Experimental and Analytical Evaluation of Equipment Sensitivity to DC Voltage Ripple and AC Voltage Sags

This paper presents results of experimental and analytical evaluation of equipment sensitivity to dc voltage ripple and ac voltage sag. The selected equipment under test (EUT) is a standard computer monitor, with a diode bridge rectifier and a dc link capacitor at the front end. In the experimental part, different sets of test waveforms (TWs) with adjusted dc voltage mean and ripple values, as well as ac voltage sag magnitude and duration values, are applied in two testing procedures generally based on two IEC standards (61000-4-17 and 61000-4-11). The two general test procedures are applied for: a) sensitivity tests to ac voltage sags using ac TWs applied at the input ac power terminal/port of the EUT, and b) sensitivity tests to dc voltage ripple using dc TWs applied directly at the dc link of the EUT. In the analytical part, the relationships between the ac supply voltage (and sag magnitude and duration during the sag events) and resulting dc link voltage and current mean and ripple values, as well as energy stored in the dc link capacitor, are compared for different EUT operating powers and malfunction conditions. The combined analysis of equipment sensitivity to ac voltage sags and dc voltage ripple allows to better understand and quantify actual conditions for which considered EUT will operate normally, or malfunction.