Method for operating power factor correction circuit and method for operating uninterruptible power supply apparatus

A method for operating an uninterruptible power supply (UPS) apparatus, wherein the UPS apparatus includes a PFC circuit, a DC-DC converting circuit, and an inverter circuit coupled to the PFC circuit and the DC-DC converting circuit, wherein the PFC circuit includes two T-type converters, and each of the T-type converters includes four switching tubes, wherein the method comprises:

• converting, by the PFC circuit, AC input voltage into a positive bus voltage across a first capacitor and a negative bus voltage across a second capacitor that is connected in series with the first capacitor and converting, by the inverter circuit, the positive bus voltage and the negative bus voltage into AC output voltage when the UPS apparatus is operated under a normal supply mode;
• converting, by the DC-DC converting circuit, DC input voltage into the positive bus voltage and the negative bus voltage and converting, by the inverter circuit, the positive bus voltage and the negative bus voltage into the AC output voltage when the UPS apparatus is operated under a battery supply mode;
• and
• controlling conduction states of the switching tubes of the T-type converters to balance the positive bus voltage and the negative bus voltage when the UPS apparatus is operated under the battery supply mode.