Mrakes Posted October 10, 2019 Share Posted October 10, 2019 Hello! I have 5X 5kVA axpert inverters connected in parallel (1 master and 4 slaves) running a PV home solar system with batteries. When the AC in is off the system is operating well with the inveters' output frequency of 50 Hz, but when the AC in is switched on, the inverters' frequency suddenly drops to 40 Hz and when i switch off 3 inverters the frequency peaks to 49.6 Hz and this is an issue because the grid frequency is 50 Hz. Any idea what could be the issue here, please help? Quote Link to comment Share on other sites More sharing options...
Jaco De Jongh Posted October 10, 2019 Share Posted October 10, 2019 Welcome Mrakes 4 hours ago, Mrakes said: but when the AC in is switched on, the inverters' frequency suddenly drops to 40 Hz and when i switch off 3 inverters the frequency peaks to 49.6 Hz I really dont have an idea, but I would follow your thread just to see the outcome, quite an interesting situation. I however have two questions: Have you maybe seen if the inverters are drawing any power from the grid when that happens? Does all the units run on the same version firmware? Quote Link to comment Share on other sites More sharing options...
Morakeng Posted October 11, 2019 Share Posted October 11, 2019 Hello every one! I have 5X 5kVA axpert inverters connected in parallel (1 master and 4 slaves) running a PV system with batteries. When the AC in (single phase) is off the system is operating well with the inveters' output frequency of 50 Hz, but when the AC in is switched on, the inverters' frequency suddenly drops to 40 Hz and when i switch off 3 inverters the frequency peaks to 49.6 Hz and this is an issue because the grid frequency is 50 Hz. Any idea what could be the issue here, please help? Thank you. Quote Link to comment Share on other sites More sharing options...
Morakeng Posted October 11, 2019 Share Posted October 11, 2019 Hi Jaco, yes all the units are running on the same firmware version but with regard to drawing power when the utility is switched on its something i have not got to but what i can say is that when the utility is switched on, the inverters switch on and off continuously. Quote Link to comment Share on other sites More sharing options...
Coulomb Posted October 11, 2019 Share Posted October 11, 2019 21 hours ago, Mrakes said: but when the AC in is switched on, the inverters' frequency suddenly drops to 40 Hz and when i switch off 3 inverters the frequency peaks to 49.6 Hz Yikes! The inverters are attempting to synchronise in phase (and therefore in frequency) with the incoming mains. One of the reasons for doing this is to make transfers from battery mode to line mode easier on the relays, and less brown-out time for the loads. Of course, when in parallel, they all have to be synchronised with each other, but presumably they do that via the CAN bus on the paralleling cables. All I can think of is some weird problem with the AC-in wiring (perhaps a neutral missing or loose?), or a problem with the master's AC in detection hardware. Or possibly extremely noisy mains; do you have any harsh AC loads? It would be good to see the waveform on an oscilloscope, but make sure that your probes are rated for 250 VAC if you attempt this. I assume that this is all single phase, and that all the inverters have setting 28 (AC Output Mode) set to PAR (not 3P1, 3P2, or 3P3, and definitely not SnG). And of course that all inverters are fed from the same phase. Finally, I assume that these are all genuine Voltronic Power manufactured Axperts, not clones. Quote Link to comment Share on other sites More sharing options...
Jaco De Jongh Posted October 11, 2019 Share Posted October 11, 2019 40 minutes ago, Coulomb said: but presumably they do that via the CAN bus on the paralleling cables. One Question we did not ask. @Morakeng / @Mrakes , did you check if the Parallel cables as well as the Current sharing cables are installed correctly? ibiza 1 Quote Link to comment Share on other sites More sharing options...
Coulomb Posted October 13, 2019 Share Posted October 13, 2019 3 hours ago, Centurionsolar said: It logs the incoming grid frequency and volts, and by monitoring each inverter individually, they saw that one of them was consistently out. I would think you could do the same by using the LC Displays and buttons. ICC is certainly useful if you like monitoring your inverters, but I don't see that it had any special advantage diagnosing that situation. I also can't see how a parallel board could cause a misread of the input voltage or frequency. Quote Link to comment Share on other sites More sharing options...
Morakeng Posted October 16, 2019 Share Posted October 16, 2019 Thank you all for your responses. I have measured the frequency on each inverter without AC in and it is still fluctuating but surprisingly on the inverter's display its 50 Hz but the actual one is going up and down. All the 5 inverters are using the same firmware version. Quote Link to comment Share on other sites More sharing options...
Coulomb Posted October 17, 2019 Share Posted October 17, 2019 On 2019/10/16 at 2:39 PM, Morakeng said: surprisingly on the inverter's display its 50 Hz but the actual one is going up and down. Um, are you confident that your multimeter (or whatever) is measuring frequency accurately? Fresh battery? Another meter? It seems so odd that 5 inverters can't keep time. Quote Link to comment Share on other sites More sharing options...
Morakeng Posted October 18, 2019 Share Posted October 18, 2019 Yes, i even used two multimeters, the battery is still new. Quote Link to comment Share on other sites More sharing options...
Craig G Posted November 22, 2019 Share Posted November 22, 2019 Just to provide some closure to this topic.... We tried a full rewiring of the parallel and load sharing cables. We changed some parallel boards. We flashed updated firmware.... all to no avail. The issue was resolved after reading about another installer of a Victron system who accidentally coupled the AC output to the circuit to the AC input circuit. When the AC grid returned the 2 waveforms were naturally out of sync and the Victron made some unpalatable noises for about 20 seconds before shutting off with the overload light "ON". One of the observations that this person made was that the Victron's reported frequency fell to around 40hz! This would make sense. It led us to wonder whether there was not a possibility that somewhere in the inherited installation there wasn't a direct connection between the AC input and the AC output. We eventually found this in the rotary changeover switch at the main supply DB! The terminals on this rotary switch are very close together and a single strand of the 16mm^2 incoming live cable was touching another terminal which bridged it to the output live only when the changeover was switched! A new changeover switch with better spaced terminals was installed - job done! Everything is now operating exactly as it should! School fees! The upshot however is that all the inverters have been reflashed with the latest 73.00e LF1 firmware (Which is fantastic!) and the system has been checked with a fine tooth comb! Thank you to everyone who provided input. podarok and Fuenkli 2 Quote Link to comment Share on other sites More sharing options...
___ Posted November 23, 2019 Share Posted November 23, 2019 18 hours ago, Craig G said: reported frequency fell to around 40hz! Yup, the inverter will slow down its own frequency to sync with the grid frequency, If you put it in situation where this can't be achieved, it will end up at some extreme value. podarok 1 Quote Link to comment Share on other sites More sharing options...
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