Uninterruptible power system with backfeed detection and method of operating the same

A method of operating an uninterruptible power supply system, wherein the uninterruptible power supply system comprises:

• a power conversion apparatus having an input terminal and an output terminal, the input terminal receiving an AC power source and converting the AC power source to supply an AC load, and the power conversion apparatus comprising an energy storage apparatus;
• a switch unit having a first input terminal, a second input terminal, and an output terminal switchably connected to the first input terminal or the second input terminal, the second input terminal connected to the output terminal of the power conversion apparatus and the first input terminal connected to the input terminal of the power conversion apparatus,
• wherein the method comprises:
• (a) determining the uninterruptible power system is operated in a backup supply operation when the AC power source is disabled, the switch unit output terminal is disconnected from the first input terminal and connected to the second input terminal, and the power conversion apparatus provides a backup power to supply the AC load;
• (b) determining whether a bypass input voltage at the input terminal of the power conversion apparatus of the uninterruptible power system is detected when the uninterruptible power system is in the backup supply operation;
• (c) determining by a comparison unit whether an output voltage of the output terminal of the switch unit is identical to the bypass input voltage and lasts for more than a predetermined time period when the bypass input voltage of the uninterruptible power system is detected, the bypass input voltage and the output voltage are determined to be identical when their frequency, phase, and magnitude are determined to be completely identical;
• and
• (d) determining that the switch unit is in a backfeed failure operation when it is determined that the output voltage is identical to the bypass input voltage and lasts for more than the predetermined time period, and represents that the first input terminal and the second input terminal are shorted.

A method of operating an uninterruptible power supply system, wherein the uninterruptible power supply system comprises:

• a power conversion apparatus having an input terminal and an output terminal, the input terminal receiving an AC power source and converting the AC power source to supply an AC load, the power conversion apparatus comprising an energy storage apparatus;
• a switch unit having a first input terminal, a second input terminal, and an output terminal switchably connected to the first input terminal or the second input terminal, the second input terminal connected to the output terminal of the power conversion apparatus and the first input terminal connected to the input terminal of the power conversion apparatus;
• wherein the method comprises the following steps:
• (a) determining whether a bypass input voltage at the input terminal of the power conversion apparatus of the uninterruptible power system is detected;
• (b) determining whether the uninterruptible power system is operated in a backup supply operation when the bypass input voltage of the uninterruptible power system is detected, the switch unit output terminal disconnected from the first input terminal and connected to the second input terminal, and the power conversion apparatus provides a backup power to supply the AC load;
• (c) determining by a comparison unit whether an output voltage of the output terminal of the switch unit is identical to the bypass input voltage and lasts for more than a predetermined time period when the uninterruptible power system is in the backup supply operation;
• the bypass input voltage is determined to be identical to the output voltage when their frequency, phase, and magnitude are determined to be completely identical;
• and
• (d) determining that the switch unit is in a backfeed failure operation when it is determined that the output voltage is identical to the bypass input voltage and lasts for more than the predetermined time period, and represents that the first input terminal and the second input terminal are shorted.