A DETAILED ANALYSIS OF 6-PULSE CONVERTER HARMONIC CURRENTS

Classical methods for the determination of six-pulse converter harmonic currents often do not adequately describe the harmonic current magnitudes actually found in practice. To accurately determine the magnitude of characteristic converter harmonics, a calculation procedure which takes into account the ripple of the dc current reflected back into the ac line current must be performed. Various methods from the literature for the determination of six-pulse converter harmonic currents are compared and a method which takes the Fast Fourier Transform of the time domain equations is described. Evaluation of these ripple effects tends to increase the magnitude of the 5th harmonic while decreasing the magnitudes of higher order harmonics. Noncharacteristic harmonic orders or frequencies will sometimes also be encountered. These orders typically will be less than the 5th and can be of concern because of possible coincidence with 5th harmonic filter anti-resonance points.