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marekp avatar image
marekp asked

How to ajust energy feeding to grid to keep grid voltage below 253V?

Is there a way for the system to adjust grid feeding per phase in such a way that the amount of energy fed to the grid be controlled by the grid voltage on each phase?

The more my system feeds the grid the higher the grid voltage gets.

When 253V is reached PV inverter turns off and waits for the grid voltage to drop below 253V. It is enough for one phase to reach 253V for the all phases to turn off.

Can the system redirect power from phase with the highest voltage to the phase with the lowest and this way avoid turning PV inverter off. If transferring power is not enough to avoid grid over-voltage, freqency shifting could be used to lower the PV power.

gridvoltage
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4 Answers
Robert Riebli avatar image
Robert Riebli answered · 
Good day

The following will cause high voltage. You are far from a transformer or your feeder is too small. Or the power delivered to the grid is too high, then the voltage is increased.

The question is, how much power was allowed by the grid operator to feed into the grid? Are you among them? If so, talk to the network operator.

An improvement could possibly also be possible with cos phi specifications in the inverter.


Greetings

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marekp avatar image marekp commented ·

@Robert Riebli

Thank you for your input.

I have 3 phase grid and I am allowed to feed 12kW total to the grid.

Talking to my network operator is pointless because he uses the grid voltage to control how much power is fed to the grid from PV installation. Cheap and dirty. Grid voltages at night are at 245 -250V.

The grid quality is so poor that sometimes only feeding 2kW results in grid voltage to increase above 253V and sometimes above 260V, measured at the grid junction box.

My feeder is big enough because I only get 0.5V drop when transferring 4kW.

My question is, can the system control power fed to the grid not only based on the "maximum grid feed" or "Grid set point" but also based on grid voltage? Preferably phase by phase with power balancing between phases.

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Robert Riebli avatar image
Robert Riebli answered · 
Aha interesting, the power control via the mains voltage.
Are you absolutely sure about this?
In peripheral regions with long lines, the voltage automatically increases when the power is fed in. And the high voltage is also problematic for other devices.
In Switzerland, the grid operator must guarantee + - 10 at the grid connection point.
208-253 v

Three-phase grid-connected inverters basically feed in the same amount of energy on all 3 phases, this is due to the design.

If Victron could do anything, it would be to throttle the overall power via the mains voltage.

This would then have to be done using the PV assist with Fronius.

But I don't know if it's possible now. I do not think so.

It's a mains voltage issue, I would really check that with the mains operator. Since they were allowed 12 k
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marekp avatar image marekp commented ·
@Robert Riebli

As I said, discussion with my mains operator is pointless.

It is normal situation that the voltage of the grid goes up when PV is feeding it, but when you start from 245-250V it is closer to 253V than when you start from 230V.

In Poland grid operator must "guarantee" that average voltage in 10 minute intervals in 95% of those intervals during the week must be within the 207-253V. So you can see that for 8 hour in the week the voltage can be anything they want. Even 16kV.

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shaneyake avatar image
shaneyake answered ·

With External control anything is possible.
If you have NodeRed running on a Cerbo or GX device it is pretty easy. Also doable via Modbus or MQTT. Control Loop time will be around 5 seconds tho.
You could set ESS to external control and then have your own control system that manages the inverters.
You could have it setup so that if voltage less than 250V, ESS operates like normal but if greater than 250V then you limit the amount each inverter is allowed to export based on voltage. This can be done on a per phase level. You could also totally disconnect your system if voltage greater than 255V and SOC is high.

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marekp avatar image marekp commented ·
@shaneyake

Than you for this info.

It looks that I will have to learn more about this external control in ESS.

Is there some literature on the net about it?

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shaneyake avatar image shaneyake marekp commented ·

Here is Victrons Mode 3 manual, which is full external control. Manual is written assuming modbus control but NodeRed is easier if you run the Large Firmware.
https://www.victronenergy.com/live/ess:ess_mode_2_and_3

Large Firmware
https://www.victronenergy.com/live/venus-os:large
I can also help you remotely if you are using the large firmware with NodeRed as it is remotely accessible.

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marekp avatar image marekp shaneyake commented ·

@shaneyake

Thanks allot for the info.

I will look into it after complete overhaul of my system.

I will be replacing all inverters and GX unit so now I will be busy. At the moment I have GX inside EasySolar-II and will be changing this GX to Cerbo.

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shaneyake avatar image shaneyake marekp commented ·

If you are going to replace your inverters, rather use Multiplus-II 48/5000. They just seem to always work. Also 3 inverters is going to give you less hassle than 6.

