What are the key differences between online, offline and line-interactive UPSs?

05 Sep.,2024

 

When it comes to uninterruptible power supplies, there are a range of solutions to choose from. One of the most common questions that we often get asked, is what the difference is between online, offline and line-interactive UPSs and which one a particular business needs.

The UPSs used in most applications today use solid-state technology to manage their power control and communications functions, and are therefore described as static UPS systems.

Before static UPS systems a rotary system was typically used. This system used flywheels to convert and store energy, before converting it back into electrical energy when needed. Nowadays, static systems have largely superseded rotary systems due to their reduced size and weight, their increased efficiency and the high cost and complexity of maintaining a rotary system.

Types of Static UPS Systems

Static UPS systems are available in various power topologies. Generally speaking, there are three main operational design architectures for UPS units and modules, which are offline, online and line-interactive. All are designed around a stored energy source – usually a lead/acid battery – that accumulates power from the electrical mains supply during normal power availability, and then dispenses it to the critical load during mains supply disturbances or blackouts. This means that they use common building blocks; a rectifier/charger to convert incoming AC into a DC charging current for the battery; an inverter to generate AC current for the critical load; and a static switch to connect either the inverter output or the mains supply to the critical load as circumstances demand.

These components interact in protecting the load within either an online, offline or line-interactive topology. As we shall see, these modes represent different trade-offs between capital, operating costs, and levels of protection. It is up to each user to decide which approach is most appropriate to the needs of their communications and data processing load, and the business that it supports.

 

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