The working process of an online UPS is that when the power grid is supplying power normally, the AC power is input into the transformer, and on the one hand, it is charged by the charger to the battery, and on the other hand, it is converted into DC by the rectifier and sent to the inverter. After being converted into AC by the inverter, it is sent to the load through the output transformer, and finally sent to the load through the conversion switch (K-connection 4 points). The current flow of electrical energy is as follows:

          From the above, it can be seen that an online UPS refers to a system in which the power grid charges the battery while processing and transforming it internally before delivering it to the load during normal power supply; When there is a power outage or abnormal power supply in the power grid, the battery provides electrical energy to the inverter to ensure uninterrupted power supply to the load. When the power supply from the grid is interrupted or the battery is used, there is no interruption in the load power supply. Of course, this is the situation when there are no internal faults within UPS. If any unit inside the UPS fails, the control circuit can switch the transfer switch from point K to point A to point B, thus achieving bypass output. This kind of conversion has two reasons: firstly, there is a conversion time (power supply is interrupted), and secondly, the mains power must not be interrupted at this time, otherwise the load power supply will not be guaranteed. In order to ensure that the conversion process does not affect the load operation, the conversion time should be as short as possible. Considering the energy storage effect of larger filtering capacitors, the conversion time should generally be less than 3ms. At present, UPS with slightly higher power mostly uses static contactless electronic switches to shorten the conversion time, which greatly reduces the conversion time.