A Practical Primer On Motor Drives (Part 14): Power Measurements On Distorted Signals

by Ken Johnson, Teledyne LeCroy, Chestnut Ridge, N.Y., How2Power Today, Mar 15 2017

Focus:
Motor drives do not output sinusoidal signals—they are PWM signals and they have high harmonic content, which implies multiple harmonic current and voltage waveforms with a unique phase angle for each harmonic. We cannot directly measure the phase angle between distorted voltage and current waveforms, but must use a digitally sampled waveform technique, as described previously, to accurately calculate the power values of these waveforms. This part discusses additional considerations such as advanced cyclic period detection and display, harmonic filtering of power measurements, and the impact of line-to-reference voltage probing, which aid in correct measurement of power. These issues will be explained and demonstrated using measurements taken on Teledyne LeCroy’s Motor Drive Analyzer, which contains certain built-in functions specifically geared toward distorted waveform measurements as found on motor drive PWM outputs.

What you’ll learn:

• How to accurately measure the power of motor drive signals (and other PWM signals) with high harmonic content

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