question

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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Hi @Keith Arnold

What kind of batteries are you using?

And what is the VRM id?

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

I have 2 x Huawei ESM48100.

17_Perth

additionally I notice the moment it trips the multi inverter overload and battery low (almost as if there is a short circuit?) inverter load only about 500 W or less, so far from overload.

I have seen that it did start charging the other day when we had power shedding. We scheduled for load shedding at 8 am SA time this morning.

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4 Answers
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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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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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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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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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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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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