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marekp avatar image marekp shaneyake commented ·
@shaneyake

But even with 6 MP-II/3k I had 8 overload warnings in the last 6 months.

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shaneyake avatar image shaneyake marekp commented ·
Was the overload warning while grid-tie? Because that is normal if they are running at max power.


If you look at your actual load data, what are your peaks?

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marekp avatar image marekp shaneyake commented ·

@shaneyake

I quickly looked at my VRM data and found this.

screen-shot-2022-04-25-at-100108-pm.png

and getting closer

screen-shot-2022-04-25-at-100453-pm.png

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screen-shot-2022-04-25-at-100453-pm.png (36.1 KiB)
shaneyake avatar image shaneyake marekp commented ·
You will have to zoom in to see the actual peaks as VRM averages the valves but it doesn't look that high at all. 15kva system should cover your load.
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marekp avatar image marekp shaneyake commented ·
@shaneyake

I added one cose-up.

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marekp avatar image marekp shaneyake commented ·

@shaneyake

Here is the last overload warning.

screen-shot-2022-04-26-at-123050-am.png

screen-shot-2022-04-26-at-123111-am.png

screen-shot-2022-04-26-at-123132-am.png

It does not look like it was caused by excessive load but it happened at max production by PV inverter.

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screen-shot-2022-04-26-at-123050-am.png (20.1 KiB)
screen-shot-2022-04-26-at-123111-am.png (34.5 KiB)
screen-shot-2022-04-26-at-123132-am.png (48.6 KiB)
shaneyake avatar image shaneyake marekp commented ·
Looks like you would need more than a 5kva on L3.

Can you move some loads around to reduce the L3 load? You don't have much on L1 and L2 it seems.

That overload warning is most likely due to grid conditions rather than a true overload. The inverters can be maxed out while you have grid without any problems. You only really need the sizing for your PV and Max load when off-grid.

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marekp avatar image marekp shaneyake commented ·
@shaneyake

Thank you again for your help.

That load on L3 is a water heater (2.4kW) installed last year. Up til than phases were reasonably balanced. I will go with 3x MP-II/5k units and this water heater will be moved to AC-out2 so it will not load the system when grid is down.

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smart-home avatar image
smart-home answered ·

I have the same issue with high grid voltage during solar peak times and inverter disconnection.

I believe the inverter should ramp down grid feed-in to avoid disconnection, but no-one wants to address this issue and check my settings!


So, currently I use Node Red in an elaborate setup to adjust the grid set point.

I force grid export early instead of waiting for battery to be fully charged first and instead let it take most of the day to charge. This means that during the solar peak hours when I have to reduce export to keep the grid voltage down, the battery can absorb the remainder.


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shaneyake avatar image shaneyake commented ·
What country are you in? Some grid code's allow for inverter limiting based on voltage but most don't support it.
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smart-home avatar image smart-home shaneyake commented ·
I’m in Australia
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shaneyake avatar image shaneyake smart-home commented ·

screen-shot-2022-04-30-at-73719-am.png
In the Australian grid code you can set the Volt-Watt response. The inverter would then automatically reduce output while voltage increases.

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screen-shot-2022-04-30-at-73719-am.png (12.8 KiB)
marekp avatar image marekp commented ·
@Smart-Home

I am experimenting with setting values for max grid feed and max battery charge lower.

It gives me a mix results because my grid sometimes has voltage so high the even 1kW feed brings its voltage over 253V and Fronius turns itself off.

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smart-home avatar image smart-home marekp commented ·
Yes, I had the same results.….

So, I calculate a desired SOC% throughout the day from the sunrise & sunset times and change the grid set point as needed to let the battery take all day to charge, but also watching, amongst other things, the grid voltage. If export is reduced due to high grid voltage, the battery SOC will get ahead of the desired charge level and once the grid voltage drops again it will try to export more to get back on track.
It also means it will adapt to any loads that come or go.

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marekp avatar image marekp smart-home commented ·
@Smart-Home

I will investigate this NodeRed because my way is just a "band-aid" solution.

To bad that the ESS does not have an option to frequency shift PV inverter based on grid voltage.

Before Fronius I had PV inverter that had this option in the settings, but that was the only good thing about this inverter. One day it just exploded and I had to buy Fronius.

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shaneyake avatar image shaneyake marekp commented ·
You can control the output of the fronius on the Dbus, so NodeRed on a GX should pick it up automatically as a PV inverter node. Else you can control output power via ModbusTCP.
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Paul B avatar image Paul B commented ·
the Multiplus inverter/charger CANNOT control the grid voltage as it does not have the power to do so, the grid is huge the inverter small and thus cant do it, so if the grid voltage is going up thats a grid issue (ie two much solar on the grid overall more than likly) the multi will just follow it as its been told to export.


so the only option I am aware of is to Use the high voltage disconnect to turn ac-1 in / off at the point you dont want it not go any higher. and thus the inverter wil then resum its micro grid status - and thus have full control of the output voltage then.

