Analysis of personal computer ride through capability during voltage sags

Voltage sags have emerged as one of the most serious power quality problems, particularly for sensitive equipments such as personal computers (PCs). It is a complex electronic computing device designed to be powered by a switch mode power supply (SMPS). This paper presents an investigation of vulnerability of PCs to voltage sags and development of methods to enhance the voltage sag ride through capability of PCs. Based on recent testing standards, extensive tests were conducted for a wide range of PCs. For standard reboot/restart malfunction criterion, sag depth and duration were varied to construct individual voltage immunity curves for PCs. Based on the analysis, two methods were implemented to improve the voltage sag ride through capability of the PCs. These methods include the use of additional dc capacitors and alteration of the under voltage detection (UVD) signal in the housekeeping block of the SMPS. The experimental results on different PCs show that installation of additional capacitors can only expand PCs' immunity duration to voltage sag while shift in the UVD signal helps to enhance the tolerance level in terms of sag magnitude. Finally, the advantages and disadvantages involved in the implemented methods to enhance voltage tolerance level of PCs are highlighted.