UPS Inverter Waveforms

A common misconception is that a UPS System will provide continuous power, the same as, or better than the utility. In many cases, the power supplied by the UPS when on battery is inferior to the standard mains supply, and this article is designed to make you, the user, aware of the differences and to explain the best choice of UPS Inverter.

For anything other than online double conversion technology, when a UPS goes into battery mode the UPS inverter will activate, and this may be a sine wave inverter, or a non-sine wave inverter. In low cost systems, the inverter will be non-sine-wave, also known by a multitude of other names such as Pseudo Sine Wave, Modified Sine Wave, Approximated Sine Wave, Step Wave, Stepped Sine, Square Wave, Generalised Sine Wave etc.

In fact, unless the specifications state “Sine Wave”, with a Total Harmonic Distortion (THD) of less than 8%, the system is non-sine, regardless of what the description states. So what does this mean with your choice of UPS inverter?

Well, square wave (or non-sine wave systems) are only suitable for certain loads, such as computer type power supplies known as Switched Mode Power Supplies (SMPS). They are not suitable for anything else. In addition, it is bad practice to allow a non-sine-wave inverter to power loads for extended periods of time. This is because the square wave nature is in effect high frequency transients which are responsible for electronic component degredation. For long runtime battery backed solutions we recommend you only use sine wave systems – as you would ordinarily get from the utility.

A sine wave UPS System has maximum application compatibility and is suitable for extended run applications as all loads can be powered by a sine wave power source, as they are designed to do.