Editing Power factor (section)

=== Power factor correction (PFC) in non-linear loads ===

==== Passive PFC ====
The simplest way to control the [[Harmonics (electrical power)|harmonic]] current is to use a [[electronic filter|filter]] that passes current only at [[utility frequency|line frequency]] (50 or 60&nbsp;Hz). The filter consists of capacitors or inductors and makes a non-linear device look more like a [[linear]] load. An example of passive PFC is a [[valley-fill circuit]].

A disadvantage of passive PFC is that it requires larger inductors or capacitors than an equivalent power active PFC circuit.<ref>{{Citation |url=http://www.nuvation.com/corporate/news/newsletter/fall2006/powersupply.html |publisher=Nuvation |date=Fall 2006 |title=Power Supply Design Principles: Techniques and Solutions, Part 3 |newspaper=Newsletter |first=Ben |last=Schramm |url-status=dead |archive-url=https://web.archive.org/web/20070309134617/http://www.nuvation.com/corporate/news/newsletter/fall2006/powersupply.html |archive-date=2007-03-09 }}</ref><ref>{{Citation | newspaper = Xplore | title = Quasi-active power factor correction with a variable inductive filter: theory, design and practice | volume = 18 | issue = 1 | pages = 248–255 | publisher = IEEE| doi = 10.1109/TPEL.2002.807135 | bibcode = 2003ITPE...18..248W | year = 2003 | last1 = Wolfle | first1 = W.H. | last2 = Hurley | first2 = W.G. }}</ref><ref>{{Citation |publisher=Nuigalway |type=project |url=http://www.nuigalway.ie/power_electronics/projects/quasi_active.html |place=[[Ireland|IE]] |title=Power electronics |contribution=Quasi-active Power Factor Correction: The Role of Variable Inductance |last1=Wölfle |first1=W. H. |last2=Hurley |first2=W. G. |access-date=2008-11-05 |archive-date=2020-08-06 |archive-url=https://web.archive.org/web/20200806105647/http://www.nuigalway.ie/power_electronics/projects/quasi_active.html |url-status=dead }}</ref> Also, in practice, passive PFC is often less effective at improving the power factor.<ref name="effi">{{Citation | url = http://www.xbitlabs.com/articles/coolers/display/atx-psu5_3.html | title = ATX Power Supply Units Roundup | publisher = xBit labs | quote = The power factor is the measure of reactive power. It is the ratio of active power to the total of active and reactive power. It is about 0.65 with an ordinary PSU, but PSUs with active PFC have a power factor of 0.97–0.99. […] hardware reviewers sometimes make no difference between the power factor and the efficiency factor. Although both these terms describe the effectiveness of a power supply, it is a gross mistake to confuse them. […] There is a very small effect from passive PFC – the power factor grows only from 0.65 to 0.7–0.75. | url-status = dead | archive-url = https://web.archive.org/web/20081120040707/http://www.xbitlabs.com/articles/coolers/display/atx-psu5_3.html | archive-date = 2008-11-20 }}</ref><ref>{{Citation|date=Mar 16, 2006 |publisher=Find articles |url=http://findarticles.com/p/articles/mi_m0EIN/is_2006_March_16/ai_n26797888 |archive-url=https://web.archive.org/web/20090901140721/http://findarticles.com/p/articles/mi_m0EIN/is_2006_March_16/ai_n26797888/ |url-status=dead |archive-date=September 1, 2009 |title=The Active PFC Market is Expected to Grow at an Annually Rate of 12.3% Till 2011 |quote=Higher-powered products are also likely to use active PFC, since it would be the most cost effective way to bring products into compliance with the EN standard. }}</ref><ref>{{Citation | url = http://www.techarp.com/showarticle.aspx?artno=81&pgno=1 | publisher = TECHarp | title = Power Factor Correction | quote = Passive PFC […] the power factor is low at 60–80%. […] Active PFC ... a power factor of up to 95%}}</ref><ref>{{Citation | publisher = Silverstone Technology | url = http://www.silverstonetek.com/tech/wh_pfc.php?area= | title = Why we need PFC in PSU | quote = Normally, the power factor value of electronic device without power factor correction is approximately 0.5. […] Passive PFC […] 70~80% […] Active PFC […] 90~99.9% | url-status = dead | archive-url = https://web.archive.org/web/20081222085515/http://www.silverstonetek.com/tech/wh_pfc.php?area= | archive-date = 2008-12-22 }}</ref><ref>{{Citation | publisher = Electronic products | newspaper = Taiyo | url = http://www2.electronicproducts.com/PFC_options_for_power_supplies-article-taiyo-mar2004-html.aspx | title = PFC options for power supplies | first = Tom | last = Brooks | date = Mar 2004 | quote = The disadvantages of passive PFC techniques are that they typically yield a power factor of only 0.60 to 0.70 […] Dual-stage active PFC technology [yields] a power factor typically greater than 0.98 | url-status = dead | archive-url = https://web.archive.org/web/20081202100831/http://www2.electronicproducts.com/PFC_options_for_power_supplies-article-taiyo-mar2004-html.aspx | archive-date = 2008-12-02 }}</ref>

