Power factor correction (PFC) is the set of mechanisms built into a power supply circuit to raise the power factor (PF). PFC is commonly incorporated into computer power supplies to increase their PF. A circuit's PF is the ratio of real power to apparent power. The higher the PF, the more efficiently that the electrical current is being used.
There are three types of power in an electric circuit: power factor correction capacitor
Figure 1 provides a conceptual overview of how real, reactive and apparent power fit together; it shows how apparent power is composed of both real power and reactive power. For most of today's circuits, the goal is to minimize the amount of reactive power in the circuit's load so it is only a small percentage of the overall apparent power.
This ratio between real and apparent power can be used to calculate a circuit's PF. Because real power is a portion of apparent power, you can divide the real power (W) by the apparent power (VA) to determine the PF:
Power factor = real power / apparent power
The PF value is always between 0 and 1. Most circuits aim for a PF greater than 0.9. A standard power supply has a PF of 0.70-0.75, but a power supply with PFC has a power factor of 0.95-0.99. Many countries now regulate the acceptable PF in most circuits.
The relationship among real, reactive and apparent power can also be represented as a right triangle, with the real and reactive sides forming the right angle, as shown in Figure 2. The 90-degree angle between real power and reactive power is indicated by the rectangle. The angle between real power and apparent power is indicated by the curved arrow and the Greek letter phi (Ф).
The triangle points to another method for determining a circuit's PF. With this approach, you need only find the cosine of the angle between real power and apparent power:
Manufacturers commonly incorporate PFC into their circuits to increase the PF, using different techniques in their circuits. Two of the most common techniques are passive and active:
PFC is not used solely for power supplies. In other industries, PFC mechanisms help to reduce the reactive power produced by fluorescent and high bay lighting, arc furnaces, induction welders and equipment that uses electrical motors. Energy efficiency is increasingly important for organizations pursuing green computing as part of their efforts to fulfill the goals of environmental, social and governance initiatives.
Building lighting, as well as heating and cooling systems, are important factors in data center energy efficiency. Other considerations include server efficiency, computer cooling systems and many aspects of building construction, including doors and windows.
Learn about green computing best practices and how to put them into practice.
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