Uninterruptible power supply device having independent bypass function

A method of operating an uninterruptible power supply device including a first switch for connecting an output of an inverter to a load, a second switch for connecting a bypass line to the load, and an STS control unit configured to control operations of the first switch and the second switch, the first switch including a power switching semiconductor capable of active switching control, the second switch including a power switching semiconductor capable of active switching control and an SCR switch, the power switching semiconductor and the SCR switch being connected in parallel with each other, the method comprising:

• a first step (S100) in which the STS control unit performs control such that an off signal is applied to a gate of the power switching semiconductor capable of active switching control of the first switch, and simultaneously the SCR switch of the second switch is turned on first and then the power switching semiconductor capable of active switching control is sequentially turned on when an abnormality occurs in the inverter;
• and
• a second step (S200) in which the STS control unit performs control such that the SCR switch, the mechanical switch, and the power switching semiconductor capable of active switching control of the second switch are sequentially turned on, and then the SCR switch and the mechanical switch are turned off and the power switching semiconductor capable of active switching control is maintained in a turn on state.