Static uninterruptible power supplies (UPS)

Uninterruptible power supplies (UPS) are interfaces between the electrical grid and sensitive AC loads.

• Static UPSs, which first appeared in the early 1970s, were the result of the advent of power semiconductor technology and the need for high-quality power supplies to power large-scale data centers. Since then, UPSs have undergone significant evolution, due to :

  • technologies, particularly in the field of power semiconductors;

  • the development of minicomputing and microcomputing; to meet these needs, the range of inverters on offer has expanded, and now ranges in power from a few hundred volt-amperes to several hundred kilovolt-amperes;

  • the extension of IT networks; the UPS is seen as an application peripheral, which means it must be able to communicate with these networks.

• In this article, we'll be talking about static UPS for alternating load, commonly known as inverters. In English, ASI is equivalent to UPS, which stands for "Uninterruptible Power Supply".

The term "inverter" can cover several realities depending on the context:

• the first is the entire interface between the network and the load;

• the second is the static converter, which generates alternating current from a direct current source.

To ensure continuity of service, UPS systems use chemical lead-acid or cadmium-nickel batteries.

• Before presenting the UPS, here's a brief overview of power system disturbances.

Voltage cuts correspond to an absence from the network lasting more than one minute.

Short voltage interruptions and voltage dips are phenomena lasting from 10 ms to a few tens of seconds, resulting in a voltage drop of between 10% and 100% of the nominal value. Examples include source changeover following a fault on a medium-voltage feeder, transformers switching on or motors starting up.

Micro-breaks are transient disturbances of less than 10 ms.

Overvoltages can be generated by load switching or tripping on the medium-voltage (MV) network. They are transmitted to the low-voltage (LV) network by MV/LV transformers.

Voltage distortion comes from non-linear loads, which generate voltage distortion as a function of network impedance. The level of distortion can cancel out the compatibility margin between the source and the load being supplied.