When any device always malfunctions, a redundant power supply scheme is needed to further improve the reliability of the entire power system. At present, the most widely used redundant power supply methods include primary backup redundant power supply and fully redundant parallel connection. Before discussing redundant power supply, it is necessary to first understand the four working states of online APC UPS:
1) Normal mains power: Under normal working conditions, energy is provided by the mains power. The rectifier converts AC power into DC power, and the inverter converts the rectified DC power into pure AC power and provides it to the load. At the same time, the charger float charges the battery pack.
2) Abnormal mains power: When the mains power is cut off or the voltage or frequency of the input mains power exceeds the allowable range, the rectifier automatically shuts down. At this point, the DC power provided by the battery pack is converted into pure AC power by the inverter and supplied to the load.
(3) The mains power is restored to normal: When the mains power is restored to normal, the rectifier provides rectified DC power to the inverter again, while the charger charges the battery pack.
(4) Bypass state: Static bypass is an important component of UPS system, and APC UPS is in bypass state in the following two situations.
① When the load is overloaded, short circuited (which can actually be considered a serious overload), or the inverter fails, in order to ensure uninterrupted power supply to the load, the static bypass switch is activated, and the mains power directly supplies power to the load.
② During maintenance or testing, for safe operation, close the maintenance bypass switch and supply power directly to the load from the mains. Isolating the APC UPS system ensures uninterrupted power supply to the load during UPS maintenance or testing.