Power factor (PF) is one of the most important but often misunderstood quantities of AC power. It is sometimes incorrectly referred to as a characteristic of power quality. In reality, PF is a property of the load downstream of the electric source, rather than a property of the source itself. There is another common misconception that PF is just cosφ, where φ is the phase angle between the voltage and current. This is true only in an ideal case of a linear circuit with sinusoidal input. In general, power factor is much more than cosφ, as you can learn from our tutorial.

How does PF have to be taken into account by design engineers and when should it be corrected? There are three main scenarios:

• When you design an AC source, such as a generator, you need to make sure it will handle a specified range of load power factors. Alternatively, you may need to specify a minimum allowable PF of the equipment powered from this source. For example, a capacitive load can make an electric generator unstable.
• When you design an AC-powered electronic power supply, you may have to meet the PF and harmonic limits of the applicable standards and/or specific requirements of the upstream source. This is usually accomplished by introducing active or passive power factor correction (PFC) circuit internal to the power supply.
• When you deal with electrical system in an industrial or commercial facility where the load properties are given, you may need to add external components (such as PFC capacitors) to raise the PF to an acceptable level to avoid surcharge or penalty fee.

This site is designed as a quick educational reference source for all information related to power factor correction techniques. Here you will find tutorials and calculators intended for newbie engineers, students and hobbyists. We will also discuss the question of whether or not homeowners and consumers should worry about PF of their appliances.

For all essential power electronics information (topologies, equations, magnetics, etc.) get my SMPS design reference.