question

Nikolas Stathis avatar image

Balanced generator currents in Three phase off grid system with Quattros

Hello all,

we are designing an Off-Grid solar system upgrade due to higher power demand.

The system now consists of :

1xQuattro, 1xGen (wired as single phase), 2x PVstrings, 2xMPPT, 1xBattery String

After the upgrade :

3xQuattro, 1xGen (wired as three phase), 4x PVstrings, 4xMPPT, 2xBattery String

The upgrade system will be controlled and monitored by a GX control unit (Cerbo-GX).

The generator is used as a backup power source, to feed the loads and charge the battery string, and it will be rewired back to three phase to gain some power lost by the single phase wiring.

The loads are single phase ones, and will be evenly distributed to the three phases by their nominal power, but the actual power distribution depends on the customer usage, and time/day.

My concern is the balance of the generator currents when the loads are not balanced.

So, is it possible with the Quattros to equalize / balance the three AC input currents (from the generator) while feeding loads on their outputs?


In the book "Energy Unlimited"

https://www.victronenergy.com/upload/documents/Book-Energy-Unlimited-EN.pdf

page 67, example 12.3.2, we can see the statement :

"One attractive feature of the Multi’s is that they will automatically balance the load of the generator: the Multi’s will take most power from the phase(s) which otherwise would have the smallest load."



What is saying there ?

(is this the feature I am looking for, or I am reading what I would like to read, is this possible with the Quattros?)


Thanks


Generator3 phase
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2 Answers
JohnC avatar image
JohnC answered ·

Hi @Nikolas Stathis

In this respect the Quattros should behave identically to the Multis.

Usually a current input limit would be set, the loads passed through, and the remainder used for charging up to that total limit. Having 3x set up this way they should balance out the 3 phases very well.

But that's while the batteries can accept their portion of it. I don't know what happens once the batts reach Absorb and the charge demand starts to back off. Maybe irrelevant if you'd shut down the genny around then anyway?

Frankly though, to me it seems a shame to have to go 3~ when 1~ helps keep offgrid simple. But it is as it is. Just make sure you order the exact same units so they can be paralleled up as required..


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Dear John, thanks for the reply.

A 1ph. system is definitely easier to configure and install than a 3ph., but it is a shame to loose some 30% of the generator nominal output power. The project's objective is to increase the system's power.

Your idea to use the input current limit setting (PowerControl feature) is quite nice and simple, but the difficulty would be to set the right current limit value. It seems this value has to be automatically adjusted, depended on the total load, the current from the solar regulators and the maximum charging current.

As the load changes, and as the available power from the solar regulators changes, the generator current limit should be changed accordingly.

And of course, the generator may stop when the batts reach Absorb phase.


Nikolas Stathis avatar image
Nikolas Stathis answered ·

Is there a way to accomplish an automatic current limit adjustment in relation to the total load, solar charging current and maximum charging current?


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