Battery powered uninterruptible power supplies (UPS) are crucial in protecting sensitive equipment in data centers, medical facilities, factories, telecommunications hubs, and even homes from short-term power grid spikes and outages. In the event of a prolonged power outage, they can provide the necessary short-term electricity to achieve a prepared outage and prevent data loss.
UPS can generally be classified as “Online” or “Offline”. In offline UPS, the load is directly connected to the grid. When the input power fails, the system will switch to battery power mode – the switching process usually takes about 10 milliseconds to complete, which limits the use of offline UPS in some applications. Online UPS adds an inverter circuit and battery charging and discharging circuit between the load and the grid, and the inverter remains in operation regardless of whether the input power is normal or not. Therefore, when there is an input problem, the online UPS can perform “zero interruption” switching and provide emergency power to the load through the battery.
Modular UPS is more favored by designers and users, as lower power UPS can be connected in parallel to meet greater electricity demand. Modular UPS can quickly and easily expand existing UPS systems and help customers profit in the process of establishing large-scale systems.
However, like any power supply design, the design of efficient UPS also presents challenges. Some key factors to consider include size, input-output regulation capability, battery management, and topology.
Size is crucial, especially in applications where space is extremely valuable such as data centers. In the past, transformers have always been one of the largest components in UPS, but with the emergence of more advanced semiconductor technology, high-frequency switch circuits have replaced transformers, saving space. A transformerless UPS can provide hundreds of kVA of emergency power to large data centers in standard sized cabinets.
Online UPS uses high-frequency PWM (Pulse Width Modulation) to perform dual conversion (AC-DC and then DC-AC), which can solve many input quality problems that offline UPS cannot handle, such as low voltage overvoltage and line noise, while reducing battery usage and extending battery life.