Electronics > Power/Renewable Energy/EV's
An inverter generates horrible RF jamming comms for hundreds of meters
Fflint:
I need some help in my attempt to fix this inverter. It is a solar olinverter, but that really is irrelevant , because the problem is with a high voltage DC to AC inverter module.
I know it is not a design fault because I have more than one, and only one became an RF jammer. It is a so called "a hybrid "(in quotes as it's not a real hybrid) solar inverter all in one. Its contains the following modules:
- A bypass relay that can connect AC in to AC out or disconnect them
- A bi-directional inverter between AC (voltage range 120V to 275V) and a high voltage (430 to 480V) DC bus. It is used to create AC from DC when the grid is down and bypass is opened. It can be used to feed power to the grid when grid is on. In both cases it synchronises it's phase to the grid.
- a rectifier/booster - this just converts the grid input to high voltage DC for battery charging.
- a 44 to 62V battery charger powered by the HV DC bus
- two solar mppt to HV DC bus controllers.
And that is it. A relatively simple device.
When it is "off" its AC generation is off, but it still rectifiers the grid, maintains the HV DC bus, is able to charge the battery and mppts can be active depending on config. In this state it is not generating any substantial RF.
However when it is switched "on" so the inverter is creating AC it makes horrible RF noise that exits through every single cable including ground as far as I can tell. It generates huge signals at 5Mhz and it's multiples as well as the entire range 24-44mhz (every few kb there is a huge spike 40dB over background).
The inverter design from what I read is very basic. There is no isolation between the HV DC and AC. I believe it just has a bunch of mosfets in parallel and a filter. That is it.
When it initially came to me it seemed to fail to start with "HV DC bus shorted" error, but then after I disassembled it and put it back together it started working . I thought maybe some piece of wire got inside or other thing that caused a short, but now I'm not so sure.
Let's say one mosfet or a diode failed in a bunch. Could it fail open (or it failed almost open and these few jolts opened it fully) and being connected with its neighbours in parallel, can it generate such noise in result?
This noise is practically invisible with an oscilloscope on the ACs signal. It is few mV maybe while the AC is 240V.
I also wonder if there was a cold solder joint in the filter could it result with such RFI?
Thanks in advance for any responses?
NiHaoMike:
Check the "X" capacitors in the AC filter, a common failure mode is for them to go open.
Fflint:
--- Quote from: NiHaoMike on January 14, 2025, 04:33:10 am ---Check the "X" capacitors in the AC filter, a common failure mode is for them to go open.
--- End quote ---
Thanks. I'll do that when I have it on my bench.
Just to add. A service manual (for a very similar device- they are all clones of eachother differing only in some options, like grid feed in, being enabled or not, and component numbers/quality) shows the inverter as just this:
If it is true there is indeed nothing else there to break other than the capacitors (perhaps a coil can have a short, but that would be visible in the output AC I guess). However, MOSFETS are shown here, elsewhere the manual talks about checking IGBTs in the "Check the INV full bridge on MAIN board", gives types, also shows pictures of drivers as well as optocouplers. So it is really just a conceptual drawing - ah a joy of Chinese manuals....
Same section has nothing about the filtering. It contains various SMD resistor values (which will come handy too).
This is the block diagram of the whole device:
BTW there is a swicth mode power supply fed from the battery and AC there as well. Unfortunately there is no schematic (for this model). I've heard about SPSes having such an effect. I doubt this would be it as the SPS is active even if the inverter is not creating AC and in such state no RF noise is seen.
Jeroen3:
If it's jamming RF, the noise is common mode, typically invisible to probing on the outputs.
Get a TinySA ;)
The antenna or a set of cheap amazon near fields can probably tell you more.
Fflint:
--- Quote from: Jeroen3 on January 14, 2025, 07:13:42 am ---If it's jamming RF, the noise is common mode, typically invisible to probing on the outputs.
Get a TinySA ;)
The antenna or a set of cheap amazon near fields can probably tell you more.
--- End quote ---
I have a tinysa. All it tells me is that the noise it all around.
However ,it turns out the inverter is not the source. I was mistaken. So the hunt continuous.
I'll have to make a directional antenna for the tinysa. I saw a small loop online, but i doubt it has a lot of directionality.
I wonder if a ferrite rod antenna could work on 28mhz or is the frequency too high.
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