Voltage regulation characteristics of transformer-less uninterruptible power supply without voltage divide capacitor

Power supplies prepare for a power failure often apply converters in the input side, and use inverters in the output side. The input side and the output side of power supply are coupled by high frequency transformer. This method requires a transformer. Because the switch devices included in the power flow increase, the power conversion efficiency declines. Though, high frequency transformer-less circuits are proposed, these circuits often use voltage divide capacitors. And these schemes require the voltage balance control of the voltage divide capacitors. This paper mentions about the transformer-less uninterruptible power supply which can omit the voltage divide capacitors. Delta-sigma modulation technique is introduced to the power supply and the proposed scheme has output voltage regulation function.