Correcting AC Source Distortion Enables Accurate Power Factor Measurements
by Viktor Vogman, Power Conversion Consulting, Olympia, Wash., How2Power Today, Mar 15 2022
Focus:
Ac power sources are crucial tools for validation and certification of power supplies to
standards such as 80Plus, which have requirements for both power supply efficiency and
power factor (PF). However, distortion in the sinewave output produced by the ac power
source can introduce errors in the PF and efficiency measurements required for such
certifications. This distortion consists of both the crossover distortion at the zero-
voltage crossing of the ac power source output and the first harmonic of the ac source’s
inverter switching frequency. This article analyzes how these forms of distortion interact
with the input EMI filter of the power supply under test to affect both the PF and
efficiency readings. It then quantifies the levels of distortion—mainly ac source voltage
ripple—that are acceptable for given levels of power supply output and X-capacitor values.
Finally it presents two low-pass filtering techniques for eliminating the effects of the
ac power source distortion on the PF measurements. Power supply designers can recommend
these techniques to the certified test labs if their power supply products are failing PF
testing or both PF and efficiency testing.
What you’ll learn:
- How to understand the impact of ac power source distortion on power factor measurements for power supplies
- How to correct power factor compliance failures induced by ac power source distortion
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