UPS Applications in Data Centers ( Part 1)

UPS is an abbreviation for Uninterruptible Power System. A UPS is a power conversion device that uses AC mains power/generator as its input energy source. After appropriate conversion and regulation, it provides a stable and reliable AC power supply to critical loads (or sensitive loads). A UPS contains internal energy storage and conversion devices. When the mains power fails, the internal energy storage device continues to supply power to the critical load until the mains power is restored, the generator starts supplying power, or the energy storage is depleted. When the UPS fails, the mains power is temporarily and directly supplied to the load without interruption through the conversion device. Therefore, a UPS can guarantee uninterrupted power supply to the load under any circumstances.

Backup UPS

Standby UPS systems are the most common type used for personal computers. As shown in the diagram, under normal conditions, the load is directly powered by AC mains through the UPS switch, while the AC mains simultaneously charges the battery via a charger. If the AC mains fails or its parameters exceed set values, the system switches to a battery/inverter as a backup power source. In this situation, the transfer switch must operate to switch the load to the battery/inverter backup power. The inverter only starts when the power supply fails, hence the name “standby.” The main advantages of this design are high efficiency, small size, and low cost. With appropriate filtering and surge protection circuitry , these systems can also provide adequate noise filtering and surge suppression.

Online Interactive UPS

Online interactive UPS systems are the most common design for small businesses, websites, and departmental servers. In this design, the battery-to-AC converter (inverter) is always connected to the UPS output. If the input AC power is normal, operating the inverter in reverse charges the battery. If the input power fails, the transfer switch opens, and power is supplied to the UPS output via the battery. Compared to a standby UPS topology, this design further enhances filtering and reduces switching transient overvoltages because the inverter is always on and connected to the output.