A Sag Compensator That Eliminates the Possibility of Inrush Current While Powering Transformer-Coupled Loads

Sags are the foremost power quality problem encountered by industrial consumers because they frequently cause the interruption of manufacturing processes, which can result in a significant economic loss. To resolve these problems, industrial consumers often install voltage sag compensators in critical industrial applications. However, these compensating topologies prove to be costly, and some take a few milliseconds to being operating when a sag occurs. The transformer, which is usually mounted in front of the critical load, is likely to be exposed to sag voltages during this time interval. As a result, when the compensator reinstates the load voltage, a serious magnitude of transient current begins to flow toward the sensitive load. This inrush current can either damage the equipment or activate the protection devices. In either case, the compensation will eventually fail. To eliminate the inrush current and to achieve seamless compensation for sensitive loads, we propose in this paper a sag compensator established on a customary current-regulated inverter. This compensator employs a current-regulating scheme using a stationary frame of reference to regulate the current for the load by connecting it to the secondary winding of the load transformer. We verify the operation of the proposed system through laboratory test results obtained under different possible sag types.