Trying to deeply investigate LED pulsing flickering with HF off-grid inverters

[SparkyJJO]

This is one reason why solid LF inverters are superior.

 

[jmjack]

I still have hope to find a simpler solution.

What do you think about putting an isolating transformer in front of the dirty load which may reduce the interference between the inverter and the "dirty" load?

My "dirty" loads have a max. of 100W (old slot machine) and 300W (my 3D printer) so these would cost not very much. Maybe I should give my "diry" 100W load a try.

I tried using a medical isolation transformer for the issue you are describing/experiencing, no solution. I am now using a pair of 6000XPs, solved all LED flickering (strobing) issues. Can’t be happier!

 

[rhino]

This is one reason why solid LF inverters are superior.

As I mentioned earlier my Victron Quattro 5kVA still has lights flicker when a heat gun is heating up and when the fridge turns on there is also a noticeable blip in the lights.. so not sure what the issue is.

 

[ricardocello]

As I mentioned earlier my Victron Quattro 5kVA still has lights flicker when a heat gun is heating up and when the fridge turns on there is also a noticeable blip in the lights.. so not sure what the issue is.

Presumably you mean flickering when inverting, but no flickering when in grid passthru (or maybe you are off grid).

I get some flickering with grid passthru normally anyway, same when I bypass my quattros altogether.
Grid power isn’t all that clean at the end of the line where I live.

I actually think there is less flickering when inverting, with the sole exception of the well pump kicking in.

 

[Hedges]

Filters have been tried by many, the result was never as hoped. Many here tried filters & conditioners & failed - some of it is in threads.
I am sorry BUT do not shoot the messenger... You are free to explore it and chase the proverbial tail while spending cash but it will never be what you expect.

You would not BELIEVE the scale of program where I have seen that attempted. Filtering of a practical scale can't clean up a bad inverter waveform or output characteristic. Solution was to fall back on the tried & true.

Btw. I will use the wording "dirty" load for loads which interact in a negative way with the HF inverter to make some LED loads pulsing.

Now I ask myself if it's possible to put a filter in front of the "dirty" Load2 like shown in the following picture to stop the pulsing of the "LED Load" (to stop the 3-7Hz interference oscillation between Load2 and the HF inverters which causes the "LED Load" to pulse).

I don't think that is a dirty load. As AntronX says, it is instability of regulation/feedback in the inverter.
Maybe a purely resistive load would not do that, and capacitance causes the problem. Or could be just some level of load causes inverter to hunt.

I've actually chased interference of similar frequency range (in a completely different sort of system.) Using oscilloscope with 100 second sweep time and FFT, to see the frequencies present. We're working with DC, so other guys are looking at large capacitors, while I'm designing linear regulators. Either way, we don't care about efficiency/losses.

Maybe if you had the "knobs" of the control loop (PID or whatever), you could tune it to stop the flickering. Likely the original developers just sought to hit voltage specs, didn't have any measurement of what causes your lights to flicker.

You can buy inverters that work better, and you can buy lights that don't flicker so much. Maybe. It is one thing to not flicker on chopped 60 Hz sine wave from dimmer, quite another to ride to 300 millisecond ripple. Maybe a good non-dimmable LED or fluorescent lamp with current regulator fed by capacitor.

 

[Checkthisout]

As I mentioned earlier my Victron Quattro 5kVA still has lights flicker when a heat gun is heating up and when the fridge turns on there is also a noticeable blip in the lights.. so not sure what the issue is.

This to me is not flickering. A single voltage droop when a high draw appliance is turned on is different to me than flickering which is rhythmic or random oscillation in light output from the bulbs.

 

[Steve_S]

You would not BELIEVE the scale of program where I have seen that attempted. Filtering of a practical scale can't clean up a bad inverter waveform or output characteristic. Solution was to fall back on the tried & true.

Falling back to Tried & True for some means accepting their choices were either a mistake or made in error. It's the 21st Century...

It appears this is a GENERALLY - ALL HF DO THIS type of Thread. SORRY But NOT all HF inverters flicker LEDS or have these issues... The GOTCHA is the Price Point where folks went out and bought the "Proverbial Clone" because it was cheaper than the Name Brand... DEJA-VU with Personal Computers in MANY ways !!! The Parallels are almost Spooky.

IF one of our member EE's with a lot of spare time, would "Tear Into" a Value HF AIO (like an EG4) and a Tier-1 HF AIO and compared the chips & quality, there would more than likely be a few Eye Openers... I don't know if anyone has compared the "guts" of the various devices and made it available.

