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How to Measure THD for a Single Phase Full Converter

THD or Total Harmonic Distortion is a measure of how much noise exits a system when compared to the amount of noise at the input. As power is converted from one type to another, such as converting DC to AC power, noise harmonics are created that reduce the quality of the output. The lower the THD, the higher quality signal or power you will get at the output. Measuring THD requires special equipment for accurate measurements.

Things You'll Need

spectrum analyzer or oscilloscope
Single phase converter
Pure sine wave generator

Instructions

- 1
  Connect the pure sine wave generator output to input 1 of the oscilloscope. Connect the gound to the signal generator to the ground of the oscilloscope. Turn the oscilloscope on. Adjust the display for input 1 and set the timing and the voltage scale until you get a sine wave on the oscilloscope display.
- 2
  Connect the output of the converter to input 2 on the osciloscope and turn the converter on. Adjust the display for input 2. Using the input 2 controls, adjust the timing and voltage scale until you have another sine wave on display 2.
- 3
  Adjust the display to show both inputs 1 and 2 at the same time. Adjust the voltage of the pure sine wave to match the voltage level of the converter output. Compare these two signals by using the subtract function on the oscilloscope. The difference between these two signals is the THD for this converter.

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