The DPA way - Why decentralized parallel architecture increases UPS availability and lowers cost of ownership

Overview

The starting point is availability: power availability is driven by MTBF and MTTR, and raising the MTBF while cutting the MTTR of the power protection system are the two main levers. In DPA each module contains a rectifier, inverter, battery converter, static bypass switch, back-feed protection, control logic and display; only I/O, signalling, maintenance bypass and sometimes a display are common to the frame, which removes single points of failure such as a shared static bypass.

Transfer to bypass is decided by majority vote of the module CPUs; in a split vote the load stays on the inverter. Load sharing uses one master module controlling cross-currents, and if the master fails the next module takes over. The redundancy options described are N+1, 2N and 2N+1, with 2N+1 considered sufficient for most premium requirements.

The article argues that modularity eases N+1/2N redundancy, scaling and hot-swap service. Conceptpower DPA 500 efficiency is quoted at up to 96% with a flat efficiency curve, and online module swap is credited with enabling 99.9999% availability. As a short vendor article, these figures are manufacturer claims rather than independently verified results.

Key points

1. Power availability is driven by MTBF and MTTR; raising MTBF and cutting MTTR are the two levers.
2. In DPA each module has rectifier, inverter, battery converter, static bypass, back-feed protection, control logic and display; only I/O, signalling, maintenance bypass and sometimes a display are shared.
3. Transfer to bypass is a majority vote of module CPUs; a split vote keeps the load on the inverter.
4. Load sharing uses a master module controlling cross-currents; the next module takes over if it fails.
5. Redundancy options: N+1, 2N and 2N+1, with 2N+1 considered sufficient for most premium requirements.
6. Conceptpower DPA 500: up to 96% efficiency with a flat curve; online module swap credited with 99.9999% availability (vendor claim).

Using it in design

• Give the UPS catalog an architecture field {monolithic, CPA modular, DPA modular}, module kW, modules per frame, maximum frames in parallel and per-module static bypass (yes/no).
• Count module redundancy (N+1 inside a frame) separately from system redundancy (2N between frames) in the redundancy calculator.
• In the reliability model flag single points of failure for CPA systems with a common static bypass, and use MTTR as an input so hot-swappable modules can reduce computed unavailability.

Who should read it

Electrical designers choosing UPS architecture and assessing the availability impact of modular UPS.

Related standards

• IEC 62040-3

Publication details

Authors

ABB

Publisher

ABB

Year

2014

Document language

English

Source type

Manufacturer

Access

Free to read

Licence

Copyright retained; citation only — the publisher’s terms apply to the original document

Citation