Impact of multiple adjustable speed drive system to power system harmonics

This paper presents harmonic analysis in a multiple adjustable speed drive system. In a system where multiple drives are fed from the same bus, harmonic currents produced by the various drives can reflect back to the power source and to the other drives causing distortion of the voltage waveform. If these harmonic currents are significant, they can potentially cause problems for the given system. Therefore studying the harmonics at various points in the system and comparing the values of total harmonic distortion can provide guidance in choosing appropriate filtering solutions. A two AC drive system was setup in a laboratory environment and the total harmonic distortion of the voltage and current was measured at several points within the system to observe how the harmonics interact with each other. The frequency of the drives and the torque of the motors were also varied to achieve a variable torque relationship to model heating, ventilation, and air condition loads.