Hi All,

I'm sure this has come up multiple times so if people are getting tired of answering this one, please point me to the best thread.

I'm currently running a sunsynk hybrid inverter with battery and solar pannels. I've noticed a slight flickering in the lights (it lasts fractions of a second) when the grid power goes on or off. I think this flicker only happens when we have some dependency on grid power. ie: when when we are running entirely off of solar during the day, the system doesn't "care" that the grid is back on. But when running in the evening off battery and the grid comes back on and the inverter makes the decision to switch back to grid power, then it will be noticeable.

My assumption is that this happens because it's not possible to easily synchronize the phase of the AC wave coming from the inverter with that coming from the grid and so one sees a micro-fluctuation in power when switching over. Out of interest, does anyone know if that is the reason?

My more important question though, is how do I protect my home appliances from this? I have a friend who's fridge recently packed up and insurance are claiming that it is the above issue that has caused it. Is there anything that i can fit at the plugpoint (or elsewhere) of my more expensive home appliances to protect them?

Thanks

Suggestion would be to investigate appropriate grid parameter limits (Voltage and frequency) for the inverter's settings, so the inverter only transfers from battery to grid once the grid has stabilised after re-connection. The re-connection time is usually 60 seconds, which should be enough time to track the phase of the grid.

Just my 2c.

The designer of an inverter could implement a PLL (Phase Locked Loop) in the DSP (Digital Signal Processor) and this would sync and lock the 50Hz to the utility power just before switch-over.  This would mainly be a software exercise without needing special hardware resources.  It should not be that difficult but it might take a bit of time.  At the time of utility restoration things are a bit unstable and the PLL would need to lock over at least a few sinewave cycles.  In grid-tied inverters this would certainly have to be done.

I don't know the SunSynk inverters, but on Axpert inverters my guess is that no syncing takes place.  (I might be wrong on this, @Coulombcould let us know).   On Axpert inverters the switch-over is done with relays and these devices are slow.  The contact wiper of the relay will first release from one side and then travel about 3 or more mm to make contact on the opposing side.  This means that there is a dead-zone when the load is disconnected and electrically floating.

As I was writing this, I asked myself how long would a relay need?  Google says about 50mS.  (I would have thought it to be faster, but the speed depends on many factors such as the voltage rating (bigger contact distances), spring load, temperature,  etc.)  The period of a 50Hz Sinewave is 20mS.  So expect a "blackout" for about 2 sinewave cycles before the relay contacts re-connect.  I think that this is likely what you detect as a slight flicker of the lights.

When the utility fails things are even slower.  The DSP must first decide if the drop in voltage is a brownout or a blackout. It will check and wait on a number of consecutive half-cycles to make that determination.

1 hour ago, Modina said:

but on Axpert inverters my guess is that no syncing takes place. 

The axpert employs grid tieing internally in the same manner the Sunsynk does, with the only exception being that the Axpert is programmed not to allow exporting of grid power. This incidentially is the reason why Axpert can also blend grid with the inverter output. 

The Axpert will synchronise to grid and when done, the input grid safety relay is energized and this connect grid, inverter and load together (given the load relay is also energized). 

The only barrier between the inverter output and the grid input is a reactance in the form of  large inductor. This is the grid tie. The direction and magnitude of current flow between grid and inverter is now controlled solely by the relation of voltage phase angle (not voltage magnitude) between grid and inverter. When the grid is charging the battery or blending the load, this phase angle is adjusted accordingly.  

So the notion of relay switching to accomplish changeover from grid to inverter does not exist anymore. It is now seamless. 

However, when grid falls away when it was carrying substantially the load, there will be metastable conditions in order for the inverter to instantsneously absorb and cope with the full amount of load current. I suspect this is where some flickering is visually observed.  However this condition does not affect my computer workstation and other appliances which is dependant on non-interruption. A fridge will certainly not be affected by this. 

Edited March 12, 20232 yr by BritishRacingGreen

20 minutes ago, BritishRacingGreen said:

The axpert employs grid tieing internally in the same manner the Sunsynk does, with the only exception being that the Axpert is programmed not to allow exporting of grid power. This incidentially is the reason why Axpert can also blend grid with the inverter output. 

