**Subject: High THD on 2nd and 3rd Harmonics of a 5kW Single-Phase UPS**
Hi everyone,
I'm measuring the input current harmonics on a single-phase 5kW UPS with a 120V AC, 60Hz input. I noticed that the Total Harmonic Distortion (THD) is high specifically on the 2nd and 3rd harmonics.the ups has a boost pfc and isolation transformer on input.
**My questions are:**
1. In general, aren't even harmonics (like the 2nd harmonic) usually a sign of a DC offset or asymmetry in the waveform?
2. Can such low-frequency harmonics be effectively filtered using an LC filter, or would other methods be more appropriate?
Thanks in advance for your insights!