Which load category is described as correcting harmonics within the device, exemplified by low THD rectifiers?

Which load category is described as correcting harmonics within the device, exemplified by low THD rectifiers?

• A. Programmable logic controllers
• B. Solid-state relays
• C. DC to AC power inverters
• D. Low THD rectifiers

Answer: (D)

Harmonic distortion comes from non-sinusoidal current drawn by loads. A rectifier that is designed to keep its current draw nearly sinusoidal—thus having a low total harmonic distortion (THD)—acts to correct harmonics at the source. These low THD rectifiers use techniques like active power factor correction, controlled switching, and multi-pulse or PWM methods to shape the input current, reducing the harmonics that flow back onto the electrical system. That’s why this load category is described as reducing or correcting harmonics within the device itself. In contrast, programmable logic controllers and solid-state relays are control devices and aren’t defined by their harmonic-correction capabilities. DC to AC inverters can have varying THD depending on design, but the explicit emphasis on minimizing harmonic content is captured by the term “low THD rectifiers.”

Harmonic distortion comes from non-sinusoidal current drawn by loads. A rectifier that is designed to keep its current draw nearly sinusoidal—thus having a low total harmonic distortion (THD)—acts to correct harmonics at the source. These low THD rectifiers use techniques like active power factor correction, controlled switching, and multi-pulse or PWM methods to shape the input current, reducing the harmonics that flow back onto the electrical system. That’s why this load category is described as reducing or correcting harmonics within the device itself.

In contrast, programmable logic controllers and solid-state relays are control devices and aren’t defined by their harmonic-correction capabilities. DC to AC inverters can have varying THD depending on design, but the explicit emphasis on minimizing harmonic content is captured by the term “low THD rectifiers.”