Zero-crossing distortion in grid-coupled AC-DC converters

Zero-crossing distortion in modern rectifiers and inverters may have different causes: the commutation dead time, the use of diode bridge rectifiers, discontinuities in the PWM-generation. In this paper, another cause of zero-crossing distortion is analysed: when a security dead time is inserted between the gate signals of two switches in the same leg, some line current distortion may appear close to the zero-crossing of the line current due to errors in the sampling of that line current. An overview of the sampling requirements for a digitally controlled full-bridge AC-DC converter is given and a detailed analysis of the line current distortion is performed. The analysis is verified with experimental waveforms and a solution is proposed to decrease the line current distortion.