Harmonics in Adjustable Speed Drives: Causes, Effects, and Solutions

At present, it is unusual to operate machines at fixed speed throughout their operating lives. The need to adjust speed depends upon the load demand, load fluctuations, or for improving machine efficiency. This realization of the need of adjustable speed drives (ASDs) has led to rapid growth in this area. The emergence of semiconductor based control devices in the early 70 ´s contributed greatly to the development in ASDs. However, all the positives had to have a negative side; one of them in the form of the harmonics, which continue to provide food for thought to drive engineers. This paper aims to provide a panoramic view of the problem of harmonics caused by ASDs, starting with the brief introduction to harmonics, proceeding to its ill effects in power systems to some of the solutions that are being employed to overcome these harmonics.