THD stands for Total Harmonic Distortion, and it is a measure of the amount of harmonic distortion present in a signal compared to its original frequency. It can be calculated for various signals, such as audio signals, power signals, or any other periodic signal.
In an inverter, the THD of the output signal can vary depending on the type of inverter and the load being driven by the inverter. In general, the output waveform of an inverter is a pulse width modulated (PWM) signal, which is a series of low- and high-voltage pulses within the frequency range of the inverter.
The THD of the output waveform can be affected by various factors, such as the switching frequency of the inverter, the shape of the output waveform, and the type of load being driven. In general, the THD of an inverter output waveform should be as low as possible to ensure proper operation of the load and to minimise electromagnetic interference.
To measure the THD of an inverter output waveform, a distortion analyser or a spectrum analyser can be used. The THD is typically expressed as a percentage and is calculated by measuring the total harmonic content of the waveform and dividing it by the amplitude of the fundamental frequency. A low THD value indicates a clean output waveform with little distortion, while a high THD value indicates a waveform with significant harmonic distortion.
There are several ways to minimise the THD of an inverter output waveform, such as:
Increase the switching frequency
Higher switching frequencies result in smaller voltage steps, which reduces the amount of harmonic distortion in the output waveform.
Improve the waveform quality
The output waveform can be improved by using advanced pulse width modulation (PWM) techniques, such as sinusoidal PWM, third harmonic injection PWM, or space vector PWM.
Use a filter
A filter can be added to the output of the inverter to reduce the amount of harmonic distortion. The most common filter used for this purpose is a low-pass filter, which attenuates the high-frequency harmonic components of the waveform.
Match the load
The load being driven by the inverter can affect the THD of the output waveform. Matching the load to the inverter’s output characteristics can reduce the amount of harmonic distortion.
Use high-quality components
Using high-quality capacitors and inductors can reduce the amount of harmonic distortion in the output waveform. By implementing one or more of above techniques, the THD of an inverter output waveform can be minimised, resulting in a cleaner output signal with reduced electromagnetic interference.