Inverters and harmonics (case studies of non-linear loads)

Introduction to static UPS

Static UPS are virtually perfect electric generators. They are highly reliable and, by nature, ensure (within the performance limits of the battery) the uninterrupted availability of electric power. As regards electrical characteristics, the inverter (which constitutes the UPS generator) possesses from the point of view of frequency stability as well as voltage stability, performances superior to those of the mains.

The only doubtful characteristic is, in the opinion of many engineers, its ability to deliver a sinusoidal voltage regardless of the shape of the current drawn by the load. The aim of this «Cahier Technique» is to clarify this point and to demonstrate that modern inverters are excellent generators of sinusoidal voltage even when they supply non-linear loads. This is considered quite normal as UPS are designed and very often utilised to supply computer/ microprocessor systems which draw non-sinusoidal currents.

Harmonic analysis of a periodic function

As alternating non-sinusoidal currents and voltages are the main topic of this study, it will be worth while to review the electric quantities in the presence of harmonics.

AUTHOR: Schneider Electric expert | Jean Noël FIORINA