The Axpert will synchronise to grid and when done, the input grid safety relay is energized and this connect grid, inverter and load together (given the load relay is also energized). 

The only barrier between the inverter output and the grid input is a reactance in the form of  large inductor. This is the grid tie. The direction and magnitude of current flow between grid and inverter is now controlled solely by the relation of voltage phase angle (not voltage magnitude) between grid and inverter. When the grid is charging the battery or blending the load, this phase angle is adjusted accordingly.  

So the notion of relay switching to accomplish changeover from grid to inverter does not exist anymore. It is now seamless. 

However, when grid falls away when it was carrying substantially the load, there will be metastable conditions in order for the inverter to instantsneously absorb and cope with the full amount of load current. I suspect this is where some flickering is visually observed. 

For any member interested in further gridtie theory, the following link has a video that demonstrates is very nicely, visually. 

 

@BritishRacingGreen thanks for the explanation.  Is that true for all Axpert inverters?  I thought it's only the King Axpert inverters that can do blending.  I still have much to learn...

Yes, for AC blending the phase angle relationship would need to be finely controlled, but the right voltage matching would also be required.  Luckily 50Hz is so slow, that it's no hardship for a DSP.

Clicking on that link you provided, only takes me to the long discussion regarding the Repair of Axperts.  I will have another look if I can find the video amongst all those posts.  I would like to see that explanation.

14 hours ago, NickM said:

I'm currently running a sunsynk hybrid inverter with battery and solar pannels. I've noticed a slight flickering in the lights (it lasts fractions of a second) when the grid power goes on or off. I think this flicker only happens when we have some dependency on grid power. ie: when when we are running entirely off of solar during the day, the system doesn't "care" that the grid is back on. But when running in the evening off battery and the grid comes back on and the inverter makes the decision to switch back to grid power, then it will be noticeable.

I get that too with my Goodwe. Round where I live the voltage seldom gets to 220, so when load shedding starts the voltage switches from whatever was on the grid to the nice 230 the Goodwe puts out. And there's a small but finite period of time to change over. So a slight flicker of the lights seems to me to be expected. 

I also get a flicker on restore. This is the reverse situation with the Goodwe having to drop down from 230 to grid. 

11 hours ago, Modina said:

@BritishRacingGreen thanks for the explanation.  Is that true for all Axpert inverters?  I thought it's only the King Axpert inverters that can do blending.  I still have much to learn...

Yes, for AC blending the phase angle relationship would need to be finely controlled, but the right voltage matching would also be required.  Luckily 50Hz is so slow, that it's no hardship for a DSP.

Clicking on that link you provided, only takes me to the long discussion regarding the Repair of Axperts.  I will have another look if I can find the video amongst all those posts.  I would like to see that explanation.

To see the video you need to click on the topmost title, the one with the arrow next to it. 

The generic range of Axperts all employ gridtied ac-coupled technology, allowing ac blending. 

The Axpert King is a bit of an outlier in this family. Its not ac-coupled, instead the grid input is converted to dc, where it is dc-coupled with pv and battery. This has 2 advantages : it provides for the best UPS  working one can wish for, because the inverter is basically always in full dc mode wether grid is on or not. Secondly, it is not prone to very bad/noisy  grid sinusoids, and  generator friendly.  It does not have to sync on the grid, because the grid for all intend and purpose is reconstructed for inverter use. 

Its disadvantage is double conversion on the grid side (AC-DC and then DC-AC), which is perhaps not that efficient. 

 

 

 

Edited March 13, 20232 yr by BritishRacingGreen

My built in microwave and oven makes a beeping noise when the eskom power goes of or back on with my sunsynk system.

I had the issue with LED downlights flickering when eskom was off and also one particular light switch that shocked you when you touched it, while eskom was off.

Turns out it was a earthing issue that my installer rectified. 

