The input voltage of THD (Total Harmonic Distortion) is the voltage waveform being analyzed to determine the level of harmonic distortion present. Specifically, it's the voltage signal whose frequency components are being evaluated relative to its fundamental frequency.
Understanding THD and Input Voltage
THD quantifies the amount of harmonic distortion present in a voltage (or current) waveform. Harmonic distortion arises from the presence of harmonic frequencies, which are integer multiples of the fundamental frequency (e.g., for a 60 Hz system, harmonics would be 120 Hz, 180 Hz, 240 Hz, etc.).
The "input voltage" in the context of THD analysis is simply the voltage signal that contains these harmonic components. This could be:
- AC Line Voltage: Measuring the THD of the voltage supplied by the power grid.
- Output of an Inverter: Assessing the THD produced by an inverter converting DC to AC.
- Voltage Signal from a Sensor: Analyzing the THD in a voltage signal generated by a sensor.
- Any other voltage waveform: Subject to harmonic analysis.
The THD is calculated by comparing the Root Mean Square (RMS) value of the harmonic components to the RMS value of the fundamental component of the input voltage waveform. The formula for THD (expressed as a percentage) is:
THD (%) = (RMS value of harmonic components / RMS value of the fundamental component) * 100
Where:
- The fundamental component is the voltage at the base frequency (e.g., 60 Hz in the US).
- Harmonic components are the voltages at integer multiples of the fundamental frequency.
Examples
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Scenario: Analyzing the THD of a wall outlet voltage. The input voltage is the 120V AC voltage present at the outlet.
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Scenario: Evaluating the performance of a solar inverter. The input voltage is the AC voltage output by the inverter, which ideally should be a clean sine wave.
Key Takeaways
- The input voltage for THD analysis is the voltage waveform under scrutiny.
- THD measures the distortion of the input voltage waveform due to harmonic frequencies.
- The fundamental frequency component of the input voltage is used as the reference.
