A novel simple voltage regulation method for uninterruptible power supply without transformer and voltage divide capacitor

The inverters and converters included in uninterruptible power supplies are often coupled by high-frequency transformers. But using transformer results in high cost and heavy weight power supply. Therefore, a circuit, which omit transformer, is suggested. This method uses dc bus voltage divide capacitors and these capacitors needs comparative large capacitance and voltage balance control is required. This paper treats an uninterruptible power supply which does not need for voltage divide capacitors. The proposed method adopts an improved delta-sigma modulator and the scheme has the output voltage regulation feature without PI controller design.