong with another project? If you double the number projects that you say you have, and I stop half of the projects I've recently started, then I'd still have twice as many as you.
So assuming a +/-1Hz hysteresis: monitor frequency, and if at 50 Hz act normally, if below, say 49Hz, stop the discretionary things, if above 51Hz then start those things that have been delayed.
Are you sure the grid frequency is a suitable measure? It sounds good on the surface, but my reflex is to think of the coal-fired steam turbines slowing down as the city's load goes up. In a micro-grid situation it might be different.
DamonHD:
Hi,
I have a bunch of data that says grid frequency is a good measure of some types of urgent trouble, and this is already used as a signal for automatic load shedding (to the tune of ~2GW in the GB I think).
But the tolerances are tighter than +/- 1Hz:
--- Quote --- An analysis of figures supplied by National Grid for August 2008 (.xls) (a frequency sample every minute for the entire month) indicates only one sample out of nearly 45,000 potentially below the operational -0.2Hz target, but ~3% at or below -0.1Hz (ie frequency ≤49.9Hz) and ~17% at or below -0.05Hz (ie frequency ≤49.95Hz).
Thus if dynamic demand control in domestic appliances is to be of help with (and reduce the cost of) 'balancing' of today's UK grid, it would have to start to intervene before the -0.2Hz operational limit. Somewhere between one half and one quarter of that limit looks plausible, especially if the response can be graded and smoothed, where it will help a small proportion of the time but with the current/normal grid mechanisms doing the fine tuning.
--- End quote ---
http://www.earth.org.uk/note-on-dynamic-demand-value.html#when
Already a patent minefield I'm sure, but the balancing with local PV microgeneration may be useful a much higher fraction of the time, and the randomised part of it should help to ensure that the local substation sees a fairly smoothly-reduced load from a number of houses/appliances downstream of it using the technology.
Anyhow, all idle talk until I do it. May make up a generic design and PCB first to put off having to think too hard for another fortnight!
Rgds
Damon
Larsmartinxt:
Interesting Project.
I'm sure that you've found this http://www.mainsfrequency.com/
DamonHD:
Yes, not our bit of the grid, but talking about the same thing.
Rgds
Damon
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