==== Active PFC ====
[[File:Active pfc PSU packaging.svg|right|thumb|Specifications taken from the packaging of a 610 W [[Power supply unit (computer)|PC power supply]] showing active PFC rating]]

Active PFC is the use of [[power electronics]] to change the waveform of current drawn by a load to improve the power factor.<ref>{{Citation | publisher = Fairchild Semiconductor | year = 2004 | type = application note | number = 42047 | title = Power Factor Correction (PFC) Basics | url = http://www.fairchildsemi.com/an/AN/AN-42047.pdf | access-date = 2009-11-29 | archive-url = https://web.archive.org/web/20140611063712/http://www.fairchildsemi.com/an/AN/AN-42047.pdf | archive-date = 2014-06-11 | url-status = dead }}</ref>  Some types of the active PFC are [[Buck converter|buck]], [[Boost converter|boost]], [[Buck-boost converter|buck-boost]] and [[synchronous condenser]].  Active power factor correction can be single-stage or multi-stage.

In the case of a switched-mode power supply, a [[boost converter]] is inserted between the bridge rectifier and the main input capacitors. The boost converter attempts to maintain a constant voltage at its output while drawing a current that is always in phase with and at the same frequency as the line voltage. Another switched-mode converter inside the power supply produces the desired output voltage from the DC bus. This approach requires additional semiconductor switches and control electronics but permits cheaper and smaller passive components. It is frequently used in practice.

For a three-phase SMPS, the [[Vienna rectifier]] configuration may be used to substantially improve the power factor.

[[Switched-mode power supply|SMPSs]] with passive PFC can achieve power factor of about 0.7–0.75, SMPSs with active PFC, up to 0.99 power factor, while a SMPS without any power factor correction have a power factor of only about 0.55–0.65.<ref>{{Citation |last1=Sugawara |first1=I. |last2=Suzuki |first2=Y. |last3=Takeuchi |first3=A. |last4=Teshima |first4=T. |contribution=Experimental studies on active and passive PFC circuits |title=INTELEC 97, 19th International Telecommunications Energy Conference |date=19–23 Oct 1997 |pages=571–78 |doi=10.1109/INTLEC.1997.646051|isbn=978-0-7803-3996-5 |s2cid=109885369 }}</ref>

Due to their very wide input voltage range, many power supplies with active PFC can automatically adjust to operate on AC power from about 100&nbsp;V (Japan) to 240&nbsp;V (Europe). That feature is particularly welcome in power supplies for laptops.

==== Dynamic PFC ====
Dynamic power factor correction (DPFC), sometimes referred to as real-time power factor correction, is used for electrical stabilization in cases of rapid load changes (e.g. at large manufacturing sites). DPFC is useful when standard power factor correction would cause over or under correction.<ref>{{Cite conference|last1=Chavez |first1=C. |last2=Houdek |first2=J. A. |title=Dynamic Harmonic Mitigation and power factor correction |publisher=IEEE |book-title= EPQU'07 |conference=9th International Conference Electrical Power Quality and Utilisation: October 9–11, 2007, Barcelona, Spain |pages=1–5 |doi=10.1109/EPQU.2007.4424144 |isbn=978-84-690-9441-9 }}</ref>  DPFC uses semiconductor switches, typically [[thyristor]]s, to quickly connect and disconnect capacitors or inductors to improve power factor.