In today’s world we are all inevitably and heavily dependent on technology to run our lives. One of the most important items in our lives is the computer. At work and at home we use our computers for communicating with others, information gathering and entertainment. We store huge amounts of vitally important data in our computers. The computer is no longer just a machine; rather, it has become a central part of our lives.
Power cuts and voltage fluctuations spell doom for computers. A UPS system or Uninterrupted Power Supply system protects our computers from power problems. Often, power cuts not only lead to the loss of data, they may also damage the internal hardware components. The recovery of the lost data is often impossible, and also leads to waste of precious time, money and energy.
Globally there are many manufacturers and suppliers of UPS competing for this market. Although the main function of this device is to provide power to the load in case of failure of the mains power, every brand is subtly different and there are many ways of providing this essential function. This paints a confusing picture for buyers of this product.
As a designer and manufacturer of AC and DC UPS Magellan power recognises its responsibility to clarify this confusing picture. So in a series of easy to digest articles Magellan power will demystify the technology and help you make an informed decision when it comes to specifying a UPS.
We sincerely hope that you find these articles of practical use.
An overview to AC UPS Topologies
Commonly available UPS's fall into the following categories:
Offline UPS: systems monitor the load voltage and generate a non-sinusoidal signal (square wave) once a blackout occurs.
The load is normally powered by the grid, there is no AC generation from the UPS as long as grid power is healthy.
This is a simple and low cost device and mostly come without self-diagnosis functions. This type of system is single phase and ranges up to 1kVA.
Advantages: Low cost.
Disadvantages: Transfers mains quality problems to the load, low quality square wave inverter output. Not suitable for some loads.
Line-Interactive UPS systems are similar to Offline UPS systems as they again generate mostly non-sinusoidal signal following grid power loss.
The only difference is that they come with a voltage regulator function which is basically an auto-transformer which changes its voltage in order to
regulate incoming voltage into desired output voltage (240VAC) during mains operation. These systems don’t contain self-diagnosis availability.
Following a mains loss, the inverter starts generating square wave signal with the stored energy in batteries, which may cause a disturbance of
between 10-20msec . Not all types of loads are immune to such disturbance but most computer power supplies can stand up to 20msec power loss.
Therefore, line interactive systems are considered a cheap solution where such interruption is bearable. This type of UPSs range between 500VA up to 3kVA.
Advantages: Low cost, solves most of mains voltage problems.
Disadvantages: Transfers mains disturbance problems to the load, mostly non-sinusoidal output. Not suitable for some loads.
Bi-Directional UPS: this type of system employs both rectifier and inverter in one single block. This means, the components that are allocated for battery charging and discharging is same. The Bi-Directional UPS synchronized to the grid connects directly across the load and the grid. The load is normally fed by filtered grid power and the UPS is in the charging mode. In the instance of power failure the direction of the UPS changes from charging to discharging and the load is fed by the Inverter. This can be classed as ideal UPS. It the most efficient and reliable type as the load is normally powered by the grid when it is available and so it is not necessary for the inverter to be constantly operating. The turn-around time is between 5-19mS. Nearly all loads will work with this type of UPS.
Advantages: Lower cost than double conversion UPS, high efficiency, high reliability. Employs advanced battery management system. Suitable for nearly all loads. Only loads that monitor zero-crossing of supply power may suffer.
Disadvantages: Load voltage not regulated during grid operation.
Online (Double Conversion) UPS, This topology simply converts AC incoming mains power into DC and converts it again into AC power for feeding critical loads. Thus, no matter what the quality of input signal, output signal is pure sinusoidal and at the desired frequency /amplitude without any negative effect to the Grid. The PWM (Pulse Width Modulation) technique employed caused small amount of Total current harmonic (THD) distortion to the load and the grid power. This type of UPS (depending on the brand) can also help to correct the input power actor. Moreover double conversion units protect the load against voltage surges, dips and harmonics likely to be delivered by grid to the load.
This type of unit ranges from 1kVA and goes up to 1200kVA in one frame. These units can also be paralleled for capacity increase or achieving redundancy.
Advantages: Produces constant, high quality pure sinewave power for the load, employs advanced battery management system.
Disadvantages: More costly, less reliable than Bi-Directional UPS.
As Magellan is an Australian designer and manufacturer we have more knowledge than most when it comes to UPS. Why not use this knowledge?
Please contact us with any UPS questions you may have.