A NOVEL ONLINE UPS WITH UNIVERSAL FILTERING CAPABILITIES

A novel line-interative uninterruptible power supply (UPS) is proposed that offers the characteristics of an ''on-line'' or ''inverter-prefe rred'' UPS [which incorporates a pulse-width modulation (PWM) rectifie r] at a reduced cost. This new UPS is based on the combination of two full-bridge VSI converters: one in series with the input and the other in parallel with the load. The UPS acts as a line conditioner and out put-voltage stabilizer in the presence of input power while charging t he battery at a controlled rate, In case of loss of input power, the U PS can make a seamless transition to backup mode while supplying the l oad with a controlled sinusoidal voltage, drawing power from the batte ry. The series converter sees only a small percentage of the input vol tage (typically, 10%-20%) while carrying the input current and therefo re has a small kilovoltampere rating. The parallel converter supplies the load during blackout and hence determines the total kilovoltampere rating of the UPS. The reduced kilovoltampere rating of the series co nverter results in reduced system cost compared to conventional on-lin e systems without sacrificing any desirable characteristics. A laborat ory version of the proposed UPS has been built to demonstrate the clai med capabilities, and both simulation and experimental results are inc luded in the paper.