Output Isolation transformer-based UPS is most commonly used in all the critical applications where the load characteristics are non-linear, inrush, and high starting current. Any critical facility using this technology gives higher reliability and rigidness.
The UPS is connected between the three-phase input power and important loads (like computers) and offers quality three-phase power to the loads. It has the following features:
The operating principle of the stand-alone UPS. The first AC-DC conversion adopts a three-phase full-wave rectifier to convert the three-phase AC input voltage into the steady DC bus voltage.
The rectifier can also be used as a charger. The inverter takes the IGBT half-wave circuit as its inversion topology. The advanced Space Vector Pulse Width Modulation (SVPWM) is used to control the system, which inverts the DC bus voltage into AC voltage output. When the AC is normal, the rectifier and the inverter work at the same time and simultaneously charge the battery. In case of abnormal AC, the rectifier stops working, and the battery supplies power via the inverter. If the battery voltage drops below the cutoff voltage and the AC is not yet back to normal, the UPS shuts down. (If the major circuit and the bypass circuit are not of the same source and the bypass circuit is normal, the system is powered by the bypass circuit). The cutoff voltage is preset (e.g. the factory setting is 1.67V, and the battery cutoff voltage is 320Vdc). In case of abnormal AC, the battery powers the UPS until its voltage drops to the cutoff voltage. This period is called the “backup time”, the length of which depends on the battery’s capacity and the loads.