 

[fmeili1]

Thanks a lot for all your feedback and hints!

A short interim review of your experiences and comments about this problem and possible solutions.

Where it happens

• Usually HF inverters are much more prone to LED pulsing problems compared with LF inverters, but even with LF inverters it was seen by some
• Depending on the brand and models of HF inverters the issue is more or less visible, but even with high price / high quality HF inverter models the problems are known but usually much less common compared to low-cost inverters
• There are users out there which have no issues with pulsing LED's even with low-cost HF inverters
• When it comes to LED pulsing, this is not the case with all brands LED brands, cheaper LED's usually are more problematic compared to high quality LED's

When it happens

• Some users have LED pulsing always
• Others have LED pulsing only if a specific additional load is active (e.g. laptop charger, fridge, 3D-printer, etc.)
• If the inverters have low overall load, the problem is more visible. Sometimes the pulsing went completely away if there is a high load active - sometimes with pure resistive load sometimes with inductive load also.

Possible solutions

• From what I've learned so far, it's at least problematic (if not at all impossible) to reduce the problem by adding a "typical" filter in front of the "dirty" loads, which causing the LED's to pulse (to reduce the "dirty" feedback between the HF inverter and the problematic load which causes the HF inverter to produce "dirty" output voltage). I've tried 4 different passive filters and none of them worked.
• Replace cheap LED's with better quality LED's. In case of lamps with integrated LED's, it's possible to add additional and rectifier and capacitor to reduce the pulsing
• Replace the HF inverter with an LF inverter (not an option for me)
• Add an small additional LF inverter just for the lights - this would require an additional "light" sub-panel and a lot of re-wiring.
• Add a "dummy" load in case of low inverter load (e.g. heating water or drive a chargeverter to charge the battery by itself ) to reduce inverter voltage fluctuations.

The problem really doesn't seem to be simple and easy solvable, or if at all, it's difficult to solve.

I still have hope and not yet given up to find a "sort of filter" to block my "dirty" loads (which causing the HF inverter to fluctuate the voltage). It would be much easier to have such a solution compared to modding all my pulsing LED's in the house which are not possible to replace with high quality LED's.

Idea:
Even if such a "sort of filter" would be a "small online, double conversion UPS", it would be the better solution to place just ONE of these "sort of filter" in front of the "dirty" load to totally cut the interaction between the inverter and the "dirty" load to stop the inverter from voltage fluctuations.

A "small online, double conversion UPS" is just a small off-grid inverter with a small battery and an AC charger. I've already built one for my solar black-start situation. It's funny, but I've used a small Victron Phoenix with 500VA which is in fact an LF inverter (together with a 8Ah battery).

If I'll find time over the next couple of weeks, I will try to add such an DIY online double conversion UPS in front of my 3D printer and hope that this will stop the flickering... hope dies last.

 

[Hedges]

• Add a "dummy" load in case of low inverter load (e.g. heating water or drive a chargeverter to charge the battery by itself ) to reduce inverter voltage fluctuations.

Hey, at least the seeming "free energy device" would be more efficient than a dump load which wasn't needed!

Similarly, a grid-tie inverter would be a good load for testing a DC power supply.

 

[johnnysolar]

Add a "dummy" load in case of low inverter load (e.g. heating water or drive a chargeverter to charge the battery by itself ) to reduce inverter voltage fluctuations.

Wouldn't power going from batt, to inverter and back to battery thru chargeverter make it a physical circuit, literally? Like circle all the way back, connected? Sounds potentially hazardous. Man I gotta learn more ?

 

[Hedges]

Not hazardous (except to battery state of charge.) Just call it a "Solid State Free Energy Device"

 

[fmeili1]

After a bit more investigation I think the HF inverters (or at least the EG4-6500EX) are more sensitive about bad power factors. It looks like my old slot machine using a huge classic rectifier circuit with a big capacitor which produces a lot of phase shifted current harmonics which results in a bad power factor which is about 0.6 and a simple passive PFC will not work in this case.

Next week I will try to do some tests with a complete decoupled connection of the slot machine to my mains (via an online double conversion UPS). In case this will be successful, I'll try to do some additional tests with an active PFC circuit to learn more about these type of problems and possible solutions.

I've looked a bit deeper into the specs of the EG4-6500EX to find out something about apparent power - but nothing really useful.

