energy systems

Despite all UPS protect their loads against power cuts, there are three main base types: off-line, line-interactive and on-line.

The advantage or disadvantage of using any of the types sticks mainly to the type of loads to be protected (sensitivity of loads to the mains problems).

Off-Line Typology

Typology off-line is the simplest of the three typologies and can be described by the following block diagram.

The four main components of the unit are: the battery charger, the battery bank, the inverter and the by-pass switch.

The charger converts the mains’ AC voltage into DC voltage to be stored in the batteries. The converter generates an alternate voltage from the DC voltage of the batteries, which will be used to power the load; finally, the “bypass” switch allows connecting the load to the mains or to the inverter.

The operation of off-line units can be described as follows: when the supply voltage is present the switch is in the position mains -> load and all the problems of the electricity pass to the load. For all intents and purposes, in this case, the load is on the situation as if it were attached directly to the mains.

In addition to the mains being feeding the load, it’s also powering the batteries through the charger.

When there is a power failure, the switch moves to the lower position and the load is being powered by energy from the batteries that is converted to AC current by the inverter. In this case, the charger can no longer feed the batteries, and autonomy time depends on the number of batteries and their capacity.

UPS of this type are typically used to power appliances that do not require good protection and tolerate easily power micro cuts, since the bypass switch is most often implemented using electromechanical relays with reaction times above the recommended, for ex. for computers.

Units with this type of typology have, however, the advantage of having lower prices.

Line – Interactive Typology

The typology Line-Interactive is very similar to the off-line, with the added advantage of protecting the load against brownouts and surges, having to this purpose a voltage regulator module. The block diagram of this typology is shown in the following figure:

When the supply voltage is present the switch is in the position mains -> load and feeding proceeds in the way mains -> voltage regulator -> load and the load is protected against brownouts/surges.

In addition to the mains being feeding the load, it’s also powering the batteries through the charger.

When there is an electrical failure, the switch moves to the bottom (inverter -> load) and the load is being powered by energy from the batteries that is converted to AC voltage by the inverter. In this case, the charger can no longer feed the batteries, and autonomy time depends on the number of batteries and their capacity.

With this type of UPS typology load is protected against brownouts/surges and cuts. If the by-pass switch is implemented using electromechanical relays the micro cuts continue to exist. However, if the bypass switch is of the static type (using semiconductors), the time switching network -> inverter is almost nil.

On-Line Typology

This is the best of the three types of typologies because it protects the load of all kinds of problems from the mains.

As showed in the figure, in this typology there is no bypass switch. The input voltage (sine wave) is rectified by the charger resulting in DC voltage that charges the batteries and powers the inverter; the latter converts the DC voltage to alternate voltage that will supply the load.

When there is a power failure the batteries provide the power needed to run the inverter.

There is a total isolation between input and output which enables the load protection against all the mains’ existing problems.