Micro Inverter Momentary Dropouts

I've been trying to troubleshoot momentary dropouts with my Micro Inverters.

I have 10 x 250W Panels on Enphase M215 Inverters and 2 x 255W Panels on Enphase M250 Inverters and I see an irregular drop of between 1 and 3 panels of between 5 and 15 seconds every few minutes. I've confirmed the drops with a scope across the CT output, and I can see the sine wave drop in amplitude during a drop. I've also changed the Micro's from Renesola and if anything the Enphases seem worse, but they do recover quicker. Additionally turning on the 8 Flourescent tubes in the garage used to put at least 10 of the 12 Renesola's off line with a Grid Overvoltage error, whereas the Enphase's seem unaffected.

Mains voltage is supposed to be 230V, however in reality it sits around 237V-241V and the protection settings are set to trip at 253V for 0.5 Seconds, which is 10% above 230V, not above 237V. I have a phase angle power diverter, and turning it off seems to make no difference.

This morning we didn't have a lot of sun, and the dropouts increased dramatically for a short time - see picture.

Can anyone help me troubleshoot this?

dBC's picture

Re: Micro Inverter Momentary Dropouts

My first guess would be there's something nasty on your mains that is triggering either a deliberate retreat, or a bug in the inverter.  Switching on a bank of fluro tubes knocks an impressive notch in the V sinewave if you time it right. I have some scope pics of that somewhere, but can't find them at the moment.  From memory, it was knocking a good ~30V notch right at the peak.

Are you in a position to be able to safely probe the mains with your scope, perhaps through an isolation / stepdown transformer?  You'd then need a way to trigger the scope at the time of a dropout so you could look for anything unusual in the sine wave.  If the external trigger proves too complicated, a lot of scopes let you trigger on sudden changes to a signal (rise time / fall time trigger).  You could set that up so that it doesn't trigger with the standard sine wave, but does with any notches, and test the trigger with the fluros.  Then leave the scope armed, and at the time of the next dropout, it will have hopefully triggered.

sheppy's picture

Re: Micro Inverter Momentary Dropouts

I have a battery powered scope with a x10 probe so I can either probe it directly or preferably through the EMONTX transformer. I can't see the flouro spike, but I suspect its lost in the triggering. Do you think I am likely to see everything through the transformer or will it filter out what I need to see?

Maybe I could trigger it via the solar power output from the Current Transformer whilst displaying the mains voltage on the other trace.

Its a recently acquired cheap DSO203 so I'm not sure what its capabilities are

dBC's picture

Re: Micro Inverter Momentary Dropouts

I'd expect the glitches to pass through the transformer well enough to be seen.  Yes, you won't see the fluro notch I described unless you can set up rise-time triggering (or external triggering from the device that notices it).

Comment viewing options

Select your preferred way to display the comments and click "Save settings" to activate your changes.