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kaffeetasse asked

Flimsy regulation of frequency shift & Charge current limitation in ESS offgrid mode

I have a system running with a Multiplus II 3000/48 and 8kWh LiFePo battery, and a Fronius Primo 3.0-1 PV inverter. The Microgrid setup on the Fronius is active and the system is working properly overall, also the power reduction via frequency shift works in general.
However, I find the regulation of the frequency shift to be not optimal. While the rate of frequency change was mentioned many times, another problem is the amount of frequency shift.

Since the Multi can provide 35A max. to the battery, that is about 2000W AC in, it's never neccesary to lower the power of the Primo below that 2000W, hence the frequency should never have to rise above ~51.6Hz (unless the battery voltage reaches it's maximum).
However if the AC load or sunlight is fluctuating only a tiny bit, the charging current will rise above 35 Amps and the Multi will "panic" and rise the frequency to 52.7 instantly, killing the Primo and it will take a long time to return to normal, which is in most cases at ~51.1 to 51.3Hz with a bit of AC idle loads.

Why is the regulation this way? The Multi knows the maximum PV inverter Power is 3000W, so technically it should know that rising to ~51.6 Hz would be enough, even in the worst case.

Since there doesn't seem to be a way to solve the problem directly, I've tried to lower the charging current, so the regulation has a bit more room for error. However, I found that neiter lowering "Charging current" setting to 33 Amps in the calibration, nor setting a "Charging power limit" in the control settings is affecting this regulation in ESS - No grid mode, it always tries to maintain 35 Amps.

Why are these settings only working while connected to a grid?

Thanks for your help!

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@Kaffeetasse Is the PV connected to AC in or AC out? Also ES is not designed for off-grid unless there is an exception for Fronius inverters?

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@Jason - UK is correct if you are off grid (or using an intentional islanding system) ESS is not deigned for that.


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