Or setup assistants to to open the ac1 in. using the general flag assistant and the programmable relays

make shore your PV grid tie is also turning off/derating if loads are less than what the PV is producing, this is by frequency shift (again using assistants) and or some external connection to the grid tie units.


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marekp avatar image marekp Paul B commented ·
@Paul B

I respectfully disagree.

If Multiplus can adjust power fed to the grid to keep the set grid point or follow the max feeding limit, it could do the same in reaction to grid voltage.

You are correct by saying that "to much solar on the grid" can lift the grid voltage, but at the same time lowering power from solar can bring grid voltage down.

By keeping grid voltage high, My grid operator is controlling PV power fed into the grid, by turning the PV inverters off or forcing them to lower their production. Very cheap and dirty method but effective.

There are grid-tie inverters on the market that can adjust power fed to the grid in reaction to the grid voltage. My previous one could do it.

Multiplus should be able do it to.

Apparently there are methods of more advanced programing (Node-Red) that can achieve this feat.

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Paul B avatar image Paul B marekp commented ·
I can see your point and I stand to be corrected, but

1. if the grid raises to 253v then you have to turn the export off no matter what (Yes) from what you are saying. otherwise the only way to export is to have the systems voltage higher than the grid voltage.

2. If thats the case then the multi/or Quattro CANT export power if its lower or even equal to what the Grid voltage is - it cant lower the grid Volt as that is imposiable as its not in control of the grid voltage in any way, so really all that can happen is that at 253 volts you have to disconnect from the grid and then the multi will raise the freq so that the grid tie units derates so that its own microgrid voltage can be controlled. (presuming the batteries are also full that is)

3. or there is some other control that lets the grid tie units derate but they still have to derate to zero (or what ever consumption is at that point) when the grid voltage is 253 or above.

Any way I hope you find a solution that resolves your Delmar.



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marekp avatar image marekp Paul B commented ·

@Paul B

1. if the grid raises to 253v  then you have to turn the export off  no matter what (Yes) from what you are saying. otherwise the only way to export is to have the systems voltage higher than the grid voltage.

All depends on what is the reason the grid voltage is at or above 253V. My grid operator is setting a grid voltage on the transformer to 245-250V at least since this is a voltage I have at 2AM at night. As a result there is only so much power you can feed into the grid before voltage goes over 253V. If you lower the feed the voltage goes lower.

2. If thats the case then the multi/or Quattro CANT export power if its lower or even equal to what the Grid voltage is -  it cant lower the grid Volt as that is imposiable as its not in control of the grid voltage in any way,  so really all that can happen is that at 253 volts you have to disconnect from the grid and then the multi will raise the freq so that the grid tie units derates so that its own microgrid voltage can be controlled. (presuming the batteries are also full that is)

I do not know how it is in other countries but in mine, when voltage goes above 253V but is below 260V, grid-tie inverter has 10 minutes to turn itself off. Above 260V it is 3 seconds (I think). So we have 10 minutes to lower the PV power fed and this way lower the grid voltage. Grid voltage is not hard fixed since it depends on power line resistance. This is why it can legally be between 207V-253V.

3. or there is some other control that lets the grid tie units derate but they still have to derate to zero (or what ever consumption is at that point) when the grid voltage is 253 or above.

No, they do not have to "derate" to ZERO. Just lower the power fed to grid to the point when grid voltage drops below 253V

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shaneyake avatar image shaneyake Paul B commented ·
You must remember that your connection to the grid isn't perfect and has some resistance.


Inorder for the inverter to Export it has to output slightly high voltage than what is coming into the inverter but as the export current goes up the loss in the cables feeding the property goes up and because of this the inverter will have to increase its output voltage even more to maintain an export setpoint.

The same is true for when you have huge loads at your property your grid voltage will drop. You can reduce this drop by using the inverters to cover some of the load, reducing the line voltage drop and increasing the voltage at your property.

By controlling the load positive or negative you put on the lines feeding the property you can control the voltage greatly, especially if the grid connection isn't the best which is the case in lots of places.

Disconnecting from grid while sometime necessary is the worst option in my opinion as this can happen several times in a short period and every time the inverter output voltage drops to 0V for 10-20ms. This isn't great for electrical appliances if it is happening often.

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