Curbing Harmonics in HVAC Systems - New-technology reduces distortion, improves AC-drive performance

摘要

Abyproduct of modern electronics, harmonic distortion occurs when large numbers of personal computers, uninterruptible power supplies, variable-frequency drives (VFDs), and other devices using solid-state power-switching supplies to convert alternating-current (AC) power to direct-current (DC) power are present. In HVAC systems, AC drives are the most prevalent source of harmonic distortion. Harmonic distortion can be present in both voltage and current. In a balanced three-phase power system, even-numbered harmonic waveforms are 120 degrees out of phase and cancel each other, while odd-numbered harmonic waveforms remain. For a three-phase rectifier load, odd-numbered harmonic currents are expressed in the following equation: 6 × n ± 1, such as 5, 7, 11, 13, etc. The magnitude of the sinusoidal waveform for harmonic currents decreases as frequency increases and vice versa.