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Keith Arnold avatar image
Keith Arnold asked

Multiplus trips in inverter mode, why?

I have a Multiplus and Fronius AC coupled on AC out1. Li-ion Batteries.

When grid fails the inverter takes over.. Fronius continues. as soon as the PV power is higher than the load everything trips, including the ccgx. then the inverter starts up again and restores power on AC out 1. Primo sees life and switches on... bang, everything trips.

if i add a load the the system (heater) then everything is ok. The frequency shift is set up correctly. maybe just not fast enough to reduce pv so that the inverter stays inverting.

So can this system not work in my configuration? using the excess pv to charge while grid is off? Seems as soon as the multi changes from inverting to charging the fronius loses the supply it is latched to.

AC PV Coupling
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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ commented ·

Hi @Keith Arnold

What kind of batteries are you using?

And what is the VRM id?

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

Hi @Keith Arnold

Ok I've looked at the system, your batteries are either empty, disconnecting or defective they seem to hover around 48-49 volts most of the time, I don't know these batteries and how your system is setup, but I'd first check charging parameters.

Do the batteries have a CANbus or other BMS interface?



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Keith Arnold avatar image Keith Arnold commented ·

Check please this morning. We had grid outage from about 8 am. I was out. It seems it tripped a few times then came on line for a while. Output frequency shows it to be controlling the fronius. Not much charging going on..!. Then for some reason it tripped and did not come right. Every time the fronius comes on line, bang, it trips. KWhen I got back I switched my fronius off until grid was back.

if I load the system then this issue does not occur even if grid is off.

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Keith Arnold avatar image Keith Arnold commented ·

We on load shedding. So system tripped again. I have put a heat on (nice sunny day in summer). Now system is on. But just supplying the load and a trickle charge. Frequency shift is working.

note though that with 53.5 v on dc the battery is not taking much amp so maybe there lies the issue? However, no idea why it trips in the way it does if there is low load. Seems I must select a load to come on when grid is off.

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Keith Arnold avatar image Keith Arnold commented ·

Good day. So yesterday evening we were scheduled for load shedding at 4 pm. So i had a look at how the Multi will handle it. the Solar from Fronius was in the order of 1.5kW, fluctuating due to light cloud cover. Multi was charging at one stage 1.2kW, load was about 500W.

When mains dropped there was a blink of a light i had on , the Fronius reacted to this by dropping the line. The inverter continued to supply the load, about 300-400 W. The Fronius was busy re-synchronizing. As soon as the fronius came back on the system tripped. Low battery? it is really as if something causes a momentary virtual short. Immediately inverter starts inverting and all is good. Now i switch the PV input to the Fronius off, but this is not right.... The load shedding is for 4 hours and the battery continues to supply load.

So i do not think it is the battery at fault here. there is something that happens at the moment charging should start that causes the problem? it is so quick i would need a high speed recorder to capture exactly what is happening.

Yet, there has been a time when i was not home. and eventually it did not trip. i could see the output frequency controlling the fronius, but with little to no charging taking place. and for whatever reason it started tripping until i switched PV to Fronius off.

I am going to add a charge controller on the DC bus next week. See what happens. while mains is on i have no trouble. charging, discharging, all good.

Any thoughts on the issue?

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Daniël Boekel (Victron Energy Staff) avatar image Daniël Boekel (Victron Energy Staff) ♦♦ Keith Arnold commented ·

Hi @Keith Arnold

What happens:

-AC is lost, so all PV power has to be put into the batteries before the frequency shift is 'done' and PV power reduced, you can see a spike in the DC voltage.

Above might be preventable by charging the batteries less full, so there is a bit of a buffer where energy can go to for a short time until PV throttles back

-After PV has shut down, your battery drops to a very low voltage, probably the BMS disconnecting it, this might be because of the previous voltage spike, but I can't be sure.

Please consult your battery manufacturer on how to properly setup the system so it works as it should work.

