Simplified Voltage Notch Filler for Interactive Uninterruptible Power Supplies

There are three types of Static Uninterruptible Power Supplies (UPS): off-line, interactive and double-conversion. The last one protects the load against all types of line disturbances but it is the most expensive and the one with the lowest efficiency. On the other hand, off-line and interactive UPS have higher efficiency and lower cost, but they show an important drawback: a switching time from normal mode to stored-energy mode. As a consequence, there is a notch in the UPS output voltage during this switching time. In a previous paper [1], authors proposed a method for filling these voltage notches with a sinusoidal waveform generated by a switch-mode converter. In this one, a simplified notch filler is proposed. It consists of two capacitors charged one with positive and the other with negative voltage. If the fault occurs in the positive period, the positive charged capacitor is connected to the load. This connection is then modulated in order to obtain a sinusoidal waveform at the load. In the negative period, the other capacitor is used in the same way.