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Tuesday, September 18, 2018

Power Factor Correction (PFC) – Understanding International Regulations



International Regulations for Power Factor Correction

We know that, how fine the shape of the input current waveform matches the shape of the input voltage is determined by the total harmonic distortion (THD). A THD of 0% represents a pure sine wave (no distortion). Without PFC, power supplies are likely to draw the AC line current in a non-linear way; many unwanted harmonic currents are generated and reflected back on the AC power lines.

Consider example of European countries where;
·        First Harmonic (primary input frequency) is typically 50 Hz.
·        The third harmonic is 150 Hz.
·        39th harmonic is 1,950 Hz.
      
These unwanted harmonic currents have a direct association to the power factor of switchmode power supplies.

The main reason to have PFC within your  power  supply  is  to comply  with  international  regulations,  specially  if  you  want or intend  to sell  your  equipment or end product  in  Europe.

Let’s see the history of implementation of laws regarding to Power Factor Correction;

Year 1899 = Initially to avoid flickering of incandescent lamps a regulation is made. Main aim is here to avoid the interference in AC line which causes flickering of lamps.

Year 1978 = This year regulation is made to integrate power factor correction with consumer products. Generated regulatory standard named as IEC 555-2.

Year 2001 = Birth of EN 61000-3-2. The European Union put EN 61000-3-2 into effect to set up limits on the harmonics of the ac input current up to the 40th harmonic. This regulation complies with power supplies with input power of 75 watts or greater and drawing 16 amps of current from the AC line. Power supplies with PFC circuits that meet EN 61000-3-2 essentially have high power factor that is usually 0.97 or better.
     Today, EN 61000-3-2 is the most important regulation is the “European Norm”.

Further EN 61000-3-2 is split into four classes:

Class A: Balanced three-phase equipment, household appliances excluding equipment identified as Class D, tools (except portable), dimmers for incandescent lamps (but not other lighting equipment), and audio equipment, anything not otherwise classified.

Class B: Portable power tools.

Class C: All lighting equipment's (incandescent lamp dimmers not included).

Class D: Single phase, less then 600 W, personal computer, computer monitor, TV receiver.

As per Energy Star guidelines for computer’s power supply a power factor of ≥ 0.9 at 100% of rated output is required. As per U.S. Environmental Protection Agency, computers with internally assembled power supplies will have to use active power factor correction to meet the ENERGY STAR 5.0. For external power supply and for TV power factor requirement should meet ENERGY STAR 2.0.

Below figure shows, an example of the base sine waveform, the third harmonic waveform and the resultant distorted waveform.


The base sine waveform, the third harmonic and the resultant distorted waveform
Base sine waveform, Third harmonic and Resultant distorted waveform

*IEC 61000-3-2
Electromagnetic compatibility (EMC) - Part 3-2: Limits - Limits for harmonic current emissions (equipment input current ≤ 16 A per phase)

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