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raphael avatar image
raphael asked

3 Phase unbalanced ESS Grid feed-in MultiPlus-II 48/5000

I resently built a 3-Phase ESS System and hope to get some of my questions answered from the community.

The feed-in into the Grid is not always equally distributed over the Multis. Why is that?

multiplus-ii-3-phase-unbalance.png

As you can also see in the Graph "System - Grid", there is more Grid feed-in on L2 then on L1 or L3.
35 minutes later, the MultiPlus-II for L3 feeds in more power then the other phases.
Can anybody explain that behavior? How is that internally controlled?

load-unbalance-grid-feed-in.pngGrid feed-in: L1 -2336W, L2 -4007W, L3 -1901W

In the thermal image, you can also see the difference.
The efficiency is decreased by the unbalanced Grid feed-in distribution over the 3 phases.thermal-image-multiplus-ii.png

A equally balanced Grid feed-in, would increase efficiency and longevity of the whole system.

By the way...what is the design-life of the MultiPlus-II?
Does it make sense for longevity, to not feed into the Grid and only compensate for the loads in the house? In Summer I can easily produce 50kWh per day and I only consume 10kWh.
Does the lifetime decrease linear to the produced kWh?

Is the stress for the components higher without grid or while being connected to the grid?
Without grid, it sometimes go into overload on L2 while cooking...but not serious overload...just 5300VA.
With grid connected, it takes Energy from the grid instead...no compensation from the other Multis so far...I hope that true L1 + L2 + L3 = 0 phase compensation will be available in future.
(EDIT: A firmwareupdate of the Multis fixed all the issues. Thank you Victron Team!)

System components:

  • 3x MultiPlus-II 48/5000/70-50 230V
  • 2x SmartSolar MPPT RS 450/100-Tr
  • Cerbo GX (Firmware v2.71-1)
  • EM24-DIN Energy Meter Carlo Gavazzi
  • REC-BMS with 16S LiFePo4 200Ah 51,2V 10,24kWh
  • PV: 10,4kWp, 4 strings, each 8 Panels in series (Glas/Glas M60 Bifacial 325Wp Voc=40,22V)

system-components.jpg


Multiplus-IIESS
load-unbalance-grid-feed-in.png (160.0 KiB)
system-components.jpg (2.1 MiB)
thermal-image-multiplus-ii.png (792.9 KiB)
multiplus-ii-3-phase-unbalance.png (79.0 KiB)
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raphael avatar image raphael commented ·

Short update: Sometimes, the feed-in is in a good balance, sometimes not.
What is the reason for that? Is the phase angle of the public grid the problem?


1624454411967.png Bad balance: L1:19% L2:15% L3:66%

1624454790396.png Good balance: L1:33% L2:35% L3:32%

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7 Answers
markus avatar image
markus answered ·

Hi,

The Multi can make one of three decisions in its overvoltage-feedin control loop, it can 1) increase power, 2) decrease power, 3) leave it the same.


Once they reach a stable point, all the Multis take option 3 repeatedly. So depending on what they were doing immediately before, or perhaps also on the distribution of loads that come and go, you could well end up in a situation where a stable feeding in of DC-PV is reached that is not symmetrical.

Best Regards,

Markus

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raphael avatar image raphael commented ·

Thank you for explaining that! It is good to know how it works!
I am sure that victron will work on a improovement one day.

Do you know anything about the longevity of the MultiPlus II and the potential lifetime of the electronics or the designlife under a certain load?

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raphael avatar image
raphael answered ·
The problem is gone now. I guess it was a temporary inbalance with the public grid.

Even with full grid feedin the voltage does not spike over 240V anymore.
Also I use multiphase regulation and after a new firmware update, the feed is evenly distributed over the multis.


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Warwick Bruce Chapman avatar image
Warwick Bruce Chapman answered ·

What is your phase compensation configured as - ESS -> Multiphase Regulation.

Try Individual Phase.

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raphael avatar image raphael commented ·
I tried that for a couple of minutes, it didn't change. But I'll try it again and restart the System.
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David avatar image
David answered ·

Where are you located? The phase compensation setting is important depending on how your usage is metered.

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raphael avatar image raphael commented ·
I am located in Germany.
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Marco Nijholt avatar image
Marco Nijholt answered ·

I have noticed similar behavior on mine ever since i installed a EM24 external meter. I used to use the internal meter as grid meter and there it was pretty much always fully balanced.

I really wish it was balanced equal for efficiency sake. At the end of the day it doesnt matter for metering.

Overview:

1660392276094.png

Internal measuring of the AC-In phases

1660392509319.png

Overview on VRM that includes the grid meter EM24 measured voltages

1660392422329.png


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1660392422329.png (84.4 KiB)
1660392509319.png (24.3 KiB)
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raphael avatar image raphael commented ·

Are your Multis on the latest firmware?

I have the EM24-DIN installed too, but I just connected the whole house
on Critical loads anyways, because of the faster response time.

If I connect the House to AC Loads, it takes a couple of seconds to ramp up the Multis, when the electric stove kicks in. Therefore, the meter still counts some grid consumption, even in summer. And since most stoves are using on-/off- operation for temperature regulation, this adds up to 15 kWh per Month.
Also I set the grid setpoint to -100 W or -50 W to reduce the consumption in summer to less than 2 kWh per Month.

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Marco Nijholt avatar image Marco Nijholt raphael commented ·
Hi!

