Here's the answer as I personally see it.
I am guessing the the topic revolves around voltage harmonic distortion caused by inverter based DERs. There are, to my knowledge a few ways to deal with harmonic distortion on the grid due to the increased presence of inverter based DERs. These are as follows:
- Increase system strength (fault current). This is a lot easier said than done. System strength is increased by installing more rotating synchronous generators that produce fault current on the level of 4 to 5 times their rated MVA power output. The drive toward increasing renewable inverter based generation will continue to erode system strength as it is coupled with the drive to retire synchronous generators (baseload generation driven by fossil fuels).
- Another option that has historically been used to reduce voltage harmonics is to install passive filters tuned to integer harmonics (3rd, 5th, 7th, 11th, 13th . . . ) at the DER facility. This is problematic since today’s voltage source converters produce inter-harmonics (not multiples of the fundamental frequency of the grid). Active filters may work but they will likely be too costly.
- The only viable solution currently being seriously considered to increase system strength is to install strategically located synchronous condensers. These are basically synchronous generators without a prime mover (turbine). Instead they draw a small amount of power from the grid to rotate the machine. Coupled with a flywheel, synchronous condensers can produce significant fault currents and thus increase system strength, aka Short Circuit Ratio (SCR).
I hope this helps. I understand that this is extremely technical, but power harmonics is a complicated subject.