Uninterruptible Power Supplies and Harmonics

Harmonic pollutants is a developing hassle in Europe and one which designers of energy continuity programmes and producers of UPS (uninterruptible energy supplies) can’t ignore. Typical harmonic issues consist of the distortion of mains energy deliver voltage, overheating of wiring, impartial conductors, deliver transformers and switchgear and nuisance tripping of breakers. Harmonics also can reason disruption to gadget at the equal deliver and cause random failures.

Harmonics are resulting from voltage or present day waveforms with frequencies which can be multiples of the essential frequency – in Europe, 50Hz (50 cycles according to second). The multiples are constantly ordered in a particular sequence: for example, the second harmonic is 100Hz (2x50Hz), the 0.33 150Hz and the fourth 200Hz and so on.

The unique hassle of Triplens (0.33 order) harmonics. Harmonics are a selected problem for energy continuity control because of the huge quantity of transfer mode energy deliver (SMPS) masses being related to trendy electric distribution networks – and their related UPS structures. These are the maximum not unusualplace shape of energy deliver unit (PSU) in use today. As a non-linear load, they draw their energy in normal modulated pulses of present day from a mains energy deliver in preference to as a non-stop linear deliver. This can cause SMPSs producing excessive stages of harmonics, mainly while many are being provided from a unmarried 3-segment mains energy deliver.

In unique, gadget designers need to be aware about the doubtlessly unfavorable Triple-Ns (or Triplens) whose harmonic order numbers are multiples of 3 and consist of the infamous 0.33-harmonics in addition to ninths and fifteenths. Thirds are in all likelihood the maximum hard harmonic in phrases of impartial conductor loading inside a 3-segment gadget. Whereas different harmonics cancel every different out, 0.33-harmonics are in segment with every different and showcase a summing impact which substantially will increase the present day – doubtlessly overloading conductors and switchgear.

Harmonics and overall energy element – implications for UPS sizing. Harmonics also are carefully associated with energy element control – and every other key issue of uninterruptible energy deliver gadget layout and implementation. The displacement energy element is best relevant to the essential frequency (50Hz in Europe) and consequently does now no longer remember the energy element generated with the aid of using any harmonics triggered into the mains energy deliver with the aid of using the burden itself (known as the distortion energy element and produced with the aid of using the harmonics produced with the aid of using non-linear masses). The mixture of the displacement energy element and the distortion energy element offers what is thought to UPS structures specialists because the genuine energy element. When efficaciously sizing a UPS, an know-how of that is critical.

Mitigation of overall harmonics distortion. Harmonics problems want to be addressed on the layout degree of any energy continuity plan. Not least, due to the fact clients are answerable for the harmonic stages brought into their 3-segment mains energy deliver.

A UPS can on occasion be equipped with a harmonic clear out out (publish set up) however this will be a high priced and inelegant answer as large inner wiring modifications can be required. For a transformer-primarily based totally UPS, the use of a 12-pulse rectifier in vicinity of a 6-pulse set will lessen the stages of THDi (overall harmonic distortion). Coupling this with a passive clear out out will offer similarly discount to round 4%.

For a transformerless uninterruptible energy deliver, THDi stages of much less than 4�n be carried out with the aid of using putting in an energetic harmonic clear out out. However, stages as little as 3�n now be carried out with the aid of using a few designs whose rectifiers are IGBT (Insulated Gate Bipolar Transistor) primarily based totally. This can get rid of the want for a further energetic harmonic clear out out and simplify the UPS layout process. Such designs are anticipated to turn out to be the norm: now no longer best do they lessen preliminary costs, however they permit a smaller UPS gadget footprint while growing enter energy elements.

Active harmonic filters lessen the effect of main energy elements. When designing a energy continuity plan and UPS gadget, diverse techniques may be carried out to lessen the effect of main energy elements (wherein the present day waveform leads the voltage waveform): making sure that main energy elements constitute a smaller percent of the UPS load, putting in energy element correction among the UPS and the burden, growing UPS size (and that of any standby technology capacity) and specifying a UPS with main energy element capabilities.

A famous method to lessen the impact of main energy elements on a UPS set up is to apply an energetic harmonic clear out out with energy element correction at the UPS output. This affords the UPS with a extra applicable load, however effects in better capital and set up costs, decreases performance and an extra footprint.