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kopi-andi avatar image
kopi-andi asked

Multiplus 2 Charge/Discharge Oscillation

Hey community,

I've got an MP2 installation flawlessly running for months with a Gobel Power 14.3kWh battery pack. I have a MPPT as well as an AC-coupled Fronius Primo. The MP2 is configured in ESS mode and has FW v505 and the Cerbo v3.01. Grid power is measured using an EM112.

Some weeks ago (I turned the MP2 off during vacation) I noticed weird discharge/charge oscillations in inverter mode. They appeared out of a sudden without changing any parameter or firmware version and are so frequent that I don't even see them as clearly in the VRM. But they are clearly visible on the battery as well as in the Home-Assistant DB that gets the values from the Cerbo (BMS connected over CAN) via MQTT.

The test shown here starts with powering on the MP2. In the first minutes there are only some small background loads and the oscillations are quite small. Then I turn on a bigger load (an oven) and the oscillations are quite pronounced.

screenshot-from-2023-08-29-17-09-56.png

The next plot shows the grid power and we can clearly see that it also fluctuates between injecting and drawing power from the grid.

screenshot-from-2023-08-29-17-11-10.png

I've turned the MP2 off around 9:12h.


Any ideas about what might be causing those oscillations?

Thanks

Andi

Multiplus-II
screenshot-from-2023-08-29-17-09-56.png (99.3 KiB)
screenshot-from-2023-08-29-17-11-10.png (121.4 KiB)
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5 Answers
dmsims avatar image
dmsims answered ·

Those graphs are from Home Assistant, do they look the same in VRM ?

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kopi-andi avatar image
kopi-andi answered ·

The graphs in VRM have a too-low temporal resolution. I get a value every minute which isn't enough to see the oscillations. At least that is my interpretation.

1693329550858.png


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derrick thomas avatar image derrick thomas commented ·

FYI while you are logged into VRM logging is in realtime. Next time you are experiencing an issue that you are trying to troubleshoot like this, logon to VRM and just keep the window open. It will begin logging.

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kopi-andi avatar image kopi-andi derrick thomas commented ·
Thanks for the tip. I'll rerun the experiment later tonight and try to see if VRM also captures the changes.
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dmsims avatar image
dmsims answered ·

There has been a lot of discussion about this in the past. A CT clamp provides a much faster response

"Ok just some additional information after completing basic test with the ET112 and 1m CT clamp. Switching on a 3kW load and measuring the dc current with a clip in ammeter. The ET112 took around 10s to slowly ramp up to 60A after switching the 3kW load on and a further 10s to ramp down after switching off ie exporting to grid. The CT clamp reacted in less than 0.5s both switching on and off. The system appears to react much faster with CT clamp and must therefore be more efficient."


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kopi-andi avatar image kopi-andi commented ·
I've noticed the relatively slow reaction time of the ET112 as well in my test (also before noticing the issue I am having right now). I also agree that a faster reaction time would result in a more efficient export/import control. But they were nowhere near 10s. After turning on a load, after ~3s I can see the load in the RemoteConsole and also in HomeAssistant. The same is true for turning it off, takes approx 3s to show up in the RC.
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kopi-andi avatar image
kopi-andi answered ·

I did some more digging and finally came across the "3.5mm jack trick" mentioned in e.g. this post https://community.victronenergy.com/questions/120680/is-anyone-working-on-ac-input-1-not-displaying-any.html

This seems to have fixed the issue.

Still it's unclear to me why this has been an issue after it worked for months without any problem.

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kopi-andi avatar image
kopi-andi answered ·

For reference here is the plot of the power drawn from the battery. I start with the MP2 turned off, then it tries to power the constant load (~350W) but starts oscillating and doing short but high discharge/charges. Then I plugged in the 3.5mm jack a few times and the issue was gone.

1693431490971.png


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kopi-andi avatar image kopi-andi commented ·

And here a post with a much more detailed description of the issue https://community.victronenergy.com/questions/136511/total-overcompensation-with-the-multi-plus-2.html

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