Abstract
This paper introduces a transformer inrush current reduction technique for the conventional double-conversion uninterruptible power supply (UPS) feeding multiple loads and their transformers. As these loads are engaged or disengaged, their transformers are also connected or disconnected from the power lines. To avoid the inrush current, a closed-loop flux linkage control and a phase winding energizing sequence control for the incoming transformer are proposed to maintain the flux of transformers which are already engaged and of the transformer which is switched on. The proposed method can utilize the existing voltage and current sensor feedback of the UPS, and it can be seamlessly integrated with the voltage and current control. Experimental test results are provided to validate the effectiveness of the proposed method. © 1972-2012 IEEE.