How True Sine Wave Inverters Reduce Harmonic Distortion

Total Harmonic Distortion (THD) is a measurement of the difference between the harmonic frequency of an input signal and the harmonic frequency of an output signal. The greater the difference between the two frequencies, the greater the percentage of harmonic distortion. True sine wave inverters produce sinusoidal current that helps reduce harmonic distortion by delivering an input signal that, when measured against the output signal, results in less than three percent THD. THD of just under three percent is the maximum percentage of THD that sinusoidal power inverters produce. In many instances, the THD is a fraction of a percent.

How the Devices Work

The impact of true sine wave inverters is best understood by comparing them to their closest counterpart in the inverter family: modified power inverters. Whereas true sine wave inverters emit sinusoidal current, which is visualized as a smooth, undulating line of identical peaks and valleys, modified power inverters emit a non-sinusoidal current that is visualized as an angular line of evenly spaced squares. When equipment is designed to receive sinusoidal current -- which is type of current that utility lines supply -- receives non-sinusoidal current, a significant percentage of THD is noticed. Although many devices still operate when they receive non-sinusoidal current, harmonic distortion can significantly affect their operation.

Common Signs of Distortion

Signs of high THD vary by device but are unmistakable when they occur. For example, speakers exhibit distinct buzzing noises; fluorescent lighting ballasts emit a loud hum and contain lamps that flicker; computers have lines that roll across the screen; conventional telephone systems have static in the line; and circuit breakers switch off unnecessarily. The source of the distortion varies. In some buildings, it is created by solid state, non-linear loads, such as computers, which contain microprocessors that frequently create distortion. In other cases, the problem comes from an outside source, such as a building that shares the same transformer as the affected building.

Conclusion

There are several strategies for resolving harmonic distortion. If the problem comes from outside the building through the utility line, installing an inverter that produces sinusoidal current may be the best option. If the problem comes from within the building, using filtering devices or establishing isolated circuits may be helpful. When a building has equipment that demonstrates the effects of harmonic distortion, its manager should contact a provider of commercial power solutions for assistance identifying and resolving the problem.