A novel on-line UPS with universal filtering capabilities

A novel line-interactive uninterruptible power supply (UPS) is proposed that offers the characteristics of an “on-line” or “inverter-preferred” UPS (which incorporates a pulse-width modulation (PWM) rectifier) 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 output-voltage stabilizer in the presence of input power while charging the battery at a controlled rate. In case of loss of input power, the UPS can make a seamless transition to backup mode while supplying the load with a controlled sinusoidal voltage, drawing power from the battery. The series converter sees only a small percentage of the input voltage (typically, 10%-20%) while carrying the input current and therefore 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 converter results in reduced system cost compared to conventional on-line systems without sacrificing any desirable characteristics. A laboratory version of the proposed UPS has been built to demonstrate the claimed capabilities, and both simulation and experimental results are included in the paper