question

Nico Bayer avatar image
Nico Bayer asked

DVCC Limit charge current not working with grid feed in enabled

My System:

ESS with:
3x Multiplus II 48/5000
2x MPPT 250/100
1x Fronius Symo 15 on AC out
8x Pylontech US3000
Cerbo GX

I have a problem with the DVCC feature "limit charge current". I have set the max charge current in DVCC to 60A.
If i enable grid feed-in (AC & DC) the system ignors the max charge current and charges up to the max current of the pylontech battery 296A.
With grid feed-in disabled everything works as expected, the system limits the charge current to 60A.

Is this normal? Am i missing something?



DVCC
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I also have issues with dc feed in. When the batteries are full and BMS brings down the Charge current, the MPPTs run full on, but my multi doesn’t invert that power and feed it into the grid, so the power goes into batteries, against the DVCC current limit. I have to disable DC feedin to stop my batteries over charging.

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3 Answers
Nico Bayer avatar image
Nico Bayer answered ·

I noticed that the when "limit charge current is enabled", the MPPTs will ignor the max charge current, but the multiplus will stop charging if the max charge current is reached.

So the ve.bus system uses the max charge current, but the MPPTs on ve.can only if feed in is disabled.

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This is a shot in the dark, but probably worth trying as part of the process of elimination. Connect the MPPT’s via ve.direct and see if that makes a difference to the behaviour. Also look at the D.C. voltage readings in the device list on the Cerbo, and see if there is are large differences between the D.C. voltage measured at the MPPT’s, Multi or the Pylontech itself

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Same here. Also, the max. charge current set by the BMS is ignored by the MPPTs when operating in the feed-in mode. Saw over 120A when the BMS only requested like 20A. My battery is also a pylontech. The dealer did not seem to care too much and gave me a written statement that this is fine and does not cancel the warranty as stated by pylontech, so I did not pursue this any further...

The regulation is currently broken...

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Hi Lukas

That does not seem right. Is this just a short spike or continous?

My system uses the charge current set by the bms, even with feed in enabled. When the battery is nearly full und the BMS reduces the current, the multis start to export the power.

This works as expected. Only the manual reduction of the max charge current is ignored.

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Hey Nico,


Hm, thats strange. I regulary saw 120A+ when the BMS commanded around 40A for about a minute or two. There was ne regulation, since the mppts drove the current up and down with solar availability...eventually the voltage is high enough for the inverters to kick into feed in, but the behavior is totally different with feed in disabled. Then the current limit is precisely followed immediatly. I only have MPPTs (one RS and one 150/60) anf no external inverters...

Bit as I said, the dealer could not care less, which is also awkward...if the balancing gets damaged due to excessive current, they have to replace the battery...and I dont get why you would risk that and explicity give that statement...AFAIK the issue was also escalated to victeon but then the ticket was rapidly closed...


Sorry for typos...wrote this on my mobile...



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Daniël Boekel (Victron Energy Staff) avatar image
Daniël Boekel (Victron Energy Staff) answered ·

Hi all,

When 'feed in excess DC PV power' is selected, the MPPT's run full power so as much solar as possible can be exported.
If this leads to a too high battery charging current, the system should be designed or configured differently, sometimes the battery is chosen to small for the available charging power.

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Hi,

my battery can handle the current, thats not the problem. The system is stable and works fine as it is.

My intention is to limit the battery charge current, so the battery does not charge to 100% during the morning.

My system is set up in a way that my energy provider can reduce the feed in power of my system remotely. This happens mostly in the afternoon with realy good weather. In that case i want to have spare battery capacity that can be charged when i'm not allowed to export.

Is there an other way to disable charging and just export all pv to the grid? My idea was to automate that by setting the max charge current over modbus by my energy management, that can look at the weather forecast and knows how much sun it hast to expect for that day.

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Hi Nico,


Ah now I understand what you want to achieve.

I think the best way to do this is to use Venus OS Large and make some rules (set grid setpoint based on SOC / PV / time?)

https://community.victronenergy.com/questions/73741/venus-os-large-node-red-and-signal-k.html

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lukas avatar image lukas Daniël Boekel (Victron Energy Staff) ♦♦ ·
@Daniël Boekel (Victron Energy Staff)


Sure, we understand that the MPPTs will run full-tilt when the feed-in is selected...but nonetheless, limits set by the BMS should be followed, right? Usually, there is a reason why a lithium BMS commands lower charge currents (e.g. balancing)...and to much current can (and eventually will over time) damage the balancing dump load inside the battery....

I see currents of over 120A when the BMS tells the installation it does not want more than 40A...and that's for an extended period (minutes...which is forever in electronics...). When feed-in is disabled, the MPPTs track the limit perfectly and almost instantly.

Having reported this to my dealer, I think the issue was also reported to victron but then the support ticket at the dealer was very rapidly closed and they told me that the pylontech battery is fine with the dramatic overcurrent during balancing. But maybe someone has a battery type which does not allow this...

Anyway, this is not how the system should behave with a BMS. Best case: Not pretty and anoying. Worst Case: Extremely Dangerous.


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Hi @Lukas , can you explain in what circumstances the BMS only allows low current while target voltage (CVL) is not reached?


What size batteries vs inverters do you have?

Maybe you can limit the maximum charge voltage in DVCC menu to prevent this situation?

PS your question is different from @Nico Bayer

Also, your battery will protect itself when things go out of boundaries.

