According to the working mode of UPS, it can be divided into online UPS and offline UPS Offline UPS, also known as various types of UPS, can be divided into sine wave output, square wave output, with or without voltage regulation.

(1) Various types of UPS refer to the inverters in UPS that only work when the mains power is interrupted or under voltage is abnormal (under voltage value is about 170V, which is the UPS input voltage), to supply power to the load, while the inverters do not work normally and are in various states of use.

Figure 1 shows the power flow diagram of various UPS systems. When the mains power supply is normal, on the one hand, the mains power is directly converted through the AC bypass branch switch and output to the load through the filter; On the other hand, through a power transformer, it is rectified and converted into direct current, which is then charged to the battery pack through a charging circuit. When the mains power supply is interrupted, the stored energy in the battery is converted into AC power through the inverter and continues to supply power to the load through the filter. In various types of UPS, the actual circuit also contains various protection, alarm and other control circuits, which are relatively complex.

(2) Figure 2 shows the power flow diagram of an online UPS. When the mains power supply is normal, the mains power passes through the power transformer and rectifier, and then outputs to the load through the inverter and filter; Another way is to charge the battery pack through the charging circuit. When the mains power is interrupted, the voltage at the end of the battery pack is lower than the set value, or the inverter fails, the mains power is supplied to the load through the bypass branch through the conversion switch and filter. From this, it can be seen that regardless of whether the mains power is normal or interrupted, the inverter of the online UPS is always working.

(3) The main components of UPS include inverters, batteries, rectifiers/chargers, and transfer switches. The inverter is mainly composed of a transistor, a transformer, and a control circuit. Its function is to convert DC into AC output. It is the core part of UPS, and the technical performance and quality of UPS mainly depend on it. The battery is a UPS energy storage device. The batteries in UPS should have good high current discharge characteristics, be able to withstand repeated charging and discharging, and have a long lifespan. Currently, maintenance free sealed lead-acid batteries are commonly used in UPS. A rectifier/charger is a device that converts mains electricity into direct current, providing electrical energy for inverters and batteries. The function of the transfer switch (static switch) is to quickly switch the UPS to the bypass output through an instantaneous high-speed detection circuit when there is interference or a large surge in the mains power, in order to protect the UPS; Its second function is to provide a maintenance channel. Require fast switching time and high overload capacity for the conversion switch.