VFD Novel Inter-Harmonics Active Damping Solution

Despite obvious advantages of utilizing large VFDs, they have some design parameters, which require special attention. In particularly, VFDs distort the input current and voltage sinusoidal waveforms which affect the power supply quality leading to undesirable consequences, such as overheating due to the harmonics content and torsional oscillations due to inter-harmonics. There are some mitigation techniques available to date to mitigate negative effects of interharmonics, however, all those mitigation techniques have some side effects and therefore may result in equipment design complexity and unnecessary restricting the VFD train operation speed range. This paper will provide an overview of both VSI and LCI VFD's and will discuss general theory behind inter-harmoninc's and associated torque pulsations. It aims to explain what inter-harmonics are, how they are generated in the VFD and what are typical solutions to mitigate negative inter-harmonics effects. Also, it will show a novel development for inter-harmonics mitigation based on both theory, factory testing and successful field operation.