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Keith Arnold avatar image
Keith Arnold answered ·

They have canbus but not compatible with victron. So the multi is the only charger /bms on the system.

under normal conditions there does not seem to be an issue. Only when grid is off.

we had load shedding this morning from about 8 am. Eventually I just switched the solar off, then the inverter continues, no problem.

the batteries have different charge and cut off volts than normal Li ion. So ess is set to suit the battery.

yesterday pm the battery was very low although it was 80% soc. When grid came back i lifted minimum soc to 100 so that it could get a full charge.

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

Hi Keith,

I think your SOC readings are way off, so best to first fix that.

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Keith Arnold avatar image
Keith Arnold answered ·

Hi Daniel. It seems the battery upper voltage is 55 V, probably disconnects until the voltage is in limits an reconnects. So I am going to see what happens if I run my battery lower. The 2 combined should take 100 A, to sure at what volts.

not sure this would help. But if the mains fail would it be quick enough to immediately send 53 hz, or on fronius zero feed in set point of zero. Then ramp up solar according to load. ( by the way why not just stick to the normal fronius zero feed in control? And not do the frequency shifting.) which one is the fastest to react on?

i am also not sure at what stage the fronius drops the line? There seems to be a very short gap in ac out 1 when mains drops and inverter kicks in. Would that make the fronius resynch?

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manoj avatar image
manoj answered ·

@Keith Arnold did you sort out this issue


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Harry Petrakis answered ·

@Keith Arnold did you manage to sort out the issue, having the same problem. Thanks

Hi Keith,

Am having the same issue. Have a Fronius 8.2 Primo on AC Out1 connected to two in parallel Multiplus II 48/5000/70, one a master the other a slave using a Cerbo GX and connected to Two UP 5000 batteries. As soon as load Shedding starts the Fronius will power and when the PV wattage is reached and exceeded it trips.

What was the solution.

Thanks


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Keith Arnold avatar image
Keith Arnold answered ·

Not resolved. in your case it might be the factor 1 rule, which has 2 parts to it. the kW rating you have 10:8.2, so that should be ok. but on the minimum battery one needs 4.8 kWh of battery (100 Ah at 48 V, Li-ion) for every 1.5 kW Fronius. So, in your case of 8.2 kW Fronius you should have 26.24 kWh battery (4.8*8.2/1.5), minimum.

Now even if you have 26 kWh capacity battery and it is full, there is still going to be a trip because there is nowhere to put 8 kW of energy when grid fails and the frequency shift reduction is not quick enough to reduce Fronius output.

I have 4 kW Fronius and 20 kWh Battery (required is 4.8*4/1.5=12.8). but these batteries can't seem to take a sudden overvoltage increase around 60 V plus. Still want to measure with fast max/min fluke 187 to see exactly what happens. If there is sufficient load on out 1 it is ok so I have toyed with an idea to bring in a dummy load when grid fails, just not sure it will be quick enough. But i have also found that if the grid fail change did not result in a trip then some stage sudden load change can trip the inverter.

An install i designed with 2x5 multis, 4.6Fronius, and 6 us3000 Pylon, has no problem. Another system design i added a 3.6 kW Fronius on 2x3000 multi (24V) and has 4 x us2500 Pylon (on 24V system need 200Ah per 1.5kW Fronius), also no problem.

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Harry Petrakis answered ·

Thanks for taking the time to reply Keith, what’s wired though is that all worked perfectly well for around 11 months till the last firmware upgrade from V497 - V500 on the Multiplus II’s; where I lost the ESS assistant.
It was working awesomely with our South African load shedding issues.

The idea was that I would add two more batteries in due course to allow for a total of 4.8K W/h x4 thus for a total of 19.2 KW/h of back up.

Thanks again for the reply


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Keith Arnold avatar image
Keith Arnold answered ·

ok. if it was working then there could well be something in the firmware update. should not lose ESS assistant. make sure that is back and set up correctly on the frequency shift, the default is normally correct.

If the previous firmware worked without issue, then it might be good to reinstall that. i had understood that there has been issues with certain firmware, not sure about this one? if you have used VE Flash before you can go back, it's tricky, but once you master the switch off, switch on sequence it works well.

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Keith Arnold answered ·

By the way, what was your previous firmware version?

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Harry Petrakis answered ·

Hi Keith, previous firmware version on the Multiplus was V497, which when I upgraded went to V500.
Thanks

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