I've a 3-phase PM brushless motor. It's operated as a BLDC drive. The output of one of the phase current sensors is connected to Agilent Dynamic Signal Analyzer 35670A to obtain the FFT of the phase current. I find out that there are triplen harmonics (their amplitudes are not very high compared to other non-triplen odd harmonics, e.g. 5th, 7th, 11th, 13th, etc) in the FFT spectrum. If I'm not mistaken, for a star-connected 3-phase system, triplen harmonics should not appear because neutral (star point) is left open (i.e. not connected to ground). So, any idea why triplen harmonics are observed in the phase current in my system?
Thanks.