Understanding "Softrun" Operating Status

“Softrun” is a function to mitigate the impact any unstable inverter operations could have on the grid.  While the inverter is starting up, it needs to match AC voltage output with the AC voltage of the grid. Once the AC is matched, the inverter will close its relays and start generating AC power. 


If an inverter enters “Softrun” mode during startup, it means the inverter is taking extra time to verify it can match the grid so that any undesired impacts are mitigated.  If “Softrun” occurs at all, it is usually very brief, and nothing to be concerned about.  If the inverter stays in "Softrun" for a longer time, it is likely that either the PV input voltage is problematic or the grid is not stable at that point in time.


Examples of DC issues that could cause long “Softrun” periods include but are not limited to incorrect DC polarity on one of the DC inputs, or homerun positives and negatives being mixed up between different MPPTs.  Examples of temporary AC issues could be large power sources or loads going online or offline during the inverter grid matching phase of startup, or a faulty utility voltage regulator.


If an inverter stays in "Softrun" mode indefinitely, even after DC voltages and polarities are verified and grid voltage and frequency are confirmed to be within nominal range, it is likely due to an internal problem with the inverter.  This is especially likely if a project has multiple inverters installed, and all the other inverters are operating normally but one is stuck in “Softrun.” 


However, if grid frequency and voltage is measured and found to be outside the nominal range and an inverter is stuck in “Softrun,” the problem most likely lies with the local grid.  If all the inverters on a site are stuck in “Softrun,” it is likely there is either a problem with the local grid, or that a weather event occurred that damaged the inverters.


NOTE: “Softrun” mode will not protect inverters from the effects of prolonged exposure to reverse DC polarity.  Any cases of reverse polarity must be corrected as soon as possible to ensure the health and proper operation of the inverter.

J
John is the author of this solution article.

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