Power Factor Basics

March 17, 2005
We've all been taught that power factor (PF) is the ratio of real power to apparent power, or the cosine of the phase angle between sinusoidal current and voltage waveforms. When the current isn't sinusoidal (and the voltage is), PF includes a distortion

We've all been taught that power factor (PF) is the ratio of real power to apparent power, or the cosine of the phase angle between sinusoidal current and voltage waveforms. When the current isn't sinusoidal (and the voltage is), PF includes a distortion factor related to total harmonic distortion (THD). Specifically, PF relates to THD by:

where THD is expressed as a decimal.

When the switch closes in a non-PFC boost converter like the one in Figure 1 in the main article, the current through the inductor increases linearly and the voltage across it grows exponentially until it equals the input voltage. Then the switch opens, causing the inductor current to fall, while the voltage across it changes sign. Together with the voltage from the rectifier bridge, it charges the output capacitor through the diode. In the steady state, the capacitor is charged to a higher voltage than the voltage from the bridge.

Without PFC, the input current waveform in a boost converter draws pulses of current only at the peaks of the voltage waveform. Therefore, it generates many rather powerful harmonics. In some cases, the third harmonic can be nearly as large as the fundamental.

Sponsored Recommendations

Understanding Thermal Challenges in EV Charging Applications

March 28, 2024
As EVs emerge as the dominant mode of transportation, factors such as battery range and quicker charging rates will play pivotal roles in the global economy.

Board-Mount DC/DC Converters in Medical Applications

March 27, 2024
AC/DC or board-mount DC/DC converters provide power for medical devices. This article explains why isolation might be needed and which safety standards apply.

Use Rugged Multiband Antennas to Solve the Mobile Connectivity Challenge

March 27, 2024
Selecting and using antennas for mobile applications requires attention to electrical, mechanical, and environmental characteristics: TE modules can help.

Out-of-the-box Cellular and Wi-Fi connectivity with AWS IoT ExpressLink

March 27, 2024
This demo shows how to enroll LTE-M and Wi-Fi evaluation boards with AWS IoT Core, set up a Connected Health Solution as well as AWS AT commands and AWS IoT ExpressLink security...

Comments

To join the conversation, and become an exclusive member of Electronic Design, create an account today!