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1. PLL with NCO (first diagram) yes, 2. (adaptive filter) almost, depending on filter Q.

Due to limited gain of current control loop, actual grid current current has some THD, need harmonic compensation for perfect grid waveform.

2. We did occasionally tests for dip and drop scenarios (EN/IEC 61000-4-11), requirement is to ride through short drops or at least perform an automatic restart.

Requirements for grid frequency variation (EN 61000-4-28) are rather relaxed, max  0.5 % df/f per cycle, PFC can easily track it.

Don't have measurement results available. Many detailed results in Teodorescos book.