Experts explain how uninterruptible power supplies work

1. Normal operation mode

The power supply principle of the uninterruptible power supply system is that when the mains power is normal, the machine will convert the mains AC power into DC power, and then charge the battery for use when the power is cut off. What I want to emphasize here is that the uninterruptible power supply system will not only work when there is a power outage. For example, when the voltage is too low or too high, or there is a momentary surge, etc., which is enough to affect the power quality of the normal operation of the equipment, the uninterruptible power supply system will work to provide the equipment with stable and clean power.

When the mains is supplying electricity normally, after passing through the filtering circuit, it is divided into two circuits that operate simultaneously. One is to charge the battery pack through the charging circuit, and the other is to pass through the rectification circuit as the input of the inverter, and then provide power to the load through the inverter conversion. It can be seen that the output of the online uninterruptible power supply system is completely supplied by the inverter, so no matter what the quality of the mains power is, its output is stable and not affected by anything.

2. Battery working mode

Once the mains power fails, the DC power stored in the battery will be converted to AC power. At this time, the input of the inverter will be supplied by the battery pack, and the inverter will continue to provide power to the load for continuous use, achieving the function of uninterrupted power supply. The power source of the UPS uninterruptible power supply system is the battery, and the capacity of the battery is limited. Therefore, the uninterruptible power supply system will not be as unlimited as the mains power supply. Therefore, no matter how large the capacity of the uninterruptible power supply system is, when it is fully loaded, the power supply time must be limited. If you want to extend the discharge time, you must purchase a long-term uninterruptible power supply system.

3. Bypass operation mode

When the online UPS is overloaded, bypass command (manual or automatic), inverter overheats or the machine fails, the UPS generally converts the inverter output to bypass output, that is, it is directly powered by the mains. Since the UPS output frequency phase must be the same as the mains frequency phase during bypass, the phase-locked synchronization technology is used to ensure that the UPS output is synchronized with the mains. The bypass switch bidirectional thyristor parallel working mode solves the bypass switching time problem and truly achieves uninterrupted switching. The control circuit is complex and is generally used in medium and high power UPS. If overloaded, the load must be reduced manually, otherwise the bypass short circuit will automatically cut off the output.

4. Bypass maintenance method

When the UPS is under maintenance, the normal power supply of the load equipment is guaranteed by manual bypass. After the maintenance operation is completed, the UPS is restarted and the UPS returns to normal operation. The extremely low maintenance rate, MTTR is 150,000 hours, greatly improving the availability of the UPS uninterruptible power supply.