7 hours ago, Bobster. said:

I get that too with my Goodwe. Round where I live the voltage seldom gets to 220, so when load shedding starts the voltage switches from whatever was on the grid to the nice 230 the Goodwe puts out. And there's a small but finite period of time to change over. So a slight flicker of the lights seems to me to be expected. 

I also get a flicker on restore. This is the reverse situation with the Goodwe having to drop down from 230 to grid. 

I also find that some brands of LED lamp are either very sensitive, or are just prone to random flickers.

Thanks for the input everyone. Some good ideas and I'll investigate a bit more. I'll keep an eye on it and try to narrow down exactly when it happens. I've also noticed a UPS that we still have connected occasionally beeps (just once) on changeover. I'd imagine these are quite sensitive to any drop in power as that is their whole reason for being.

I would suggest you use a dedicated refrigiration surge protected plug on all your fridges and freezer. They are different to a "normal" surge protected plug, in that if the supply goes outside the parameter settings of (170 >275V) it switches off and will only switch on again 3 minutes after the supply is back in the parameters. This stops your refrigiration compressor from trying to start againt back-pressure. You get the plugs in different price brackets eg. Clearline, Ellies etc. 

What I don't know is how fast the plug reacts to any power deviations?

My Ellies unit has never tripped/engaged whit any fluctuations from my Sunsynk's side. 

On 2023/03/19 at 7:47 AM, Vaal said:

I would suggest you use a dedicated refrigiration surge protected plug on all your fridges and freezer. They are different to a "normal" surge protected plug, in that if the supply goes outside the parameter settings of (170 >275V) it switches off and will only switch on again 3 minutes after the supply is back in the parameters. This stops your refrigiration compressor from trying to start againt back-pressure. You get the plugs in different price brackets eg. Clearline, Ellies etc. 

What I don't know is how fast the plug reacts to any power deviations?

My Ellies unit has never tripped/engaged whit any fluctuations from my Sunsynk's side. 

There is no use in having a surge protection plug behind your Sunsynk. You should already have surge protection installed on both the grid feed to the inverter and the inverter load.

Your Sunsynk will also disconnect from the grid should the grid supply voltage drop out a certain range (and you can set this range yourself).

 

1 hour ago, I84RiS said:

There is no use in having a surge protection plug behind your Sunsynk. You should already have surge protection installed on both the grid feed to the inverter and the inverter load.

I see the value of the protection on the input side of the inverter, but why the output side? 

I have that protection in place BTW, but because the installer put it there, not because of any bright ideas I had. 

The protection on the input side is a no-brainer - it protects the inverter (not the cheapest piece of kit in my home). The protection on the output side is less intuitive. 

@Bobster.  If you have a faulty, misbehaving or poorly designed appliance, it could create high voltage spikes that could backfeed into your inverter.  These spikes might be beyond the voltage the MOSFETs or IGBTs can handle, in the very same way the 230VAC input section could feed-in damaging spikes.

Remember that voltage spike/transient generation is more or less proportional to the power usage of an appliance.  What I mean is that a small device using 50 or 100W is less likely, than a power hungry device (such as an air-con) to produce large transients.  The spikes are always produced by motors, transformers and inductors that create a back-EMF.

People that mainly run TVs, lights, laptops and other small items should be fine.  High power resistive loads such as geysers and hobs/ovens are also no problem.  If, however, you plan to hook-up your microwave, air-cons or, dare I say, arc-welder, then definitely fit the extra protection.

On 2023/03/13 at 6:43 AM, WAP said:

My built in microwave and oven makes a beeping noise when the eskom power goes of or back on with my sunsynk system.

I had the issue with LED downlights flickering when eskom was off and also one particular light switch that shocked you when you touched it, while eskom was off.

Turns out it was a earthing issue that my installer rectified. 

Most shocks we feel can be traced back to a earth that is not connected. Always the 1st thing to check 

6 hours ago, I84RiS said:

There is no use in having a surge protection plug behind your Sunsynk. You should already have surge protection installed on both the grid feed to the inverter and the inverter load.

Your Sunsynk will also disconnect from the grid should the grid supply voltage drop out a certain range (and you can set this range yourself).

 

I use the protector plug just for the 3min delay before startup.