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Knackered_lot t1_iqqsen7 wrote

Reply to comment by mastapsi in The US's National Renewable Energy Laboratory wants to make decentralized microgrids as simple to set up and operate as diesel generators, and has created a prototype that is much simpler than existing microgrid technology. by lughnasadh

This is not correct. You may be confusing frequency with voltage.

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mastapsi t1_iqrkx61 wrote

No, it's not voltage. In an AC system, voltage will be determined more by reactive loads and generation than by real load mismatches. If your generators are not producing the right amount of VARs to negate the VARs produced by the system, then your voltage will deviate from your intended system voltage. This is probably not a huge deal on microgrids, since most loads will be unity power factor loads.

Now you can get voltage changes from real load mismatches, but usually you'll trip generators from deviating too far from nominal frequency long before that happens. Rotating generators are very sensitive to frequency, they are designed to run at a specific speed (which correlates directly to system frequency) and deviating too far can cause serious problems, so there is protection on them to trip them offline if they deviate too far from nominal.

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Knackered_lot t1_irrqji2 wrote

Oh ok. I understand the AC generator part of things, but I am less sure about how this frequency works on a renewable energy microgrid. Does the variable frequency work in a way with the AC (capacitive/inductive) reactance equation? for say, you need a lower current so in an inductive circuit, higher frequency -> higher reactance -> higher impedance -> lower current.

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mastapsi t1_irrytcm wrote

I don't think it would have much impact at all. The amount of deviation from nominal frequency is minimal, half a Hz in each direction, which is less than 1%. That's why they are using it for signaling.

Most renewables are designed to run their inverters based on a reference frequency from grid mains. For devices with no regulation capability, there would be no change to how this works. But devices that have some regulation (battery storage, hydrogen, wind) would have extra modules to interpret that frequency signal just like a droop controller would and vary their output to help balance the system.

Plus if you have existing rotating generation with droop control, like microhydro or diesel, they can tie in and still function.

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