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lukas avatar image lukas Daniël Boekel (Victron Energy Staff) ♦♦ ·

The pylontech BMS gradually reduces the max. allowed charge current when it approaches 52V, and reaches around 40A in my case (4 modules, 200Ah, max. rec. charge current 100A 0.5C, allowed up to 200A 1C). I have 3x MP-II 3000 with a 6kW dump load heater and a feed-in limit of 2kW. The multis can sink 8kW (limited only by the multis itself when they get hot), which is more than the installation currently can provide in terms of PV power.


screenshot from today:

1624350431816.png


I already limited the charge voltage, since the overvoltage feed-in adds 0.4V, so i lowered the charge voltage to 52.2V, in order to compensate a bit. That seems to work but has nothing to do with the voltage control. From my last tests, I think the current limit also had no effect when the dc feed-in was activated.


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1624350431816.png (67.8 KiB)
lowering charge voltage in DVCC settings overrides the batteries CVL
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lukas avatar image lukas Daniël Boekel (Victron Energy Staff) ♦♦ ·

Oh ok, good to know. I'll remove the setting and retry. If we have a sunny day tomorrow, I'll report back immediatly.

Is this documented somewhere?

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@Daniël Boekel (Victron Energy Staff)

Oh, just saw that you actually wrote "CVL". Not talking about charge voltage though...the pylontech BMS commands a max. charge current. So is the charge current limit also affected by the voltage setting?

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2.71 did not solve this. Any news? Or should I open a new thread for this issue?
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Hi @Daniël Boekel (Victron Energy Staff)

Today I performed a test on the "Limit Charge Current" feature. In my configuration I have an AC-OUT attached 3-phase Fronius inverter (6kW) and a DC-attached Victron MPPT (5kW-firmware 3.05). Battery is a BYD LVL, VenusOS on version 2.72. Setup as 3-phase system.

After having set the charge current limit to a very low value (e.g. 10A, 5A or 0A) the Fronius inverter power got fully redirected instead to battery into grid. However the MPPT continued pushing all energy into battery. So the MultiPlus-II did not invert that energy and directed that into grid as well. MPPT shows "External Control", so it should be actually under control of DVCC.

As I understood your explanation with activated feed-in option, the MPPT should continue with max capacity, but the enery should be inverted to grid instead of pushing that to the battery.

Maybe there is a bug in currrent releases?

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Hi @ThomasW.

I don't know your other settings, is there a feed-in limit set?

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thomasw-1 avatar image thomasw-1 Daniël Boekel (Victron Energy Staff) ♦♦ ·

Hi @Daniël Boekel (Victron Energy Staff) ,

Yes, a feed-in limit of 7.800W is defined (prescribed by electricity supplier).
Described behavour occurs also with minimal inverter/MPPT power (e.g. <1.000W).

If you require more configuration details or access to the system please let me know.

  • MultiPlus-II 48/5000/70-50 in 3-phase (firmware 481)
  • Grid setpoint defined at -30W
  • Multiphase regulation on all phases
  • Fronius Symo 6.0-3-M (firmware 3.16.7-1) with 6 kWp
  • Victron MPPT VE.can 250/100 rev2 (firmware 3.05) connected via VE-Bus with 5kWp
  • BYD LV 15.4 - BMS connected via CAN-bus (firmware 1.20)
  • VenusGX (firmware 2.72)

Motivation of the requirement is to externally defer battery charging during that phase when feed-in limit is expected. Prediction uses PV forecast by solcast.com.

1627118209671.png

1627118094389.png

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Hi @ThomasW.

As you can understand, this would be very difficult to implement in our ESS algorithms.

For such advanced requirements, there used to be only the option of using ESS mode 2 or 3 (external control),
https://www.victronenergy.com/live/ess:ess_mode_2_and_3


but now there is also the option of using 'Venus os-large':

https://community.victronenergy.com/questions/73741/venus-os-large-node-red-and-signal-k.html

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thomasw-1 avatar image thomasw-1 Daniël Boekel (Victron Energy Staff) ♦♦ ·

Hi @Daniël Boekel (Victron Energy Staff) ,

Thanks for your reply.

Yes, I actually wanted to implement my solution exactly by the functionality via ESS-Mode 2 that you described, in particular via Modbus register 2705.

However as I tried to explain, the "ESS charge limit" (register "DVCC system max charge current") only reverts the AC-OUT attached Fronius inverter power into grid, bot not that power from the DC-attached Victron MPPT.
The MPPT related power continues to flow directly into battery.

Since @Nicko Bayer's problem seems to have potentially the same route cause, I posted my problem in that post.

When that issue gets solved, my node-red based implementation should be functional. Therefore I would appreciate if Victron support and/or you spend some time in fixing this issue.

1627218951885.png


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Hi @ThomasW.
I think you need to combine that with disabling register 2707, you have to regulate by controlling 2700

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thomasw-1 avatar image thomasw-1 Daniël Boekel (Victron Energy Staff) ♦♦ ·

Hi @Daniël Boekel (Victron Energy Staff) ,

Your proposal would actually expect to replace wide parts of actual ESS functionality. This approach works only delayed and not satisfactory.
After ESS influences the energy-flow, the manual correction settings takes again a few seconds to contra-act against unwanted engery flow. Overall the outcome is not time-responsive, in particular in case of changes power consumption.
Therefore your proposal cannot be a reasonable approach.

From my point of view current behaviour has to be considered as a bug and Victron should fix the actual ESS functionality, so that with charging limit setting not only AC-OUT attached inverters are redirected into grid, but also the MPPTs.



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lukas avatar image
lukas answered ·

Hi,

for me, the issue withe the DVCC completely ignoring the BMS max. charge current seems to have vanished during one of the most recent MP-II firmware updates - don't know which one solved it, since I skipped some versions, but I'm currently on 490 and the inverter seems to properly dump power towards the grid (overvoltage feed-in) as soon as the Pylontech BMS signals a lower max. charge current. Have to monitor this over the upcoming days (PV power becoming available again after the winter) but so far it looks very promising. May I ask what exactly was changed? Was this fixed while doing all of these other VeBus BMS things lately?

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