• Right at the beginning of the EG4-6500EX users manual there is the following headline:
  EG4 6500 EX-48
  SOLAR INVERTER/CHARGER
  6.5KVA 120V AC
  This is the only place in the manual where VA is mentioned as apparent power.
• In the specifications table there is only 6500W mentioned as Rated Output Power, no more hints about a possible difference between apparent power (VA) and true power (W)
• SolarAssistant is showing both 6500W for true power and 6500VA as apparent power int the settings specification section which SA gets from the inverter itself via modbus - but I think, this can't be true because the true power is usually always at bit less than the apparent power. Most inverter brands specify both values separately.

I'll keep you updated - I still have not given up to solve the problem at the root (beside replacing the HF inverter with a LF inverter).

 

[fmeili1]

This seems to be a classics case of an underdamped system. When the load is high, the PWM controller has to dump enough power into the pulse to not let the voltage drop, but when you drop the load near zero, it can't get the pulse width small enough to prevent overshoot. The number of inverters could also be an issue, since the latency between them has the effect of limiting the lower end of the PID controller bandwidth.

The user @nkhorman made a very interesting measurement with a 2-channel oscilloscope showing the EG4-6500EX output while some LEDs are pulsing (different topic):

EG4 6500EX Voltage/Frequency Fluctuations #1
EG4 6500EX Voltage/Frequency Fluctuations #2

Do you think this is the underdamped system behavior you describe to prevent overshoot, or is this something else?

 

[AntronX]

Hard to tell just from looking at the waveform. Does it flicker when inverter is running alone and not paired with 2nd inverter? Problem could be related to paralleled mode of operation possibly due to synchronization data latency causing voltage overshoot.

 

[nkhorman]

Hard to tell just from looking at the waveform. Does it flicker when inverter is running alone and not paired with 2nd inverter? Problem could be related to paralleled mode of operation possibly due to synchronization data latency causing voltage overshoot.

I'd have to bypass, and break the pairing to try... something I could do, but.... It's in operational use... didn't really want "go backward".
But I guess I'll have to do that eventually.
Sigh.
It wouldn't be a big a deal if I didn't have a 240v well pump load.
I guess I'll shut off that load breaker and give it a shot when I have time.

 

[nkhorman]

A little more scope capture this morning, EG4 6500EX Voltage/Frequency Fluctuations #3.
The previous two videos where with the units in SBU mode.
In this one, the units are in USB mode with, PV, 120v load on both phases, and some intermitent 240v load (well pump).
Is this kind of behavior really expected and/or normal for HF ?

 

[webbbn]

The issues that I see are some intermittent transients, and the waveform seems to be clipping the tops of the waveform. I don't know if it's normal, but could the transients be when the well pump turns on/off. I could imagine a large inductive load causing such transients in a HF inverter. I don't know what would be causing the clipping, though.

 

[Hedges]

I've seen grid waveform clipped, sine wave with flat tops.
It was at a factory in Guadalajara with rows and rows of X-boxes being tested. (well, may have been on UPS due to grid power issues.)
When load is rectifier/capacitor front end, zero current is drawn until AC voltage exceeds capacitor, then capacitor presents a short. So flat tops.

Try resistive loads. Try inductive loads (with no SMPS or LED lamps.)

 

[Kornbread]

The user @nkhorman made a very interesting measurement with a 2-channel oscilloscope showing the EG4-6500EX output while some LEDs are pulsing (different topic):

EG4 6500EX Voltage/Frequency Fluctuations #1
EG4 6500EX Voltage/Frequency Fluctuations #2

Do you think this is the underdamped system behavior you describe to prevent overshoot, or is this something else?

176v?

 

[andrew-d]

176v?

What we call 120V AC is actually 170V at peak; the name "120V" is actually the "root mean square" (RMS) voltage. Long story short, a sine wave at 60Hz with voltage peaking at 170V (referred to as "Vp") is equivalent to 120V DC in terms of power dissipation, which is why it's called that.

Another way to think about it: while the sine wave peaks at 170V, we only have 120V that can actually do work. If you hook a 120V DC power supply up to a resistor, it'll generate some amount of heat. If you hook an AC power supply up to that same resistor, configured to output a peak of 120V (not RMS), then it'll generate less heat than with the 120V DC power supply! An AC supply with a peak of 170V will produce the same amount of heat ("power dissipation") as a 120V DC power supply, for that same resistor. For more details:

RMS Voltage and Current- Explained

This is an article that explains what rms voltage and current is, real life examples of it, and how RMS power can be calculated.

www.learningaboutelectronics.com