on a network analyzer's measurement what's the meaning of a negative PF?
As I suspected from the beginning, your load Active PFC is working very well and is near unity. The polarity seems to only indicate a very minor shift in RMS current vs voltage &lt; +/-1 degree.  

This is more useful than just the absolute value method often calculated as it indicates the polarity of VAR error on the unity PFC.

What's the problem?  Harmonics?