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Good power quality is necessary for providing stable, sustainable power for the world's increasing and varying load demands. Power quality  management  is an essential way to maximize the efficiency of the power grid, lessen the burden for resources and reduce operating costs. Power Factor (PF) is a measure of power quality.  Power Factor Correction (PFC) is the implementation of methods to increase power factor, thereby increasing power quality.  This article is a quick review of Power Factor (PF) and Power Factor Correction (PFC). PFC circuits are beyond the scope of the article. Power Factor Definition 

Power Factor in it's simplest terms is the ratio of true  power to apparent power. True power is the working or useful power measured in watts (W), while the apparent power is the  total voltage and current consumed by the load, measured in volts x amps (VA). In cases where the true power and apparent power are equal the PF is considered ideal and expressed as the number 1. All the power consumed by the load has been turned into useful power. This  occurs when the  voltage and current are  in phase and the wave shape of the current is sinusoidal.   See Figure 1 Linear loads that are purely resistive have a power factor of 1.
  
Figure 1.
PF < 1

Power quality is decreased whenever the power factor is less than 1. This happens for 2 reasons. See Figure 2   
Figure 2.
1. Distortion factor: 

Non-linear loads which draw current in short bursts or spikes distort the current waveform causing it to be non-sinusoidal. These distorted waveforms appear at multiples of the fundamental frequency, also known as harmonics.  Distortion adds a fourth type of power called distortion reactive power (QDIST).  Switching power supplies are non-linear loads that cause waveform distortion. 

2. Displacement factor:

Linear loads that are inductive or capacitive result in an additional power called  reactive power (Q). The impedance of the reactive power causes a displaced phase angle. The cosine of the angle θ = PF.  This is considered the traditional or displacement power factor (DPF).  Electric motors and pumps are linear loads that cause phase displacement or shifting.  Switching power supplies are non-linear loads that cause waveform distortion. See Figure 3 Vector representation of linear and non- linear loads.   
Figure 3.
The Math 

Displacement or traditional power factor = True power (P)/Apparent power (S) or the cosine of the displacement phase angle θ. In the case of ideal power factor P=S, therefore the phase angle is 0 and the power factor = 1 

Distortion Factor = 1/ (√1 + THD^2) where THD equals Total Harmonic Distortion
Total PF = Displacement Power Factor x Distortion Power Factor or cos θ ? (1/ (√1 + THD^2) 
Standard 

While there isn't  a formal PFC regulation, there is an important  EN standard to limit harmonic content  which  is often  accomplished by raising power factor  EN 61000-3-2:

This is a standard for line power utilization. PFC is often used to meet limits on harmonic currents. The standard is divided into 4 classes and covers electrical equipment  greater  than 75W, except for class C.  Note: the Nominal voltage is 230Vac for this standard. 

  • Class A  Balanced three phase equipment 
  • Class B  Portable Tools 
  • Class C  Lighting equipment 
  • Class D  Information Technology Equipment  (ITE)
 
Program 
 
Energy Star / 80 plus is a voluntary certification program. It certifies products to have more than 80% energy efficiency at 20%, 50% and 100% of rated load, and a power factor of 0.9 or greater at 100% load. 
 
Power Factor Correction 
There are two types of Power Factor Correction, Passive and Active.
 
  • Passive PFC: Passive PFC yields a  PFC number of approximately  0.6 to 0.9 , much less than the ideal power factor of 1.  The elements used  to implement passive PFC  are components like  inductors, capacitors and ferrite cores. 
  • Active PFC: Active PFC uses semiconductors and switching elements like transistors to reach PFC numbers greater than 0.9 
 
There are advantages and disadvantages  such as cost and complexity to each method and you will need to determine what's necessary for your application 
 
PSUI have a full range of power factored products for all your design needs.
 
By John Benatti 
 
POWER FACTOR CORRECTION Links