Improved single-phase line-interactive UPS

An improved single-phase line-interactive uninterruptible power supply (UPS ) is proposed for low-power applications with low cost. The proposed UPS is comprised of two push-pull converters based on low-voltage battery for red uced cost: one in series with the input and the other in parallel with the load. In the presence of input power, the UPS acts as an output voltage reg ulator and at the same time as an active filter while charging the battery. In case of loss of input power, the UPS supplies a regulated sinusoidal vo ltage to the load, drawing power from the battery. The series converter com pensates only a small percentage of the input voltage carrying the input ca r-rent and, therefore, a reduced rating is made. The parallel converter alw ays supplies a nominal voltage and makes a seamless transition to backup mo de. In the voltage determination of the parallel converter, the nominal vol tage is derived using the feedback linearization concept and then a perturb ed voltage is determined for the reactive power control or output voltage r egulation. Experimental results obtained from a 1-kVA prototype are discuss ed.