Case study of a unique power quality problem and solution. Application of a damped harmonic filter to a cycloconverter

As detailed in numerous references, variable speed drives cause degradation of power quality by distorting current and voltage waveforms in the distribution systems. Commonly applied solutions incorporate devices of a passive shunt filter design connected at the nearest power distribution bus. Apart from improving harmonic distortion at the point of their connection, such filters, consisting of capacitors, also provide necessary power factor correction to the application. Cycloconverters represent a special type of variable speed AC drive. Most commonly applied variable speed drives, such as variable frequency and variable speed DC drives, produce harmonics at their characteristic frequencies. These frequencies are essentially constant in time. In addition to the characteristic frequencies, cycloconverter spectra also contain frequencies that vary with the output converter frequency. Therefore, when passive harmonic filtering is considered for a cycloconverter application, special precautions have to be observed. It is the intent of this paper to discuss such an approach based on an example of an actual filter design. The motivation for the filter application was similar to most situations; to reduce the electrical costs by improving the power factor and to prevent equipment misoperation due to poor power quality. While the goal was common, the solution was not. The case study is detailed in the following steps: data collection and analysis, problem and solution identification, detailed filter engineering, implementation, and verification.