Grid sync requires that the voltage your inverter produces matches the grid voltage so the best way of achieving this is to compare, via a transformer, the two voltages. If perfectly matched, the transformer output will be zero and measurement errors are minimized.

Grid sync requires that the voltage your inverter produces matches the grid voltage so the best way of achieving this is to compare, via a transformer, the two voltages. If perfectly matched, the transformer output will be zero and measurement errors are minimized.

^{simulate this circuit – Schematic created using CircuitLab}

If there are harmonics present on one power signal relative to the other, the output voltage of the transformer will show these but at a reduced amplitude due to the increased eddy current losses as frequency rises. However, if the harmonics are identical on both, the harmonics will become zero when matched.