# Online double-conversion UPS

Canonical URL: https://eloragrid.ai/symbols/online-double-conversion-ups
Publisher: Elora Grid
Updated: 2026-10-28
Lookup label: UPS VFI
Drawing use: SLD
Reference families: IEC, IEEE / ANSI

A UPS whose rectifier and inverter carry the load continuously, with the battery on the DC link and a static bypass.

## In plain English

### What does Online double-conversion UPS mean?

In an online double-conversion UPS the load is always supplied by the inverter. The rectifier converts incoming AC to DC, the battery floats on the DC link, and the inverter produces a regulated output that is independent of input voltage and frequency variations. When the input fails, the battery simply takes over the DC link with no transfer.

### A simple example

Single-line diagrams show rectifier and inverter blocks in series with the battery connected between them, a static bypass switch in parallel, and often a separate bypass input and an external maintenance bypass. Output isolation transformers may also be shown.

### What the drawings help you do

The double-conversion path costs a few per cent in efficiency and some units offer an eco mode that runs on bypass, which changes the protection the load actually receives. The symbol does not show which mode is set, battery autonomy or the bypass source arrangement.

### This particular reference

A UPS whose rectifier and inverter carry the load continuously, with the battery on the DC link and a static bypass. An online UPS powers the load through the inverter all the time; a line-interactive UPS passes mains to the load and only inverts during disturbances.

### Terms

- DC: Direct current: electricity flowing in one direction.
- AC: Alternating current: electricity whose direction changes periodically.
- Winding: A coil of conductor inside an electrical machine or transformer.

Concept diagram: Identify the device and form → Read the connections and state → Check the equipment reference
A guide to reading this reference. The original symbol illustration and its drawing notes appear below; these boxes are not a wiring diagram.

- [DC UPS, AC UPS and capacitor buffer modules](https://www.phoenixcontact.com/en-gb/products/uninterruptible-power-supplies-ups)
- [Multilevel NPC converter application context](https://www.infineon.com/product-information/sic-modules-for-ups-design-and-efficiency-guide)


## What it represents

In an online double-conversion UPS the load is always supplied by the inverter. The rectifier converts incoming AC to DC, the battery floats on the DC link, and the inverter produces a regulated output that is independent of input voltage and frequency variations. When the input fails, the battery simply takes over the DC link with no transfer.
Single-line diagrams show rectifier and inverter blocks in series with the battery connected between them, a static bypass switch in parallel, and often a separate bypass input and an external maintenance bypass. Output isolation transformers may also be shown.
The double-conversion path costs a few per cent in efficiency and some units offer an eco mode that runs on bypass, which changes the protection the load actually receives. The symbol does not show which mode is set, battery autonomy or the bypass source arrangement.

## How to read it

- Look for separate rectifier and bypass inputs; they may come from different boards.
- Check whether eco mode is enabled.

## Information to show or reference

- State kVA, kW and battery autonomy.
- Show static bypass and maintenance bypass.
- Reference operating mode.

## Important distinction

An online UPS powers the load through the inverter all the time; a line-interactive UPS passes mains to the load and only inverts during disturbances.

## Facts

- Load path: Rectifier, DC link, inverter
- Transfer on input failure: None
- Bypass: Static and maintenance
- Preview: Independent educational illustration; consult the applicable standard and project legend for the exact graphic

## Public references

- [DC UPS, AC UPS and capacitor buffer modules](https://www.phoenixcontact.com/en-gb/products/uninterruptible-power-supplies-ups) — Phoenix Contact. Public UPS function context.
- [Multilevel NPC converter application context](https://www.infineon.com/product-information/sic-modules-for-ups-design-and-efficiency-guide) — Infineon Technologies. Public UPS converter design context.

## Graphic scope

Independent original educational concept illustration by Elora Grid. Not a certified standards graphic or manufacturer footprint. Unitless; not to scale. Original artwork licence: https://creativecommons.org/licenses/by/4.0/. Publisher material is linked only.