Uninterruptible power supply system

An uninterruptible power supply system, comprising:

• a regular uninterruptible power supply device configured to (i) in a normal state where AC power is supplied from a first AC power supply, convert the AC power from the first AC power supply into DC power, store the DC power in a power storage device and convert the DC power into AC power, and supply the AC power to a load, and (ii) in a power failure state where supply of the AC power from the first AC power supply is stopped, convert the DC power in the power storage device into AC power and supplies the AC power to the load;
• and
• an auxiliary power conversion device that does not use a battery and is configured to convert AC power supplied from a second AC power supply into DC power, convert the DC power into AC power, and supply the AC power to the load when the regular uninterruptible power supply device has a failure, wherein
• the auxiliary power conversion device includes:
• a first converter configured to convert the AC power supplied from the second AC power supply into DC power,
• a first inverter configured to convert the DC power generated by the first converter into AC power, and
• a first control device configured to control the first inverter such that:
• (i) in a first case where a DC voltage generated by the first converter is higher than a predetermined voltage, an output voltage of the auxiliary power conversion device is set to an AC voltage having a sinusoidal waveform and falling within an acceptable input voltage range of the load;
• and
• (ii) in a second case where the DC voltage generated by the first converter is lower than the predetermined voltage, the output voltage of the auxiliary power conversion device is set to an AC voltage having waveform distortion within an acceptable range for the load and falling within the acceptable input voltage range of the load,
• the regular uninterruptible power supply device includes:
• a second converter configured to convert the AC power supplied from the first AC power supply into DC power,
• a second inverter configured to convert the DC power into AC power, and
• a second control device configured to control the second converter and the second inverter such that an output voltage of the regular uninterruptible power supply device is set to a rated AC voltage having a sinusoidal waveform, and
• in the normal state, the DC power generated by the second converter is stored in the power storage device and is supplied to the second inverter, and in the power failure state, the DC power in the power storage device is supplied to the second inverter.