The firmware is indeed up to date.

My whole house is also on the critical, the only thing thats grid paralel is the 3phase group that goes to my poolhouse for all the pool tech.

I currently still have net metering in the netherlands (salderen) so slow response time doesn't bother me. Also the loads for the pool house are very consistent. Its mostly the circulation pump that slowly ramps up/down and a full inverter heat pump that slowly ramps up as well.

The main thing is that 1 unit is just delivering consistently way more to the grid than the others. And based on the graphs provided by victron, the efficiency graph indicates the more a unit inverts, the less efficient it becomes. Also increasing the temp of the unit makes it less efficient. So having all 3 units equally inverting DC to AC to me makes the most sense.

Could it have to do anything with the power factor? L3 has the cleanest power factor (also delivers back the most) and L2 is the worse power factor (delivers back the least).

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raphael avatar image raphael Marco Nijholt commented ·

I didn't get my hands on a MultiPlus-II 10kVA jet and Victron does not publish any further efficiency curves.
In March, you already saw my post when I tested the 5kVA inverter:
https://community.victronenergy.com/questions/56351/multiplus-485000-efficiency-curve.html

I assume, that it'll be a similar curve for the 10kVA MultiPlus-II.
Since the 10kVA Multis are quite new, some months ago, 3-Phase operation was not even supported by Victron jet.
So I think that time and future firmware updates might solve your problem.

With the 5kVA Multis, there is no imbalance problem anymore.
Also, the efficiency is already fairly good. You get more than 95% efficiency, when the Inverter load is between 10-50% of its maximum load. In your screenshot, the inverters are basically in this high efficiency range.

I doubt, that the power factor causes the imbalance, but I'm no expert in this field.

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Marco Nijholt avatar image Marco Nijholt raphael commented ·

Hmm interesting, what do you mean with they did not support 3 phase operation? I have this system since februari and its always supported 3 phase operation.

I never noticed an imbalance (and even if i look in the historic graphs now) before i switched to a EM24 external meter vs internal, but that also coincided with a firmware upgrade on the multiplusses to v497.

The EM24 can also measure PF so maybe it utilizes that information. I'm not sure if delivering back to grid on a phase where theres less capacitive loads is more efficient. But if thats the case then its possible that can explain the imbalance.

These are the loads without inverting enabled. You can see L1 has a worse factor than L2. But in absolute terms (because l1 only has 200w loads) L2 has clearly way more reactive power. So the phases with the least reactive loads go L3 < L1 < L2. Which also seems to be the order of phases which get the most grid feed in.

Then again, correlation does not mean caussation and I do not have the proper understanding to make more sense of it.

edit:

Another change i realised i made since installing the EM24 is that my pool house used to be connected to the non critical AC out of the multiplus, but now they are Grid Parralel.

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raphael avatar image raphael Marco Nijholt commented ·

Sorry, in the datasheet it states, that the 8kVA and 10kVA don't use VE.Bus communication for parallel... But 3-Phase works.

1660572569304.png

In May, I was at the Intersolar in Munic and had a talk with some victron staff. Back than, parallel operation was not supported jet for the 8kVA and 10kVA model. But it might have changed since then.

My 3-Phase ESS runs very smooth:
1660572923136.png

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raphael avatar image raphael Marco Nijholt commented ·

You chose a "Total of all phases", right?

1660573296450.png


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janvi avatar image
janvi answered ·

For my opinion, the 245 Volt for L2 are a little too high. This touches the maximum 10% limit and power goes up by square with the voltage. Start checking the impedance of your grid connection. Disconnect all Multis as well as all your appliance. Then measure the voltage of each phase, preferably in the night where neighbours are not feeding their PV power. Results should not show that much diffrence. Then take a strong one phase load e.g. 2 or 3 x2 kw heaters what will be ok for a short time with 16 Amp wall outlet. Examine the voltage drop by switching on your the heavy load. The drop should be equal on L1 through L3. Law of Ohm: R=U/I where U is the delta U with and without your load, I is the current of your load and R gives the internal apparent resistance of your grid resulting from your individual grid installation. If you are already over 240 Volt with diffrent feed 1:2, the Multi may consider the limit to avoid over voltage. My experience with asymmetric loads are not only consumers but also PV owner neighbours what feed asymmetric. Close to the grid limits, this may limit your feed. E.g. my Diesel engine with absolutely constant regulated output is normally not able to feed back to the grid at day time. After phase sync in daytime, the currents go down to almost plusmins null. After sun disappeared, 15 kVA or more are no problem to feed back to the grid using the same machine and regulator setup.




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raphael avatar image raphael commented ·

img-20230603-151759.jpg

The MultiPlus-II on Phase 2 is just reading wrong values (AC Loads). The Energy Meter is showing the correct values (Grid). I checkt directly at the clamps of the MP-II...238V on Phase 2.

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schollex avatar image
schollex answered ·

I'm also facing the unbalanced Multiplus loads during feed-in of exceeding PV-power.
To get rid of this, I wrote a Nodered-flow which averages the power on my L1-Multi and compares with the average power of my L2-Multi. If the delta is >200W, this flow disables Feed-in of exceeding Power and re-enables this after 1 sec.
Works fine for me.

My workaround proves that I don't have a problem with the surrounding of my installation (PV-enabled neighbours, my house load). Instead the Victron-control-logic causes this issue.

Both Multis are up-to-date, as well as Venus 3.2.

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